bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Cu2ZnSnS4 Thin Films Prepared by Photo-Chemical Deposition
Authors: Moriya Katsuhiko , Tanaka Kunihiko , Uchiki Hisao
Published: July 2005

Cu2ZnSnS4 thin films were prepared by photo-chemical deposition (PCD) from aqueous solution containing CuSO4, ZnSO4, SnSO4 and Na2S2O3. The compositional ratio of the films was dependent little on pH of aqueous solution and the surface of the samples became smooth by use of aqueous filter. A sample annealed at 400°C was a p-type semiconductor and showed photoconductivity. This is the first observation of photo-conductivity from semiconductor films deposited by PCD, to the best of our knowledge.
Defect States in CuInS2 Crystals Grown by Traveling Heater Method
Authors: Onishi Takashi , Abe Kenichiro , Miyoshi Yoshihiro , Iwai Masaya , Wakita Kazuki
Published: July 2005

The defect-related donor-acceptor pair emissions in photoluminescence spectra of CuInS2 crystals grown by the traveling heater method have been investigated to characterize the defects in the crystals. The energy levels of donors have been deduced to be 36 and 63–69 meV. Acceptors have been estimated to lie much deeper with energy levels at 113, 150, 180 and 220 meV. The origin of the donor and acceptor levels is discussed.
Crystal Structure and Optical Properties of Defect-Chalcopyrite-Type MnGa2S4
Authors: Tsuboi Nozomu , Ogihara Koh , Suda Yasuhiro , Oishi Koichiro , Kobayashi Satoshi , Kaneko Futao
Published: July 2005

The crystal structure of MnGa2S4 grown by the iodine transport method was refined by Rietveld analysis of its powder X-ray diffraction data, and it was confirmed to be the defect chalcopyrite structure. No emissions can be observed near the absorption edge region, but a red broad emission band having an asymmetric spectral shape with a low-energy tail is observed in the deep region at room temperature. The red broad emission band is considered to be due to the transition from the lowest excited state 4T1(4G) to the ground state 6A1(6S) of the Mn2+ ion, because five photoluminescence excitation bands corresponding to five optical absorption bands are assigned to transitions from the ground state 6A1(6S) to the excited states 4T1(4G), 4T2(4G), 4E(4G)+4A1(4G), 4T2(4D) and 4E(4D). The role of the Mn2+ ion with respect to the luminescence property of the defect-chalcopyrite-type MnGa2S4 is similar to its role with respect to the luminescence property of zinc-blend-type Mn-doped ZnS. This is reasonable because the Mn2+ ion is tetrahedrally coordinated by four S2- ions in both the defect-chalcopyrite-type MnGa2S4 and the zinc-blend-type Mn-doped ZnS.
Preparation of Ce-Doped CaGa2S4 Crystals by Melting Method and Their Optical Properties
Authors: Takayama Katsuhiko , Tanaka Kunihiko , Uchiki Hisao
Published: July 2005

Transparent Ce-doped CaGa2S4 bulk crystals were synthesized using a self-flux method. These bulks had high transmittance in luminescence region of 450 nm to 600 nm. Dependence of luminescence intensity on excitation power was observed using a pulsed dye laser excitation. Saturation of luminescence intensity was observed for the first time in this material when the excitation power density exceeded 10 MW/cm2. This saturation was assumed to result from excited state absorption (ESA), and analyzed with a 4-level transition model involving ESA.
Preparation of Nano-Structured C60 Thin Films
Authors: Kinjo Akane , Okuyama Hiroki , Iwata Nobuyuki , Yamamoto Hiroshi
Published: July 2005

Sapphire (0001) substrates were annealed at 1000°C for 12 h in air to obtain flat surfaces with a step-terrace structure. Au films were deposited on the substrates using the molecular beam epitaxy (MBE) method, at various substrate temperatures. The surface morphology of the films was observed by means of atomic force microscopy (AFM). A quasi one-dimensional alignment of Au particles was partially prepared along the steps at the substrate temperature of 620°C. On the other hand, an atomically flat Au thin film was obtained at the low substrate temperature of 130°C. A C60 monolayer was obtained by re-evaporating the C60 molecules deposited on the Au films, which was confirmed by X-ray photoelectron spectroscopy (XPS).
Effect of Oxidation Temperature on the Morphology of ZnO Nanowires Fabricated by Directed Melt Oxidation of Al-Zn Alloy
Authors: Kim Ssang-Jo , Lee Won-Jae , Shin Byoung-Chul , Kim Il-Soo , Lee Geun-Hyoung
Published: July 2005

ZnO nanowires were synthesized by directed melt oxidation of Al-Zn alloy at the temperature over 900°C in an air. Straight type nanowires were formed on the surface of the alloy oxidized at 950°C. However for the alloys oxidized over 1000°C, tetrapod-shaped ZnO nanowires with four legs, extended from center, were found in high yield and distributed uniformly on the whole surface. No other shaped crystals and powders were found. X-ray diffraction (XRD) pattern revealed that the nanowires were ZnO with wurtzite structure of hexagonal phase. The diameter of nanowires was controlled to 80 nm and the length to 20 micrometers. Higher temperature produced nanowires with larger diameter and longer length.
Synthesis of Single-Walled Carbon Nanotubes by Pulsed Wire Discharge
Authors: Kobayashi Ryouta , Nishimura Seigo , Suzuki Tsuneo , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2005

Experimental studies have been carried out to produce single-walled carbon nanotubes (SWCNTs) by pulsed wire discharge (PWD). To prepare soot, carbon fibers were discharged in nitrogen gas by PWD. Soot was collected after the discharge and was observed by means of high-resolution transmission electron microscopy. In the soot collected, we found SWCNTs of 1.2 nm in diameter. On the basis of these results, we have concluded that PWD could be a novel SWCNTs synthesis method.
Synthesis of Fe-N Nanosized Powders by Pulsed Wire Discharge
Authors: Suwa Koji , Suzuki Tsuneo , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2005

Fe-N nanosized powders were prepared by pulsed wire discharge (PWD). The powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD revealed that the powder synthesized in N2 gas was α-Fe, while that synthesized in N2/NH3 mixed gas was a mixture of α-Fe, γ-Fe, and γ'-Fe4N. The XRD relative intensity ratios of α-Fe to γ'-Fe4N and γ-Fe increased with a decrease in the total gas pressure. The energy deposited in the Fe wire before explosion decreased significantly with a decrease in total gas pressure. The number of submicron-sized particles observed by TEM decreased with an increase in total gas pressure.
Structural Studies of High-Performance Low-k Dielectric Materials Improved by Electron-Beam Curing
Authors: Yoda Takashi , Nakasaki Yasushi , Hashimoto Hideki , Fujita Keiji , Miyajima Hideshi , Shimada Miyoko , Nakata Rempei , Kaji Naruhiko , Hayasaka Nobuo
Published: July 2005

With the use of a newly developed electron beam (EB) curing process, an advanced methylsilsesquioxane (MSQ) low-k dielectric (LKD) film of k=2.9 was developed. It is noteworthy that the EB curing process can drastically improve the mechanical strength of LKD film and reduces the thermal budget without increasing the k value. The X-ray absorption fine structure (XAFS) study on the LKD was conducted to clarify the structural change upon EB curing. The structure of the film was compared with those of two different types of other MSQ films, the ladder-network structure and the random-network structure, and a chemical vapor deposition (CVD) film. The Si–O–Si bond angle and Si–O (Si–C) bond length were determined by fitting the Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra. Si–O–Si bond angle of LKD film was found to be between those of the ladder and the random structure, which are 135° and 147°, respectively. The X-ray absorption near-edge structure (XANES) spectra of LKD film revealed two broad features corresponding to a mixture of the two structures. In contrast, Si–O–Si angles of the EB-cured LKD film and the CVD film were similar, and the XANES features of both films were almost identical with those of the random structure. The electronic structure as determined from XANES spectra was also discussed by comparing three-dimensional-linkage models obtained by ab initio calculations. We confirmed that the EB curing process of LKD film causes a drastic structural change. The change from the mixture of ladder and random structures to the completely random structure was caused by C–H bond breaking followed by the formation of new polymer-like clusters with C–C bonds.
Growth of ZnO Nanorods on Cu Implanted Substrates
Authors: Takeyama Akinori , Yamamoto Shunya , Yoshikawa Masahito , Ito Hiroshi
Published: July 2005

ZnO nanorods were successfully synthesized on Cu implanted substrates by chemical vapor transport (CVT). Hexagonal shaped nanorods with a diameter of 200 nm were grown nearly perpendicular to the Cu implanted substrate. ZnO nanorods were selectively grown on the Cu implanted area of the substrate, and the average density of the ZnO nanorods increased as the average density of the Cu precipitates resulting from the nucleation of the implanted Cu atoms increased. The facts strongly indicate the Cu precipitates served as the catalytic particles. For the first time it is shown ion implantation and subsequent annealing are an effective tool for the fablication of substrates dispersed with the catalytic particles as the growth site of the ZnO nanorods.
New Developments in Experimental and Analytical Aspects of Light Figure Spectroscopy
Authors: Mamedov Nazim , Shim Yonggu , Yamamoto Nobuyuki
Published: July 2005

Recent developments in light figure spectroscopy are reviewed with a purpose to promote their large-scale application to anisotropic materials and thin films. Both absolute and relative analytical approaches and the results of the experimental approval on the well-known uniaxial calcite, CaCO3, are given. Further generalization and extension onto optically active materials are described with a stress on a shrinkage effect that was predicted and observed for the first time. The numbering of the interference curves in the presence of gyration is shown to be different in comparison with gyration-free case. A universal approach to the determination of the correct interference order is proposed and found to be in a good agreement with experimental data on CaCO3, TeO2 and AgGaS2. The effectiveness of the light figure method with regard to the nanomodulated structures is demonstrated by the recent application to the novel thallium-contained incommensurate materials, TlInS2 and TlGaSe2. Thin film applications are discussed in terms of the merits of homogeneously and non-homogeneously polarized testing beams and isotropic and anisotropic substrates. A preference is given to anisotropic substrates which can provide creation of the optical vortexes with ellipsometric or higher sensitivity to film parameters and open a gateway to the light-figure-based characterization of the anisotropic films with vanishing thickness and optical anisotropy.
Photoluminescence of Praseodymium-Doped Srn+1TinO3n+1 (n=1, 2, ∞)
Authors: Inaguma Yoshiyuki , Nagasawa Daisuke , Katsumata Tetsuhiro
Published: July 2005

Perovskite-related compounds, Sr
n+1Ti
n
O3n+1: Pr3+ (n=1, 2, ∞), were prepared by a Pechini-type polymerizable complex method using a citric metal complex and their photoluminescence properties were investigated. The photoluminescence spectra of these compounds show distinct peaks at approximately 490 nm and/or 610 nm, which correspond to the intra-4f transitions from the excited state 3P0 to the ground state 3H4, 1D2 to 3H4 of Pr3+, respectively. The excitation process is consistent with the transition between the valence band and the conduction band in host materials. The most intense red emission was observed for the compound with n=2 (Sr3Ti2O7: Pr3+), following by the compounds, n=1 and n=∞. The differences in luminescent properties among the compounds originate from the structural dependence of the energy transfer from the host to the activator Pr3+, and the site symmetry of Pr3+.
Luminescence Properties of Delafossite-Type CuYO2 Doped with Calcium, Oxygen or Rare Earth Tb
Authors: Tsuboi Nozomu , Ohara Hiroshi , Hoshino Takanobu , Kobayashi Satoshi , Kato Keizo , Kaneko Futao
Published: July 2005

Delafossite-type CuYO2 and CuY1-x
Ca
x
O2 (x≤0.05) samples exhibited a green-PL-emission band due to the Cu+ interconfiguration transition from 3d94s1 to 3d10 at room temperature. With increasing Ca concentration, the Cu+ emission shifted slightly to the shorter-wavelength side with a slightly weaker emission intensity. This slight change in Cu+ emission property is considered to be caused by the increase in hole concentration within the Cu+ layer arising from the increase in Ca concentration. On the other hand, oxygen-annealed CuYO2 samples exhibited no emissions. The increase in nonradiative relaxation processes in the oxygen-annealed CuYO2 samples is possibly related to structural changes such as orthorhombic distortion during the oxygen annealing. In the photoluminescence of delafossite-type CuY1-y
Tb
y
O2 (y=0.05) at room temperature, no Cu+ emission band was observed, but sharp emission lines were observed. All the emission lines were assigned to the f-f transitions of Tb3+ (5D4→7F
J
, J=3–6).
Upconversion Luminescence of Rare-Earth-Doped CaGa2S4
Authors: Hamano Fumio , Tanaka Kunihiko , Uchiki Hisao
Published: July 2005

Upconversion luminescence and photoluminescence (PL) from Er-doped CaGa2S4 crystal were investigated. Opaque polycrystalline samples were grown by the solid state method and transparent single crystalline samples by the self-flux method. The samples were excited by a laser line of 532 nm, 514.5 nm, 488.0 nm, 476.5 nm or 457.9 nm for the observation of upconversion luminescence and excited by a laser line of 532 nm, 457.9 nm or 325 nm for PL measurement. Four upconversion luminescence bands were observed at 385 nm, 410 nm, 455 nm and 495 nm which were attributed to the transitions of 4G11/2→4I15/2, 2H9/2→4I15/2, 4F5/2→4I15/2 and 4G11/2→4I13/2 in Er3+ ion, respectively, from the samples grown by the solid state method and by the self-flux method.
Optical Properties of Sn-Doped CaGa2S4
Authors: Dohashi Toshihiro , Tanaka Kunihiko , Uchiki Hisao
Published: July 2005

The optical properties of Sn-doped and Sn-and Ce-codoped CaGa2S4 polycrystals were studied. Broadband (green to infrared) and bright photoluminescence was observed under 313 nm, 345 nm and 365 nm excitation. The full width at half maximum of Sn-doped CaGa2S4 PL spectra was more than 300 nm.
Built-in Quantum Dots in Nano-Porous Crystal 12CaO·7Al2O3: Simplified Views for Electronic Structure and Carrier Transport
Authors: Kamiya Toshio , Hosono Hideo
Published: July 2005

12CaO·7Al2O3 (C12A7) has a unique crystal structure composed of subnanometer-sized cages and free oxygen ions in the cages. C12A7 exhibits a variety of active functions if the free oxygen ions are substituted with other active anions. Electronic conduction was attained by introducing high-density F
+-like centers, which was the first demonstration of electronic conduction in oxides composed only of light elements. Chemical active species such as O- and H- are produced in C12A7 at high densities. In this paper, we first review the structure and properties of C12A7-drived materials and related ab-initio works, and then provide simplified views for the stability of the crystal lattice and the clathrated anions, electronic structure, and carrier transport mechanism using simple models based on crystal chemistry, classical molecular dynamics simulation and effective-mass approximation.
Investigation of Cu2ZnSnS4-Based Thin Film Solar Cells Using Abundant Materials
Authors: Kobayashi Takeshi , Jimbo Kazuo , Tsuchida Kazuyuki , Shinoda Shunsuke , Oyanagi Taisuke , Katagiri Hironori
Published: July 2005

Aiming to develop the solar cells free from both environmental contaminants and rare metals, thin film solar cells were produced by using Cu2ZnSnS4 (CZTS) as an absorber. CZTS thin films could be successfully formed by the vapor phase sulfurization of precursors prepared by the electron-beam evaporation on the soda-lime glass substrates. The atomic ratio of Cu/(Zn+Sn) was varied from nearly 0.5 to 1.2 to investigate the influence of the composition on the surface morphology and the optical properties. In order to optimize the sulfurization condition, we varied the sulfurization temperature from 510°C to 550°C. As the results, the value of the conversion efficiency of 4.53% was obtained for the cell of which CZTS absorber sulfurized at 520°C.
Quantum Confinement Effect of Amorphous GaN Quantum Dots Prepared by Pulsed-Laser Ablation
Authors: Yoon Jong-Won , Shim Seung Hwan , Shim Kwang Bo , Koshizaki Naoto , Kwon Young-Soo
Published: July 2005

Amorphous GaN quantum dots (a-GaN QDs) smaller than the Bohr radius (11 nm) were successfully fabricated at room temperature by a laser ablation using a highly densified GaN target. The mean particle size of the a-GaN QDs was 7.9 nm for the films deposited at the Ar pressure of 50 Pa, 5.2 nm at 100 Pa and 4.4 nm at 200 Pa. In particular, the room temperature photoluminescence (PL) and absorption spectra revealed that the a-GaN QDs fabricated under the Ar pressures of 100 and 200 Pa exhibited a strong emission band centered at 3.9 eV, which is about 0.5 eV blue-shifted from the band gap energy of the bulk GaN crystal, confirming the quantum confinement effect.
Site-Dependent Vibrationally Assisted Sticking Effect on H2–Si(001)2×2 Surface Interactions
Authors: Jr. Nelson B. Arboleda , Kasai Hideaki , Diño Wilson A. , Nakanishi Hiroshi
Published: July 2005

We performed quantum dynamics calculations using available potential energy surfaces for the dissociative adsorption of H2 incident on a Si(001)2×2 surface. In this study, we show that the probability of adsorption for H2 and the effect of vibrationally assisted sticking (VAS) vary at different sites along the Si-dimer bond. Based on the sticking probability plots for H2 as functions of its initial translational energy, we show that the H2-silicon surface interactions are all activated, with the lowest potential barrier being found in the case of H2 coming down the Si surface with its center of mass roughly above the down Si-dimer atom. On the other hand, the VAS effect is strongest when H2, while coming down the silicon surface along the surface normal, approaches the point farthest from the up Si-dimer atom along the Si-dimer bond. Here, the potential barrier is closest to the curved region along the reaction path in the corresponding potential energy surface for this system.
Gold-Free Fully Cu-Metallized InGaP/GaAs Heterojunction Bipolar Transistor
Authors: Chang Shang-Wen , Chang Edward Yi , Biswas Dhrubes , Lee Cheng-Shih , Chen Ke-Shian , Tseng Chao-Wei , Hsieh Tung-Ling , Wu Wei-Cheng
Published: July 2005

A gold-free, fully Cu-metallized InGaP/GaAs heterojunction bipolar transistor using platinum as the diffusion barrier has been successfully fabricated. The HBT uses Pd/Ge and Pt/Ti/Pt/Cu for n-type and p+-type ohmic contacts, respectively, and Ti/Pt/Cu for interconnect metals with platinum as the diffusion barrier. The Ti/Pt/Cu structure was stable during annealing up to 350°C judging from the X-ray diffraction (XRD) data and sheet resistance. A current-accelerated stress test was conducted on the device with a current density J
C=140 kA/cm2 for 24 h, and the current gain showed no degradation. The devices were also thermally annealed at 250°C for 24 h and showed little change. We have successfully demonstrated that an Au-free, fully Cu-metallized HBT can be realized using Pt as the diffusion barrier and Pd/Ge and Pt/Ti/Pt/Cu as the ohmic contacts.
Rapid Thermal Annealing Characteristics of P+-Ion-Implanted Si(100) Wafers Studied by Spectroscopic Ellipsometry
Authors: Yoshida Keiya , Adachi Sadao
Published: July 2005

Spectroscopic ellipsometry (SE) has been used to study structural changes in P+-ion-implanted and rapid thermally annealed Si(100) wafers. P+ ion implantation was performed at 150 keV and a fluence of 2×1015 cm-2 at room temperature. Rapid thermal annealing was performed between 550° and 600°C in a dry N2 atmosphere. A model dielectric function (MDF), which was developed for modeling the optical constants of crystalline semiconductors, has been applied to investigate the optical properties of the ion-implanted and annealed layers. The recrystallization is found to occur from an amorphous/crystalline interface via two different thermally activated stages. The fast recrystallization rate of ∼10–200 Å/s, represented by that in the first stage, is probably caused by the rapid reordering of a poorly disordered region in the damage profile tail. Regular recrystallization subsequently occurs, which proceeds at a rate of ∼1–20 Å/s. The activation energies for the first and second recrystallization stages are determined to be 3.3 and 3.0 eV, respectively.
High Tilt Angle Ion Implantation into Polycrystalline Si Gates
Authors: Suzuki Kunihiro , Kataoka Yuji , Aoyama Takayuki
Published: July 2005

We previously reported about the profiles of ion-implanted B in 400-nm-thick polycrystalline Si (poly-Si) and evaluated the profiles, showing that the channeling phenomenon is significantly suppressed by high-tilt-angle ion implantation. Here, we show that the prominent features of B profiles in poly-Si are the same as those of As and P and established a corresponding database. We also clarified that the significant channeling in poly-Si is related to the channeling in (110)-oriented grains.
Numerical Analysis for the Application of Electric Current to Silicon Semiconducting Materials
Authors: Wang Jong Hoe
Published: July 2005

The application of electric field to silicon semiconductors materials is used to modify the melt convection mode in the Czochralski growth configuration and to control the structures at the crystal surface. Nonlinear phenomena, namely, the decrease of the stabilized applied voltage in a closed circuit with the increase of the electric current, were observed experimentally. A mathematical model for predicting the temperature of silicon crystal and the electric field in a closed circuit has been developed to study the electric current-induced Joule heating phenomena in silicon semiconductor materials. In this work, numerical simulations have been performed using the Newton method and implicit Euler time integration. It has been demonstrated that numerical analyses are in qualitative agreement with the experimental results, and it is possible to reproduce the nonlinear behavior and to simulate the transport phenomena in the application of electric current to silicon materials.
DC Characterization of InP/InGaAs Tunneling Emitter Bipolar Transistor
Authors: Cheng Shiou-Ying , Chen Chun-Yuan , Fu Ssu-I , Lai Po-Hsien , Tsai Yan-Ying , Liu Wen-Chau
Published: July 2005

An InP/InGaAs tunneling emitter bipolar transistor (TEBT) is studied and demonstrated. From the simulation results, the band diagram, tunneling transmission, and carrier distribution of the device are analyzed as functions of barrier thickness. The higher the emitter injection efficiency, the higher the current gain and the larger the current drivability for the device studied by employing a tunneling barrier layer of suitable thickness. In addition, experimentally, InP/InGaAs TEBT has been fabricated successfully. Due to its excellent tunneling barrier structure, the studied device can be operated under an extremely wide collector current range. The operation range is larger than 11 decades of collector current (10-12to 10-1A). Moreover, the studied device exhibits a very small collector-emitter offset voltage (ΔVCE) of 40 mV and an extremely wide operation range of output current. Thus, the studied device is suitable for low-voltage and low-power circuit applications.
Studies of Ultrathin InGaAs Quantum Wells Grown at Different Temperatures by Magneto-Photoluminescence
Authors: Tyan Shing-Long , Wu Chih-Hao , Lin Yun-Ging , Chu Sheng-Yuan
Published: July 2005

Here, the ultrathin InGaAs/GaAs single-quantum-well (QW) structures grown at different temperatures are studied using magneto-photoluminescence in magnetic fields of up to 15 T both parallel (B||) and perpendicular (B⊥) to the growth axis. The dimensionalities and the effective diameters are deduced from the low-field diamagnetic shift. The dimensionalities are approximately the same, 0.3, and the effective diameters obtained inB||are almost the same for the QWs grown at different temperatures. The effective diameter measured inB⊥is larger than that inB||for the QW grown at high temperature while it becomes smaller than that inB||for the QW grown at the lowest temperature due to the exciton localization. The anomalous diamagnetic shift shows a cusp at approximately 4 T inB⊥, and the high-field diamagnetic shift can be well-described asB4/3dependence based on the effective width well model.
Characterization of Microcrystalline Silicon Film Growth on ZnO:Al Using the High-Density Microwave Plasma
Authors: Jia Haijun , Shirai Hajime
Published: July 2005

The growth kinetics of microcrystalline silicon (µc-Si) film has been investigated on ZnO:Al/Ag by utilizing the high-density microwave plasma-enhanced chemical vapor deposition of a SiH4-and-H2 mixture at the different deposition rate conditions of 2–3 and 20 Å/s. In situ spectroscopic ellipsometry and Fourier-transform infrared reflection absorption spectroscopy (FTIR-RAS) studies revealed that there exists an induction time at which the nucleation starts at a low deposition rate of 2–3 Å/s, similar to that of the conventional rf plasma. The deposition proceeds and is accompanied by the relaxation of the Si network during the film growth. On the other hand, the deposition proceeds without any induction time at a high deposition rate of 20 Å/s along with the formation of an intermixing layer of ZnO:Al and the deposition of Si of ∼500 Å thickness. The structural relaxation of the Si network is also still promoted with a long time constant even after the plasma excitation is turned off.
Change in Electrical Resistance of Diamond Surface Conductive Layer due to Acid Mist
Authors: Iida Masamori , Yasumori Yoshio , Choe Il Yong , Kato Takahiko , Kurosu Tateki , Kimura Hideki
Published: July 2005

Experimentally obtained results of the change in electrical resistance of the p-type diamond surface conductive layer (PSCL) are simulated using a rate equation. According to a model that simulates the process responsible for the decrease in electrical resistance caused by acid mist containing oxonium ions (H3O+), H3O+ ions react with hydrogen atoms terminating dangling bonds on the diamond surface and cause the creation of holes in diamond films. The rate equation describing these hole creation processes is set up and time-dependent electrical resistance is simulated. The simulated results are in agreement with the experimental results.
Characterization of Surface Chemical States of a Thick Insulator: Chemical State Imaging on MgO Surface
Authors: Yi Yeonjin , Cho Sangwan , Noh Myungkeun , Whang Chung-Nam , Jeong Kwangho , Shin Hyun-Joon
Published: July 2005

We report a surface characterization tool that can be effectively used to investigate the chemical state and subtle radiation damage on a thick insulator surface. It has been used to examine the MgO surface of a plasma display panel (PDP) consisting of a stack of insulator layers of approximately 51 µm thickness on a 2-mm-thick glass plate. The scanning photoelectron microscopy (SPEM) image of the insulating MgO surface was obtained by using the difference in Au 4f peak shift due to the surface charging at each pixel, where a Au adlayer of approximately 15 Å thickness was formed on the surface to overcome the serious charging shift of the peak position and the spectral deterioration in the photoelectron spectra. The observed contrast in the SPEM image reveals the chemical modification of the underlying MgO surface induced by the plasma discharge damage. The chemical state analysis of the MgO surface was carried out by comparing the Mg 2p, C 1s and O 1s photoemission spectra collected at each pixel of the SPEM image. We assigned four suboxide phases, MgO, MgCO3, Mg(OH)2 and Mg1+, on the initial MgO surface, where the Mg(OH)2 and Mg1+ phases vanished rapidly as the discharge-induced surface damage began.
Microscale Metal Patterning Using Photosensitive Silver Organometallic Compounds
Authors: Kim Jin Young , Son Hae Jung , Byun Young-Hun , Lee Sang Yoon , Hwang Eok Chai , Song Ki Yong , Noh Chang Ho , Kim Jin Baek
Published: July 2005

We report a simple method for realizing the direct lithographic patterning of metallic silver and its alloy from amorphous films of photosensitive silver organometallic compounds. In this process, ultraviolet (UV) light was used to selectively activate organometallic compounds, converting organometallic compounds to metallic states in illuminated regions. The photolysis process was monitored by FTIR spectroscopy and the products were analyzed by UV–visible light spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction analysis (XRD). A feature size of 5 µm was demonstrated through the process.
Electrical Characteristics of Thin HfO2 Gate Dielectrics Prepared Using Different Pre-Deposition Surface Treatments
Authors: Chen Ching-Wei , Chien Chao-Hsin , Perng Tsu-Hsiu , Yang Ming-Jui , Liang Jann-Shyang , Lehnen Peer , Tsui Bing-Yue , Chang Chun-Yen
Published: July 2005

We have investigated the effects that various pre-deposition surface treatments, such as HF dipping (HF-dipped), NH3 surface nitridation (NH3-annealed), and rapid thermal oxidation (RTO-treated), have on the electrical properties of HfO2 gate dielectrics. The NH3-annealed technique is superior to the others because the dielectric subject to NH3 surface nitridation possesses a tremendously reduced leakage current, the lowest equivalent oxide thickness (EOT), and a moderate hysteresis width. In contrast, the RTO-treated preparation can only effectively reduce the leakage current by its resultant increased physical thickness and displays considerably severe hysteresis. We have also studied the dependence of hysteresis on the initial inversion bias (V
inv), temperature, and frequency for all splits. The hysteresis width increases upon increasing the initial inversion bias and decreasing the temperature, but it is rather insensitive to the measuring frequency. In addition, our experimental results indicate that the hysteresis width depends exponentially on both the initial inversion bias and the temperature, and it can be described well by a general empirical relationship that has the form C(T)·exp
(R
v
V
inv). Finally, the conduction currents through the dielectrics are probably dominated by trap-assisted tunneling (TAT) because the current densities display stronger temperature dependence at low voltage than they do at higher voltages. Based on the trap-assisted tunneling model, the corresponding parameters have been extracted and are presented.
Atomic Arrangement in a Triple-period A-type Ordered GaInP Layer Grown with Sb Addition during Metal Organic Vapor Phase Epitaxy Observed by Cross Sectional Scanning Tunneling Microscope
Authors: Ohkouchi Shunsuke , Furuhashi Takahisa , Gomyo Akiko , Ichihashi Toshinari , Hsu Chung-Chi , Suzuki Tohru
Published: July 2005

We observed the atomic arrangement of a triple-period (TP-) A-type ordered GaInP layer with Sb added during metalorganic vapor-phase epitaxy, by using an ultra-high-vacuum cross-sectional scanning tunneling microscope (STM). STM imaging of the ordered GaInP region revealed the arrangement of the TP-A-type ordered GaInP layer, and that the layer was composed of two InP-like planes and one GaP-like plane.
Diameter Dependent Magnetic and Electronic Properties of Single-Walled Carbon Nanotubes with Fe Nanowires
Authors: Kisaku Masanori , Rahman MD. Mahmudur , Kishi Tomoya , Matsunaka Daisuke , Roman Tanglaw Abat , Diño Wilson Agerico , Nakanishi Hiroshi , Kasai Hideaki
Published: July 2005

We investigate the electronic and magnetic properties of single-walled carbon nanotubes (SWNTs) filled with Fe nanowires, based on the spin-polarized density functional theory. We find that in the stable structure, the Fe-filled (3,3) and (5,0) SWNTs exhibit semiconducting properties, and the magnetic moment of Fe nanowires inside disappears. On the other hand, the Fe-filled (4,4), (5,5), (6,6) and (6,0) SWNTs, having larger radii, are metallic and exhibit ferromagnetic properties. The corresponding magnetic moment increases with increasing nanotube diameter.
Numerical Simulation of Thermal Effects of Read Current on Magnetoresistive Signal
Authors: Li Hui , Liu Bo , Chong Tow-Chong
Published: July 2005

A read-back magnetoresistive (MR) signal is thermally affected by an increase in the temperature of an MR sensor due to a bias current. The unstructured adaptive triangular mesh and Voronoi polygon control volume methods are adopted to solve the two-dimensional (2D) heat conduction equation for a slider. Numerical simulation results show that, for a typical femtoslider, MR resistance sharply increases with increasing bias current. In ultralow flying height (FH) magnetic recording, a slider designed with a big trailing pad, a low pitch flying attitude and a high thermal conductivity can significantly resist the MR temperature increase and enhance the heat dissipation of a slider body.
Reactive Ion Etching of NiFe Thin Films from First-Principles Study: A Case Study
Authors: Watanabe Susumu , Diño Wilson A. , Nakanishi Hiroshi , Kasai Hideaki , Akinaga Hiroyuki
Published: July 2005

We propose a reactive ion etching (RIE) process design from first-principles calculations for implementation to NiFe thin-film etching. We consider the interaction between the magnetic metal surface NiFe and various gases. We found that the gases CO/NH3, or CH3OH/O2(/NH3,H2) enable the NiFe surface to be etched.
Monolithic Fabry–Perot Wavelength Tunable Filter with Electrothermal Actuation
Authors: Kim Chang Kyu , Lee Myung Lae , Jun Chi-Hoon , Choi Chang Auck
Published: July 2005

We report on a micromachined monolithic Fabry–Perot wavelength tunable filter with a thick moving structure operated by an electrothermal actuation. The monolithic structure simplifies the fabrication process and the electrothermal actuation mechanism reduces the required operation voltage. For the wet etching of the AlGaAs sacrificial layer, an HCl-based solution rather than a HF-based one was used because it results in a larger selectivity between the Al
x
Ga1-x
As layers and less damage to the suspended structure. The wavelength tuning range of the 7.64-µm-thick structure was 47 nm for the power consumption of 5 mW, which results in the high tuning efficiency of ∼9.9 nm/mW. The wide tuning range of 81.2 nm for the 5.2-µm-thick structure, that is not possible with an electrostatic actuation mechanism due to the occurrence of breakdown, is achieved at the driving voltage below 5.7 V. Due to the simplicity of fabrication and the ease of integration, this structure is advantageous for use in wavelength tunable light sources and photodetectors.
Applications of Wide-Band-Gap Materials for Optoelectronic Functional Devices Fabricated by a Pair of Interfering Femtosecond Laser Pulses
Authors: Kurobori Toshio , Yamakage Tomoya , Hirose Yukio , Kawamura Ken-ichi , Hirano Masahiro , Hosono Hideo
Published: July 2005

A pair of interfering near-IR femtosecond pulses from a mode-locked Ti:sapphire laser with a regenerative amplifier have been applied to wide-band-gap materials such a lithium fluoride (LiF) to create laser-active F2and F3+color centers and to encode nonerasable periodic gratings with fine fringe spacings of submicrometer size simultaneously. Using such a photon-written microstructure, a distributed-feedback LiF laser oscillation based on F2color centers has been realized at room temperature. A lasing output performance with a linewidth of less than 1 nm, slope efficiency of ∼10%, and beam divergence of ∼20 mrad was obtained at 710 nm.
Effect of ZnMA on Optical and Holographic Characteristics of Doped PQ/PMMA Photopolymer
Authors: Hsiao Yi-Nan , Whang Wha-Tzong , Lin Shiuan Huei
Published: July 2005

We report on the fabrication and experimental characteristics of doping Zinc methylacrylate (ZnMA) and 9,10-phenanthrenequinone (PQ) into a poly(methyl methacrylate) (PMMA) photopolymer. The effects of a ZnMA dopant on the optical and holographic characteristics of ZnMA/PQ/PMMA have been examined. From the optical and holographic measurements of different samples with different composition ratios, we found that the time to reach the maximum diffraction efficiency has been reduced from 102 to 59 (reduced by 1.7 times) and the diffraction efficiency has been raised up from 0.57 to 1.62% (increased by 2.9 times). We also found that holographic gratings can be recorded in pure PQ-doped PMMA, but cannot be recorded in pure ZnMA-doped PMMA. The higher the concentration of PQ in codoped PMMA, the higher the diffraction efficiency. In contrast, the higher ZnMA concentration in the codoped PMMA, the shorter the response time. It is proposed that PQ serves as a photosensitive reactant and plays a major role in the formation of phase gratings. ZnMA serves as a sufficient catalyst to accelerate the reaction of PQ with a polymer or ZnMA. By adding ZnMA with a proper concentration into a PQ/PMMA photopolymer, we succeeded in improving the holographic characteristic of the photopolymer.
Bending-Sensitive Fiber for Macrobend Fiber Sensors
Authors: Lee Dong-Ho , Kwon Kwang-Hee , Song Jae-Won , Park Jaehee
Published: July 2005

A bending-sensitive fiber (BSF) that exhibits a moderate change in bending loss according to the bend conditions is fabricated for application to a macrobend fiber sensor. Simple macrobending experiments are then performed to verify the bending sensitivity of the BSF.
Measurement of Electrical Properties of GaN Thin Films Using Terahertz-Time Domain Spectroscopy
Authors: Nagashima Takeshi , Takata Kazue , Nashima Shigeki , Harima Hiroshi , Hangyo Masanori
Published: July 2005

We demonstrate the noncontact and nondestructive evaluation of electrical properties of n-type GaN thin films on sapphire substrates using time domain spectroscopy in the THz frequency region (THz-TDS). DC resistivities of the GaN films with various free carrier densities are deduced by fitting the transmission spectra of the sample to the Drude model. The DC resistivities obtained by the THz-TDS show good agreement with those obtained by the conventional contact measurements. Mobilities of the free carriers in lightly doped GaN films are also determined by the Drude fit. It is found that the temperature dependence of the mobilities for the lightly doped films shows a peak at ∼150 K. The temperature dependences of the free carrier densities for the lightly doped films obtained by the THz measurements are compared with that predicted by a model with two kinds of donors reported previously.
Electrical Prestressing of High-Electric-Field Conduction in Composite of Low-Density Polyethylene/Nano-SiOx
Authors: Chen Jiong , Yin Yi , Li Zhe , Xiao Dengming
Published: July 2005

An electrical prestressing in a composite of low-density polyethylene (LDPE)/nano-SiO
x
was observed when measuring high-electric-field conduction in the composite. This means that the DC conduction of a composite after being electrically prestressed with a high DC electrical field (about 8×107 V/m) for 2 h was lower than that of a non-prestressed composite. It is interesting that the electrical prestressing becomes more distinct with increasing nano-SiO
x
content. The interfaces between nano-SiO
x
particles and LDPE molecules were investigated by transmission electron microscopy (TEM), so did the dispersal status of nano-SiO
x
in LDPE. The effects of nano-SiO
x
on the crystallinity and crystal morphology of LDPE were verified by X-ray diffraction (XRD) analysis. In addition, the interaction between nano-SiO
x
particles and LDPE molecules was studied by Fourier transform infrared (FTIR) spectroscopy. Finally, the relationship between the electrical prestressing of high-electric-field conduction and the microscopic structure of a LDPE/nano-SiO
x
composite was discussed.
Effects of Membrane Thickness on the Pyroelectric Properties of LiTaO3 Thin Film IR Detectors
Authors: Chan Chao-Chin , Kao Ming-Cheng , Chen Ying-Chung
Published: July 2005

High-performance pyroelectric infrared (IR) detectors have been fabricated using lithium tantalite (LiTaO3) thin films deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the diol-based sol–gel method. The thermal isolation of detecting elements was achieved by anisotropic wet etching of the back of the silicon substrate. In order to reduce the thermal mass and thermal time constant of the detector, the sensing element was fabricated on a thin membrane. The effects of membrane thickness on the response of pyroelectric IR detectors were studied by changing the membrane thickness (20–350 µm). As the membrane thickness decreased, the voltage responsivity (R
v) increased from 4300 up to 8398 V/W, and the specific detectivity (D
*) also increased from 1.2×108 to 2.7×108 cm·Hz1/2/W. Experimental results reveal that the thermally isolated detectors with membrane thickness of 20 µm exhibit excellent sensitivity.
Effect of Ta2O5 on Microstructure and Microwave Dielectric Properties of Ba(Zn1/3Ta2/3)O3 Ceramics
Authors: Jeong Young-Hun , Kim Min-Han , Nahm Sahn , Lee Woo-Sung , Yoo Myong-Jae , Kang Nam-Kee , Lee Hwack-Joo
Published: July 2005

When Ta2O5 was added to Ba(Zn1/3Ta2/3)O3 (BZT) ceramics, the degree of the 1:2 ordering increased and the Ba3Ta5O15 second phase was formed. Grain growth and liquid phase were also found in Ta2O5 added BZT ceramics sintered above 1580°C. The liquid phase, which is responsible for grain growth, is related to the Ba3Ta5O15 second phase. The Q-value of BZT ceramics sintered above 1580°C was considerably increased with the addition of a small amount of Ta2O5. Since the relative density decreased with the addition of Ta2O5, the increase of the Q-value is not related to the relative density. In contrast, the improvement of the Q-value could be explained by the increase in the grain size because the average grain size increased with the addition of Ta2O5. When a large amount of Ta2O5 was added, however, the Q-value became very low even though the grain size was very large. The low Q-value might be attributed to the low relative density and the presence of a large amount of the Ba3Ta5O15 second phase.
Study on Polarization Properties of Randomly Oriented Bi3.35La0.85Ti3O12 Ferroelectric Thin Film Utilizing Three-Dimensional Piezoresponse Image
Authors: Choi Seokheun , Heo Jinhee , Chung Ilsub , Hong Suk-kyoung
Published: July 2005

We investigated the domain structures of randomly oriented Bi3.35La0.85Ti3O12 (BLT) ferroelectric thin films by mapping the three-dimensional piezoresponse images of the film. Such BLT films were prepared by the sol–gel method. The domain arrangement in the patterned BLT thin films without a top electrode was recorded along all three components of the x-, y- and z-axes by monitoring lateral deflection and vertical displacement. In particular, to obtain lateral deflection along the y-axis, the patterned sample was physically rotated by 90°. In addition, polarization reversal was investigated by applying dc voltage through a conductive tip during the area scanning. We observed that various types of domain behavior such as 54.7° and 90° domain switchings, and pinned domain formation occurred.
Lasing in Photonic Crystals based on Dye-Doped Holographic Polymer-Dispersed Liquid Crystal Reflection Gratings
Authors: Wu Shing-Trong , Fuh Andy Ying-Guey
Published: July 2005

We describe the observation of lasing in photonic crystals (PCs) based on a polymer-dispersed liquid crystal (PDLC) reflection grating, which has a periodic structure of nano-sized (< 200 nm) LC droplets/polymer in a film. It is fabricated using two counter propagation laser beams similar to those used in standard holography. The structure has a periodicity in the range of optical wavelengths, and reflects light selectively governed by Bragg reflection. When doped with a laser dye whose emission spectrum overlaps the reflection spectrum of the grating, the PDLC reflection grating can be lased at the band edges of the reflection band gap.
Bend-Mode Liquid Crystal Cells Stabilized by Aligned Polymer Walls
Authors: Kikuchi Hiroshi , Yamamoto Hirofumi , Sato Hiroto , Kawakita Masahiro , Takizawa Kuniharu , Fujikake Hideo
Published: July 2005

We have studied ways of stabilizing the bend configuration in π-cells by forming polymer walls. This novel device with polymer walls, which makes an initial splay-bend transition unnecessary, incorporates minute structures fabricated by applying the processes of local photopolymerization-induced phase separation and electric field orientation. In fabricating the device, a mixed solution of nematic liquid crystal and an ultraviolet (UV)-curable liquid-crystalline monomer was subjected to an electric field to induce the bend transition, and UV light was illuminated on selected regions in this mixed solution to cause photopolymerization, so that minute aligned polymer walls could be selectively formed inside the device. We examined the operation of the device and found that the bend-alignment cells performed basic functions in the stable bend state, and that this state can be maintained even if the cells are set to a small pre-tilt angle, such as 1°.
The Electro optic Characteristics of Multi-Cell Gap Fringe-Field Switching Mode
Authors: Park Jun Baek , Kim Hyang Yul , Kim Kwi Hyun , Kim Seo Yun , Lim Young Jin
Published: July 2005

The electro optic characteristics of the fringe-field switching (FFS) mode can be investigated by a combination of in-plane switching (IPS) at electrode center and low-twist TN (= electrode edge). In other words, the smaller optimal optical retardation and higher operating voltage of the IPS mode compared with the low-twist TN mode mean that the retardation and operating voltage (=V
op) of the FFS mode can not be optimized for maximum transmittance at both the center and the edge of the electrode. In the multi-cell gap (= MCG)-FFS mode, the operating voltage at the edge is increased by heightening the cell gap at the edge and is shifted near V
op at the center. One notable result is that the transmittance at the center with increased value D (= the cell gap at the near edge) becomes higher owing to the increased twist angle. In conclusion, the novel FFS mode has a higher transmittance than the conventional FFS mode.
Anomalous X-ray Scattering Study on Site Preference of Co and Fe Ions in Hexagonal Z-Type Barium Ferrite
Authors: Nakagawa Takashi , Takada Yukio , Fukuta Yasunari , Nishio Takuya , Tachibana Takeshi , Shimada Takeshi , Yamamoto Takao A.
Published: July 2005

Anomalous X-ray scattering experiments were performed at Fe-K edge with hexagonal Z-type barium ferrite samples Ba3Co2-x
Fe24+x
O41 (x=0, 0.2 and 0.4) in order to study distributions of iron and cobalt atoms over ten crystallographically different sites in the structure. The results were consistent with those determined by the neutron diffraction technique combined with the Rietveld analysis and with those by extended X-ray absorption fine structure (EAXFS) analyses.
Synthesis of GaN Crystal Using Gallium Hydride
Authors: Kawamura Fumio , Imade Mamoru , Yoshimura Masashi , Mori Yusuke , Sasaki Takatomo
Published: July 2005

A new method for synthesizing a large area of c-axis GaN film was developed. The gallium hydride which was formed by the reaction between metal-Ga and hydrogen gas was used as the Ga source, and reacted with NH3 gas to grow GaN crystals on the sapphire (0001) substrate. 2.7 µm-thick GaN film with c-axis orientation could be grown on the substrate. Stable conditions for the synthesis of gallium hydride by the reaction of H2 gas with metal-Ga were examined. As a result, gallium hydride is stable at about 1000°C which is a temperature commonly used for the growth of GaN. These results show that the use of gallium hydride as the predominant species of the Ga source can provide a relatively inexpensive method of growing GaN crystals at a high level of purity.