bluuebunny/crossref_metadata_2025 huggingface dataset:
ADHESION TEST OF CARBON NANOTUBE FILM COATED ONTO TRANSPARENT CONDUCTING SUBSTRATES
Authors: LEE SANG WON , KIM KI KANG , CUI YAN , LIM SEONG CHU , CHO YOUNG WOO , KIM SOO MIN , LEE YOUNG HEE
Published: November 2010

We examined the adhesion of carbon nanotube films coated on transparent substrates. Single-walled carbon nanotubes (SWCNTs) dispersed with sodium dodecylbenzene sulfonate (NaDDBS) in water were sprayed onto polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates to form thin films. Scotch™ tape was then used to detach some loosely bound SWCNTs. Conventional peel-off method to measure adhesion fails in carbon nanotube (CNT) film mainly due to ill-defined detached area of entangled CNTs. We propose here a new adhesion factor which is defined by using transmittance before and after detachment. The adhesion factor was strongly correlated to film thickness. We also found that the SWCNT adhesion to the substrate was strongly dependent on the surface roughness of the substrate due to mechanical interlocking effects.
SYNTHESIS AND CONTROL SIZE OF SnS2 NANOPARTICLES ON THE SURFACE MULTI-WALLED CARBON NANOTUBES
Authors: MORADIAN ROSTAM , ASTINCHAP BANDAR
Published: November 2010

Multi-walled carbon nanotubes have been decorated by SnS2 nanoparticles with different sizes using a simple chemical method. In this work, first multi-walled carbon nanotubes (MWCNTs) functionalized by using acid mixture, then this system coated by tin disulfide ( SnS2 ) nanoparticles with nanoparticle sizes controlling. The samples have been characterized by X-Ray diffraction and transmission electron microscopy (TEM). We found size and uniformity of the SnS2 nanoparticles influenced by increasing reaction temperature and time. By increasing reaction temperature and time, size of the SnS2 nanoparticles became larger and nonuniform. Also we found that ultrasound waves could be used instead of organic compounds for avoiding agglomeration of the SnS2 nanoparticles on the surface of MWCNTs.
HIGHLY EFFICIENT HYBRID SUPERCAPACITOR MATERIAL FROM NICKEL-MANGANESE OXIDES/MWCNTs/PEDOT NANOCOMPOSITE
Authors: KIAMAHALLEH MEISAM VALIZADEH , CHENG CHAN IOU , SATA SUHAIRI ABD , BUNIRAN SURANI , ZEIN SHARIF HUSSEIN SHARIF
Published: November 2010

A novel ternary nanocomposite of nickel-manganese oxides/multi-walled carbon nanotubes (NMO/MWCNTs) coated with poly (3,4-ethylenedioxythiophene)(PEDOT) was prepared by chemical oxidation method. The filling of NMO particles inside MWCNTs and the uniform coating of NMO/MWCNTs with PEDOT intensified the capacitive behavior of MWCNTs. The lowest IR drop (0.1 V) and highest specific capacitance (SC) values of 526.55 F/g of NMO/MWCNTs/PEDOT imply it as highly efficient hybrid supercapacitor materials in 6 M KOH electrolyte.
COAXIAL NANOTUBES FROM POLY(ETHYL 2-CYANOACRYLATE)/POLY(p-XYLYLENE) CONFORMAL COATINGS VIA VAPOR DEPOSITION
Authors: LU ZHIXIANG
Published: November 2010

Ultra-thin (10–100 nm) conformal coatings of poly(ethyl 2-cyanoacrylate) and poly(p-xylylene) have been synthesized via vapor deposition in the confined nanochannels of anodized alumina membranes. Poly(ethyl 2-cyanoacrylate) nanotubes and coaxial poly(ethyl 2-cyanoacrylate)/poly(p-xylylene) nanotubes with precisely-controlled wall thickness were obtained after the removal of the inorganic anodized alumina membrane. Platinum nanoparticles have also been deposited in the coaxial nanotubes via supercritical carbon dioxide.
IRON (III) CHLORIDE AS FLOATING CATALYST PRECURSOR TO PRODUCE MULTI-WALLED CARBON NANOTUBES FROM METHANE
Authors: KHAVARIAN MEHRNOUSH , CHAI SIANG-PIAO , TAN SOON HUAT , MOHAMED ABDUL RAHMAN
Published: November 2010

Multi-walled carbon nanotubes (MWCNTs) were prepared by floating catalyst (FC) method, using methane as a carbon source and iron (III) chloride ( FeCl3 ) as a catalyst precursor, followed by purification with air oxidation and acid treatment. The as-grown and purified MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry analysis and Raman spectroscopy. The average inner and outer diameters of the MWCNTs were 25 and 39 nm, respectively. The purity and yield of the purified MWCNTs were more than 92% and 71% weight fraction, respectively.
FORMATION OF NANOLITER BUBBLES IN MICROFLUIDIC T-JUNCTIONS
Authors: FAN JING , ZHANG YUXIANG , WANG LIQIU
Published: November 2010

A numerical study on nanoliter bubble formation process in microfluidic T-junctions is conducted. The simulated bubble sequence agrees well with experiments. The pressure and velocity distribution in liquid phase, and streamlines of relative velocity of liquid to bubbles are obtained. We also studied pressure variation at the junction and gas flow rate for the first several bubbles, and illustrated the special impact of channel width ratio on bubble formation process. Finally, we derived the critical nondimensional gas pressure above which bubbles can be generated.
SYNTHESIS OF PEG-ENCAPSULATED SUPERPARAMAGNETIC COLLOIDAL NANOCRYSTALS CLUSTERS
Authors: WANG HUI , LI YIMING , LUO ZHAOFENG , ZHOU SHUAI , SHENG JIN , CHEN QIANWANG
Published: November 2010

PEG-encapsulated colloidal nanocrystal clusters (CNCs) have been synthesized via a one-step solvothermal process at a temperature of 230°C. The composition, phase, and morphology of these CNCs have been characterized by X-ray diffraction and transmission electron microscopy. Studies show that each particle is a cluster structure consisting of small primary iron oxide nanocrystals. Magnetic measurements reveal the superparamagnetic nature of these CNCs at room temperature. The CNCs with different sizes (80 nm or 95 nm) can be obtained by changing the time of reaction. The dispersibility and colloidal stability of these CNCs with PEG as the major surface group have also been discussed. In vitro cytotoxicity of these CNCs with different thickness PEG layer on HeLa cell has also been assayed. Cytotoxicity results reveal that the CNCs concentration and the incubation time can influence the cell viability, and the size of CNCs almost does not affect the cell viability.
INVESTIGATING HYDROGEN STORAGE BEHAVIOR OF CARBON NANOTUBES AT AMBIENT TEMPERATURE AND ABOVE BY ION BEAM ANALYSIS
Authors: SAFA S. , LARIJANI M. MOJTAHEDZADEH , FATHOLLAHI V. , KAKUEE O. R.
Published: November 2010

Hydrogen storage capacity of a carbon nanotube (CNT) sample is investigated using Elastic Recoil Detection Analysis (ERDA) at constant hydrogen uptake pressure of 5 bar and different adsorption temperatures within 30°C–500°C. The results of hydrogen concentration versus temperature revealed three distinct temperature intervals in which a certain adsorption or desorption mechanism is dominant. Moreover, the results showed that hydrogen storage capacity of CNTs at the applied conditions of pressure and temperature is about 0.1 wt.% which is well below the DOE requirements for a viable hydrogen storage system. The physidesorption activation energy is calculated using the Arrhenius plot to be 6 kJmol-1.
HETEROGENEOUS SOLIDIFICATION OF ALUMINUM ON BORON-NITRIDE NANOTUBE
Authors: LI Y. F. , YU H. Q. , LI H. , LIEW K. M. , LIU X. F.
Published: November 2010

Molecular dynamics simulations are carried out to examine the heterogeneous solidification of aluminum solution seeded by foreign boron-nitride nanotubes (BNNTs). The final structure indicates noticeably that Al atoms are concentrated to form incredible hierarchical nanostructures composed of coaxial and equidistant cylindrical shells with the BNNTs as the heterogeneous core. The structures of so-formed Al cylinders show strict structural matching and strong structural relevance with BNNTs. Heterogeneous solidification occurred on BNNTs follows a spiral nucleating mechanism. Heredity effect of these hollow cylinders can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around BNNTs is found to be responsible for the formation of the coaxial cylindrical Al shells.
EFFECT OF PARA-HYDROXYBENZENE SULFONIC ACID ON THE PROPERTIES OF EX SITU PREPARED POLYANILINE/MULTIWALLED CARBON NANOTUBES–MnO2
Authors: RAZAK SAIFUL IZWAN ABD , ZEIN SHARIF HUSSEIN SHARIF , AHMAD ABDUL LATIF
Published: November 2010

New ex situ polyaniline (PANI)/ MnO2 -filled multiwalled carbon nanotubes (MWCNTs) nanocomposites using para-hydroxybenzene sulfonic acid (PHBSA) as a dopant and linker exhibit enhanced electrical conductivity and interfacial interaction. Strong and enhanced interfacial interaction was observed on the surfaces of the filled carbon nanotubes and PANI. Transmission electron microscope (TEM) demonstrated clearly the improved bonding at the interface compared to the nanocomposite without PHBSA.
Improved Strain-Free GaN Growth with a Nearly Lattice-Matched AlInN Interlayer by Metalorganic Chemical Vapor Deposition
Authors: Oh Tae Su , Jeong Hyun , Seo Tae Hoon , Lee Yong Seok , Park Ah Hyun , Kim Hun , Lee Kang Jea , Suh Eun-Kyung
Published: November 2010

Using metalorganic chemical vapor deposition, a strain-free GaN layer has been successfully grown by employing a 40-nm-thick nearly lattice-matched (NLM) Al1-xInxN as an interlayer. The Al1-xInxN interlayers having an InN molar fraction ofx∼0.11 and 0.13 led to crack-networking at the GaN surface due to excessive tensile strain by lattice-mismatching. In the case of the GaN layer with a NLM Al1-xInxN interlayer (x∼0.18), however, strain-free GaN structure with improved structural and optical properties was demonstrated from the results of atomic force microscopy, Raman scattering and photoluminescence. By using transmission electron microscopy (TEM), the origin on strain-free state and improved properties of the GaN layer with the NLM AlInN interlayer was investigated. Based on TEM observations, we suggest that the faulted zone-like growth mechanism on roughed AlInN surface and partial compensation of tensile thermal stress are major factors on the improved strain-free GaN film.
Voltage-Pulse Induced Resistance Switching Characteristics in a Cr-Doped SrZrO3
Authors: Yang Min Kyu , Jung Kyooho , Kim Yongmin , Ko Tae Kuk , Im Hyunsik , Park Jae-Wan , Lee Jeon-Kook
Published: November 2010

The time resolved bipolar resistance switching in a Pt/Cr-doped SrZrO3/SrRuO3 device has been investigated using pulse voltage. The required switching time between the high and low resistance states (HRS and LRS) is studied as a function of the pulse height and width. The resistance switching is found to be less dependent on the pulse height in the short pulse region. For LRS→HRS and HRS→LRS switching minimum switching times of ∼500 and ∼100 ns are required respectively, at a pulse height above the dc switching voltage. The authors attribute the distinction in the switching time to different switching mechanisms.
Effect of Added Metallic Elements in Ag Alloys on the Durability against Heat and Humidity of Indium Zinc Oxide/Ag Alloy/Indium Zinc Oxide Transparent Conductive Multilayer System
Authors: Cho Sun-Hee , Lee Won-Jong
Published: November 2010

We studied the effects of added metallic elements in the Ag alloy layers of the indium zinc oxide (IZO)/Ag alloy/IZO transparent conductive multilayer system on the optical and electrical properties of the multilayer. The correlation between the thickness of the Ag alloy layers and the optical and electrical properties of the multilayer was also investigated. The transmittance and sheet resistance were estimated from the optical constants and specific resistivities of Ag alloy and IZO, and then compared with the experimentally measured values. A high transmittance of 95.3% at a 550 nm wavelength and a low sheet resistance of 4.3 Ω/□ were achieved from the IZO (40 nm)/Ag (15 nm)/IZO (40 nm) multilayer. The effect of added metallic elements in the Ag alloy layers of the multilayer on the durability against heat and humidity was also investigated. The durability against heat was improved by the added metallic elements in the Ag alloy layers of the IZO/Ag/IZO multilayer system. When Ag film was heat-treated, agglomeration occurred owing to the surface diffusion of Ag atoms. The added metallic elements such as Pd, Cu, and Au increased the onset temperature and the activation energy for agglomeration. The optical and electrical properties of the IZO/Ag/IZO multilayer markedly deteriorated after the humidity test at 85 °C–85% relative humidity (RH) in air. The degradation of Ag alloy layer was due to the combined effect of heat, water vapor, and sulfur in air. However the deterioration did not occur in the IZO/Ag alloy/IZO multilayer with a AgAu layer after the humidity test. The IZO/Ag alloy/IZO multilayer with the AgAu layer containing 10 wt % Au especially exhibited superior characteristics with a high transmittance of 93.5% at a 550 nm wavelength and a low sheet resistance of 6.3 Ω/□ after the humidity test at 85 °C–85% RH in air for 720 h.
Effects of Wet Chemical and Trimethyl Aluminum Treatments on the Interface Properties in Atomic Layer Deposition of Al2O3 on InAs
Authors: Trinh Hai-Dang , Chang Edward Yi , Wong Yuen-Yee , Yu Chih-Chieh , Chang Chia-Yuan , Lin Yueh-Chin , Nguyen Hong-Quan , Tran Binh-Tinh
Published: November 2010

The reduction of native oxides on an InAs surface using various wet and dry chemical treatments, including hydrochloric acid (HCl) treatment, sulfide treatment, and in situ trimethyl aluminum (TMA) treatment before the atomic layer deposition (ALD) of Al2O3 on InAs is studied. X-ray photoelectron spectrum (XPS) results show that the effect of surface cleaning by TMA was apparent almost after the first pulse but that TMA cleaning is not as effective as wet chemical surface cleaning. The combination of wet chemical treatment and TMA pretreatment is the most effective method for InAs surface cleaning, as indicated by the XPS analysis. Capacitance–voltage (C–V) and current density–voltage (J–V) characteristics on metal–oxide–semiconductor capacitance (MOSCAP) structures were also investigated to evaluate the Al2O3/n-InAs interface quality after different surface treatments, and the results are consistent with the XPS analysis.
Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar
Authors: Choi Seok-Gyu , Han Min , Baek Yong-Hyun , Ko Dong-Sik , Baek Tae-Jong , Lee Sang-Jin , Kim Jin-Ho , Lee Seong-Dae , Kim Mi-Ra , Chae Yeon-Sik , Kathalingam Adaikalam , Rhee Jin-Koo
Published: November 2010

In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.
Electron Field Emission of Silicon-Doped Diamond-Like Carbon Thin Films
Authors: Ray Sekhar Chandra , Ghosh Sarit Kumar , Chiguvare Zivayi , Palnitkar Umesh , Pong Way-Faung , Lin I-Nan , Papakonstantinou Pagona , Strydom André Michael
Published: November 2010

In this work we demonstrate that the field emission characteristics of disordered Si-doped diamond-like carbon (DLC) thin films depend not only on properties of the conductive clustered sp2phase and the insulating sp3matrix (or sp2/sp3ratio) but also on the presence of Si–Hnand C–Hnspecies in the film. The presence of such species reduces the hardness of the film and simultaneously enhances the field emission performance. A turn on electric field (ETOF) of 6.76 V/µm produced a field emission current density of ∼0.2 mA/cm2, when an electric field of ∼20 V/µm was applied. The Fowler–Nordheim (FN) tunneling model is appropriate to explain the field emission mechanism only within limited range of the current density. However, it is found that there is an apparent crossover between space charge limited current (SCLC) and the Frenkel effect due to impurities incorporated during the fabrication of Si-DLC films. This combined effect (SCLC + Frenkel) allows for the emission of electrons from the top of the reduced barriers due to the formation of comparatively soft DLC:Si films. The emission also occurs through tunneling from one conductive cluster (sp2C=C) to another separated by an insulating matrix (sp3C–C) after reducing the effective depth of a trap on application of high electric field.
Process-Induced Damage Characterization of Patterned Low-κ Film Using Electron Energy Loss Spectroscopy Technique
Authors: Otsuka Yuji , Shimizu Yumiko , Kawasaki Naohiko , Ogawa Shinichi , Tanaka Isao
Published: November 2010

A patterned low dielectric constant (κ) film composed of a porous Si–O–C layer (p-SiOC) and a Cu interconnect is characterized by electron energy loss spectroscopy (EELS) with transmission electron microscopy. The relative thickness distribution map is obtained by the valence EELS (VEELS) log-ratio technique with nanometer scale resolution. Two regions with depleted carbon composition and varied relative thickness are found in the p-SiOC layer near the side wall of Cu lines, which are ascribed to the process-induced damage. They cannot be identified only by the conventional elemental mapping obtained by the core EELS (CEELS). Since the VEELS log-ratio technique is convenient to perform, this should be a useful method to routinely characterize the process-induced damage of the patterned low-κ films with Cu interconnects for advanced integration devices.
DC Bias Effects on Piezoelectric Constants of Rhombohedral Pb(Zn1/3Nb2/3)O3–PbTiO3 Single Crystals
Authors: Song Hyun-Cheol , Morita Takeshi , Yoon Seok-Jin , Jeong Dae-Yong
Published: November 2010

DC bias effects on piezoelectric constants of rhombohedral Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) single crystals were characterized using optical measurements. Piezoelectric constants decreased with increasing DC bias due to a decrease in the dielectric constant. The 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystal, which approximates morphotropic phase boundary (MPB) composition and may have a smaller phase transition energy barrier from rhombohedral to tetragonal, showed a bigger change in piezoelectric constant than the pure PZN and 0.955PZN–0.045PT single crystal, which are far from MPB composition. The different behavior in the piezoelectric constant under DC bias for the composition implies a different domain orientation energy from <111> to <001> or <011> directions.
Electrical Properties of Metal-Oxide-Containing SiO2 Films Formed by Organosiloxane Sol–Gel Precursor
Authors: Watanuki Kohei , Inokuchi Atsutoshi , Banba Akinori , Suzuki Hirokazu , Koike Tadashi , Adachi Tatsuhiko , Goto Tetsuya , Teramoto Akinobu , Shirai Yasuyuki , Sugawa Shigetoshi , Ohmi Tadahiro
Published: November 2010

High-quality SiO2 film formation is important for many applications, such as large-scale integration (LSI) circuit and micro-electro-mechanical system (MEMS) industries. We evaluated the structural and electrical insulation properties of SiO2 films using an organosiloxane-based silica sol–gel precursor derived from a mixture of tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) by changing the molar ratio of TEOS/MTMS. This sol–gel precursor was converted not only to a low-dielectric-constant film with a relative dielectric constant of 2.8 but also to a dense SiO2 film by optimizing baking conditions. The dense SiO2 film from this sol–gel precursor has excellent dielectric characteristics of low leakage current density and high breakdown voltage, whose values are comparable to those of thermal oxide SiO2 films. Furthermore, the breakdown field intensity of these films was improved by adding a small amount of metal oxides, such as TiO2, HfO2, and ZrO2. A maximum breakdown field intensity of 15 MV/cm can be achieved in the case of 10% TiO2 addition.
Local Dielectric Property of Cubic Hafnia
Authors: Fukushima Akinori , Senami Masato , Tsuchida Yasushi , Tachibana Akitomo
Published: November 2010

The dielectric property of the cubic hafnia is investigated in terms of the polarizability density and the dielectric constant density defined by one of the authors. We study it by using the cluster model embedded in point charges which represent the surrounding atoms. It is shown that the cubic hafnia show complicated responses to external electric fields, in particular, rotational ones. We stress that the nanosize material should be studied in the local and tensor quantity analysis to describe rotational responses correctly. We also show that the choice of models, in particular, termination condition, is important for these analyses, by comparing the point charge model and the hydrogen termination model.
Low Temperature Cofiring and Compatibility with Silver Electrode of Li3NbO4 Ceramics with B2O3 Addition
Authors: Zhou Huanfu , Chen Xiuli , Fang Liang , Chu Dongjin
Published: November 2010

B2O3 was added to Li3NbO4 ceramics to promote the densification process of the ceramics at low temperatures (≤ 825 °C). When the B2O3 content was ≤ 0.5 wt %, a porous microstructure was developed for the specimens sintered at 825 °C. However, when the amount of B2O3 exceeded 0.5 wt %, the Li3NbO4 ceramics were well sintered due to the formation of a liquid phase containing B2O3. The microwave dielectric properties of the Li3NbO4 ceramics were influenced by the amount of B2O3, and the 0.75 wt % B2O3-added Li3NbO4 ceramic sintered at 825 °C for 2 h showed good microwave dielectric properties of ε
r = 15.3, Q×f = 24600 GHz, and τ
f
= -45 ppm/°C. The compatibility between the dielectric and Ag electrode indicated that this ceramic might be a good candidate for microwave low temperature-cofired ceramics (LTCC) devices.
Improvement in Photoconductive Properties of Coumarin 30-Evaporated Film by Fullerene Doping for Blue-Sensitive Photoconductors
Authors: Seo Hokuto , Aihara Satoshi , Kubota Misao , Egami Norifumi
Published: November 2010

We fabricated two types of organic photoconductive film consisting of coumarin 30/tris(8-hydroxyquinoline)aluminum (Alq3) and fullerene (C60, 10%) : coumarin 30 (90%)/Alq3 by vacuum evaporation and measured the effect of doping C60 as an electron acceptor on the photoconductive properties of the film. The spectral photoresponse characteristics of both films showed good wavelength selectivity in the blue-light region: the peak wavelength of a coumarin 30 neat film was 410 nm and that of a C60:coumarin 30 codeposited film was 440 nm. The external quantum efficiency of the codeposited film reached 64% at an applied voltage of 10 V, while that of the neat film remained at 10% at its highest. These results clearly indicate that the dissociation of electron-hole pairs at the coumarin 30/C60 interface occurs in the codeposited film.
Low-Voltage Organic Thin-Film Transistors Using a Hybrid Gate Dielectric Consisting of Aluminum Oxide and Poly(vinyl phenol)
Authors: Kim Kang Dae , Song Chung Kun
Published: November 2010

This study presents low-voltage organic thin-film transistors (OTFT) using a hybrid gate dielectric consisting of aluminum oxide and poly(vinyl phenol). Aluminum oxide with a thickness of 5 nm is directly formed on an aluminum gate electrode by an oxygen plasma process. The poly(vinyl phenol) film with a thickness of 10 nm is deposited on the aluminum oxide by a spin coating process. The proposed OTFTs are able to operate at low voltages lower than 5 V because of the thin gate dielectric. The surface of the hybrid gate dielectric is finished with a hydrophobic poly(vinyl phenol) so that a pentacene semiconductor, which is deposited on the gate dielectric, produces a high quality channel, resulting in a high mobility with 0.63 cm2 V-1 s-1. Additionally, the poly(vinyl phenol) layer reduces the leakage current through the gate dielectric, generating a low off-state current of 0.02 pA/µm and thus a high on/off current ratio of 4.4×105. Finally, the pin-hole free poly(vinyl phenol) layer protects the thin aluminum oxide gate dielectric from being penetrated by source and drain electrodes; thus, an OTFT with a bottom contact structure is achieved with short channel length.
Simultaneous Formation of Two types of Periodic Nanostructure in ZnO Single Crystal by Femtosecond Laser Direct Irradiation
Authors: Song Juan , Qian Bin , Xu Jian , Guo Xiaodong , Qiu Jianrong
Published: November 2010

In this paper, we report the simultaneous fabrication of nanogratings and three-dimensional (3D) concentric circles in the same bulk of ZnO single crystal by femtosecond laser irradiation of a single spot. For nanogratings, polarization dependence and selective growth characteristics are two main characteristics; for 3D concentric circles, a noticeable feature is their close relationship with the development of the deep crater ablated by the femtosecond laser. On the basis of the above key points observed from scanning-electron-microscope (SEM) images, possible formation mechanisms for these nanostructures are analyzed.
Enhancement of Light Output Power and Modification of Beam Profile in InGaN/GaN Light Emitting Diodes with Micro Polygon Column Shaped Transparent
Authors: Lee Mi So , Kim Hyung Gu , Kang Ji Hye , Ryu Jae Hyoung , Kim Hyun Kyu , Kim Hee Yun , Uthirakumar Periyayya , Hong Chang-Hee
Published: November 2010

We report on the fabrication of GaN-based light-emitting diodes (LEDs) with micro-polygon columns (MPC) obtained by selective area growth (SAG) using the technique of metal organic chemical vapor deposition (MOCVD). The SAG makes it possible to control the density, size and position of the micro polygon columns. The facet structure consists of a polygon column covered with {1101} facets. Columns with rough occur on the (0001) surface. The light output power of the MPC-LED was 53% higher than conventional LED. In addition, the light extraction efficiency of InGaN/GaN LEDs is significantly improved owing to the photon path length is shorter. It is possible to modify the beam profile via shaped transparent layer. Thus, this structure can provide photons with multiple chances of escaping from the LEDs surfaces.
Analysis of Time-resolved Photoluminescence of InGaN Quantum Wells Using the Carrier Rate Equation
Authors: Kim Hyunsung , Shin Dong-Soo , Ryu Han-Youl , Shim Jong-In
Published: November 2010

A measurement method has been developed that can estimate carrier lifetimes and internal quantum efficiency (IQE) in semiconductor materials at room temperature. From the analysis of time-resolved photoluminescence (TRPL) response based on the carrier rate equation, the physical meaning of the TRPL response is clarified and expressions for carrier lifetimes and IQE are obtained. It is found that the final stage of the TRPL response is mainly governed by the non-radiative recombination carrier lifetime. The proposed analysis model is applied to the TRPL measurement results on InGaN-based quantum-well structures, and the non-radiative carrier lifetime and IQE of the measured samples are determined.
Formation of Thermally Stable AgCu-Based Reflectors by a Two Step Alloy Method for Vertical Light-Emitting Diodes
Authors: Jeong Tak , Kim Seung Hwan , Lee Sang Hern , Jeong Seong Hoon , Lee Seung Jae , Ju Jin Woo , Baek Jong Hyeob , Lee June Key
Published: November 2010

Two-step alloyed indium–tin-oxide (ITO)/Ni/AgCu/Pt reflectors for high-performance GaN-based vertical light-emitting diodes (VLEDs) were investigated. The ITO layer was first annealed at 650 °C for 1 min in air to make an Ohmic contact and then the Ni/AgCu/Pt reflectors were deposited and subsequently annealed at 400 °C for 1 min in air to improve their reflectance and mechanical adhesion with the ITO layer. It was shown that the reflectance of the ITO/Ni/AgCu/Pt reflectors at 460 nm was slightly increased from 82 to 87% after two-step annealing. Based on the secondary ion mass spectrometry depth profiles, this improvement was attributed to the formation of a transparent Ni-oxide and the existence of Cu atoms near ITO/AgCu/Pt interface regions suppressing the inter and out-diffusion of Ag. The VLEDs fabricated with the ITO/Ni/AgCu/Pt reflectors showed an approximately 4.4% higher output power and much better current–voltage characteristics than those with the Ag-based reflectors.
Carrier Suppression of Phase Modulated Beam Using Optical Cavity for Coherent Population Trapping Clock
Authors: Choi In Ho , Park Sang Eon , Lee Sang-Bum , Park Hae Yong , Kim Jae-Eun , Kwon Taeg Yong
Published: November 2010

We present a method of carrier suppression of a phase-coherent laser beam produced by an electro-optic modulator for coherent population trapping (CPT) clock. To suppress the undesired strong carrier mode of the phase-modulated beam, a Fabry–Perot (FP) cavity is used as an optical filter. The intensity of the carrier mode is reduced by 70% without significant loss of the two first-order side modes for CPT clock. The contrast of the CPT signal is improved by a factor of 1.4 when the carrier-suppressed phase-coherent laser beam is applied to a 87Rb CPT clock.
Magnetoresistance of a Spin Metal–Oxide–Semiconductor Field-Effect Transistor with Ferromagnetic MnAs Source and Drain Contacts
Authors: Nakane Ryosho , Harada Tomoyuki , Sugiura Kuniaki , Tanaka Masaaki
Published: November 2010

Transport characteristics were investigated in a spin metal–oxide–semiconductor field-effect transistor (spin MOSFET) with ferromagnetic MnAs source and drain (S/D) contacts. A bottom-gate type spin MOSFET was fabricated by photolithography using an epitaxial MnAs film grown on a silicon-on-insulator (SOI) substrate. In-plane magnetoresistance showed a square like hysteretic behavior, when measurements were performed with constant source–drain and source–gate biases. From the comparison with the magnetization-related resistance change resulting from the MnAs contacts, a highly possible origin of the feature obtained for the spin MOSFET is the spin-valve effect originating from the spin-dependent transport in the Si channel.
Study of Wasted Space Effect in Avalanche Photodiodes: A New Look at the Size-Dependent Impact Ionization Properties under Submicron Scale
Authors: Zheng Zhiyuan , Xu Kunyuan , Wang Gang
Published: November 2010

Impact ionization is one of the most important behaviors for carrier transport in high-field region. In this paper, we study the size-dependent impact ionization coefficients induced by the distance that the carriers have to travel to leave out of the terminal of the multiplication layer after the last impact ionization event, which is defined as the “wasted space”. Monte Carlo method is carried out to calculate the size-dependent impact ionization coefficients under submicron scale, and to investigate the effect of wasted space. The conventional model of mean multiplication gain in avalanche photodiodes (APDs) is revised with the adoption of size-dependent impact ionization coefficients, and a good agreement is achieved in the device characteristics of multiplication gain of InP-based APD devices.
Investigation of Field Concentration Effects in Arch Gate Silicon–Oxide–Nitride–Oxide–Silicon Flash Memory
Authors: Lee Jung Hoon , Lee Gil Sung , Cho Seongjae , Yun Jang-Gn , Park Byung-Gook
Published: November 2010

In this paper, arch gate silicon–oxide–nitride–oxide–silicon (SONOS) flash memory is studied. The key technology for this device lies in making the device channel on an arch-shaped silicon fin. This feature enhances the electric field across the tunneling oxide by field concentration, and at the same time, reduces the field across the barrier oxide. Thus, when the high gate voltage is applied in the program operation, the tunneling current, and in turn, the program speed is drastically improved. The lowered electric field at the top oxide prohibits the electron back-tunneling from the polycrystalline silicon gate, which enables more reliable and faster erase operation. Full fabrication processes and the measurement results are presented in detail. The process and device simulation results are also given to confirm the critical electrostatic characteristics of the Arch SONOS flash memory device at each step and design the process integration.
A Direct Observation of the Distributions of Local Trapped-Charges and the Interface-States near the Drain Region of the Silicon–Oxide–Nitride–Oxide–Silicon Device for Reliable Four-Bit/Cell Operations
Authors: An Ho-Myoung , Zhang Yongjie , Kim Hee-Dong , Seo Yu Jeong , Kim Byungcheul , Kim Joo-Yeon , Kim Tae Geun
Published: November 2010

This paper reports the direct observation of the threshold voltage shifts with trapped-charge densities as well as the interface-state densities after 104program/erase (P/E) cycles at each state of the four levels in the drain edge of the silicon–oxide–nitride–oxide–silicon (SONOS) structure. We prepared a SONOS device with a 3.4-nm-thick tunnel oxide, showing 2-bit and 4-level operations at program voltages of 4–6 V, with a 10-year retention and 104P/E endurance properties. Then, by using charge pumping methods, we observed the vertical and the lateral distributions of the trapped-charges and their interface-states with the gate biases at each level of the four states in the drain edge. The trapped-charges densities at the “10”, “01”, and “00” states in the drain region were estimated to be 1.4×1012, 3.0×1012, and 4.9×1012cm-2, respectively, with a lateral width of 220 nm. The peak location of the interface-state density was shifted from the drain edge to the channel with an increase in the gate bias. These observations will be quite useful to optimize the program conditions for reliable 4-bit/cell SONOS operations.
Monte Carlo Simulations of Electron Transport in In0.52Al0.48As/In0.75Ga0.25As High Electron Mobility Transistors at 300 and 16 K
Authors: Endoh Akira , Watanabe Issei , Shinohara Keisuke , Awano Yuji , Hikosaka Kohki , Matsui Toshiaki , Hiyamizu Satoshi , Mimura Takashi
Published: November 2010

We performed two-dimensional Monte Carlo (MC) simulations of 200-nm-gate InP-based In0.52Al0.48As/In0.75Ga0.25As pseudomorphic high electron mobility transistors (HEMTs) at 300 and 16 K to clarify the effect of temperature on electron transport. On decreasing the temperature, the calculated maximum transconductance g
m increases from 1110 mS/mm at 300 K to 1400 mS/mm at 16 K. On the other hand, the calculated cutoff frequency f
T increases from 168 GHz at 300 K to 223 GHz at 16 K. The electron velocity overshoot under the gate is enhanced by reducing the temperature. The resulting average electron velocity under the gate increases from 3.60×107 cm/s at 300 K to 5.26×107 cm/s at 16 K. The average velocity of the electrons and electron occupancy in each valley were calculated to clarify the trend of the electron velocity with temperature. We found that the intervalley phonon scattering as well as the intravalley scattering plays a very important role in determining the average electron velocity at 300 K. The contribution of the intervalley scattering to the average electron velocity is almost of the same degree as that of the intravalley scattering at 300 K.
Suppression of Threshold Voltage Fluctuation by Control of Channel Profile for NOR Flash Memory Scaling
Authors: An Hojoong , Kim Kyeongrok , Jung Sora , Yang Hyungjun , Song Yunheub
Published: November 2010

The threshold voltage fluctuation of one cell in NOR flash memory is investigated for the first time. The threshold voltage fluctuation of one memory cell is significantly increased by the dopant fluctuation and random telegraph signal (RTS) as the cell size is scaled down. The threshold voltage fluctuation due to RTS occupied over 50% of the total variation of one NOR memory cell, and this impact continues to increase for smaller cell area, according to the experimental result. Furthermore, the RTS amplitude for the charge trap position in a tunnel oxide is investigated by device simulation, and it is revealed that the channel doping profile significantly affects the RTS amplitude. This result indicates that the threshold voltage fluctuation of one cell in NOR flash memory is one of the most critical issues in further cell size reduction, and it is expected to be suppressed by adopting an optimal channel doping profile.
Large Enhancement of Field Emission from ZnO Nanocone Arrays via Patterning Process
Authors: Shim Ee Le , Bae Joonho , Yoo  , Kang Chijung , Choi Young Jin
Published: November 2010

We report on the direct observation of enhanced field emissions from patterned ZnO nanocones compared with the plain geometry of ZnO nanocones. For the unambiguous comparison of field emissions from patterned nanocones and plain(nonpatterned) nanocones, periodic arrays of ZnO nanowires were fabricated on Si by photolithography, RCA-1(aq) solution etching, and the hydrothermal growth method. The conelike morphology formation was achieved by anisotropic etching on the different crystal planes of ZnO nanowires in an aqueous solution of acetic acid [CH3COOH(aq)]. As the control sample of plane ZnO nanocones, the ZnO nanowires with a plain geometry were synthesized under the same conditions as the patterned sample. The field emission measurements on the plain ZnO nanocones and patterned ZnO nanocones reveal that the turn-on field decreases from 6.0 V/µm (plane nanocone arrays) to 3.8 V/µm (patterned nanocone arrays).
Calculation of the Electronic State in Electronic Current for Nanowire Models
Authors: Senami Masato , Ikeda Yuji , Fukushima Akinori , Tachibana Akitomo
Published: November 2010

The first results of the calculations of our program code are shown for nanowire models. In our code, the electronic current is treated as quantum states, and the effects of the coulomb and exchange interaction by conductive electrons on electrons in system are included. We show our results as the local electronic current density defined by one of the authors. The magnetic field induced by the electronic current is studied by including effects of vector potential in electronic state calculations. The effects on the electrons in systems by the conductive electrons are also studied. By the existence of the conductive electrons in the systems, the energy eigenvalues of higher orbitals rise, while the lower orbitals are stabilized by the conductive states. It may imply that materials is made more conductive by conductive electrons since the electons in the materials are unstabilized by them.
Photoluminescent ZrO2:Eu3+ Nanofibers Prepared via Electrospinning
Authors: Suryamas Adi Bagus , Munir Muhammad Miftahul , Ogi Takashi , Jr. Christopher J. Hogan, , Okuyama Kikuo
Published: November 2010

Europium-doped zirconium oxide (ZrO2:Eu3+) nanofibers were prepared via electrospinning, in which a mixture of zirconium chloride oxide octahydrate, europium nitrate hexahydrate, poly(vinyl pyrrolidone), dimethylformamide, and ethanol were electrospun at atmospheric conditions. Subsequent calcination to produce ZrO2:Eu3+ nanofibers with diameters around 300 nm. The crystal structure and photoluminescence of the ZrO2:Eu3+ nanofibers were studied as a function of dopant concentration and heating temperature. At a dopant concentration of 5 mol %, tetragonal phase crystals were observed. Photoluminescence spectra revealed several emission bands in the red region corresponding to the transition of 5D0→7F
J
(J=1,2,3,4). Two most intense emission bands were observed at wavelengths of 606 and 591 nm due to the forced electric dipole (5D0→7F2) and magnetic dipole (5D0→7F1) transitions, respectively. This work demonstrates that one-dimensional photoluminescent materials can be generated by a two step electrospinning and calcination process.
Carbon Nanotubes Oscillation under Electric Field
Authors: Khazaei Mohammad , Farajian Amir Abbas , Lee Sang Uck , Belosludov Rodion Vladimir , Kawazoe Yoshiyuki
Published: November 2010

Oscillation mechanism of carbon nanotubes (CNTs) under various external electric fields is investigated by performing first principles molecular dynamics (MD) calculations on closed and open-ended CNTs. From MD calculations we observe that, in addition to the strength of the induced dipole moment, temperature, chirality, and moment of inertia of a CNT affect its oscillation frequency. We propose a procedure to discriminate CNTs with different moments of inertia and/or chiralities based on their different oscillation frequencies. The implication of our results in the process of nanotube insertion into biological cells, where the existing field across the cell membrane facilitates CNT penetration, is also discussed.
Dual Gate Single-Electron Transistors with a Recessed Channel and Underlapped Source/Drain Structure
Authors: Lee Joung-Eob , Kim Garam , Yun Jang-Gn , Kang Kwon-Chil , Lee Jung-Han , Kim Dae-Hwan , Lee Jong-Ho , Shin Hyungcheol , Park Byung-Gook
Published: November 2010

In this work, we have fabricated and characterized the dual gate single-electron transistors (DG-SETs). This device has recessed channel and underlapped source/drain structure. Fabrication flow and device structure are described as well as operation schemes. Clear Coulomb oscillation peaks and negative differential trans-conductance curve are observed at room temperature (300 K). Measurement results obtained at period of Coulomb oscillation is 0.9 V due to an ultra-small control gate capacitance, and oscillation peaks are shifted through the sidewall gate bias. Also, in order to confirm that single electron tunneling is caused by the electrically induced tunneling barriers, and not by random fluctuations along the silicon-on-insulator (SOI) active, room temperature measurement results for device with different parameters is compared.
Room-Temperature Operation of a Single-Electron Transistor Made by Oxidation Process Using the Recessed Channel Structure
Authors: Lee Joung-Eob , Kim Garam , Wan Kim Kyung , Shim Won Bo , Lee Jung-Han , Kang Kwon-Chil , Yun Jang-Gn , Lee Jong-Ho , Shin Hyungcheol , Park Byung-Gook
Published: November 2010

We have fabricated single-electron transistors (SETs) with a recessed channel structure using a thermal oxidation process for decreasing the size of quantum dots (QDs). Moreover, the QDs are defined on a one-dimensional silicon nanowire by two tunneling barriers induced through thermal oxidation. Also, for decreasing the control gate capacitance, the dimension of the control gate depends not on the electron beam or photolithography method. The control gate is formed by the controllability of chemical vapor deposition (CVD). Owing to this small capacitance, we have clear Coulomb oscillation peaks and negative differential trans-conductance curves at room temperature. The oscillation period of the fabricated device is approximately 1.9 V.
Strain Dependence of Formation Mechanism of Growth Layer in Molecular Beam Epitaxy of Gallium Nitride
Authors: Kobayashi Yasunori , Doi Yusuke , Nakatani Akihiro
Published: November 2010

In this study, the epitaxial growth of gallium nitride (GaN) on a GaN substrate is investigated by a molecular dynamics (MD) method. Furthermore, the difference between the surface diffusion of atoms of a strained substrate and an unstrained substrate is examined. From the results of this examination, it is found that the diffusion characteristic in the unstrained case is higher than that in the strained case. Therefore, in the unstrained case, GaN grows layer-by-layer. On the other hand, in the strained case, multiple layers of GaN grow simultaneously. Furthermore, it is also found that the wurtzite structure of GaN differs between the strained case and the unstrained case.
Annealing Temperature Dependence of Crystallization Process of SiGeAu Thin Film
Authors: Takiguchi Hiroaki , Fukui Kazuto , Okamoto Yoichi
Published: November 2010

The large thermoelectric power of SiGeAu thin film depends on the sizes of microcrystals and the crystalline fraction of thin films. We investigate the crystallization process and control method of the microcrystal size and crystalline fraction. In the samples with 7 and 12 at. % Au, the crystallite diameter of Si1-x
Ge
x
was constant when the annealing temperature was between 573–773 K and increased with 873 K annealing. These results suggest that there are two crystallization processes depending on annealing temperature: metal-induced crystallization (573–773 K) and liquid phase crystallization (873 K). The crystallite diameter increased with increasing Au composition and crystalline fraction increased with increasing annealing temperature. These new findings provide a strong hint to the control of the sizes of microcrystals and the crystalline fraction of thin films.
Electrical Conduction across the Direct Contact between Indium–Tin Oxide and Al–Ni Alloy Layers
Authors: Kugimiya Toshihiro , Goto Hiroshi , Okuno Hiroyuki , Kobayashi Nobuhiro , Nakai Junichi , Yoneda Yoichiro , Kusumoto Eisuke
Published: November 2010

The electrical conduction across direct contacts between indium–tin oxide (ITO) and the newly developed Al–Ni alloys, used for amorphous silicon thin-film transistors (a-Si TFTs) in liquid crystal displays (LCDs), has been studied. The ITO/Al–Ni alloy interfaces were examined by both electrical measurements using nanoprobes and cross-sectional transmission electron microscopy (XTEM). It was found that the major conduction path across the ITO/Al–Ni alloy interface was via Al3Ni precipitates, and that the resistivity of the ITO/Al–Ni alloy contact strongly depended on the conditions of the Al–Ni alloy surface. It was thus concluded that the generation of non-oxidized Al3Ni precipitates after photoresist stripping is important for high-quality direct contacts. The present results on the Al–Ni alloy compositions and ITO/Al–Ni alloy interfaces have already been considered in the actual production of a-Si TFTs for LCDs.
A First Principles Study on Dissociation and Adsorption Processes of H2 on Pd3Ag(111) Surface
Authors: Dipojono Hermawan Kresno , Padama Allan Abraham B. , Ozawa Nobuki , Nakanishi Hiroshi , Kasai Hideaki
Published: November 2010

We investigated dissociative adsorption of H2 molecule on Pd3Ag(111) surface based on the constructed potential energy surfaces (PESs) from the results of first principles calculations. This study is performed to understand H2 dissociative adsorption mechanism on Pd3Ag(111) surface which acts as permeable film for H2 which is a product of biomass gasification. The PES results indicate that when the H2 molecule approaches the Ag atom of the 1st atomic layer, the activation barriers for dissociation start to increase. The dissociation of H2 on the surface has negligible activation barrier when the H2 center of mass (CM) is directly above the bridge site of Pd atoms while the hydrogen atoms are directed towards the hcp and fcc hollow sites. The average local density of states (LDOS) of the d-orbital of surface Pd atoms show peak in the region around the Fermi level which is not observed from the LDOS of the Ag atom in Pd3Ag(111) surface. This strongly supports the results of the constructed PES for H2 dissociative adsorption mechanism towards Pd3Ag(111) surface. This study will be significant for the design of hydrogen-permeable films which has applications on biomass-operated fuel cells.