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Effective Elastic Moduli of Magnetic Disks with Molecularly Thin Liquid Lubricant Films Determined using Ar-Gas Cluster Ion Beam

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Evaluating the Elastic Moduli of Ultra-Thin Liquid Perfluoropolyether Lubricant Films on Diamond-Like Carbon Films Using Ar-Gas Cluster Ion Beams

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Electric Field Effect on Friction Coefficient of Diamond‑Like Carbon Film Heated by Laser Irradiation,

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media Deutschland GmbH  

The formation of head smears during the heat-assisted magnetic recording is a significant problem that must be addressed to ensure the reliability of the head-disk interface. In this study, the formation of a head smear by diamond-like carbon (DLC) films on magnetic disks was analyzed through simulated heating experiments. DLC films with a thickness of 100 nm were prepared and heated on a hot plate in an environmental gas chamber. A smear was observed on a silicon wafer placed 3 mm above the DLC surface film after the heating of the film. The smear amount was quantified based on the intensity of the carbon peak of the smear, which was measured by X-ray photoelectron spectroscopy. In air, the carbon concentration decreased with the heating temperature, while in nitrogen, it increased. Further, the carbon concentration of the smear formed in air was lower than that in nitrogen. A comparison of the smears formed by DLC films with different hydrogen concentrations showed that a greater amount of the decomposition gases was generated from the DLC films with a higher hydrogen concentration and that this value increased at lower temperatures. This result suggests that DLC films with low hydrogen concentrations generate smaller amounts of the decomposition gases during heating than those with high hydrogen concentrations. In addition, the results of Raman spectroscopy suggested that the DLC films get degraded during heating, resulting in the generation of hydrocarbon gases because the films contain carbon and hydrogen. Moreover, since peaks related to fragments with atomic masses of 250–500 atomic mass units were observed in the time-of-flight secondary ion mass spectrometry spectra of the smears, it can be concluded that the smears consist of hydrocarbons with relatively higher molecular weights.

DOI： 10.1007/s00542-020-05041-y

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

We propose a novel electromagnetic energy-harvesting device (EHD) for structural health monitoring systems of transportation infrastructures. The EHD is embedded in the road surface and uses the tread force of cars as the input force when tires of cars pass over it. Because the input force is very fast, the proposed EHD can generate a large amount of energy. The footprint of the device is 20× 20 mm, its height is 7.5 mm, and its volume is 2.4 cm3. We measured the energy generated when a bicycle passed over the EHD 34 times at various speeds between 5 and 15 km/h. Subsequently, we obtained the regression curve from the results, which showed the relationship between the bicycle speed and generated energy, and estimated the electric energy generated by car at higher speeds. The results showed that, even though the size of the EHD was small, electric energies of 100 ?J, and 1.0 mJ could be generated at car speeds of 17 km/h, and 52 km/h, respectively.

DOI： 10.1115/ISPS2021-63672

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

In this study, the dependence of the electric field between the magnetic disk and Si wafer, used as the counter surface, on the hydrocarbon smear generated from the diamond-like carbon (DLC) overcoat was investigated. As a result, the positive electric field from the disk to the Si wafer increased the amount of smear, and the negative field reduced it. The positive electric field was estimated to extract hydrocarbon ions from the thermal plasma toward the Si wafer, and the opposite field attracts the hydrocarbon ions to the DLC surface. Therefore, the electric field between the slider and disk possibly controls the smear generation from the DLC overcoat, which is heated by laser irradiation in the heat-assisted magnetic recording).

DOI： 10.1115/ISPS2021-63202

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00542-020-04806-9

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Other Link： http://link.springer.com/article/10.1007/s00542-020-04806-9/fulltext.html

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/sensors47125.2020.9278840

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11249-020-01333-6

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Other Link： https://link.springer.com/article/10.1007/s11249-020-01333-6/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：MYU K.K.  

DOI： 10.18494/sam.2020.2827

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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

DOI： 10.2474/trol.15.186

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

The formation of head smear from DLC films on magnetic disks was confirmed by a simulated heating experiment. DLC films of 100-nm thickness were prepared and heated on a hot plate in an environmental gas chamber. Smear on a silicon wafer placed 3 mm above the DLC surface was observed after heating of the DLC film. The smear amount was quantified using the carbon intensity of the smear measured by XPS. In air, the carbon concentration decreased with the heating temperature
however, the carbon concentration increased with temperature in nitrogen. The carbon concentration of the smear in the air environment was smaller than that of nitrogen. As the result of comparison of smears on DLCs with various hydrogen concentrations, more decomposed gas is generated from the DLC film as the amount of hydrogen contained in the DLC increases, and this value increases at lower temperatures. This result suggests that DLC films with low hydrogen concentrations generate a smaller amount of decomposition gas than those with high hydrogen concentrations during heating. In addition, Raman spectra suggest that the DLC degraded by heating and the hydrocarbon gas-like materials were generated from the DLC film because the DLC films include carbon and hydrogen. Because fragments of 250–500 atomic mass units were observed in the TOF-SIMS spectra of smears, the smear is estimated to consist of a hydrocarbon of relatively high molecular weight.

DOI： 10.1115/ISPS2020-1902

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coecient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly--olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives.

DOI： 10.3390/LUBRICANTS7120112

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In this study, we developed the new deposition method of Perfluoropolyether(PFPE) lubricant on diamond like carbon(DLC) overcoat by the photoelectron assisted chemical vapor deposition(PAcvd).Pfpe lubricant in vapor phase was deposited on DLC surface of magnetic disks with a RF pulse bias voltage between a disk surface and a counter electrode above disk surface during the ultra violet(UV) irradiation. Then, we evaluated the thermal stability for the laser beam heating and the corrosion resistance of magnetic disks with lubricant film deposited by PACVD. These disks showed higher thermal stability and high corrosion resistance than Z-tetraol lubricant film, because the lubricant film deposited by PACVD has no hydrocarbon segment in the molecular structure and has much high water repellency.

DOI： 10.1109/APMRC.2018.8601076

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Czech Scientific Society for Mycology  

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coefficient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly-α-olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives.

DOI： 10.3390/lubricants7120

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Pleiades Publishing  

Because the diamond-like carbon (DLC) thin film overcoat on either a hard disk surface or an air bearing surface plays an important role in maintaining the reliability and durability of the head-disk interface, nanoscale DLC wear and degradation is a critical issue in heat-assisted magnetic recording (HAMR). The use of helium in hard disk drives (HDDs) has been developed and put into practical use to decrease air-induced structural vibrations, and temperature rise. In this study, fundamental experiments were conducted to understand the wear and related degradation characteristics of an ultra-thin DLC overcoat subjected to laser heating in both air and inert gas environments, using a pin-on-disk tester. An inert gas environment was simulated using helium gas. The experiments were conducted using DLC-coated glass pins and actual magnetic disks without a lubricant film. The differences in the wear and degradation characteristics of a DLC overcoat on the pin and disk surfaces between inert gas and air environments were investigated after wear tests were performed, primarily through Raman spectroscopy. We found that wear and graphitization of DLC films became greater with laser heating, while the friction coefficients between the pin and magnetic disk became markedly smaller. However, our tests also revealed that wear and graphitization of the DLC film were significantly less in an inert gas environment than in an air environment. This is because the wear observed in this experiment was predominantly due to a wear mechanism that is based on tribo-chemical oxidation.

DOI： 10.1007/978-981-13-0411-8_62

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Vytautas Magnus University  

We investigated the smear characteristics upon laser heating in air and helium. We used magnetic disks coated with the perfluoropolyether (PFPE) lubricant D-4OH. The surface of the rotating disk was heated by laser irradiation using a pin-on-disk tester setup in a sealed chamber. The temperature was varied from 258°C to 540°C. When the lubricant film was heated by the laser, the lubricant evaporated from the surface of the disk by desorption or decomposition and adhered onto a hemispherical glass pin placed 5 μm above the disk surface as smears. The smears on the pin were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was found that the amount of smear under exposure to helium gas is greater than that to air at high temperatures. In addition, this interesting result may be attributed not only to the different lubricant depletion mechanisms due to laser heating under the two environmental conditions, but also to the diamond-like carbon (DLC) thin film at a relatively low temperature of approximately 260°C.

DOI： 10.15544/balttrib.2019.44

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

The lotus and taro leaf surfaces are superhydrophobic. We fabricated different surface patterns of lotus and taro leaves on Si surfaces and compared their contact angles and tribological properties. Three types of lotus patterns, consisting of a simple dot matrix of circular pillars with different pitches, and six types of taro patterns having the pillars distributed within a field of hexagonal ridges with different central pillar diameters and pitches, were prepared. The contact angles of water and hexadecane on these patterns were measured, and the wear resistance of each pattern was evaluated by reciprocating wear tests. The taro pattern showed a significantly higher contact angle for hexadecane and a lower coefficient of friction than the lotus pattern. The taro pattern ridges are supposed to contain air in the valleys between the ridges and pillars, which prevented sticking between the pillars and cloth fibers. Thus, the taro pattern exhibits better oleophobicity and a lower frictional force.

DOI： 10.2474/trol.13.311

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In this paper, we applied the Hilbert-Huang transform (HHT) to the time series of the torque exerted on the carriage arm of a hard disk drive, which was calculated using the finite-element analysis. Then, a Fourier transform (FT) was implemented to perform frequency analysis
the results were subsequently compared with the HHT results. A comparison of both spectra revealed the superior ability of HHT to perform frequency analysis of flow phenomena via disturbance torque analysis. Furthermore, the HHT results confirmed that to achieve more precise head positioning, it is necessary to decrease torque fluctuations induced by the non-stationary phenomena that are not always observed in the power spectrum obtained via the FT analysis, such as vortex shedding around an arm.

DOI： 10.1109/TMAG.2018.2835839

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

Tribofilms are critical for the management of wear and the control of friction. This study focused on the tribological properties of tribofilms to clarify their antiwear and low-friction mechanisms. By monitoring tribofilm growth and measuring friction-coefficient mapping, we found that a tribofilm was generated in a dynamic process of formation and wear. The friction coefficient decreased with an increase in film thickness. The friction coefficient distributions of the tribofilms depended on the chemical nature more than the surface morphology. ZDDP formed a tribofilm with good antiwear properties, whereas MoDTC accelerated the tribofilm formation and decreased the friction coefficient.

DOI： 10.2474/trol.13.157

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Verlag  

In this study, the smear by the lubricant and siloxane pickup at the laser heating in the heat assisted magnetic recording (HAMR) was evaluated using our developed noncontact pin-on-disk test. The smear area on the glass pin surface was measured on the disks with three types of different lubricant films prepared by changing the ultraviolet exposure condition, rinse condition, and lubrication process. The amount of siloxane adsorbed on disk surface relates with the siloxane wettability obtained from the contact angle of siloxane for disk surface and that increased as the siloxane wettability increases. On the other hand, the lubricant pickup increases as the physical and hydrogen bonding fractions increase. Overall, these data suggest that the sufficiently low surface free energy is needed by the lubricant film with only the chemical bonding fraction to reduce the lubricant and siloxane smear at the laser heating of HAMR, because the lubricant fractions of physical and hydrogen bonding increase the lubricant pickup and the much amount of siloxane adsorbs on disks with the large surface free energy.

DOI： 10.1007/s00542-018-3839-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules
the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.

DOI： 10.1109/TMAG.2017.2724038

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules
the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.

DOI： 10.1109/TMAG.2017.2724038

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

The tribocharge sensor to monitor the rotational speed and the temperature of ball bearing was fabricated and we studied the basic feasibility this tribocharge sensor. The tribocharge sensor was built up by the segmented electrode on rotor, the segmented electrode on stator. Electrode material is Cu of 35 μm thick and the material of base film is polyirude of 25 μm thick, This sensor was attached on the side on the ball bearing. This tribocharge sensor outputted the pulse voltage from the stator electrode. The output voltage was proportional to the rotational speed of ball bearing. The generated electric power was 0.2 μW at 2000 rpm, however, the electric power of 20 μW was expected by the reduction of PFTE film thic mess. On the other hand, the temperature of ball bearing was estimated by the envelope of negative voltage from the tribocharge sensor, and the estimated temperature approximately agreed with the temperature estimated by the friction force.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：euspen  

It is expected that, in the future, quadrotor helicopters (quadcopters) will be employed in many applications, several of which require the quadcopters to be extremely small. However, it is difficult for smaller quadcopters to achieve a sufficient lift force for flight because, with reduction in the propeller diameter, the lift force decreases more sharply than the mass does. To miniaturize flying robots, we developed a flapping-flight robot employing self-excited vibration based on dry friction, inspired by the flight mechanism of bees. The proposed structure uses a simple DC motor and is easy to control
a large flapping angle can be obtained by operating at the resonant frequency using dry friction-based self-excited vibration with robustness. The designed flapping-flight robot is similar to a hornet in size with a body length of 5.4 mm and wingspan of 57.2 mm
it weighs 970 mg, including the weight of a motor and battery.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

The contact type of tribocharge power generator was developed. This tribocharge power generator has a simple structure which two types of tribocharging films on electrode are laminated by silicon rubbers. That generated the volume density of electric power of 94μW/cm3 under the condition of 40 Hz, 2G, and 55kPa. As the results, we confirmed that the tribocharge power generator was useful for the energy harvesting and sensing the acceleration.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

The structural and molecular weight changes to lubricant picked up following laser heating in heat-assisted magnetic recording (HAMR) were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of the ion mass fragments depended on the decomposition pathways and changed drastically, as did the average molecular weight of the picked-up lubricant as heating temperature increased. The fragment series formed by the dissociation of end groups with low molecular weights (CH3O+) showed a high intensity at temperatures under 300 °C, whereas at temperatures over 400 °C, the fragments series formed by the dissociation of the end-group component (C5H9O4F2+) increased. Overall, the results presented herein suggest that the chemical and thermal stability of the hydrocarbon terminal ends of lubricants should be improved in order to decrease depletion of the lubricant film and lubricant pickup by laser heating in HAMR.

DOI： 10.1115/ISPS-MIPE2018-8515

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We investigated the laser-heating-temperature dependence of the friction characteristics of magnetic disks coated with boundary lubricant films by using a pin-on-disk tester and discussed the fundamental characteristics observed. In the contact area of the glass pin and disk, we observed the area that showed a buildup and depletion of the lubricant film thickness. The amount of buildup and depletion increased with increasing heating temperature. It was found that the friction coefficient of each lubricant film initially decreased as the temperature increased. Thereafter, the minimum value of the friction coefficient of each test lubricant occurred at a specific temperature, resulting in an increase in the friction coefficient inversely as the temperature further increased. It was suggested that the specific temperature corresponds to the transition temperature at which the test lubricant film evaporates. In addition, it was also suggested that the thermal durability of the lubricant film improved because of ultraviolet treatment.

DOI： 10.1109/TMAG.2017.2697478

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Molecular alignment is key to achieving an ultra-low friction coefficient. We prepared associated carboxylic acids using oleic acid and p-pentylbenzoic acid via hydrogen bonding, involving a benzene ring and an eight-membered cyclic carboxylic acid in the molecules. We investigated frictional properties when these were added into a base oil and found that the associated carboxylic acids decreased the traction coefficient in EHL and boundary lubrication, although the viscosity increased. An in situ micro Fourier transform infrared spectroscope showed that both the eight-membered cyclic carboxylic acid and the benzene ring were oriented parallel to the shearing force, leading to the low friction coefficient.

DOI： 10.1016/j.triboint.2016.10.042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Viscoelastic (VE) materials are widely used in daily life. For the effective utilization of VE materials, it is necessary to know their viscoelasticity with accuracy over a wide range of frequencies, especially for high frequencies. Currently, the viscoelasticity of solid-state materials is directly measured only in the low-frequency range; for high frequencies, it is estimated based on the time-temperature superposition (TTS) principle. However, it is generally recognized that the TTS principle is suitable only for estimating the viscoelasticity of rheologically simple materials for temperatures within a limited range that is higher than the glass-transition temperature. In this paper, we propose a device that can directly measure the shear modulus and tan delta values of solid-state VE materials at high frequencies. We also propose a method for compensating for the shear deformation mode resonance of VE materials based on the mass of the moving part, to gain a more accurate understanding of viscoelasticity in the high-frequency range, and discuss the causes of errors in the compensation method. Finally, we report the VE properties of natural rubber (NR 65 IRHD) measured using the developed device and compensation method, and compare the measured results with those obtained using commercial VE measurement equipment.

DOI： 10.1007/s00397-017-1010-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We developed a new method for using photoelectron-assisted chemical vapor deposition to deposit perfluoropolyether (PFPE) lubricant on a diamond-like carbon (DLC) overcoat. PFPE lubricant in the vapor phase was deposited on the DLC surface of a magnetic disk with a bias voltage between the disk surface and a counter electrode above the disk surface during ultraviolet irradiation. The bias voltage accelerated photoelectron emission from the DLC surface, and the photoelectrons partially dissociated the PFPE molecules in the vapor phase. The dissociated molecules then chemically bonded to the DLC surface. According to the experimental results, the bonded ratio of PFPE molecules to the DLC surface was approximately 100%. An ultrathin PFPE/DLC hybrid overcoat was produced as a monolithic film. This hybrid film exhibited a much lower surface energy than the reference Z-tetraol lubricant film and a high water contact angle of over 100 degrees. This hybrid film can increase the head-media clearance and improve some read/write characteristics by using the actual heads.

DOI： 10.1109/TMAG.2016.2626297

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The thermal decomposition of a thin film of D-4OH lubricant under heating conditions on air-bearing surfaces, such as those found in magnetic recording devices, was investigated using time-of-flight secondary ion mass spectroscopy. The substrates used in this experiment were those of actual magnetic head sliders with diamond-like carbon (DLC) thin-film coatings. Two kinds of surfaces were prepared: an undisturbed DLC thin-film surface and an Al2O3 surface exposed by sputtering of the DLC thin film. Changes in the positive mass spectra as a result of heating confirmed that thermal decomposition of the D-4OH lubricant thin-film occurred, and that it was catalytically accelerated by Al2O3 at heating temperatures below 150 degrees C. This observation contrasts with the fact that the D-4OH lubricant thin film on the undisturbed DLC thin-film surface did not decompose.

DOI： 10.1109/TMAG.2016.2627532

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

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Language：Japanese   Publisher：Japanese Society of Tribologists  

DOI： 10.18914/tribologist.62.01_37

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Siloxane outgas is well known to cause smears on magnetic head sliders. Siloxane outgas is vaporized from certain components in hard disk drives (HDDs), that adsorbs on the magnetic disk surfaces, and SiO2 that is denatured from siloxane by flash temperature at a slider and disk contact gets accumulated on the slider surface. On the other hand, heat assisted magnetic recording (HAMR) is being developed to improve areal density. In HAMR, a laser light heats the magnetic disk surface to 400-500 K. Siloxane adsorbed on a disk surface easily gets desorbed from the disk surface owing to thermal evaporation and dissociation by laser heating. In this study, we have studied smear growth from siloxane outgas on laser heating. We observe that the siloxane adsorbed on the disk surface grew on the glass surface above the disk surface at the laser heating spot.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Among many organic vapor contaminations released from structural components of hard disk drives, organic sioloxanes are particularly ominous, as they can be released in a relatively large quantity. Adherence of organic pollutants to the disk surface is a factor that hinders the normal operation of the head and the disk surface. It is known that volatile siloxane oligomers such as D4 (octamethyl cycletetrasiloxane) often form cyclic polydimethylsiloxane polymers in the presence of acidic catalysts. We investigated the reaction between D4 and some carbon materials such as diamond-like carbon in hard disk and graphite. The effect of the protection of carbon materials by Perfluoropolyether (PFPE) lubricants was observed.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>PFPE/DLC hybrid overcoat was deposited by the photoelectron assisted CVD (PACVD) with RF pulse bias voltage. The properties of PFPE film on DLC surface deposited by PACVD was compared with those by the CVD with the glow discharge plasma. The deposition rate of PACVD was much lower than that of the glow discharge plasma. The surface energy of PFPE films by PACVD was approximately 15 mJ/m² and that by the glow discharge plasma was 50 mJ/m², and the estimated monolayer thickness of PFPE film deposited by PACVD was 7−8 Å. The PFPE film deposited by PACVD had much CF₂ structure at the surface, however, that deposited by the glow discharge plasma had much COO and CF structures. From these results, we estimated that the glow discharge plasma much dissociated the chemical structure of monomer PFPE gas molecules as precursor and the deposited film could not show low surface energy.</p>

DOI： 10.1299/jsmeiip.2017.A-08

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>To increase HDD capacity, the thickness of lubricant film on the magnetic disks need to be reduced. The lubricant film deposited by using the photoelectron assisted chemical vapor deposition (PACVD) with low molecular weight perfluoropolyether (PFPE) lubricant showed high bond ratio, low surface energy and high coverage. In this study, we compared the tribological performances on head-disk interface of PFPE lubricant films deposited by PACVD with DC bias voltage and RF pulse bias voltage. As the result, the lubricant film deposited by DC and RF pulse voltage showed very high touch down power (TDP). In addition, the lubricant film deposited by RF pulse voltage showed low slider wear.</p>

DOI： 10.1299/jsmeiip.2017.A-09

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To further increase recording density of disk storage drives, the heat assisted magnetic recording (HAMR) can solve the coercive force problem of thermal fluctuation and is regarded as the key technology for achieving recording density of more than 1Tb/in^{2 (1)(2)}. In this technology, it is suggested that there are serious issues for the diamond like carbon (DLC) overcoat on the disk surface. Because that is heated to high temperature with laser beams⁽²⁾. In this study, first, we measured temperature dependence of friction properties of non-lubricated DLC surface on magnetic disks. Second, we considered the influence of the accumulated smear on test pin surface during the friction test. As a result, it was estimated that the smear on pin surface accumulated by the laser irradiation was originated from the hydrocarbon contamination adsorbed on DLC surface.

DOI： 10.1299/jsmeiip.2017.A-12

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In recent years, the information society rapidly developed. It is required to increase density of hard disk drives （HDDs）. In order to achieve the high density HDDs, it is important to research details of magnetic disk surface and some properties related with the head-disk interface. However, diamond like carbon (DLC) film on disks have been too thin to analyze chemical structure of DLC surface using Raman spectroscopy. In this study, we fabricated the plasmon lens with the sliver thin film on the surface by the vapor deposition and evaluated the structure change of ultra-thin DLC after laser-heating using surface enhanced Raman spectroscopy with the plasmon lens.

DOI： 10.1299/jsmeiip.2017.H-01

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

The thermal decomposition of D-4OH lubricant thin film on an actual air-bearing surface under heating conditions was investigated using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The substrates used in this experiment are those of actual magnetic head sliders with diamond-like carbon (DLC) thin-film coatings. Two kinds of surfaces were prepared
an undisturbed DLC thin-film surface and an AhO3 surface exposed by sputtering of the DLC thin film. Comparison of the changes in the positive mass spectra due to heating confirmed that thermal decomposition of the D-4OH lubricant thin-film occurred and that it could be accelerated by the catalysis of Al2O3 at heating temperatures below 150°C. This is despite the fact that the D-4OH lubricant thin-film on the undisturbed DLC thin-film surface did not decompose.

DOI： 10.1109/APMRC.2016.7524262

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we focused on the diamagnetism of grease oil for pivot bearings in hard disk drives (HDDs) and investigated the effect of a magnetic field on oil vapors. We vaporized the grease oil and compared the amounts of oil adsorbed on disk surfaces through two slits-one with magnets and the other without-in a preliminary experiment. As a result, we confirmed that it is possible to reduce the amount of oil adsorbed on a disk surface with the aid of a magnetic field. Based on the preliminary experiment, the grease oil vapor from the pivot bearing unit of HDDs was compared with regard to a narrow slit and clearance with and without the magnetic field gradient of permanent magnets. The amount of oil vapor was decreased by the magnetic field gradient, and the reduction ratio depended on the environmental temperature. The amount of oil vapor from the actual pivot bearing unit could be reduced by the ring magnet around the pivot unit. Finally, our results suggested the possibility of a gas seal generated by the magnetic field gradient for the pivot bearing unit in HDDs.

DOI： 10.1109/TMAG.2015.2511740

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We studied the effect of bias voltage between slider and disk surfaces to reduce lubricant pickup by the slider. A perfluoropolyether (PFPE) lubricant film, which is coated on the disk surface, has been considered to be charged to a negative voltage by the airflow on the rotational disk surface. Because the PFPE lubricant film is negatively charged, the lubricant pickup should be reduced by a bias voltage with a negative voltage on the slider surface. We confirmed changes in the lubricant pickup in a lubricant pickup test conducted at different bias voltages. A positive voltage of the slider accelerated the lubricant pickup, whereas a negative voltage reduced it.

DOI： 10.1007/s00542-016-2814-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

Our previous study confirmed that the photo-electron-assisted ultraviolet (UV) irradiation with a bias voltage between the magnetic disk and the counter electrode above the disk surface increased the bonded ratio of a perfluoropolyether lubricant film on the disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and coated on disks. After coating the lubricant films, UV irradiation of the lubricated disk surface was performed using the normal process and the photoelectron-assisted process, and the depletions of these lubricant films were compared using the pin-on-disk test with the laser heating function. The results showed that the lubricant film treated with normal UV irradiation without the bias voltage showed a deeper depletion of the lubricant film than that treated with photo-electron-assisted UV irradiation, and the ADOH film showed a shallower depletion than the Z-tetraol film. However, the molecular weight distributions of the ADOH films on DLC surfaces treated by UV irradiation were compared using time-of-flight secondary ion mass spectroscopy, and the film treated with photoelectron-assisted UV irradiation did not change owing to dissociation after photoelectron capture. Photoelectron-assisted UV irradiation led to the decomposition of the cyclo-triphosphazene end groups. Therefore, it is assumed that the depletion of lubricant films treated with photoelectron-assisted UV irradiation was reduced, since the bonding strength to the DLC surface increased because of the greater decomposition of end groups.

DOI： 10.1007/s11249-016-0668-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A large skew angle in a hard disk drive (HDD) adversely affects the flying stability of the head sliders and the off-track capability of the read/write head. A novel actuator in the form of a separated pivot-shaft actuator (SPA) with a small skew angle is proposed in this paper. The SPA was particularly designed for a four-disk 3.5-in. HDD and has a skew angle of +/- 1.6A degrees, which is approximately one-tenth of that of a conventional voice coil motor. The SPA was numerically analyzed by a finite element method, and its mechanical characteristics were compared with those of a long-arm actuator (LAA) (which is a strong candidate for a small-skew-angle actuator) with respect to the seek performance and frequency response. It was found that the SPA had a higher resonant frequency, which enabled the achievement of a wider servo-bandwidth compared to the LAA, and that the average seek time of the SPA was significantly shorter than that of the LAA.

DOI： 10.1007/s00542-015-2516-5

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：euspen  

Viscoelastic (VE) materials are widely used in our daily lives. To utilize VE materials effectively, it is necessary to understand the accurate viscoelasticity over a wide frequency range, especially in the high frequency range. Currently, viscoelasticity is directly measured only in the low-frequency range, and viscoelasticity in the higher frequency is estimated based on the time- Temperature superposition (TTS) principle. However, it is generally recognized that estimation by the TTS principle is adequate only for rheologically simple materials in a limited range of temperatures above the glass- Transition temperature. In this study, we proposed a shear- Type measuring device that can directly measure the shear modulus and tan δ of VE materials. We also proposed a compensation method for the shear deformation mode resonance of the VE material based on the mass value of the moving part to gain a better and more accurate understanding of viscoelasticity in the high frequency range.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

We investigate the thermal behavior of the friction property of ultra-thin perfluoropolyether (PFPE) lubricant film on diamond-like carbon (DLC) overcoats of magnetic disks. We use a newly developed pin-on-disk tester with laser irradiation heating. Results show that the friction coefficient of a lubricated DLC surface with Z-tetraol decreased with increased temperature, while for lubricated disks with Z-03, it gradually decreased at around 120°C and increased over 120°C. This minimal point may indicate the transition temperature. The friction coefficient of both lubricant films on the DLC surface varied with the kinematic viscosity of the lubricant materials, and decreasing the kinematic viscosity decreased the friction coefficient.

DOI： 10.2474/trol.11.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

For dual-stage actuator systems in hard disk drives, stroke-saturation of the secondary actuator must be avoided to prevent the servo system from becoming unstable. In this study, a reduction in the secondary-actuator displacement was investigated by imparting a rotational stiffness to a voice coil motor (VCM). It is shown that an increase in the first resonant frequency of the VCM is largely effective for decreasing the secondary-actuator displacement in the general dual-stage actuator system. Then, an actuator, which can impart a rotational stiffness to the VCM, was designed and facilitated. A new control system for dual-stage actuators employing the actuator was also considered. It was confirmed that the proposed servo system reduced the head-positioning errors due to air-flow-induced carriage vibration by more than 35 % compared with a conventional dual-stage actuator system. Furthermore the secondary-actuator displacement was reduced 52 % on average.

DOI： 10.1007/s00542-014-2368-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper investigates the depletion of a thin lubricant film subjected to laser heating in an inert gas environment, and we experimentally elucidate the fundamental characteristics and mechanisms related to lubricant depletion in air and inert gas environments. In addition, fundamental experimental studies are conducted to understand the structural stability or degradation, such as through oxidation and graphitization of diamond-like carbon (DLC) thin films subjected to laser heating, in an inert gas environment compared to air environment. The degradation and its mechanisms are investigated using Raman spectroscopy. The results suggest that less degradation would occur by oxidation for a DLC thin film in an inert gas environment than air environment. It is found that, from the view point of the reliability in the head/disk interface, the lubricant depletion issue is more crucial than DLC thin-film degradation for thermally assisted magnetic recording in an inert gas environment.

DOI： 10.1109/TMAG.2014.2359058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper presents a disk-spacer damper (DSD), a new damper structure, for reducing disk flutter. Three types of DSD structures, which consist of an aluminum disk spacer having grooves embedded with viscoelastic (VE) films, have been developed in this paper. First, we investigated the material properties of the VE film, such as shear modulus and discrete relaxation spectra, and then carried out numerical analysis of the damping effect using the material properties. Further, we measured the damping effect of each DSD structure and confirmed that the proposed DSD reduces the disk flutter amplitude between the (0,1) mode and the (0,4) mode by 20%-30%.

DOI： 10.1109/TMAG.2014.2318032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we sought to determine if, during ultraviolet (UV) exposure, the external electric field could control the bonded lubricant thickness. During UV irradiation, the effect of the external electric field on both the bonded lubricant thickness and surface free energy was studied. The lubricant films after UV irradiation were analyzed using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Because of the negative electric field, the polar component of the surface free energy was reduced, while the bonded lubricant thickness increased. Based on the results of the TOF-SIMS analysis, we concluded that these findings resulted from the negative electric field accelerating the photoelectron emission, and because of these photoelectrons, the bonding between the end groups and diamond-like carbon surface increased.

DOI： 10.1109/TMAG.2014.2318015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Because the diamond-like carbon (DLC) thin film overcoat on a hard disk surface plays an important role in maintaining the reliability and durability of the head-disk interface, DLC degradation is a critical issue in thermally assisted magnetic recording (TAMR). The use of helium in hard disk drives (HDDs) is being developed to decrease air-induced structural vibrations, windage loss, and temperature rise. TAMR technology is suggested to be put to practical use in a helium environment in HDDs. In this paper, fundamental experiments have been conducted to understand the structural stability or degradation of an ultrathin DLC overcoat subjected to laser heating in an inert gas environment. An inert gas environment was simulated using nitrogen gas. The degradation of DLC thin films fabricated through chemical vapor deposition was investigated by varying the laser irradiation duration and controlling the intensity of the laser, and it was evaluated through Raman spectroscopy. The differences in the damage mechanisms between an inert gas and air environments were elucidated. We found that the degradation of DLC thin films by oxidation would be significantly less in an inert gas environment than in an air environment.

DOI： 10.1109/TMAG.2014.2321006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In this study, the structural stability of ultra-thin diamond-like carbon (DLC) films subjected to heating was investigated experimentally. The thermal robustness of nanometer thick DLC films for thermally assisted magnetic recording was demonstrated, and their damage mechanisms were elucidated using chemical vapor deposition and filtered cathodic vacuum arc DLC films. In addition, the refractivity of disk substrates with heated DLC thin films was evaluated using a scanning microellipsometer. This measurement system is suggested to be an effective method for evaluating the thermal stability of DLC films. The effect of the heating duration on the thermal stability of DLC films was also investigated by this method. Further, it was suggested that DLC thin films on an air bearing surface may be affected by laser heating because this surface may be heated for a significantly longer duration owing to the magnetic head read/write operation. However, the DLC thin films on the disk substrate may not be affected as severely by laser heating.

DOI： 10.1007/s00542-014-2131-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

The wear resistance of two types of nanotextured surfaces, fabricated on polyethylene terephthalate films and coated subsequently with a diamond-like carbon (DLC) layer and then a self-assembled monolayer (SAM) film with perfluoropolyether main chains, was compared. Nanotextures with hole and pillar patterns were fabricated by a nanoimprint process. The hole nanotexture with DLC and SAM films showed better wear resistance than the pillar nanotexture, and that film showed higher oil repellency than the pillar nanotexture with DLC and SAM films. The von Mises and shear stresses of the pillar nanotexture were concentrated on the center and at the bottom of the asperity surface, and it was estimated from finite element method calculations that these stresses accelerate the wear of asperities.

DOI： 10.1007/s11249-013-0218-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In this study, the wear properties of a magnetic head slider on disks lubricated by ultra-thin perfluoropolyether (PFPE) lubricants with different molecular weights were evaluated by the continuous sliding of magnetic head sliders using the slider contact by the dynamic flying height control. Two types of PFPE lubricants (Z-tetraol and D-4OH) with different molecular weights were evaluated. Results show that the slider wear depended on the coverage of the lubricant film; i.e., the lubricant film with sufficient coverage reduced slider wear. The lubricant film with a low molecular weight (low-Mw), including a lubricant material with a Fomblin and Demnum main chain, exhibited better coverage on a diamond-like carbon surface. Sliders with a low-Mw lubricant film showed less wear than those of a high molecular weight (high-Mw), and the depletion of the low-Mw lubricant film was less than that of the high-Mw lubricant film.

DOI： 10.1007/s11249-013-0242-7

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The drag friction of the laminar air flow in a steel pipe with permanent magnets attached was compared to that in a pipe without magnets. The drag reduction rate decreased as a function of the Reynolds number in the laminar flow regime, and it reduced to a low percentage when the Reynolds number was greater than 3000 in the turbulence air flow regime. These results suggest that the velocity of the boundary air flow on the pipe wall surface was accelerated by the magnetic field gradient produced by the permanent magnets attached to the outer pipe surface. The velocity of the boundary air flow, as roughly estimated by calculating the magnetic field distribution, could approximately express the experimental results.

DOI： 10.1109/TMAG.2013.2245106

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this study, the friction forces between a slider and disk surface with different lubricant thicknesses were measured at touchdown. Touchdown measurements of the friction and adhesion forces on a disk were made using a pin-on-disk tribotester. The friction force at touchdown could not be explained by a monotonic behavior, where the friction force gradually decreased with the lubricant thickness. Based on a comparison of the results measured using the pin-on-disk tribotester, it was estimated that the optimal adhesion force and a lower friction force are needed for the surfing regime at touchdown.

DOI： 10.1109/TMAG.2013.2240660

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, the adhesion and friction forces between a glass pin and disk surfaces coated by lubricants with different numbers of hydroxyl endgroups (Z-03, Z-dol, Z-tetraol, and Z-TMD) were measured using a pin-on-disk microtribotester. The adhesion force decreased in the order of Z-dol, Z-TMD, Z-tetraol, and Z-03. The friction force at the applied load force of 0 mN decreased in the order of Z-TMD, Z-tetraol, Z-dol, and Z-03. These trends could not be obviously explained by the number of hydroxyl endgroups. Next, we investigated the relationship between the adhesion energy and the total surface energy. The adhesion force was roughly proportional to the surface energy, and the friction force was proportional to the friction factor defined by the friction coefficients of the carbon overcoat and the lubricant film, the lubricant film coverage, and the total surface energy. Based on the results, we suggested a friction model of the contact between the pin and disk surfaces.

DOI： 10.1109/TMAG.2013.2253451

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

DOI： 10.007/s00542-014-2135-6

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Politecnico di Torino (DIMEAS)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Politecnico di Torino (DIMEAS)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this study, we focused on the diamagnetism of ester lubricant oil for fluid dynamic bearings (FDBs) and investigated the effect of a magnetic field on oil vapors. We vaporized the lubricant oil and compared the amount of oil adsorbed on disk surfaces through two slits-one with magnets and the other without a magnet-in a preliminary experiment. As a result, we confirmed that it is possible to reduce the amount of oil adsorbed on a disk surface with the aid of a magnetic field. Based on the preliminary experiment, the outflow of the FDB oil fromthe hard disk drive (HDD) spindle was compared with regard to a narrow clearance with and without the magnetic field gradient of permanent magnets. The amount of outflow was decreased by the magnetic field gradient, and the reduction ratio depended on the environmental temperature. Finally, our results suggest the possibility of a gas seal generated by the magnetic field gradient.

DOI： 10.1109/TMAG.2012.2201250

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this study, we focused on the adhesion and friction behaviors of probes approaching magnetic disk surfaces. In order to observe these behaviors, a micro-tribotester was newly developed to evaluate the friction and adhesion forces of the ultrathin lubricant film on magnetic disks. The contact area between the spherical glass surface and the disk surface was measured using light intensities and Newton's rings and approximated by the JKR model. An adhesion force corresponding to a pull-off force acted on the interface between the glass surface and the disk surface. The friction coefficients on disks with different lubricant thicknesses were measured and the coefficient was found to decrease as the lubricant thickness increased. The pull-off force gradually increased as lubricant thickness increased.

DOI： 10.1109/TMAG.2012.2197594

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Thus far, it has been shown that lubricant depletion occurs at a relatively low temperature of approximately 200 degrees C in thermally assisted magnetic recording (TAMR). Because the lubricant on the disk surface plays an important role in maintaining the reliability and durability of the head-disk interface (HDI), lubricant depletion is one of the critical issues in hard disk drives. Thus, there is a great need to develop technology that supplies lubricant to the HDI as the amount of lubricant decreases, so that the thickness of the lubricant film remains constant. In this study, we conducted a fundamental study of vapor lubrication using perfluoropolyether (PFPE) lubricants as the first step. In other words, we conducted an experimental study to elucidate the fundamental mechanism of vapor lubrication and to investigate the technological feasibility of applying vapor lubrication to hard disk drives. In addition, the possibility of using vapor lubrication in hard disk drives with contact sliders was also investigated. As a result, it was confirmed that vapor lubrication would be useful to overcome the lubricant depletion issue.

DOI： 10.1109/TMAG.2012.2205138

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In this study, lubricant depletion due to high-frequency pulsed-laser heating, with a heating rate of similar to 10(8)-10(9) K/s, was investigated for lubricant films with thicknesses of greater than and less than one monolayer. The conventional lubricants, Zdol2000 and Ztetraol2000, were used. It was found that the critical temperature at which the lubricants begin to deplete was strongly dependent on the lubricant film thickness. For lubricant film thicknesses of less than one monolayer, this temperature was approximately 170 A degrees C higher than that for thicknesses of greater than one monolayer. To analyze the lubricant depletion mechanism, we examined the tested lubricant films, using temperature-programmed desorption (TPD) spectroscopy, in which the heating rate was 0.3 K/s. It was found that the lubricant depletion characteristics could be explained using the experimental TPD results for the tested lubricant films. The depletion mechanism involves the desorption or decomposition of the lubricant molecules, which interact with the diamond-like carbon thin films when the lubricant film thickness is less than one monolayer. Therefore, we concluded that the TPD results were highly effective for evaluating the lubricant depletion characteristics induced by rapid laser heating, even though the heating rates are substantially different.

DOI： 10.1007/s11249-012-9968-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The adhesion and friction properties of molecularly thin perfluoropolyether (PFPE) lubricant films dip-coated on a diamond-like carbon (DLC) overcoat of magnetic disks were studied using a pin-on-disk-type micro-tribotester that we developed. The load and friction forces were simultaneously measured on a rotating disk surface under an increasing/decreasing load cycle and slow sliding conditions. Experiments were performed using two types of PFPE lubricants: Fomblin Z-tetraol2000S with functional end-groups and Fomblin Z-03 without any end-group. The curves of the friction force as a function of the applied load agree with the curves estimated using the Johnson-Kendall-Roberts (JKR) model. The friction forces on the Z-03 films having different thicknesses were not found to decrease drastically; however, the friction forces on the Z-tetraol film were found to decrease drastically when the film thickness is more than similar to 1.2 nm. This drastic change in the case of the Z-tetraol film is estimated to be affected by the coverage of the lubricant film.

DOI： 10.1021/la204327h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We studied the bonding mechanism of ultrathin perfluoropolyether (PFPE) lubricant (Fombline Z-tetraol and Moresco D-4OH) films with hydroxyl end groups by measuring the bonding film thickness after ultraviolet (UV) irradiation. Nonfunctional PFPE lubricants (Z-03 and D2 N) were compared to two types of functional PFPE lubricants. The bonded thickness of both functional lubricants increased after a short period of UV irradiation, whereas that of the nonfunctional lubricants did not increase after the same treatment. This result suggests the occurrence of three kinds of mechanisms. First, Z-tetraol and D-4OH bond because of the photodissociation of the end groups by the UV light. Second, they bond because of the interaction between the end groups and the photoelectron from the carbon surface generated by UV irradiation. Third, they bond because of the photodissociation of the main chain by the UV light. In contrast, the dynamic reaction coordinate calculations suggest that the end groups in the PFPE lubricant dissociate because of the electron capture by the lubricant. As a result, we infer that the bonding of PFPE lubricant films with hydroxyl end groups on magnetic disks occurs by selective dissociation of the end groups because of UV irradiation.

DOI： 10.1007/s11249-011-9867-6

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this study, we prepared some kinds of lubricants with different numbers of a hydroxyl end group (Z-03, Z-dol, Z-tetraol, and Z-TMD) and measured the adhesion and friction forces on the disks for different lubricant thicknesses. We successfully obtained these forces as a function of lubricant film thickness. The adhesion and friction forces were smallest on the disk with Z-03; the adhesion force was largest on disks with Z-dol, and the friction force was largest on disks with Z-TMD. Z-03 has no hydroxyl end group; hence, this was assumed to be the reason why Z-03 showed the smallest adhesion and friction forces relative to the other lubricants with hydroxyl end groups. The friction force roughly depended on the lubricant coverage or mobile lubricant thickness in the lubricants with hydroxyl end groups.

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Language：English   Publishing type：Research paper (scientific journal)  

We fabricated supersmooth probes for use in pin-on-disk sliding tests by applying gas cluster ion beam irradiation to glass convex lenses. In the fabrication process, various changes were made to the irradiation conditions
these included one-step irradiation of Ar clusters or two-step irradiation of Ar and N2 clusters, with or without Ar cluster-assisted tough carbon deposition prior to N2 irradiation, and the application of various ion doses onto the surface. We successfully obtained probes with a centerline averaged surface roughness that ranged widely from 1.08 to 4.30 nm. Using these probes, we measured the friction forces exerted on magnetic disks coated with a molecularly thin lubricant film. Perfluoropolyether lubricant films with different numbers of hydroxyl end groups were compared, and our results indicated that the friction force increases as the surface roughness of the pin decreases and that increases as the number of hydroxyl end groups increases. © 2012 H. Tani et al.

DOI： 10.1155/2012/923818

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetraol2000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In this study, a novel method was developed to evaluate the local temperature increase under steady-state conditions on disk surfaces of hard disk drives due to laser heating during thermally assisted magnetic recording (TAMR). In particular, we evaluated changes in the refractive index and the extinction coefficient of disk substrates due to laser heating by varying the laser power, and determined the relationship between the laser power and the changes in these optical constants. Simultaneously, test disks were heated using a conventional heater, under heating conditions equivalent to those associated with laser heating, by varying the temperature. We evaluated the changes in the optical characteristics of the disk substrates due to heating, and formulated a relationship between the temperature and the changes in the optical characteristics. Then, the local temperature increase due to laser heating under steady-state conditions was evaluated by calibrating both sets of experimental results. In addition, the temperature increase was compared with the numerical simulation results, and good agreement was observed between the experimental and the simulation results. Thus, it was confirmed that, this method is useful and effective for estimating the temperature increase under steady-state conditions in disk surfaces of hard disk drives due to laser heating during TAMR. This method is also a first step toward understanding the occurrence of temperature phenomena in TAMR systems.

DOI： 10.1007/s11249-011-9830-6

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Publishing type：Research paper (international conference proceedings)  

We studied the effect of the duty ratio, i.e., the ratio of hill width to pitch, of patterned diamondlike carbon (DLC) surfaces on Ar gas cluster ion beam (GCIB) planarization effect. The patterns of 40 nm depth were fabricated on Si substrates by electron beam lithography and CHF3 reactive-ion etching. The pitch of the line-and-space pattern was 300 nm and three duty ratios were adopted. Then, refilling materials were deposited to 50 nm thickness on the patterned substrates. The test samples were irradiated by Ar-GCIB and the resultant surface profiles were measured by atomic force microscopy. The acceleration energy for one cluster was 20 keV. The dose was set in the range from 5 × 1014 to 5 × 1016 ion/cm2. Although there was a difference in the dose, the patterns clearly disappeared upon irradiating GCIB. The reduction rate of the peak-to-valley height decreased as the width of the hill increased. We indicated that GCIB irradiation is effective for the planarization of patterned surfaces with various duty ratios. © 2011 American Institute of Physics.

DOI： 10.1063/1.3556783

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this study, fundamental research was conducted on lubricant depletion due to rapid laser heating in thermally assisted magnetic recording (TAMR) systems. The effects of lubricant film thickness on lubricant depletion were investigated using a conventional lubricant, Zdol2000. The lubricant depletion characteristics resulting from laser heating were found to largely depend on the lubricant film thickness. Lubricant depletion mechanisms were also studied. In this study, it was found that lubricant depletion is predominantly due to lubricant evaporation for cases in which the lubricant film thickness is greater than one monolayer. In addition, the effect of laser irradiation duration on lubricant depletion was investigated using both continuous and 300-kHz pulsed laser irradiations, since actual TAMR systems require pulsed laser irradiation lasting a few nanoseconds. The differences between the fundamental lubricant depletion characteristics of continuous and pulsed laser irradiations were elucidated on the basis of the experimental results obtained in this study. Furthermore, it has been suggested that diamond-like-carbon (DLC) thin films on the disk surfaces are also affected by rapid laser heating, because the temperature of the films increases to more than 500 K upon laser heating. Therefore, we also studied the damage to DLC thin films due to rapid laser heating and found that the reflectivity of the DLC thin films changed; this change was presumably due to the decrease in the DLC density as well as the asperity in the laser-irradiated region.

DOI： 10.1109/TMAG.2010.2083641

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Language：Japanese   Publisher：The Institute of Image Information and Television Engineers  

To further increase recording density of disk storage drives, thermally-assisted magnetic recording can solve the fundametal issues of thermal fluctuation and is regarded as the keytechnology for achieving recording density of more than 1 Tb/in^2. In this technology, it is suggested that there is critical issues for the ultra-thin liquid lubricant films on the disk surfaces. Because they are heated to high temperature with laser beams. In this study, we focused on the thermal stability of the two lubricant film materials in thermally-assisted magnetic recording. In other words, the behavior of lubricant film under the laser heating was investigated and discussed experimentally. As a result, it was found that the effects of lubricant film thickness as well as the laser irradiation conditions on the lubricant film depletion were clarified. We also considered that the depletion mechanisms of lubricant film compared with the temperature programmed desorption spectroscopy (TPD) results.

DOI： 10.11485/itetr.35.1.0_1

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Language：English   Publisher：Japanese Society of Tribologists  

The mechanism responsible for the effects of electric fields on the lubricant dip-coating process was investigated by comparing the lubricant film conformations obtained when applying an electric field for different durations. A QA-40 solution was prepared for dip-coating a magnetic disk under two conditions. The lubricant film thickness and surface free energy obtained under the two conditions were compared. It was found that the molecular conformation was changed by the electric field resulting in more end-groups being adsorbed on the disk surface when the electric field is applied during the withdrawal of the disk from the solution than during the normal dip process. As a result, the surface free energy decreased. As a consequence of applying the electric field during dipping and withdrawing, the thickness of the QA-40 layer increased 1 - 3 Å.

DOI： 10.2474/trol.6.40

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We studied Ar gas cluster ion beam (GCIB) planarization effect on patterned surfaces refilled with Cr, Ta and SiO(2). The patterns of 20 nm in depth were fabricated on Si substrate by using electron beam lithography and CHF(3)-reactive-ion-etching. The bit pattern pitches and the height of peak-to-valley were 150/200/300/400 nm and 20 nm, respectively. Then, refilling materials were deposited 30 nm in thickness on the patterned substrates. The test samples were irradiated by Ar-GCIB and the resultant surface profiles were measured by atomic force microscopy. Acceleration energy for a cluster was 20 keV. The dose was set from 2 x 10(15) to 5 x 10(15) ion/cm(2). Although there was a difference in the dose, the patterns disappeared clearly by irradiating GCIB. The reduction rate of peak-to valley height decreased with decreases of the pattern pitch. We indicated that GCIB irradiation is effective for the planarization of patterned surface refilled with Cr, Ta, and SiO(2).

DOI： 10.1109/TMAG.2010.2044379

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Irradiations of gas cluster ion beams (GCIB) on amorphous carbon films formed with chemical vapor deposition (CVD) were performed, and the affinity with lubricant was studied. The surface roughness of as-deposited amorphous CVD carbon film was improved with N(2)-GCIB irradiation. By reducing the formation of multiply charged cluster ions, large crater formations can be minimized, which helps to obtain smooth surface. It was also shown that nitrogen rich surface was formed on the amorphous CVD carbon with N(2)-GCIB. From the study of lubricant affinity and the surface free energy measurements, nitrogen containing functional groups were formed with N(2)-GCIB irradiation, as a result, adhesion between the lubricant and the amorphous CVD carbon film increased.

DOI： 10.1109/TMAG.2010.2042036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The molecular height corresponding to monolayer thickness of several types of PFPE lubricants (Z-dol2000, Z-tetraol, A20H2000, ARJ-DS, ARJ-DD, and OHJ-DS) with different molecular structures was estimated from their spreading profiles. The molecular height of Z-dol2000 was smaller than that of Z-tetraol, even though these lubricants had almost equal molecular weights. This result shows that the molecular height of the lubricant with high-polarity end groups was higher than that of the lubricant with low-polarity end groups. ARJ-DD showed higher molecular height than ARJ-DS, because the polarity of the two OH end groups in ARJ-DS was lower than that of the four OH end groups in ARJ-DD. On the other hand, OHJ-DS showed a low molecular height even though it had the highest molecular weight and four OH functional groups. Thus, a lubricant molecule with a low polarity per segment of the main chain has a low molecular height and shows a low degree of conformation on a carbon surface. These experimental results agreed with molecular dynamics (MD) simulation results. Therefore, it can be hypothesized that lubricants with multidentate functional groups having strong polarities do not exhibit a flat conformation on a disk surface because the lubricant molecules form random coil shapes on account of the strong polarity. On the basis of these results, we propose a design rule for lubricant molecules to achieve flat conformation on magnetic disks, i.e., a flat molecular conformation can be achieved on a magnetic disk surface by using molecules that have multisegments with a weak polar function like as OHJ-DS.

DOI： 10.1109/TMAG.2010.2042573

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In this study, we have carried out fundamental research on lubricant depletion due to laser heating in thermally assisted magnetic recording. In particular, we investigated the effects of lubricant film thickness and lubricant bonding ratio on lubricant depletion. Conventional lubricants Zdol2000 and Ztetraol2000 were used. The lubricant depletion characteristics due to laser heating were found to depend largely on the lubricant film thickness and material. That is, for films thicker than one monolayer, the lubricant depletion depth increased with the laser-irradiation duration, whereas the thickness of the lubricant after laser irradiation on the diamond-like carbon (DLC) films tended to remain at a constant film thickness of one monolayer. The lubricant depletion width gradually increased as the laser irradiation duration increased. The increasing trends for the lubricant depletion width were quantitatively very similar and almost independent of the initial lubricant film thickness. However, for lubricant films with thicknesses less than one monolayer, the lubricant depletion depth was very small. The lubricant depletion width increased remarkably to several hundred micrometers as the laser irradiation duration increased. The lubricant depletion depth and width were much smaller for Ztetraol2000 than Zdol2000. In addition, the lubricant-bonding ratio was found to greatly affect the lubricant depletion characteristics due to laser heating. In other words, the lubricant depletion depth and width decreased as the bonding ratio increased. The lubricant depletion mechanism involves the evaporation of mobile lubricant molecules when the maximum attained temperature is less than 100 A degrees C. Another suggested lubricant depletion mechanism involves the thermocapillary stress effect, which is induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.

DOI： 10.1007/s11249-009-9533-4

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, we conducted experiments to investigate the dynamic touchdown and takeoff hysteresis behavior of TFC sliders. The effect of lubricant film thickness on hysteresis dynamics of the TFC sliders was investigated in the experiments. We also performed similar experiments related to the hysteresis behavior of sliders without TFC and discussed the differences between the slider hysteresis dynamics for the various cases. A specific and interesting phenomenon was observed regarding the slider touchdown in the case of lubricant films with large thicknesses, suggesting the feasibility of developing surfing recording HDI based on thick lubricant films.

DOI： 10.1299/jsmemecjo.2010.5.0_131

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The influence of an electric field on the dip-coating process was studied by using the lubricants Z-tetraol, D-4OH, TA-30, and QA-40. The electric field facilitated the adsorption of lubricant molecules onto the disk surface. It also resulted in an increase in the lubricant film thickness. The surface free energy and molecular height of the Z-tetraol lubricant film were not affected by the electric field; however, they decreased in the case of other lubricant films. To elucidate these results, we estimated that the molecular conformation of the lubricants changed due to the electric field and that the OH end-groups aligned to the carbon surface. These results suggest the possibility of resistance to outgas contamination and humidity through electric field assisted dip (EFAD) coating.

DOI： 10.1299/jamdsm.4.397

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The influence of an electric field on the dip-coating process was studied by using the lubricants Z-tetraol, D-4OH, TA-30, and QA-40. The electric field facilitated the adsorption of lubricant molecules onto the disk surface. It also resulted in an increase in the lubricant film thickness. The surface free energy and molecular height of the Z-tetraol lubricant film were not affected by the electric field; however, they decreased in the case of other lubricant films. To elucidate these results, we estimated that the molecular conformation of the lubricants changed due to the electric field and that the OH end-groups aligned to the carbon surface. These results suggest the possibility of resistance to outgas contamination and humidity through electric field assisted dip (EFAD) coating.

DOI： 10.1299/jamdsm.4.397

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The influence of an electric field on the dip-coating process was studied by using the lubricants Z-tetraol, D-4OH, TA-30, and QA-40. The electric field facilitated the adsorption of lubricant molecules onto the disk surface. It also resulted in an increase in the lubricant film thickness. The surface free energy and molecular height of the Z-tetraol lubricant film were not affected by the electric field; however, they decreased in the case of other lubricant films. To elucidate these results, we estimated that the molecular conformation of the lubricants changed due to the electric field and that the OH end-groups aligned to the carbon surface. These results suggest the possibility of resistance to outgas contamination and humidity through electric field assisted dip (EFAD) coating.

DOI： 10.1299/jamdsm.4.397

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The molecular height corresponding to monolayer thickness of several types of PFPE lubricants (Z-do12000, Z-tetraol, A20H2000, ARJ-DS, ARJ-DD, and OHJ-DS) with different molecular structures was estimated from their spreading profiles. The molecular height of Z-do12000 was smaller than that of Z-tetraol, even though these lubricants had almost equal molecular weights. This result shows that the molecular height of the lubricant with high-polarity end groups was higher than that of the lubricant with low-polarity end groups. ARJ-DD showed higher molecular height than ARJ-DS, because the polarity of the two OH end groups in ARJ-DS was lower than that of the four OH end groups in ARJ-DD. On the other hand, OHJ-DS showed a low molecular height even though it had the highest molecular weight and four OH functional groups. Thus, a lubricant molecule with a low polarity per segment of the main chain has a low molecular height and shows a low degree of conformation on a carbon surface. These experimental results agreed with molecular dynamics (MD) simulation results. Therefore, it can be hypothesized that lubricants with multidentate functional groups having strong polarities do not exhibit a flat conformation on a disk surface because the lubricant molecules form random coil shapes on account of the strong polarity. On the basis of these results, we propose a design rule for lubricant molecules to achieve flat conformation on magnetic disks, i.e., a flat molecular conformation can be achieved on a magnetic disk surface by using molecules that have multisegments with a weak polar function like as OHJ-DS.

DOI： 10.1299/jsmemecjo.2010.5.0_129

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

In this study, fundamental research on lubricant depletion due to laser heating in thermally assisted magnetic recording was conducted. In particular, the effect of lubricant film thickness on lubricant depletion was investigated. The conventional lubricant Zdol2000 was used. As a result, it was found that the lubricant depletion characteristics due to laser heating depend largely on the lubricant film thickness. In addition, it was suggested that the lubricant depletion mechanism involves the evaporation of the mobile lubricant molecules, when the maximum attained temperature is not very high. Another suggested lubricant depletion mechanism involves the thermocapillary stress effect induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Three types of PFPE lubricants (Z-tetraol, TA-30, and D-4OH) with different molecular structures were coated on magnetic disks and the conformations of these films were studied by atomic force microscopy using a fluoride-coated probe. The molecular conformations of these lubricant films were found to be different from each other. The Z-tetraol film showed the highest molecular height and lowest coverage among these lubricants. The TA-30 film showed a double-layer structure and the highest coverage among the lubricant films. The D-4OH film showed a monolayer structure and higher coverage than the Z-tetraol film. These observed were in agreement with the results of molecular dynamics simulations. In these simulations, the TA-30 film showed the highest coverage and lowest molecular height among the three lubricant films because the TA-30 molecules did not form a random coil shape and were adsorbed rigidly on the disk surface. The Z-tetraol molecules were adsorbed and formed a random coil shape. The D-4OH molecules were also adsorbed and formed a spiral shape.

DOI： 10.1109/TMAG.2009.2029602

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Advanced head-disk interface (HDI) system assisted by gas perfluoropolyether (PFPE) lubrication is discussed in this paper. It is known that the lubricant spins off under the high rotation speed and high temperature. The lubricant redistribution after long-term head seeking with near-contact flying was studied. The spinoff and the redistribution of lubricant will be serious issues for the reliability of the hard disk drives. Our proposed HDI system shows high performance without the lubricant spinoff and redistribution. This is achieved by dripping only a small amount of lubricant on the suspension. This lubricant evaporates under high temperature and is adsorbed on to the disk surface. As a result, the spinoff, the redistribution, and the head contamination were significantly reduced. The lubricant on a magnetic disk could be maintained for a long time. The amount of this lubricant was optimized to maintain the constant thickness thorough the balance of the supplying and the decreasing. It was confirmed that the lubricant on the disks in this new HDI system maintained for about 10 000 hours at 70 degrees C.

DOI： 10.1109/TMAG.2009.2029617

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, the influence of the electric field on the dip-coating process was studied by using lubricants Z-tetraol and TA-30. The electric field assisted the adsorption of both lubricant molecules on the disk surface. This electric field also resulted in an increase in the lubricant film thickness. A positive electric field increased the bonded ratio of the lubricant film. The surface-free energy, step height, and head-disk clearance of the Z-tetraol lubricant film were not affected by the electric field; however, those of the TA-30 lubricant film were improved by the electric field. By molecular dynamics simulation, we confirmed that the molecular mobility of the solution increased by applying the electric field. The lubricant molecules in the solution, which show higher mobility, should have more opportunity to adsorb onto a disk surface. These results show the possibility of reducing the head flying height by the electric-field-assisted dip (EFAD) coating process.

DOI： 10.1109/TMAG.2009.2022334

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The planarization of the bit-patterned surface using gas cluster ion beams (GCIBs) was studied. By applying the features of gas cluster ions, such as low-energy irradiation and surface smoothing effects, it is possible to carry out effective smoothing of a patterned surface. We fabricated a dot pattern on the Si substrate as a model structure for bit-patterned media by electron beam lithography and inductive coupled plasma etching. A carbon overcoat covered the Si dots. On Ar-GCIB irradiation at an acceleration voltage of 20 kV, the Si dots with a diameter of 150 nm were planarized. The required ion dose for planarization was 5 x 10(14) ions/cm(2). The cross-sectional transmission electron microscope images showed that only the carbon overcoat layer was planarized without a change in the structure of Si dots. Etching depth of the overcoat increased linearly with the ion dose, indicating good reproducibility of the method with precise control of residual thickness.

DOI： 10.1109/TMAG.2009.2023064

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Thermally assisted magnetic recording (TAMR) is one of the novel technologies that are employed for achieving magnetic recording densities higher than 1 Tb/in(2). With regard to this novel technology, it has been suggested that there exists a critical head-disk interface (HDI) issue associated with the use of ultrathin liquid lubricant films on the disk surface. This problem is attributed to the fact that these films are heated to high temperatures by using laser beams in order to reduce magnetic coercivity. In this study, a fundamental research on the lubricant depletion caused due to laser heating in TAMR systems was conducted. That is, the effect of lubricant film materials on lubricant depletion was investigated. In this experimental study, four types of lubricant film materials-Zdol2000, Zdol4000, Ztetraol2000, and A20H2000-were used, and the differences in the characteristics of lubricant depletion for each tested lubricant film were investigated. The effect of the molecular weight as well as the end group of the lubricant on the lubricant depletion was discussed and clarified by analyzing the obtained experimental results. In addition, it was found that the depletion characteristics of ultrathin liquid lubricant films could be explained by using experimental results obtained from the thermogravimetric analysis for each bulk lubricant material.

DOI： 10.1109/TMAG.2008.2010663

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Perfluoropolyether lubricant films on magnetic disks were observed by means of atomic force microscopy (AFM) with a fluoride-coated probe. The lubricant films could be observed directly because the adhesion force was decreased by the anti-wetting effect of the fluoride coating on the probes. We compared the molecular conformation of Z-dol (Mw: 2000, 3000, 6000, 8000) with that of Z-tetraol. Thus, we found that the film coverage of a lubricant with high molecular weight exhibited varying (i.e., higher and lower) step heights of the lubricant film boundary. The Z-tetraol film exhibited higher coverage and the higher step height as compared to Z-dol2000. To further study the step height measured by means of atomic force microscopy, we compared the step height with the shoulder height of the spreading profiles of the films. The step heights were almost equal to the shoulder height. We observed the lubricant film after shearing by using contact scanning mode atomic force microscopy. The coverage of the sheared lubricant film increased higher than the initial coverage before shearing. Subsequently, the lubricant molecular conformation was varied due to the shearing, and the coverage was increased.

DOI： 10.1109/TMAG.2008.2010655

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Recently, head-disk-interface(HDI) spacmg in hard disk drives(HDD) has been decreased to as low as 5 nm in order to achieve an ultra-high magnetic recording density. With the increase in magnetic recording density, the HDI spacing of the head has been reduced. To reduce the magnetic spacing, the active head slider with micro-thermal actuator was developed. The magnetic spacing of these sliders can be controlled in-situ during operation of the drive. The goal of this research is to clarify the slider hysteresis behavior of dynamic flying height (DFH) sliders. In this study, the slider hysteresis behavior was compared, varying the disk roughness. As a result, it was found the slider hysteresis behavior depends on the disk roughness.

DOI： 10.1299/jsmemecjo.2009.5.0_211

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In this study, the interaction of the magnetic head slider and magnetic disk defects were studied as the function of the head flying height controlled by the dynamic flying height (DFH) control method. In the conventional glide test, the flying height is set as a function of the rotational velocity. However, in the glide test using the DFH control method, the flying height could be set as a function of DFH power on a constant rotational velocity. A magnetic disk with two types of defects-a crater and a 5 nm bump-was prepared. The acoustic emission (AE) signal at the slider-defect contacts from the conventional glide test and the DFH glide test were then compared. The results of the experiment indicated that the DFH glide test could detect these defects at a few nanometers flying height, but the conventional glide test could not detect them. This was because the AE signal burst below a flying height of 3 nm. The AE signal output of the DFH glide test was higher than that of the conventional glide test, and the AE signal of the defect contact increased at a greater rotational velocity. It was concluded that the DFH control glide testing was one of the most important techniques for the future high-density recording disks. © 2009 American Institute of Physics.

DOI： 10.1063/1.3061827

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Language：English   Publishing type：Research paper (international conference proceedings)  

Advanced head disk interface (HDI) system assisted by gas Perfluoropolyether (PFPE) lubrication was discussed in this paper. It is known that the lubricant spins-off under the high-rotation-speed and high temperature. Our proposing HDI system showed high performance without the lubricant spin-off and redistribution. That was to drip only small amount of lubricant on the slider suspension. This lubricant was evaporated into the head disk interface, and that in gas phase was adsorbed onto disk surface, where its thickness was decreased. As the results, the spin-off, the redistribution and also the head contamination were significantly reduced. The lubricant on magnetic disk is expected to be maintained for long time.

DOI： 10.1109/APMRC.2009.4925386

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Surface planarization and modification of a patterned surface were demonstrated using gas cluster ion beam (GCIB). Grooves with 100-400 nm intervals were formed on amorphous carbon films using focused ion beams to study the special frequency dependence of the planarization. Also, line and space patterns were fabricated on Si substrates, and amorphous carbons were deposited as a model structure of discrete track media. Subsequently, surface planarization using Ar-GCIB was carried out. After GCIB irradiations, all of the grooves were completely removed, and a flat surface was realized. And it showed that GCIB irradiation planarized grooves without huge thickness loss. From the power spectrum density of an atomic force microscope, GCIB preferentially removed grooves with small intervals. It was found from energy dispersive x-ray spectroscopy that surface planarization without severe damage in the amorphous carbon and magnetic layers was carried out with GCIB. © 2009 American Institute of Physics.

DOI： 10.1063/1.3073665

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, fundamental research on lubricant depletion due to laser heating in thermally assisted magnetic recording was conducted. In particular, the effect of lubricant film thickness as well as lubricant bonded ratio on lubricant depletion was investigated. The conventional lubricant Zdol2000 was used. As a result, it was found that the lubricant depletion characteristics due to laser heating depend largely on the lubricant film thickness and the lubricant film bonded ratio. In addition, it was suggested that the lubricant depletion mechanism involves the evaporation of the mobile lubricant molecules, when the maximum attained temperature is not very high. Another suggested lubricant depletion mechanism involves the thermocapiflary stress effect induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.

DOI： 10.1299/jsmemecjo.2009.5.0_215

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To further increase recording density of disk storage drives, laser-assisted magnetic recording can solve the fundamental programs of thermal fluctuation and is regarded as the keytechnology for achieving recording density of more than 1 Tb/in^2. In this technology, it is suggested that there is serious issues for the ultra-thin liquid lubricant films on the disk surfaces. Because they are heated to high temperature with laser beams. In this study, we focused on the thermal stability of the three lubricant film materials in laser-assisted magnetic recording. In other words, the behavior of lubricant film under the laser heating was investigated and discussed experimentally. As a result, it was found that the effects of lubricant materials as well as the laser irradiation conditions on the lubricant film depletion were clantied.

DOI： 10.1299/jsmemecjo.2009.5.0_217

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We studied planarization of carbon overcoat by gas cluster ion beam (GCIB) for discrete track magnetic disks. We fabricated discrete tracks with variant pitches by focused ion beam on a 30-nm-thick carbon overcoat deposited on magnetic disks, and we planarized them with an Ar GCIB using lateral sputtering effect. It was found that planarization by GCIB was more effective for lower wavelengths than for those with a few hundreds nanometers. On the discrete tracks with 100-nm pitch and 20-nm depth, the initial peaks and valleys were removed by GCIB; however, on the ones with over 200-nm pitch, the initial peaks and valleys remained though the heights were drastically decreased. These results indicate the capability of GCIB planarization as a process for the discrete track media. Furthermore, cross sections were observed by transmission electron microscopy. The GCIB with relatively low dose could also planarize the 120-nm-pitch carbon tracks without etching the magnetic layer.

DOI： 10.1109/TMAG.2008.2001618

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Each relative density of carbon overcoat and upper magnetic layer of perpendicular magnetic disks with different corrosion and scratch resistance was measured by transmission electron microscopy electron energy loss spectroscopy (TEM EELS). Corrosion resistance depends on the relative density of both layers, the carbon overcoat and the upper magnetic layer with higher density showed larger corrosion resistance. Scratch resistance did not depend on the density of carbon overcoat, but depended on the density of the upper magnetic layer. Higher density showed higher scratch resistance. This relationship between the relative density of upper magnetic layer and the scratch resistance suggests the deformation of upper magnetic layer affects to scratch damage. As the result of this study, the density evaluation by TEM EELS is useful to estimate the corrosion/scratch resistance tendency of perpendicular magnetic disks, and the higher density of upper magnetic layer is needed to improve the scratch robustness of perpendicular magnetic disks.

DOI： 10.1109/TMAG.2008.2001884

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of a slider enhanced by the friction of the head-disk contact. We studied this phenomenon using a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was estimated for the disks with large friction through the simulation of the contact hysteresis defined by the difference of takeoff height and touchdown height. In order to confirm that simulation result, several types of textured pad sliders by focused ion beam fabrication were evaluated by touchdown and takeoff measurement. These pad sliders were textured at a small area near the trailing edge on a trailing pad as a corresponding contact area. The texturing of a trailing pad did not disturb the flyability of slider because the textured area was very small and did not decrease the slider fly height. As a result, the contact hysteresis of textured sliders became smaller as a function of contact area and improved the takeoff performance.

DOI： 10.1109/TMAG.2006.878644

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of slider enhanced by the friction of head-disk contact. We studied this phenomenon using altitude test and a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was observed for the disks with small roughness. This phenomenon can be explained using a simple stick-slip model of slider vibration enhanced by friction force, and investigated through the evaluation of the pressure hysteresis defined by the difference of takeoff pressure and touchdown pressure. Hysteresis simulation based on the stick-slip model revealed that large stick-slip vibration induces hysteresis for the disk with low roughness. We confirmed by the experiment and simulation that this stick-slip vibration of slider continues in the case of large friction coefficient after one slider-disk contact. We also confirmed that, slider-disk contact in low fly height occurs due to the trigger which the slider contacts on lubricant pooling. Reduction of friction force was found to be effective to improve the pressure hysteresis and takeoff performance. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2172533

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Spin-off model was suggested from the viewpoint of lubricant molecule migration. Lubricant molecules move from the inner diameter to outer diameter on the magnetic disk when the air shear force and the centrifugal force act on the molecules. The spin-off behavior was calculated using this model, and the experimental results were clearly explained by the results of that simulation. In addition, the adsorption energy of lubricant molecules onto magnetic disk was determined as the activation energy from the measurement of replenishing velocity of lubricant film. The adsorption energies of perfluoropolyether lubricant molecule were different from the nitrogenated amorphous carbon overcoat and the DLC overcoat. (C) 2003 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0301-679X(02)00215-3

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Catastrophic damage of a disk caused by impact between a slider and a disk during loading/unloading is investigated using many variations of disk samples with the different scratch resistances. At first, the accelerated loading/unloading test condition to increase disk damage was studied as the function of disk-runout during a disk rotating, rotational speed of a disk, and sweep velocity of a slider using disk samples with the same scratch resistance. Next, in accelerated test conditions, many kinds of disk samples with different scratch resistances were tested to find a relation between disk damage and scratch resistance of thin films. Flyability of a slider over a disk during a slider sweeping in these tests was monitored using an acoustic emission transducer. Disk surface and slider surface after the test was observed using an optical microscope and an optical surface analyzer. Scratch resistance of a disk was measured using a newly developed high-speed scratch tester. As a result, film-peeling damage was broken out at the loading position of a disk with increasing disk-runout. Film-peeling damage was broken out much more with decreasing scratch resistance of a disk. When scratch resistance of a disk was lower, flyability became bad suddenly during a slider sweeping over a disk
a sweep zone of the disk surface after the test shows damage, such as cross scratches. It is found that disk damage results in not only environmental contamination but also scratch resistance of a disk. This damage is broken out catastrophically. Finally, a mechanism of catastrophic damage is discussed.

DOI： 10.1109/TMAG.2003.808916

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

The lubrication mechanism when the magnetic head is sliding on the magnetic disk in the drag test with cyclic interval rest periods, is discussed. A long rest period decreased the wear of disks and friction force. This result indicated that the reflow of lubricant into the contact areas decreased the wear of texture asperities, Next, the molecular spreading behavior of a lubricant plm was calculated by Monte Carlo method to estimate the effect of lubricant recovering velocities. The lubricant replenishment into a thinner lubricant area made by an etching technique was measured The measured profiles of lubricant replenishment were approximately agreed with the calculated profiles using a spreading model. It was clearly estimated that the reflow velocities changed in various cases of the environmental temperature, the radius of removal lubricant area, and the thickness of the lubricant films. Experimentally, the dependencies of temperature, the radius of removal lubricant area, and the lubricant thickness were measured in the drag test. This lubricant-spreading model adequately explained these results.

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Language：English   Publishing type：Research paper (scientific journal)  

Chemical modification technique with X-ray photoelectron spectroscopy has been used for a quantitative analysis of surface functional groups of the carbon overcoats. As the nitrogen content in the carbon overcoat layer increases, the total abundance of functional groups on the carbon overcoat surface increases. The increase of the functional groups leads to an increase of a physisorbed lubricant layer ratio. Increase of the physisorbed layer ratio on the carbon overcoat surface showed a higher durability on the head/disk interface, and decreased the spin-off of the lubricant on a high rotation of the disk. The increase of the physisorbed layer leads to a higher recovery of the lubricant defect by the wear, and the increase of functional groups on the carbon overcoat surface leads to a stronger interaction of the lubricant with the carbon overcoat surface is estimated.

DOI： 10.1080/10402000008982411

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

We observed how PFPE lubricant film formed to magnetic disk surface using AFM with a fluoride coated probe. We found that PFPE lubricant did not uniformly cover the carbon protective surface but concentrated in valleys of surface roughness. The lubricant film has one to two step structure and the first step height is almost as same as the radius of molecular gyration. After the pin-on-disk test, the lubricant step height decreased and the coverage increased, compared to the initial state. © 1999 IEEE.

DOI： 10.1109/20.800837

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

Performance of diamondlike carbon (DLC) film prepared by PECVD method has been investigated as the protective film of rigid thin film disk. An in-line sputtering PECVD multilayer deposition system was used for preparation of disk samples. The disks were found to be superior to those disks with conventionally sputtered carbon films in many points such as high durability against CSS tests, smooth coverage over the irregular points of magnetic layer, and as a result, good corrosion resistance even at the thickness of 15 nm or less. © 1994, American Institute of Physics

DOI： 10.1109/20.334013

Scopus

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Publisher：トライボロジスト 63(4), 260-268,  

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Publisher：トライボロジスト 62 (5), 346-349,  

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Publisher：Kansai University  

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Language：Japanese   Publisher：関西大学先端科学技術推進機構  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Heat assisted magnetic recording (HAMR) is suggested as a technique to realize next-generation high-density magnetic recording. The heat resistance of lubrication film and the diamond like carbon (DLC) film of the magnetic disk surface for the laser irradiation is important factor to realize the HAMR. In this study, we focus on the structural change of DLC film on disk surface by laser heating. Then, we observed the Raman spectra using the surface enhanced Raman spectroscopy. As the results, we confirmed that the structural change of DLC film was reduced with the disk rotational speed and it was estimated that the structural change did not occur on the actual rotation speed of HDDs.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Vibration electric power generator has been attracting attention as an energy harvesting technology. Energy harvesting technology is an effective approach for sustainable, maintenance-free, and green power source for wireless, portable, or implanted electronics. Power generation using triboelectric charging is similar to that using electret. However it is flexible and very low cost. This study, we focus on a simple and high power vibration generator used by triboelectric charging for wearable power generator.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Silicon carbide (SiC) is well known as a ceramic material which have superior friction and wear resistance characteristic in the water. That is used as a material for sliding bearings and mechanical seals. However, it have a problem that friction and wear become large in the ultra-pure water and during slow rotation. Then, we studied to improve the tribological properties of the carbon nanofiber (CNF) on the surface of sintered SiC grown by the SiC surface decomposition method. As a result, the friction force was reduced by the CNF on SiC surface.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Currently, hard disk drives (HDDs) are widely used as an auxiliary storage device. HDDs are still in great demand owing to their large capacity and low price. To achieve more recording capacity in HDDs, a more precise positioning accuracy of the magnetic heads is necessary. However, rotation of the disks causes an air-flow between the disks, and the head positioning accuracy deteriorates due to the air-flow-induced carriage vibration. In previous studies, experimental results confirmed that positioning error was improved by attaching linear protrusions on the leading edge of the carriage arms. However, the mechanism of this phenomenon has not yet been elucidated. In the current research, we evaluated the effect of leading-edge protrusions on the flow-induced carriage vibration by finite element method (FEM) analysis.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In our previous study, we confirmed the magnetic field of permanent magnet on the steel pipe could reduce the drag friction on the laminar flow of air in the pipe. Then, we focused that the magnetic field distribution affected the drag friction on the pipe wall. We prepared the ring type and cuboid type of magnets and compared the drag friction. As the results, the ring type magnets increased the drag friction, however, the cuboid type magnets reduce that. The estimated forces derived from the calculation of magnetic field distribution could explain the phenomena. We concluded that the magnetic field could control the drag friction of air flow in pipe flow.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

We successfully demonstrated the availability of TOF-SIMS (Time of flight-secondary ion mass spectroscopy) in studying the thermal decomposition of the lubricant film on magnetic head slider under heating in the vacuum chamber of TOF-SIMS. By comparing the positive mass spectrum of wide range, we found that the molecular weight distribution of lubricant changed by heating and we confirmed that the thermal decomposition of the lubricant could be accelerated by the catalysis of Al_2O_3.

CiNii Books

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Language：Japanese  

CiNii Books

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Publisher：機械の研究 67 (8), 666-671,  

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Publisher：月刊トライボロジー  

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Publisher：セラミックス 48 (9), 718-722,  

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Publisher：トライボロジスト 58 (3), 145-150,  

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Publisher：月刊トライボロジー 27 (1), 41-43,  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Fundamental research on lubricant depletion due to 300-kHz rapid pulsed-laser heating was conducted, when the lubricant film thickness is less than one monolayer. The conventional lubricant Zdol2000 was used. As a result, it was found that the lubricant depletion mechanism involves the desorption or decomposition of the lubricant molecules. The lubricant depletion characteristics when the thickness of the lubricant film is less than that of a monolayer film can be explained by using the experimental results obtained from the temperature programmed desorption spectroscopy (TPD) for tested lubricant film.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Head disk interface (HDI)system assisted by vapor Perfluoropolyether (PFPE)lubrication was discussed in this paper. PFPE on magnetic disks are widely used as the lubricants for hard disk drives to prevent from the wear at the head disk interface (HDI). The thickness of lubricant changes due to the spin-off and wear by the contact between head and disk. In this study, we confirmed that vapor lubrication replenishes the depletion of lubricant film and the adsorbed lubricant thickness saturated with disk rotation time.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Recently, head-disk-interface (HDI) spacing in hard disk drives (HDDs) has been decreased under a few nanometers by the dynamic flying control (DFH) technology in order to achieve an ultra-high density magnetic recording. However, lubricant pick-up by head slider increases on the HDI with ultra-low flying height. In order to reduce the lubricant pick-up, the pick-up phenomena should be visualized by sensitive method, and that phenomena should be understand at the point of the pick-up mechanism. Therefore, we developed the slider surface analyzing (SSA) tester to observe the lubricant thickness distribution on the slider surface at unloading point. As the results, the lubricant is picked up by the DFH protrusion on trailing pad, when the back-off power is less than approximately 2 nm. On the other hand, the dewetting phenomena were observed on slider surface. The dewetting phenomena occurs the increase of the flying height at head loading after long soak at unloading position.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To further increase recording density of hard disk drives (HDDs), it is necessary to reduce the flying height of magnetic head. Recently, the flying height of magnetic head is under 2nm by using Dynamic Flying Height (DFH) control. To more reduce the flying height, we studied the light contact recording which means that DFH protrusion is sliding on the lubricant film surface. We analyzed the DFH slider dynamics by acoustic emission (AE) from the Pzt element attached on the head suspension. As a result the different vibration modes were measured the contact of sliders with lubricant surface and carbon surface. In additions, it was found that the magnitude of the slider vibration at continuous contact with between the lubricant film depends on the lubricant material. In other words, Z-dol2000S showed lower vibration than Z-tetraol2000S.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Recently, it is important to clarify the interactive forces between slider and disk surfaces in nanometer head-disk interface region in HDD, in order to achieve ultra-high magnetic recording density. This paper describes the interactions between atomic force microscope (AFM) probes and ultra-thin liquid lubricant films. We investigated the difference in a response of the force curve and lateral force by varying the lubricant materials (Z-tetraol, TA-30, D-4OH) and lubricant film thickness. From the experimental results, it was found that meniscus bridge is easy to be extended at high lubricant film thickness. On the other hand, adhesive force and lateral force gradually decreased with an increase in the lubricant thickness. The interactive forces around monomolecular film thickness are affected the adsorption form the lubricant molecules.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Laser-assisted magnetic recording is one of the novel technology for achieving a magnetic recording density of more than 1 Tb/in^2. In this technology, it is suggested that there is serious issues for the ultra-thin liquid lubricant films on the disk surfaces. This is because these films are heated to high temperature using laser beams. In this study, we focused on the local temperature on disk surface due to laser heating in laser-assisted magnetic recording. The local temperature increase was identified using the change of refractive index and absorption coefficient of the DLC film experimentally. In addition, the estimated temperature was compared with the computer simulation results and good agreement was obtained.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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J-GLOBAL

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Publisher：トライボロジー会議予稿集 2006-5,p.C 28,  

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Publisher：トライボロジー会議予稿集 2005-11, p.E37.  

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Publisher：トライボロジー会議予稿集 2004-11, p.2E10.  

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Publisher：トライボロジー会議予稿集 2003-5, p.C9.  

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Publisher：月刊トライボロジー 17 (3) ,15-17,  

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Publisher：トライボロジー会議予稿集 2002-10, 289-290,  

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Publisher：科学と工業 15 (11), 32-34,  

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Publisher：トライボロジスト 46 (6), 433-438,  

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

17AM1-2

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

17PM1-1

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

15AM2-1

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

16PM2-4

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

18AM1-5

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

18PM1-4

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

17PM1-2

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

15AM2-2

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Event date： 2024.3

Venue：大阪工業大学   Country：Japan  

18PM1-5

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPH-2-3

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPH-2-4

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPB-2-3

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Event date： 2024.3

Venue：岡山   Country：Japan  

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPK-2-1

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPA-1-5

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Event date： 2024.3

Venue：岡山   Country：Japan  

IPH-3-1

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPA-1-3

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPA-1-2

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPJ-2-2

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Event date： 2024.3

IIPH-2-1

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Event date： 2024.3

Venue：岡山   Country：Japan  

IIPH-2-2

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Event date： 2023.12

Language：English  

Venue：Abu Dhabi  

DOI: 10.1109/PowerMEMS59329.2023.10417614.

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Event date： 2023.12

Language：English  

Venue：Abu Dhabi  

P2-15d

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Event date： 2023.10 - 2023.11

Language：English  

Venue：Vienna   Country：Austria  

DOI: 10.1109/SENSORS56945.2023.10325112.

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Event date： 2023.10

Venue：名古屋   Country：Japan  

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Event date： 2023.9

Venue：Fukuoka   Country：Japan  

28-C-05

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Event date： 2023.9

Language：English  

Venue：Fukuoka   Country：Japan  

26-PO-21

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Event date： 2023.9

Language：English  

Venue：Fukuoka   Country：Japan  

27-PO-13

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Event date： 2023.9

Venue：Fukuoka   Country：Japan  

27-PO-14

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Event date： 2020.9

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Event date： 2020.9

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Event date： 2020.6

Venue：Virtual Meeting  

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Event date： 2020.6

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Event date： 2020.5

Venue：Montreal, Canada  

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Event date： 2020.5

Venue：Montreal, Canada  

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.3

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Event date： 2020.1

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Event date： 2019.12

Venue：Krakow, Poland  

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Event date： 2019.10

Venue：Chicago, USA  

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

Venue：川越  

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2018.11

Venue：Shanghai, China  

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Event date： 2018.11

Venue：伊勢  

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Event date： 2018.11

Venue：伊勢  

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Event date： 2018.11

Venue：伊勢  

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Event date： 2018.11

Venue：伊勢  

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Event date： 2018.10

Venue：Chicago, USA  

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Event date： 2018.9

Venue：Malaysia  

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Event date： 2018.9

Venue：大阪  

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Event date： 2018.9

Venue：大阪  

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Event date： 2018.9

Venue：大阪  

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Event date： 2018.5

Venue：Singapore  

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Event date： 2018.5

Venue：東京  

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Event date： 2018.5

Venue：東京  

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Event date： 2018

Venue：寝屋川  

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Event date： 2018

Venue：寝屋川  

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Event date： 2018

Venue：埼玉  

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Event date： 2018

Venue：寝屋川  

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Event date： 2018

Venue：寝屋川  

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Event date： 2018

Venue：寝屋川  

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Event date： 2018

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Event date： 2017.9

Venue：Beijing,China  

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Event date： 2017.9

Venue：Beijing China  

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Event date： 2017.9

Venue：Beijing,China  

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Event date： 2017.9

Venue：Zhenjiang China  

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Event date： 2017.9

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Event date： 2017.9

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Event date： 2017.8

Venue：San Francisco,California,USA  

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Event date： 2017.8

Venue：San Francisco,California,USA  

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Event date： 2017.8

Venue：Tsukuba Japan  

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Event date： 2017.7

Venue：神戸  

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Event date： 2017.6

Venue：Ljubljana(Slovenia)  

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Event date： 2017.6

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Event date： 2017.5

Venue：東京  

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Event date： 2017.5

Venue：東京  

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Event date： 2017.4

Venue：Dublin,Ireland  

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Event date： 2017

Venue：高松  

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Event date： 2017

Venue：高松  

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Event date： 2017

Venue：高松  

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Event date： 2017

Venue：高松  

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Event date： 2016.9

Venue：Kuala Lumpur, Malaysia  

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Event date： 2016.9

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Event date： 2016.9

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Event date： 2016.9

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Event date： 2016.9

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Event date： 2016.9

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Event date： 2016.9

Venue：Leeds, UK  

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Event date： 2016.7

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Event date： 2016.7

Venue：Korea  

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Event date： 2016.7

Venue：Korea  

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Event date： 2016.6

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Event date： 2016.5 - 2016.6

Venue：Nottingham, UK  

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Event date： 2016.5

Venue：東京  

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Event date： 2016.5

Venue：東京  

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Event date： 2016.4

Venue：Nara, Japan  

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

Language：Japanese  

Heat assisted magnetic recording (HAMR) is suggested as a technique to realize next-generation high-density magnetic recording. The heat resistance of lubrication film and the diamond like carbon (DLC) film of the magnetic disk surface for the laser irradiation is important factor to realize the HAMR. In this study, we focus on the structural change of DLC film on disk surface by laser heating. Then, we observed the Raman spectra using the surface enhanced Raman spectroscopy. As the results, we confirmed that the structural change of DLC film was reduced with the disk rotational speed and it was estimated that the structural change did not occur on the actual rotation speed of HDDs.

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Event date： 2016.3

Language：Japanese  

Vibration electric power generator has been attracting attention as an energy harvesting technology. Energy harvesting technology is an effective approach for sustainable, maintenance-free, and green power source for wireless, portable, or implanted electronics. Power generation using triboelectric charging is similar to that using electret. However it is flexible and very low cost. This study, we focus on a simple and high power vibration generator used by triboelectric charging for wearable power generator.

researchmap

Event date： 2016.3

Language：Japanese  

In our previous study, we confirmed the magnetic field of permanent magnet on the steel pipe could reduce the drag friction on the laminar flow of air in the pipe. Then, we focused that the magnetic field distribution affected the drag friction on the pipe wall. We prepared the ring type and cuboid type of magnets and compared the drag friction. As the results, the ring type magnets increased the drag friction, however, the cuboid type magnets reduce that. The estimated forces derived from the calculation of magnetic field distribution could explain the phenomena. We concluded that the magnetic field could control the drag friction of air flow in pipe flow.

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Event date： 2016.3

Language：Japanese  

Currently, hard disk drives (HDDs) are widely used as an auxiliary storage device. HDDs are still in great demand owing to their large capacity and low price. To achieve more recording capacity in HDDs, a more precise positioning accuracy of the magnetic heads is necessary. However, rotation of the disks causes an air-flow between the disks, and the head positioning accuracy deteriorates due to the air-flow-induced carriage vibration. In previous studies, experimental results confirmed that positioning error was improved by attaching linear protrusions on the leading edge of the carriage arms. However, the mechanism of this phenomenon has not yet been elucidated. In the current research, we evaluated the effect of leading-edge protrusions on the flow-induced carriage vibration by finite element method (FEM) analysis.

researchmap

Event date： 2016.3

Language：Japanese  

We successfully demonstrated the availability of TOF-SIMS (Time of flight-secondary ion mass spectroscopy) in studying the thermal decomposition of the lubricant film on magnetic head slider under heating in the vacuum chamber of TOF-SIMS. By comparing the positive mass spectrum of wide range, we found that the molecular weight distribution of lubricant changed by heating and we confirmed that the thermal decomposition of the lubricant could be accelerated by the catalysis of Al_2O_3.

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.3

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Event date： 2016.1

Venue：SanDiego, California  

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Event date： 2015.12

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Event date： 2015.12

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Event date： 2015.12

Venue：Regent Cha-Am Beach Resort Phetchaburi Thailand  

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Event date： 2015.11

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Event date： 2015.10

Venue：Denver，USA  

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Event date： 2015.10

Venue：Denver，USA  

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Event date： 2015.9

Venue：Tokyo Japan  

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Event date： 2015.9

Venue：Tokyo  

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Event date： 2015.9

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Event date： 2015.9

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Event date： 2015.9

Language：Japanese  

In hard disk drives (HDDs), rotary-type voice coil motors (VCMs) are exclusively used for positioning head transducers on a target track. The rotary VCMs essentially have a skew angle, and its variation reaches more than 30° in the typical 3.5-in. HDDs. It is generally known that such a large skew angle deteriorates the flying stability of the head sliders and off-track capability. Recently, it has been considered that the large skew angle is capable of deteriorating the quality of the read-back signal in two-dimensional magnetic recording. The reduction in the skew angle, therefore, is strongly desired in HDDs. We previously proposed a new actuator structure, a separated pivot-shaft actuator (SPA), for reducing the skew angle, and its satisfactory capability for seeking and tracking actuations was demonstrated using finite element method analysis. In this study, we assembled a prototype SPA, measured the frequency response functions to reveal the actual mechanical characteristics.

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Event date： 2015.9

Language：Japanese  

UV irradiation with the bias voltage between the magnetic disk and the counter electrode above disk surface increases the bonded ratio of the perfluoropolyether (PFPE) lubricant film on disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and were coated on disk surface. After coating of lubricant film, the UV irradiation treatment with the bias voltage to lubricated disk surface was performed and the depletion of these lubricant films was compared by the pin-on-disk test with the laser heating mechanism. As the results, the lubricant film treated by UV irradiation without the bias voltage showed deeper lubricant depletion than that with the bias voltage, and the ADOH showed shallower lubricant depletion than Z-tetraol. On the other hand, the molecular weight distributions of ADOH film on disk surface treated by UV irradiation with and without the bias voltage were compared using the time of flight secondary ion mass spectroscopy (TOF-SIMS), and the bias voltage was estimated to increase the dissociation of hydroxyl end-groups and the chemical adsorption to disk surface.

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Event date： 2015.6

Venue：Kobe Japan  

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Event date： 2015.6

Venue：Kobe Japan  

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Event date： 2015.6

Venue：Kobe Japan  

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Event date： 2015.6

Language：English  

We studied the effect of bias voltage between the slider and disk surfaces to reduce lubricant pickup by the slider. A perfluoropolyether (PFPE) lubricant film, which is coated on the disk surface, has been considered to be charged to a negative voltage by the air flow on the rotational disk surface. Because the PFPE lubricant film is negatively charged, the lubricant pickup should be reduced by a bias voltage with a negative voltage on the slider surface. We confirmed the lubricant pickup using a lubricant pickup test under different bias voltages. As a result, the positive voltage of the slider accelerated the lubricant pickup, and the negative voltage reduced it.

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Event date： 2015.6

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