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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Applied Physics  

A Au dendrite structure was obtained by only electroplating under a suitable potential. A blanch like nanostructure was formed along the crystal orientation. In this study, we attempted to fabricate a Au dendrite structure on the electrode of a quartz crystal by electroplating to increase the specific surface area. We estimated the effective surface area by cyclic voltammetry (CV) and monitored the frequency shift induced by antigen-antibody interaction by the quartz crystal microbalance (QCM) method. The dendrite structure with the largest surface area was formed under -0.95 V for 5 min. In the measurement of the antigen-antibody interaction, the frequency shifts of 40, 80, and 110 Hz were obtained with the dendrite structured QCM chips formed at the above potential for 1, 1.5, and 2.0 min, respectively. The sensitivity was improved compared with that QCM chip having a flat surface electrode.

DOI： 10.7567/JJAP.57.02CD01

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Electrochemical Society Inc.  

We focused on a cicada wing which has superhydrophobic surface, antireflection to the light, unique tribology, and antibacterial property. From the SEM view, circular truncated cones in nanoscale were widely spread with regularly. It was just like nanopillar array. After the signature pattern was analyzed, we mimicked its structure composed of Si. Si nanostructure was fabricated mainly by wet process to decrease the cost but its dimension was controllable. We reported antibacterial property of the structure. Fabricated Si nanopillar array showed antibacterial property to E. Coli.

DOI： 10.1149/07553.0001ecst

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Nanowires embedded in nanopores are potentially tough against surface scraping and agglomeration. In this study, we have fabricated Au and Ni nanowires embedded into anodic porous alumina (APA) and investigated their reflectance to study the effects of surface plasmon absorption properties and conversion from solar energy to thermal energy. Au nanowires embedded into APA show typical gold surface plasmon absorption at approximately 530 nm. On the other hand, Ni nanowires show quite a low reflectance under 600 nm. In the temperature elevation test, both Au and Ni nanowire samples present the same capability to warm up water. It means that Ni nanowires embedded into APA have almost the same photothermal activity as Au nanowires. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.06GH09

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The CuSn alloy nanotree formed by DC electroplating is a true three-dimensional (3D) structure with many branches that separate the trunk perpendicularly. We carried out the oxidation of CuSn nanotrees in atmosphere in order to study the possibility of such nanotrees for application to sensors. It was confirmed that the oxygen concentration in the CuSn nanotree oxide increased with temperature and reached 40 at.% at 350 degrees C. The optical reflectance spectra of the CuSn nanotree oxide formed at 250 degrees C showed a 3-4% reflectance in the wavelength range between 400 and 900 nm, and its behavior differed from those of Cu and Sn oxides formed at 250 degrees C. The temperature dependence of electrical resistivity for the CuSn nanotree oxide showed a typical semiconductor behavior. By the introduction of H-2, O-2, N-2, and CO gases into the chamber, the resistance of the CuSn nanotree oxide responded against H-2 most sensitively, as well as against O-2 and CO gases. From the resistance change tendency, it is strongly suggested that the CuSn nanotree oxide is a p-type semiconductor, because it shows an increase in conductivity caused by the adsorption of a negative charge such as O-. However, the conductivity decreases with the adsorption of a positive charge such as H+. The present study suggests the high potential of the CuSn nanotree oxide as a gas sensor, since it has a very high surface-to-volume ratio. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.06GH08

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Three-dimensional nano-tree-like structures consisting of single-crystalline CuSn alloy nanowires branching perpendicularly from their parent branches were observed. The nano-trees were formed by constant potential co-electrodeposition of Cu and Sn. The geometry of the branches had a four-fold symmetry around the parent branch, which originated from the crystalline structure of the mother CuSn crystal. XRD and TEM analysis revealed that the nanowire branches consisted of single-crystalline gamma-CuSn with < 100 > preferred growth directions. The addition of polyethylene glycol (PEG) with a molecular weight of 1000 in the plating bath is essential for the formation of the nano-tree structure. It is speculated that adsorbed PEG molecules on CuSn crystal planes with high Miller indices suppress CuSn alloy deposition, enhancing anisotropic growth of the CuSn crystal to form the nano-tree structure. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2016.03.046

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

An angle-resolved linearly polarized hard X-ray photoemission spectroscopy (HAXPES) system has been developed to study the ground-state symmetry of strongly correlated materials. The linear polarization of the incoming X-ray beam is switched by a transmission-type phase retarder composed of two diamond (100) crystals. The best value of the degree of linear polarization was found to be -0.96, containing a vertical polarization component of 98%. A newly developed low-temperature two-axis manipulator enables easy polar and azimuthal rotations to select the detection direction of photoelectrons. The lowest temperature achieved was 9 K, offering the chance to access the ground state even for strongly correlated electron systems in cubic symmetry. A co-axial sample monitoring system with long-working-distance microscope enables the same region on the sample surface to be measured before and after rotation. Combining this sample monitoring system with a micro-focused X-ray beam by means of an ellipsoidal Kirkpatrick-Baez mirror (25 mu m x 25 mu m FWHM), polarized valence-band HAXPES has been performed on NiO for voltage application as resistive random access memory to demonstrate the micro-positioning technique and polarization switching.

DOI： 10.1107/S1600577516003003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

This work develops a novel method for preparing a moth eye structure, which has a sub-wavelength periodical Si nanocone structure on Si(100) substrate, using two-step metal assisted chemical etching (MACE). The 1st MACE and 2nd MACE were respectively performed with the intention to form perpendicular Si nanowire arrays on a Si substrate and sharpening the Si nanowire arrays. We found that the inhomogeneous absorption and aggregation of Au particles used as a catalyst for the 2nd MACE was important to obtain the nanocone shape. The obtained Si nanocone arrays showed superior anti-reflecting properties especially in a wavelength below 600 nm compared with the Si nanowire arrays. A possible mechanism involved in the formation of the nanocone structure by the 2 step MACE is discussed in this paper. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mee.2016.01.030

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Language：English   Publisher：IOP PUBLISHING LTD  

DOI： 10.7567/APEX.9.039201

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Silicon nitridation was investigated at room temperature using a nitrogen neutral beam (NB) extracted at acceleration voltages of less than 100 V. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of a Si3N4 layer on a Si (100) substrate when the acceleration voltage was higher than 20V. The XPS depth profile indicated that nitrogen diffused to a depth of 36 nm for acceleration voltages of 60V and higher. The thickness of the silicon nitrided layer increased with the acceleration voltages from 20V to 60V. Cross-sectional transmission electron microscopy (TEM) analysis indicated a Si3N4 layer thickness of 3.1 nm was obtained at an acceleration voltage of 100V. Moreover, it was proved that the nitrided silicon layer formed by the nitrogen NB at room temperature was effective as the passivation film in the wet etching process. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2015.11.096

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

The nano structure derived from Anodic Aluminum Oxide (AAO) is controllable by the anodizing conditions such as voltage, anodizing time, and the acid solutions. Regularly arranged nanopores were fabricated with high aspect ratio. We tried to use the nano structure as a template to build nanowire array on the quartz crystal to enlarge the surface area bond to analyte. Evaluating the shape of the nanowire, average of the height and the diameter of the nanowire were 1 mu m and 50 nm, respectively. In this case, high aspect ratio more than 20 was achieved. We fabricated nanowires on the electrode of the QCM chip and tried to detect the antigenantibody reaction.

DOI： 10.1149/07516.0229ecst

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

Cicada wings have nanostructures which shows superhydrophobic property, non reflecting to the light, and antibacterial characteristics. To mimic the nano structure of a cicada wing, we fabricated nano-pillar array using metal assisted etching. Fabricated nano-pillar array showed higher antibacterial property for E. coli. Our introduced process has advantages for industrial usage because of low cost and low environmental load based on wet process.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

QCM is one of major sensing methods for volatile organic compounds (VOC), however, the method is affected by environments such as temperature, humidity, and airflow. To cancel the signals affected by environments, we used twin sensor QCM which has two electrodes on one quartz substrate. In fact, one Au electrode was used as a reference, and ZnO thin film was electrodeposited on the other electrode to detect ethanol. The surface morphology of ZnO was changed corresponding to the applied potential on the electrodeposition. Scaly surface was obtained at -0.8 V vs. Ag/AgCl. QCM with scaly ZnO surface showed high frequency change on exposing to ethanol gas. (C) 2016 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.proeng.2016.11.192

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Electrochemical Society Inc.  

We studied magnetic conduction property of the conductive filament formed in the ReRAM device having two ferromagnetic electrodes. Anisotropic Magnetoresistance (AMR) property was observed in the ON-state of the devices, however, negative MR occurred for the one device and positive MR occurred for another devices, There were abrupt change of resistance around 250 mT for these devices. Micromagnetic simulation study strongly suggested that the abrupt change of MR was caused by the single domain switching of the magnetic conductive filament (MCF). Furthermore, it is suggested that typical MCF size was 40 x 40 x 4 nm1 by assuming that MCF was composed of Ni metals, It is also suggested that the difference of negative AMR and positive AMR is derived from the location of MCF. The present results suggest a possibility of new multilevel memory devices which can be operated by both electric field as well as magnetic field.

DOI： 10.1149/07532.0065ecst

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The nitridation of silicon at the bottom of nanoscale trench patterns using a nitrogen neutral beam (NB) extracted with a low acceleration voltage of less than 100 V was studied at room temperature. By X-ray photoelectron spectroscopy (XPS) analysis, the formation of a Si3N4 layer was confirmed at the bottom of the trench when the acceleration voltage was higher than 20 V. The XPS depth profile suggested that nitrogen was diffused to a depth of 180 nm. In contrast, the bottom of the trench was not nitrided by the low-energy N+ ions produced by inductively coupled plasma (ICP). It is suggested that most of the N+ ions bombarded the top corner of the trench owing to the concentrated electric field around it. On the other hand, the neutral N-2 or N beam was not affected by the local electric field concentration, and it was able to reach bottom of the deep trench. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.06FH07

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Resistive change memory has been expected to be a next generation memory due to high-speed response. However, wide variations of switching voltages are often found in the current-voltage (I-V) characteristics and hinder the practical applications. We have tried suppressing the variation by three tactics based on the filament model; confinement of conductive filaments, concentration of electric field, and preparation of many routes for conductive filaments with the same electrical properties. In this study, we have investigated the combination of concentration of electric field method and preparation of many routes for conductive filaments in the insulator by electrochemical treatment (ET) using sulfuric acid. The I-V curves depend on the ET time. The best result is obtained in the long ET time. With regards to switching voltage distribution, the combination of two methods provide better switching characters than those of single method. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.06FH05

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Ferromagnetic conductive filaments (CFs) were formed in a conductive-bridge random access memory (CBRAM) with a Ni electrode using high current compliances during a set process. We investigated CFs in a Ni/HfO2/Pt CBRAM using the current compliance dependences of the set process, low-temperature characteristics, and anisotropic magnetoresistance (AMR). Set processes occurred when a positive bias was applied to the Ni electrode only; therefore, the switching phenomena showed polarity. The resistance of the ON state (low resistance state) was dependent on the current compliance between 2 and 5 mA. The ON state of the device showed a metallic conduction property, suggested by the temperature dependence of resistance. When a high current compliance (5 mA) was used for programming, the ON state showed AMR, which was direct evidence of ferromagnetic CF formation. This suggests that the formation of a ferromagnetic CF is associated with the accumulation of Ni ions that diffused from the Ni electrode. The OFF-state (high resistance state) resistance slightly increased with decreasing temperature and AMR was not observed. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.05ED02

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

ReRAMs using oxygen vacancy drift in their resistive switching are promising candidates as next generation memory devices. One remaining issue is degradation of the on/off ratio down to 102 or less with an increased number of switching cycles. Such degradation is caused by a local hard breakdown in a set process due to a very high electric field formed just before the completion of a conductive filament formation. We found that introducing an ultra-thin SiO2 layer prevents the hard breakdown by dynamical moderation of the electric field formed in the TaOx matrix, resulting in repeated switching while retaining a higher on/off ratio of about 105. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssr.201409531

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Electrochemical Society Inc.  

We investigated the stability and adsorption properties of a Pd nanoparticles which are used for catalyst of electroless plating on dielectrics substrate. Some additives for Pd nanoparticle dispersion significantly improved the stability of the dispersion without deteriorating the adsorption of the Pd nanoparticles. Furthermore, the additives redispersed agglomerated Pd nanoparticles. These results suggest a method for applying Pd nanoparticles in manufacturing processes.

DOI： 10.1149/06440.0077ecst

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Electrochemical Society Inc.  

For realizing high aspect ratio TSV with a low cost, the all-wet process utilizing electroless barrier and Cu-seed layers prior to Cu electroplated fill is one of the most promising methods. However, improvement of adhesion property of electroless plated barrier and seed layers on SiO&lt
inf&gt
2&lt
/inf&gt
has been intensively required. In this study, we studied displacement plating of Cu on electroless CoWB layer formed on SiO&lt
inf&gt
2&lt
/inf&gt
in an acidic bath. It turned out that displacement-plated Cu film grew with sacrifice of the partial CoWB layer, and showed a high adhesion strength that was enough to pass CMP process.

DOI： 10.1149/06440.0057ecst

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Nanowires have attracted significant interest because of their unique characteristics. Vapor-liquid-solid (VLS) growth is the standard method for fabricating nanowires and Au is the most commonly used catalyst. However, Au catalyst droplets diffuse over the Si substrate surface with a high migration velocity and agglomerate at relatively low temperatures. In our previous work, we reported a significant improvement in the positioning and diameter distribution of VLS-grown Si nanowires by inserting a diffusion barrier layer and concluded that the barrier layer suppressed the formation of AuSi eutectic droplets and prevented the droplets diffusing on the substrate surface during nucleation. In the present study, we analyzed the nucleation of the Au catalyst and examined its behavior during nucleation. Detailed multidirectional analysis and in situ observations confirmed that the formation and agglomeration of AuSi eutectic droplets was suppressed by the formation of a silicide layer. This because of the higher reaction temperatures between the diffusion barrier and the substrate silicon, and between the catalyst and the diffusion barrier, compared with the reaction between the Au catalyst and substrate silicon. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2014.07.023

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

An attempt to reduce the SET voltage and RESET current of resistive switching (RS) memory was made using a geometric array of nanopeak (NP) structures. Bottoms of anodic porous alumina were used to form the NP structures that act as guides for the formation of conductive filaments that effectively concentrate the electric field. Samples were fabricated with flat surfaces (FS) and with two types of NP structure with different NP pitch. The NP samples provided SET voltages less than 2 V with narrow distributions and the RESET current was lower than that with the FS sample. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

DOI： 10.1063/1.4892823

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The dependence of reflectance on the morphology of Si nanowire (SiNW) arrays was investigated. Several samples including vertically aligned NW arrays and bunched NWs were prepared by a combination of a wet etching process and two types of drying process. The optical reflectance of the NW arrays depended on the length and aggregation degree of NWs. The bunched NW arrays with high aggregation degree reduced the reflectance to less than 8% in a long visible wavelength range. It is considered that the significant reduction in the reflectance of the bunched NWs is ascribed to the combination of the macrostructure with NWs. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.06JF10

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We have tried suppressing variation of switching voltages which hinder the practical application of resistive switching random access memory. On the basis of a filament model, fabrication of the top electrode with small enough size against the filament size and confining the filament are thought to be the solutions. In this study, we have investigated the confinement effects on the switching voltage variations using anodic porous alumina with ordered nano holes. Variation of the voltage has a trend to reduce with enlarging the diameters of nano holes by chemical etching. The confinement is very effective to improve the reproducibility of the switching voltages. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.06JF07

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We investigated the resistive switching characteristics and temperature dependence of resistance of a Ni/NiOx/Pt resistive switching memory. The device was operated in a unipolar operation mode. From the temperature dependence of resistance, it is suggested that the conduction mechanism of the low-resistance state is metallic. Moreover, a deformed site that may correspond to the conductive filament appeared after the forming process. Cross-sectional transmission electron microscopy with energy dispersive X-ray analysis showed that the Ni atomic content at the NiOx of the deformed area was larger than those of other areas. It is strongly suggested that the conductive filament formed in the NiOx layer is composed of Ni atoms. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.05GD01

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

The all-wet process for TSV-fill utilizing electroless barrier and seed technologies prior to electroplating of Cu is promising methods to realize low-cost and highly reliable Cu-filled TSVs for 3-D integration of Si. Although there have been numerous studies to form electroless barrier layers such as Co- and Ni-alloys, poor adhesion of these barrier layers have been a serious problem. In this study, we studied effect of various additives on the adhesion strength of electroplated CoWB film. It is shown that addition of saccharine, which has both sulfone-and amino-groups, significantly improved adhesion strength.

DOI： 10.1149/05817.0059ecst

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

There is a question whether the conductive filament (CF) formed in the oxide layer of a resistive-switching random access memory is made of oxygen vacancies or metallic atoms. We investigated the CF of Ni/TiO2/Pt device using temperature coefficient of resistance (TCR), anisotropic magnetoresistance (AMR), and cross-sectional transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDX). The low resistance state (LRS) of the device showed metallic property by TCR measurement. Furthermore, the device in the LRS showed AMR, which was a direct evidence of the formation of ferromagnetic CF. The cross-sectional TEM-EDX observation revealed that a nano-sized Ni precipitation existed in the area nearby a conductive spot. It is intensively suggested that Ni atoms migrated from the adjacent Ni electrode to TiO2 layer to form the nano-sized ferromagnetic CF.

DOI： 10.1007/s00339-014-8769-5

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

We report on an origin of the conductive filament (CF) for a Ni/HfO2/Pt resistive switching memory. The device shows SET process (from high to low resistance), when positive bias is applied to the Ni electrode. RESET process (from low to high resistance) occurs during both positive and negative biases. We investigated the temperature dependence of resistance and magnetoresistance for the low resistance states (LRS) of the device, which were formed with different amount of a current compliance. LRS formed with the high current compliance has a linear temperature dependence of resistance compared with that formed with the low current compliance. Moreover, anisotropic magnetoresistance was observed for the LRS, which was formed with the high current compliance. This suggests that CF is made of the ferromagnetic Ni atoms when a high current compliance was used to form LRS.

DOI： 10.1149/06414.0029ecst

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

In this letter, we investigated HfOx thickness dependence of current-voltage characteristics and temperature dependence of resistance for Ni/HfOx/Pt resistance random access memory (ReRAM) device. There was a significant difference in switching properties between these devices whose oxide thicknesses differ only 1 or 2 nm. The devices showed bipolar resistive switching behaviors. The ON state resistance indicated a linear decrease of resistance with lowering temperature, which was typical for a metal. It should be noted that SET voltage as well as resistance of high resistance state increased almost linearly with increasing oxide thickness from 4.0 to 5.6 nm.

DOI： 10.1149/06414.0093ecst

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An investigation of current-voltage (I-V) characteristics and the temperature dependence of resistance in a resistive switching (RS) memory with a Cu/SiO2/Au device was performed. Moreover, conductive spots were observed by scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM). Both unipolar and bipolar operation modes were obtained. From the temperature dependence of resistance, it is suggested that the conduction mechanism of the low resistance state (LRS) is metallic conduction and that of the high resistance state (HRS) is variable-range hopping (VRH) conduction. The results of observing the device support this suggestion. We propose the switching mechanism in the Cu/SiO2/Au device from these results. (c) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.06GF04

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The control of the crystal orientation and diameter of vertically grown epitaxial Si nanowires was demonstrated using a combination of a vapor-liquid-solid (VLS) growth technique and the use of an anodic aluminum oxide (AAO) template on a single-crystal Si substrate. The [100], [110], and [111] nanowires were selectively obtained by choosing the Si substrate with appropriate crystal orientation. The diameter of a Si nanowire in the AAO template could be controlled by the modification of the pore size of the AAO template with anodic voltage during anodization. (c) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.06GF06

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Resistance change random access memory (ReRAM) has been expected to be a next generation non-volatile memory. However, poor reproducibility of threshold voltage at which the dramatic change of the resistivity occurs hinders the practical application. We have attempted to improve the reproducibility of switching voltages using anodic porous alumina whose nanoholes are quite useful to restrict the filament forming area on the basis of the filament model. In this study, we have reported the pore size and film properties dependences of the variation width of the switching voltages. Two kinds of oxide films prepared by oxalic and sulfuric acids with two different anodic times were used as the insulating layer. Contrary to our expectation, just the sulfuric samples indicate good improvement about the switching voltages. Considering that the size of the effective contact area is not enough small against the filament size, the changing the film properties seems to be important for the suppressing the variation of switching voltages. (c) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.06GF07

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A conformal diffusion barrier was formed in a high aspect ratio through-silicon via using electroless plating. Dense adsorption of Pd nanoparticle catalyst on SiO2 assisted the formation of a thin electroless Co-W-B layer, upon which an electroless Cu seed layer could be deposited. The adhesion strength of the Co-W-B film was enhanced by reducing the film thickness, and the maximum strength was obtained at a thickness of 20 nm. The Co-W-B layer exhibited good barrier properties against Cu diffusion to SiO2 after annealing at 300 degrees C, although slight diffusion of the Pd atoms in Cu was observed. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mee.2013.01.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Vapor-liquid-solid (VLS)-grown nanowires are promising building blocks for next-generation devices because of their unique characteristics. Although Au is a widely used catalyst with the largest operable parameter window for Si nanowire growth by the VLS method, Au catalyst droplets diffuse at a high migration velocity over a Si substrate surface and agglomerate at relatively low temperature, thus degrading the uniformity of Au catalyst droplets and Si nanowires. Our aim is to improve the controllability of nanowire growth, positioning, and diameter, which are essential attributes for practical applications. To accomplish this, a diffusion barrier layer was inserted between the catalyst and substrate. Length and diameter uniformity were considerably improved for nanowires grown together with the formation of a silicide layer as a diffusion barrier. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2012.12.140

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

The electric conduction mechanism of electrochemically treated anodic aluminum oxide (AAO) resistance switching (RS) memory is investigated. The current-voltage characteristics of the AAO were measured for both of high resistance state and low resistant state at room temperature. The conduction mechanism of a high resistance state can be explained by separating into three regions of ohmic conduction, space charge limited current (SCLC), and Fowler-Nordheim (F-N) tunneling. It was suggested that the F-N tunneling deteriorates the reproducibility of switching voltages.

DOI： 10.1149/05034.0049ecst

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

In this study, we investigated to control adhesion property of the electroless plated barrier layer on SiO2 by addition of saccharin and its deposition profile in a high aspect ratio TSV with inhibitor and saccharin. We achieved high adhesion strength of barrier layer by addition of suitable amount saccharin. Furthermore, we succeeded in the formation of thin continuous electroless barrier layer for a high aspect ratio TSV with addition of both inhibitor and saccharin. The proposed highly adhesive and conformal electroless barrier layer formation would provide a highly reliable all-wet TSV filling process.

DOI： 10.1149/05032.0013ecst

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

We investigated resistive switching (RS) characteristics and temperature dependences of a resistance of the Ni/TiO2/Pt resistive switching memory. The device was operated in a unipolar mode. From the temperature dependence of resistance, it is shown that the conductive filament in the low resistance state (LRS) is metallic. Fabricated Pt/NiO/Pt RS memory to compare the RS characteristics showed similar RS phenomenon. The conductive mechanism of the Pt/NiO/Pt RS memory is also metallic. Temperature coefficients of resistance of various RS memory were compared.

DOI： 10.1149/05805.0027ecst

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We studied electroless Co-W-B plating in through-Si vias (TSVs) using Pd nanoparticles (Pd-NPs) as a catalyst. The density of adsorbed Pd-NPs on SiO2 in the high aspect ratio TSVs was over 8500/mu m(2) after a long adsorption treatment. No Pd-NP agglomeration was observed. In contrast, agglomerates of large particles were observed after a conventional Sn-Pd colloid adsorption treatment. Using a Pd-NP catalyst, we succeeded in the formation of a thin continuous electroless Co-W-B barrier layer in high aspect ratio TSVs. The adhesion strength of the Co-W-B layer increased with increasing particle density of the Pd-NPs. These results indicate that the process with Pd-NPs catalyst is a promising method for the formation of a thin barrier layer in high aspect ratio TSVs at low temperatures.(c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2012.04.165

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Arrays of vertically aligned Si-nanopillars, with average diameters of 100 nm and 5 mu m length, have been prepared by wet chemical etching of crystalline silicon in a special manner. Samples with smooth-and porous-walled nanopillars have been studied. In the case of the latter, Si-nanocrystals, passivated with SiOx, decorating the surface of the nanopillars are identified by the means of TEM and FTIR. When excited by UV-blue light, the porous-walled Si-nanopillars are found to have a strong broad visible emission band around 1.8 eV with a nearly perfect Gaussian shape, mu s luminescence lifetimes, minor emission polarization and a non-monotonic temperature dependence of luminescence. The Si-nanocrystal surface is found to be responsible for the luminescence. The red-shift of the emission maximum and the luminescence quenching induced by oxidation in UV-ozone confirm this assumption. A model of luminescence involving UV photon absorption by Si-nanocrystals with subsequent exciton radiative recombination on defect sites in SiOx covering Si-nanocrystals has been proposed. Possible applications of the nanopillar arrays are discussed.

DOI： 10.1088/0957-4484/23/47/475709

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The morphological changes of a nanostructured Si surface prepared by metal assisted etching were investigated. We used a mixture of silver nitrate (AgNO3) and hydrofluoric acid (HF) as an electroless plating bath of Ag, as well as an etching solution of Si. With a change in silver ion concentration in the etching solution, three types of etched Si nanostructures were observed: "nanowire", "porous wall", and "polished". We developed a phase diagram of the morphology of the etched Si surface. With increasing concentration of AgNO3 in the etching solution, the surface morphology of etched Si changes from nanowire to porous wall, and finally, polished for regardless of Si resistivity. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.11PE02

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have studied variation of switching voltage of resistive random access memory (ReRAM). Basically, the switching voltage at every switching has a different value because there are many conduction paths, which are randomly chosen at every switching with different conductivity in an oxide insulator between top and bottom electrodes. Limitation of the number of conductive paths is expected to lead the suppression of the variation of switching voltage. In this study, Ni nanorods buried into the nanoholes of an anodic aluminum oxide (MO) film have been fabricated to restrict the formation of many filaments and the switching behaviors of the In/NiO/Ni nanorods has been investigated. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mee.2012.07.035

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

The resistive switching random access memory (ReRAM) device using Ni/NiO nanowire as a building block was demonstrated
this is prepared by a combination of top-down and bottom-up techniques. The Ni nanowire arrays on Si substrates were prepared by electroplating of Ni into the anodic aluminum oxide (AAO) template, and the surface of the nanowires were oxidized by O 2 plasma treatment at room temperature. We observed an improvement of stability of the switching properties in the nanowire device compared with the device using nickel oxide thin film. © 2012 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2012.476

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have investigated the current-voltage characteristics of a resistive switching memory (ReRAM), especially the reproducibility of the switching voltage between an insulating state and a metallic state. The poor reproducibility hinders the practical use of this memory. According to a filament model, the variation of the switching voltage may be understood in terms of the random choice of filaments with different conductivities and lengths at each switching. A limitation of the number of conductive paths is expected to lead to the suppression of the variation of switching voltage. In this study, two strategies for the limitation have been proposed using an anodic porous alumina (APA). The first is the reduction of the number of conductive paths by restriction of the contact area between the top electrodes and the insulator. The second is the lowering of the resistivity of the insulator, which makes it possible to grow filaments with the same characteristics by electrochemical treatments using a pulse-electroplating technique. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.06FF11

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

The macro and micro morphology, and the crystal structure of Si nanowires prepared by singlestep catalytic metal assisted etching were investigated. Here, we prepared the Si nanowires by metal assisted etching with electroless-deposited Ag catalyst on Si (100) substrate. We used mixture of silver nitrite and hydrofluoric acid as a plating bath of Ag, as well as etching solution of Si. The morphology and crystalline structure of the nanowires as a function of concentration of silver nitrite in etching bath were investigated by SEM and cross-sectional TEM observations. With increasing concentration of the silver nitrite in the etching solution, the surface of nanowires tends to be porous structure with very fine pores of a few nm (porous Si nanowire). When concentration of silver nitrite is low, single crystal Si nanowires with a smooth surface without pores were observed. The porous Si nanowires consisted of the nano scaled crystals and partially amorphous Si nears its surface. © 2012 IEEE.

DOI： 10.1109/IMFEDK.2012.6218593

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

We demonstrated fabrication of Cu-TSV using all-wet process, which has a high potential to apply for the via-last Cu-TSV process. A Co-W alloy diffusion barrier layer was formed on SiO2 layer by electroless plating at 60 degrees C with Pd nanoparticle catalyst. The barrier layer was thin and continuous throughout a 2 phi x 24 mu m TSV and its adhesion strength on SiO2 was as high as that of PVD-Ta. The Co-W alloy layer has undergone an interdiffusion test, which showed a high resistance against Cu diffusion into SiO2 layer. Then, seed layer was formed by electroless Cu deposition on the Co-W alloy layer through displacement reaction. These results reveal a feasibility of all-wet fabrication in a high aspect ratio TSV process.

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

We investigated a method for preparation of self-ordering nanopore arrays with the interpore distance of 60nm by guided self-organization of anodic aluminum oxide (AAO) with a pre-patterned ordered array of indentations of Al film. An ordered triangular array of 100 nm-pitch indentations was formed on Al film by ion beam etching (IBE) with the EB resist mask, and then it was used as a guide for formation of AAO pore. We found it was possible to reduce an interpore distance of AAO to 1/√3 of the pitch of the indentation by the choice of appropriate IBE parameters and anodization voltage. © 2012 IEEE.

DOI： 10.1109/IMFEDK.2012.6218612

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated the effect of single-step electrodeposition methods for the fabrication of CZTS thin films as solar cell absorber layer. For deposition of CZTS thin films, a potentiostatic method and a pulsed potential electrodeposition method were examined. Near stoichiometric CZTS thin films were prepared by potentiostatic deposition method. On the other hands, the samples deposited by pulsed potential method showed wire-like CZTS nanostructures. The nanowires were composed of the Cu and S element mainly and included Zn and Sn microelements. From these results, we realized that the electrodeposition methods strongly affect the structural and compositional characteristics of as-deposited CZTS thin films. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2011.05.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An all-wet process was achieved using electroless deposition of barrier and Cu seed layers for fabrication of a high aspect ratio through-Si via (TSV). Formation of a thin barrier metal layer of Ni-B, Co-B and Co-W-B is possible using a Au nanoparticle (AuNP) catalyst, which is densely adsorbed on the SiO(2) of the TSV sidewall. A silane coupling agent of 3-aminopropyl-triethoxysilane is effective for enhancement of the density of adsorption for AuNP. A conformal electroless Cu layer is deposited on the barrier layer by displacement plating without a catalyst. The adhesion strength between the electroless barrier layer and the SiO(2) substrate is increased by annealing at 300 degrees C. These results strongly suggest that an all-wet process for the formation of Cu-filled TSV with a high aspect ratio is practically possible. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2011.02.078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Ultrahigh-density Co nanowire arrays were fabricated by the combined use of the anodic aluminum oxide (AAO) template formed on a Si substrate and pulse DC electrodeposition. The AAO templates were prepared with the anodic voltages from 3 to 40 V, whose diameters were from 15 to 40 nm. Using the AAO template with an anodic voltage less than 3 V, the wire density exceeded 2.88 Tbit/in.(2). The magnetic property of the nanowire arrays indicated a strong perpendicular magnetic anisotropy, and we observed the tendency of increase in coercivity with decreasing nanowire diameter. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.06GE01

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

A large magnetoresistance exceeding 290% at room temperature was observed in a nanoconduction path (NCP) formed by dielectric breakdown of an SiO2 layer in contact with a ferromagnetic layer. Switching of the resistance between a low-resistance state (LRS) and a high-resistance state (HRS) occurred at magnetic fields of 0.2-0.6 T. The current-voltage characteristic of HRS showed a clear tunneling behavior, while that of LRS showed a weak nonlinearity. A set-up process with some amount of current stress was necessary to observe magnetoresistance switching. It is suggested that a nanogap is formed in a ferromagnetic NCP as a result of electromigration during the set-up process. The detailed mechanism has not yet been understood, however, magnetoresistance switching seems to be caused by a reproducible change of the nanogap distance concomitant with a switching of the magnetization of a ferromagnetic NCP. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.06GG15

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

The formation of a diffusion barrier layer in a through-Si via (TSV) has been studied with a combination of nanoparticle catalyst and electroless plating (ELP). We used Au-nanoparticles (Au-NPs) or Pd-nanoparticles (Pd-NPs) as catalysts for ELP of Ni- and Co-alloy barrier layers. We studied deposition of Ni-B and Co-B films in high-aspect-ratio (AR) TSV. Then, we succeeded in controlling the deposition profile of Ni- B in a high-AR TSV by the addition of bis(3-sulfopropyl)-disulfide (SPS). SPS turned out to be an inhibitor of electroless plating of Ni-B. On the other hand, the Co-B film was deposited conformally without additive. The electrical resistivity of Cu after annealing Cu/barrier stacked structure suggests that Co-B has better thermal stability than Ni-B. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.05ED01

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

Control of crystal orientation of vertically grown epitaxial Si (111) and (110) nanowire arrays on Si substrate has been demonstrated using a combination of an anodic aluminum oxide (AAO) template and vapor - liquid - solid (VLS) growth method. The crystal orientation of the nanowire was investigated by transmission electron microscopy. A growth direction of the nanowire arrays was guided perpendicular to the surface of the substrate by the AAO template, and the crystal orientation of the nanowire arrays was selected using the single crystal Si substrate properly cut in desired orientation. © 2011 Materials Research Society.

DOI： 10.1557/opl.2011.1131

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

Assisted by noble metal particles, non-(100) Si substrates were etched in solutions with different oxidant concentrations at different temperatures. The etching directions of (110) and (111) Si substrates are found to be influenced by the concentration of oxidant in etching solutions. In solutions with low oxidant concentration, the etching proceeds along the crystallographically preferred (100) directions, whereas the etching occurs along the vertical direction relative to the surface of the substrate in solutions with high oxidant concentration. These phenomena are found for both and p-type substrates as well as in experiments with different oxidants. The experiments on metal-assisted chemical etching are complemented by additional experiments on metal-assisted electrochemical etching of (111) Si substrates with different current densities. As a function of current density, a change of etching directions is observed. This shows that the change of the etching directions is mainly driven by the oxidation rate. On the basis of these phenomena, we have demonstrated fabrication of Si nanopores with modulated orientations by periodically etching a (111) substrate in solutions of low and high oxidant concentrations.

DOI： 10.1021/jp911121q

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Silicon nanotubes (SiNTs) are compatible with Si-based semiconductor technology. In particular, the small diameters and controllable structure of such nanotubes are remaining challenges. Here we describe a method to fabricate SiNTs intrinsically connected with cobalt silicide ends based on highly ordered anodic aluminum oxide (AAO) templates. Size and growth direction of the SiNTs can be well controlled via the templates. The growth of SiNTs is catalyzed by the Co nanoparticles reduced on the pore walls of the AAO after annealing, with a controllable thickness at a given growth temperature and time. Simultaneously, cobalt silicide forms on the bottom side of the SiNTs.

DOI： 10.1088/0957-4484/21/5/055603

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A bottom-imprint method to fabricate high-quality Si [100] nanowire arrays is described (see figure). This new approach combines the functions of a highly ordered anodic aluminum oxide (AAO) template that acts as both a stamp and a template. Vertically aligned, Al-catalyzed Si nanowire (NW) arrays are grown epitaxially on the Si substrate with a narrow size distribution.

DOI： 10.1002/adma.200900995

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

The metal-assisted etching direction of Si(110) substrates was found to be dependent upon the morphology of the deposited metal catalyst. The etching direction of a Si(110) substrate was found to be one of the two crystallographically preferred < 100 > directions in the case of isolated metal particles or a small area metal mesh with nanoholes. In contrast, the etching proceeded in the vertical [(1) over bar(1) over bar0] direction, when the lateral size of the catalytic metal mesh was sufficiently large. Therefore, the direction of etching and the resulting nanostructures obtained by metal-assisted etching can be easily controlled by an: appropriate choice of the morphology of the deposited metal catalyst. On the basis of this finding, a generic method was developed for the fabrication of wafer-scale vertically aligned arrays of epitaxial [110] Si nanowires on a Si(110) substrate. The method utilized a thin metal film with an extended array of pores as an etching catalyst based on an ultrathin porous anodic alumina mask, while a prepatterning of the substrate prior to the metal depostion is not necessary. The diameter of Si nanowires can be easily controlled by-a combination of the pore diameter of the porous alumina film and varying the thickness of the deposited metal film.

DOI： 10.1021/nl803558n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A novel bottom imprint method to fabricate high-quality Si [100] nanowire arrays is demonstrated. This new approach combines the functions of a high-ordering AAO template as a stamp and template simultaneously. By the protective polymer layer in the hot imprint, the vertical 40 nm Si nanowire arrays grow epitaxially on the Si substrate with a narrow size distribution

DOI： 10.1002/adma.200802156

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

Vertically aligned epitaxial Ge/Si heterostructure nanowire arrays on Si(100) substrates were prepared by a two-step chemical vapor deposition method in anodic aluminum oxide templates. n-Butylgermane vapor was employed as new safer precursor for Ge nanowire growth instead of germane. First a Si nanowire was grown by the vapor liquid solid growth mechanism using Au as catalyst and silane. The second step was the growth of Ge nanowires on top of the Si nanowires. The method presented will allow preparing epitaxially grown vertical heterostructure nanowires consisting of multiple materials on an arbitrary substrate avoiding undesired lateral growth.

DOI： 10.1021/nl8035756

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

Large-area high density silicon nanowire (SiNW) arrays were fabricated by metal-assisted chemical etching of silicon, utilizing anodic aluminum oxide (AAO) as a patterning mask of a thin metallic film on a Si (100) substrate. Both the diameter of the pores in the AAO mask and the thickness of the metal film affected the diameter of SiNWs. The diameter of the SiNWs decreased with an increase of thickness of the metal film. Large-area SiNWs with average diameters of 20 nm down to 8 nm and wire densities as high as 10(10) wires/cm(2) were accomplished. These SiNWs were single crystalline and vertically aligned to the (100) substrate. It was revealed by transmission electron microscopy that the SiNWs were of high crystalline quality and showed a smooth surface.

DOI： 10.1021/nl802324y

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

The synthesis of epitaxial Si nanowires with growth direction parallel to Si [100] on Si(100) substrate was demonstrated using a combination of anodic aluminum oxide (AAO) template, catalytic gold film sandwiched between the template and the Si(100) substrate and vapor-liquid-solid growth using SiH4 as the Si source. After growing out from the AAO nanopores, most Si nanowires changed their diameter and growth direction into larger diameter and (111) direction.

DOI： 10.1007/s00339-007-3984-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Growth of vertical epitaxial Si(100) nanowires on Si(100) substrates is demonstrated (see figure) using a combination of an anodic aluminum oxide template, catalytic An particles embedded in nanopores directly on the Si substrate by using electroless deposition, and vapor-liquid-solid growth using SiH4. HF acid treatment of the porous alumina template is important to realize a direct contact between deposited An in the AAO nanopores and the Si substrate.

DOI： 10.1002/adma.200700153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

We established a method to clean the Si surface that exists at the bottom of anodic aluminum oxide (AAO) nanoholes after removal of the amorphous barrier layer, and we succeeded in the preparation of epitaxial Cu dot arrays on the Si surface in the nanoholes. The Si surfaces at the AAO nanohole bottoms were cleaned with dilute hydrofluoric acid after annealing at 900 degrees C in Ar ambient, and we sputtered Cu on the AAO template to form Cu dot arrays. This method for preparing nanohole arrays on a single crystalline substrate enables growth of a variety of highly regular epitaxial nanodot/wire arrays. (c) 2006 The Electrochemical Society.

DOI： 10.1149/1.2176891

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

A simple fabrication process is presented for highly-ordered, highly-oriented carbon nanotube and nanorod arrays by filling alumina nanohole templates with a carbon precursor, polyacrylonitrile (PAN). X-ray photoelectron spectra analysis indicates that PAN changes its chemical structure to sp(2) C-C structure after carbonization at 600 degrees C. Raman characterization of the resulting carbon nanostructure demonstrates a high quality graphite structure. The proposed method may be used to develop carbon nanostructure-based devices.

DOI： 10.1143/JJAP.44.5289

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Co wire array with 50 nm intervals was formed by electrodeposition in porous alumina template that was formed on Si substrate. Coercive field of Co wire array under perpendicular magnetic field significantly increased when aspect ratio increased from 1.5 to 2.5. This behavior was well explained by the micromagnetic simulation when magnetic anisotropy axis was assumed to be parallel to the substrate. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.320

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Valence-band and conduction-band electronic structure of the transparent p-type semiconductor (LaO)CuS and the Ca and Ni co-doped system (La1-xCaO)Cu1-xNixS (xless than or equal to0.10) has been investigated by means of photoemission and inverse-photoemission spectroscopies. It is confirmed that the valence bands of (LaO)CuS are composed of the bonding and antibonding states of the Cu 3d (t(2g)) and S 3p orbitals as well as the nearly localized Cu 3d (e(g)), and the O 2p states. With increasing x up to x=0.03, the structure due to the Cu 3d (e(g)) states shifts away from the Fermi level (E-F) and the energy separation between the valence-band maximum and conduction-band minimum decreases rapidly, followed by an appearance of new density of states (DOS) derived from the Ni 3d and S 3p states just above E-F of (LaO)CuS. For xgreater than or equal to0.03, the new DOS shows up with x, while the energy position of the Cu 3d (e(g))-derived structure no longer shifts. The finite DOS at E-F has been observed as a clear structure for x=0.10. These results are not understood in terms of a rigid-band model. We propose a different band model for (La1-xCaxO)Cu1-xNixS taking into account the Ni 3d and S 3p-derived new DOS.

DOI： 10.1103/PhysRevB.68.035112

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Static transport properties and transient thermoelectric effect (TTE) of beta-FeSi2 single crystals, which has received considerable attention as optical and thermoelectric devices, have been measured. The Hall and TTE data clearly showed the existence of multiple conduction carriers. From these results, the tentative band scheme is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02462-6

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Event date： 2016.10

Venue：Hawaii, USA  

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Venue：Hawaii, USA  

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Venue：Hawaii, USA  

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Event date： 2016.9

Venue：Hungary  

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Venue：Sendai, Japan  

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Venue：Tessalonik, Greece  

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Venue：Munich, Germany  

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Venue：Munich, Germany  

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Venue：Brussels, Belgium  

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Venue：Nagoya, Japan  

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Venue：Toyama, Japan  

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Venue：Phonenics, USA  

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Venue：Hague, Netherlands  

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Venue：Sendai, Japan  

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Venue：Kyoto, Japan  

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Venue：Chicago, USA  

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Venue：大阪  

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Venue：神奈川  

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Venue：大阪  

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Venue：Boston, USA  

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Venue：Sapporo  

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Venue：Taipei, Taiwan  

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Venue：京都  

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Venue：Izmir, Turkey  

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Venue：大阪  

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Venue：京都  

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Venue：Osaka  

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Event date： 2012.11

Venue：HANGZHOU. CHINA  

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Venue：Honolulu, USA  

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Venue：Honolulu, USA  

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Venue：Honolulu, USA  

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Venue：Honolulu, USA  

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Venue：KOBE, JAPAN  

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Venue：KOBE, JAPAN  

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Venue：KOBE, JAPAN  

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Venue：KOBE, JAPAN  

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Venue：TOKYO, JAPAN  

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Venue：BUSAN, KOREA  

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Venue：ZURICH, SWISS  

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Event date： 2012.5

Venue：San Diego, USA  

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Venue：Sun Francisco,USA  

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Event date： 2012.5

Venue：OSAKA, JAPAN  

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Event date： 2012.2

Venue：OSAKA, JAPAN  

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