bluuebunny/crossref_metadata_2025 huggingface dataset:
INFRARED LUMINESCENCE AT 1010 nm AND 1500 nm IN LiNbO3:Er3+ EXCITED BY SHORT PULSE RADIATION AT 980 nm
Authors: KOKANYAN E. P. , DEMIRKHANYAN G. G. , STEVELER E. , RINNERT H. , AILLERIE M.
Published: June 2012

Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitation of different power at a wavelength of 980 nm are experimentally and theoretically studied. It is revealed, that the main part of the absorbed energy gives rise to the luminescence at 1500 nm. Considered concentrations of Er3+ impurity ions allow to exclude cooperative processes in the impurity subsystem. The experimental results are interpreted in the framework of a three electronic levels system, assuming that the population of the higher lasing level 4I13/2 in the crystal under study is caused by relaxation processes from the excited level. It is shown that for obtaining of a laser radiation at about 1500 nm one can effectively use a pulse-pumping at 980 nm with a power density in a range of 50 ÷ 60 MW/cm2.
EVIDENCE OF MULTIPARTICLE OPTICAL CENTERS IN LiNbO3:Er3+-Yb3+ CRYSTAL
Authors: BABAJANYAN V.G. , KOSTANYAN R.B. , MUZHIKYAN P.H.
Published: June 2012

A characteristic feature of doped lithium niobate crystals is the liability of its structure to form complex multiparticle optical centers, which consist of two or more closely spaced trivalent impurity ions, even at low concentrations of dopants. This paper presents the results of studies aimed at identifying the characteristics of such centers in the fluorescent signal of the crystal LiNbO 3: Er 3+- Yb 3+ by combination of pulsed excitation at a wavelength of 808 nm with continuous excitation at 980 nm.
INVESTIGATION OF NONLINEAR INTERACTION OF ELECTROMAGNETIC RADIATION WITH SPACE CHARGE IN VACUUM ELECTRONIC DEVICES
Authors: MAKARYAN A.H. , HAROYAN H.S. , SAHAKYAN V.A. , TADEVOSYAN V.R.
Published: June 2012

The nonlinear interaction of electromagnetic radiation in microwave, terahertz, and optical regions with non-uniformly distributed space charge in the interelectrode space of vacuum devices is investigated. The detection of electromagnetic radiation in the vacuum electronic tubes (diode and triode) with parallel plate electrodes is experimentally demonstrated. The dependence of the detected signal on the incident radiation power, direction of wave polarization, current characteristics and frequency of modulating signal has been investigated.

The equation of motion of an electron in the field of electromagnetic wave in the presence of space charge was obtained, according to which, the detection is due to nonlinearity associated with the non-uniform distribution of electrons along the electrostatic field direction.

The measured detection characteristics are in reasonable agreement with theoretical estimates.
LASER-INDUCED THERMOMECHANICAL EFFECTS IN NEMATIC LIQUID-CRYSTAL
Authors: ALEKSANYAN A.K. , GEVORGYAN G.S. , HAKOBYAN R.S. , ALAVERDYAN R.B.
Published: June 2012

As we know there are several mechanisms allowing us to convert absorbed energy by liquid crystal (LC) to the energy of reorientation of director. One of them is the third thermomechanical effect. Third thermomechanical effect induced by Gaussian beam was recently studied both theoretically and experimentally. It was shown that thermomechanical effects can decrease the threshold of Fréedericksz transition in dye-doped nematic liquid crystal (NLC). One of the big advantages of thermomechanical effect compared with other mechanisms (for instance giant optical nonlinearity (GON)), which are absent in the case of normal incidence of laser beam, is that it emerges at any angle of incidence of laser beam. Thermomechanical effects were also studied in NLC, containing azobenzene in their molecular structure. It was suggested that one of the mechanisms of optical nonlinearity observed in the experiment in such medium may be the thermomechanical effect.
CONVECTIVE MOTIONS IN NEMATIC LIQUID CRYSTAL HOMEOTROP AND PLANAR CELLS INDUCED BY GAUSSIAN LASER BEAM
Authors: ALEKSANYAN A.K. , MINASYAN A.K. , HAKOBYAN R.S.
Published: June 2012

Laser beam heating the medium induces instability in the liquid crystal (LC) cell. This instability in conjunction with influence of gravitational force results in convective motions in the cell. In this paper theoretical modeling for studying convection induced by Gaussian laser beam in nematic LC homeotrop and planar cells is presented for the first time. Velocity field and LC director distribution are obtained for various light powers and LC cell sizes by solving Navier-Stokes, heat transfer and director equations simultaneously. The modeling allows us to solve the problems of convections induced by Gaussian laser beam due to Rayleigh-Benard and Marangoni mechanisms as well. There is a good qualitative agreement between theoretical calculations and prior experimental results. The possibility of control and stability of convective motions are studied. Instabilities of the Benard cells are of thermal origin because the Prandtl number for the medium under study is considerably larger than unity.
INTENSITY-DEPENDENT FEATURES IN HYDROGEN-BUFFERED CESIUM SPECTRA
Authors: SHMAVONYAN SVETLANA , PAPOYAN ARAM
Published: June 2012

We report the observation of a spectral feature, namely a dip (peak) in transmission (fluorescence) excitation spectra of a room temperature cesium cell with addition of 20 Torr of H 2 appearing between Doppler-broadened F g =3 - F e =2,3,4 and F g =4 - F e =3,4,5 hyperfine transition groups of Cs D 2 line when laser radiation intensity exceeds 10 mW/cm2. In the experiment we have implemented frequency modulation of the diode laser radiation with lock-in detection of the transmission and fluorescence signals. Spectra taken at different intensities are presented and compared with the spectra without the buffer gas. Possible physical mechanisms responsible for the observed distinction are discussed.
ELECTRICAL PROPERTIES OF THE PULSED-LASER DEPOSITED SURFACE-BARRIER STRUCTURES BASED ON p-Si
Authors: AVJYAN K. , KHACHATRYAN A. , MATEVOSYAN L. , VARDANYAN G. , PANOSYAN ZH. , YENGIBARYAN YE.
Published: June 2012

Surface-barrier structures based on p - Si where fabricated by pulsed-laser deposition method. Electrical properties (current-voltage and capacitance-voltage) of these structures were studied. It is shown, that the forward current ((+) on p - Si ) varies as a J = J 0 exp ( eU / nkT ) and surface-barrier structures based on high-resistivity p - Si are light-sensitive.
METHODS FOR PULSED LASER DEPOSITION OF LARGE-AREA FILMS USING MORE THAN ONE TARGET
Authors: KUZANYAN A.A. , PETROSYAN V.A. , KUZANYAN A.S.
Published: June 2012

Several new methods of pulsed laser deposition for fabricating large-area thin films of uniform thickness and composition on a rotating substrate and onto a moving ribbon are proposed. The peculiarities of the methods are the laser deposition of a compound upon a substrate through a diaphragm or the mask placed in immediate proximity of the substrate together with a use of more than one target. The proposed method makes it possible to obtain thin films of uniform thickness on substrates with sizes limited only by the deposition chamber size. Some of the methods are experimentally verified by depositing CuO thin films and the deviation of the film thickness from the average value does not exceed ±3%. Given the advantage of laser deposition, the offered methods should find practical use, in particular, in micro-electronics, optical industry, development of superconducting coated conductors, deposition of thin films of functional materials and other modern technologies.
PHONON CONFINEMENT EFFECT ON THE BINDING ENERGY OF A HYDROGENIC IMPURITY IN QUANTUM WIRES IN THE ELECTRIC AND MAGNETIC FIELDS
Authors: SHAHBANDARI ABBAS
Published: June 2012

The effect of phonon confinement on ground state binding energy of bound polaron in polar quantum wires with a finite confining potential investigated by Landau-Pekar variation technique. The effect of external electric and magnetic fields is taken into account as well. The obtained results show that the polar optical phonon confinement leads to a considerable enhancement of the polaron effect and these corrections increase with increasing of applied fields.
THE DISORDERING EFFECT ON THE ONE-DIMENSIONAL APPERIODIC OPTICAL SUPER-LATTICE IN MULTI-FREQUENCY SHG
Authors: NEMATI MAJID
Published: June 2012

A multi-frequency second harmonic generation (SHG) in one dimensional nonlinear aperiodic optical superlattice in the presence of linear spacers is considered. The effect of random fluctuations in the length of each layer on the output efficiency of SHG process is investigated, and the favorable percentage of fluctuation in the fabrication of aperiodic optical superlattice is obtained. Comparing perfect and fluctuated aperiodic structures, the researcher realized the decrease in the amount of output efficiency with the increase of fluctuation in the linear-nonlinear aperiodic crystals.
OPTICAL PROPERTIES OF SHALLOW DONOR NEAR SEMICONDUCTOR-METAL INTERFACE
Authors: DJOTYAN ANAHIT
Published: June 2012

Intraband transitions of an impurity electron from the ground state to 2Px and 2Py excited states of a shallow donor located near a semiconductor-metal interface are investigated as a function of the donor distance from the interface. Impurity states are calculated within the effective mass approximation and using a variational scheme in which the energies and the oscillator strength for the intraband absorption are obtained analytically.
OPTICAL PROPERTIES OF THE PULSED-LASER DEPOSITED AMORPHOUS FILMS OF GERMANIUM
Authors: MKRTCHYAN ARSEN Y.
Published: June 2012

Amorphous germanium ( a - Ge ) films (thickness 25-450 nm) were obtained on the glass substrates at room temperature by the vacuum (3·10-6 mm Hg ) pulsed laser ( Q -switched glass: Nd 3+ laser: wavelength — 1.06 μm, pulse duration — 30 ns, intensity in the Ge target irradiation zone — ~109 W/cm2) deposition method in non-equilibrium conditions of growth. The optical properties of fabricated films were studied in the range of 400-1000 nm using a spectrometer Filmetrics F20. It was shown that the optical properties of a - Ge films are explained by the Tauc model for amorphous semiconductors. It was also established that the optical gap of films depends on their thickness.
Potential of Directed- and Self-Assembled Molecular Nanowires for Optoelectronic Functional Devices
Authors: Wakayama Yutaka , Hiroshiba Nobuya , Hayakawa Ryoma , Chikyow Toyohiro , Kobayashi Kenji
Published: June 2012

A variety of applications of molecular nanowires is reviewed in the first part of this article. First of all, growth techniques of molecular nanowires are discussed in terms of directed- and self-assemblies. Subsequently, various kinds of functional devices, e.g., field-effect transistors, memory devices, data storage, photo-electric conversion devices, are described. These devices have been proposed by taking advantages of one-dimensional structures and a wide range of molecular functions. In the second part of this article, we demonstrate our recent work. The main purposes are to provide a guideline on molecular design for growing of one-dimensional nanowires and to discuss their optical and electronic properties. A specific stress is laid on multi-level transistor operation as an evidence of effective utilization of one-dimensional nanowires. Although these performances are still preliminary, our results demonstrate a strong possibility of molecular nanowires as components in novel molecular devices.
Electron Beam Lithography of 15×15 nm2 Pitched Nanodot Arrays with a Size of Less than 10 nm Using High Development Contrast Salty Developer
Authors: Komori Takuya , Zhang Hui , Akahane Takashi , Mohamad Zulfakri , Yin You , Hosaka Sumio
Published: June 2012

We investigated the effects of developer and hydrogen silsesquioxane (HSQ) resist thickness in the formation of dot arrays with a pitch of <18×18 nm2 by using 30-keV electron beam (EB) lithography for bit patterned media (BPM). Optimum resist thickness and developer were investigated for the formation of fine dot arrays. We found that a 12-nm-thick HSQ resist was suitable to form fine dot patterns and the addition of NaCl into tetramethylammonium hydroxide (TMAH) could improve the development contrast (γ-value) of HSQ (the highest is 9.7). By using the 12-nm-thick HSQ resist film and 2.3 wt % TMAH/4 wt % NaCl developer, we successfully fabricated very fine resist dot arrays with a dot size of <10 nm and a pitch of 15×15 nm2, which corresponds to a storage density of about 3 Tbit/in.2 in BPM.
Extreme Ultraviolet Process Optimization for Contact Layer of 14 nm Node Logic and 16 nm Half Pitch Memory Devices
Authors: Tseng Shih-En , Chen Alek
Published: June 2012

Extreme ultraviolet (EUV) lithography is considered the most promising single exposure technology at the 27 nm half-pitch node and beyond. The imaging performance of ASML TWINSCAN NXE:3100 has been demonstrated to be able to resolve 26 nm Flash gate layer and 16 nm static random access memory (SRAM) metal layer with a 0.25 numerical aperture (NA) and conventional illumination. Targeting for high volume manufacturing, ASML TWINSCAN NXE:3300B, featuring a 0.33 NA lens with off-axis illumination, will generate a higher contrast aerial image due to improved diffraction order collection efficiency and is expected to reduce target dose via mask biasing. This work performed a simulation to determine how EUV high NA imaging benefits the mask rule check trade-offs required to achieve viable lithography solutions in two device application scenarios: a 14 nm node 6T-SRAM contact layer and a 16 nm half-pitch NAND Flash staggered contact layer. In each application, the three-dimensional mask effects versus Kirchhoff mask were also investigated.
Maskless Lithographic Fine Patterning on Deeply Etched or Slanted Surfaces, and Grayscale Lithography, Using Newly Developed Digital Mirror Device Lithography Equipment
Authors: Iwasaki Wataru , Takeshita Toshihiro , Peng Yao , Ogino Hiroaki , Shibata Hiromasa , Kudo Yuji , Maeda Ryutaro , Sawada Renshi
Published: June 2012

In the trial and research phases, the fabrication of micro electro mechanical systems (MEMS) devices and integrated circuits (ICs) is both lengthy and costly, owing to the demands imposed by the use of photomasks. Maskless lithography techniques, such as electron beam (EB), laser scanning, and digital mirror device (DMD) lithography techniques, are widely used. In the MEMS field, submicron and wiring patterns are often created on uneven structures. We have developed a maskless lithography technique by modifying a DMD with two automatically switchable lenses. The first lens with a magnification power of 10× and a numerical aperture (NA) of 0.3 was used to rapidly expose wide areas, and the second lens with a magnification power of 100× and an NA of 0.9 was used for fine patterning. In the present study, we fabricated submicron patterns, wiring patterns, and alignment marks on slanted and deeply etched surfaces, and three-dimensional photoresist structures using our developed DMD lithography technique.
Defect Characterization of an Extreme-Ultraviolet Mask Using a Coherent Extreme-Ultraviolet Scatterometry Microscope
Authors: Harada Tetsuo , Nakasuji Masato , Tokimasa Akifumi , Watanabe Takeo , Usui Youichi , Kinoshita Hiroo
Published: June 2012

On extreme-ultraviolet (EUV) masks, phase structures such as bumps or pits on the substrate or particles buried in the multilayers can form printable defects. Information on the properties of these defects is required for mask repair by defect hiding and compensation methods using the absorber pattern. We have developed a coherent EUV scatterometry microscope (CSM) to observe EUV masks, which uses a simple lensless system to record a diffraction image from mask patterns. We introduce preliminary observation results for programmed phase defects. We evaluated the defect width and height from the diffraction images, and the detection limit of the CSM system reached a width of 220 nm. To characterize small defects, we proposed a micro-CSM system that focused to the illumination onto the defect with a 100 nm diameter. The diffraction image recorded by the micro-CSM system provides raw defect data, which is essential for defect compensation.
Development of Coherent Extreme-Ultraviolet Scatterometry Microscope with High-Order Harmonic Generation Source for Extreme-Ultraviolet Mask Inspection and Metrology
Authors: Nakasuji Masato , Tokimasa Akifumi , Harada Tetsuo , Nagata Yutaka , Watanabe Takeo , Midorikawa Katsumi , Kinoshita Hiroo
Published: June 2012

In extreme-ultraviolet (EUV) lithography, defect-free mask production is one of the critical issues for the high-volume manufacturing of semiconductor devices. We developed a coherent EUV scatterometry microscope (CSM), which is a simple lensless system. The CSM records diffraction from mask patterns with a charge-coupled-device (CCD) camera directly, which is illuminated with a coherent EUV light. Since a practical standalone system is required by the industry, we developed a standalone CSM system employing a high-order harmonic generation (HHG) EUV source. The 59th high-order harmonic generation of 13.5 nm wavelength is pumped by a tabletop, 6 mJ, 32 fs, Ti:sapphire laser system. The EUV output energy of 1 µW is successfully achieved. We performed the observation of an EUV mask using the HHG-CSM system. The detection limit of the line defect size is improved to 2 nm for the high output power of the HHG EUV source.
Photoresist Shrinkage Caused by Single-Line Scan of Electron Beam
Authors: Ohashi Takeyoshi , Tanaka Junichi
Published: June 2012

Shrinkage behavior caused by a single-line scan of an electron beam over a photoresist line was observed, including shrinkage distribution in the photoresist-line direction. A new method for evaluating the minute amount shrinkage and the shrinkage distribution caused by a single-line scan was developed. According to the results of evaluations with this method, the shrinkage of an about 50-nm-wide photoresist line caused by a single-line scan is less than 0.1 nm under landing energies of 200, 300, and 500 eV and probe current of 8 pA. This shrinkage is more than ten times smaller than the typical amount of shrinkage caused by a standard two-dimensional scan. This result indicates the possibility of a significant reduction of photoresist shrinkage during scanning-electron-microscope measurements. The evaluation method also yielded the first observation of the shrinkage distribution in the photoresist-line direction. The results show that the shrinkage caused by a single-line scan distributes more than 30 nm, which is wider than the calculated electron-scattering range. This result suggests that there likely to be an additional mechanism involved in photoresist shrinkage other than the microscopic interaction between incident electrons and photoresist molecules. An elastic-relaxation effect and a contribution of back-scattered electrons are plausible additional mechanisms for photoresist shrinkage.
Lower Limit of Line Edge Roughness in High-Dose Exposure of Chemically Amplified Extreme Ultraviolet Resists
Authors: Kozawa Takahiro
Published: June 2012

The line edge roughness (LER) of resist patterns is a critical issue in the high-volume production of semiconductor devices. LER is inversely proportional to the square root of exposure dose. However, LER cannot be reduced below a certain value when exposure dose is increased or when sensitivity is decreased. In this study, the cause of this lower limit was investigated by Monte Carlo simulation. The dependences of the lower limit of LER on acid generator concentration, feature size, optical image contrast, and flare intensity were clarified. The decomposition effect of acid generators during exposure is a dominant factor for the lower limit of LER in the relationship between LER and exposure dose (or sensitivity).
Sensitivity of Process Parameters on Pattern Formation of Litho–Cure–Litho–Etch Process
Authors: Kim Sang-Kon
Published: June 2012

Semiconductor manufacturing has depended on the high resolution of optical lithography. As the wavelength becomes shorter for the resolution, the light source and optics become increasingly complex and expensive. Therefore, to extend optical lithography's useful life at greater resolution, the litho–cure–litho–etch (LCLE) process has been introduced as an alternative technique. In this study, the LCLE process is modelled and simulated to explore the pattern formation between the two lithography processes (litho 1 and litho 2). This process allows for the physical phenomena of pattern formation to be better understood. The sensitivity of simulation parameters for simulated profiles is analyzed by Taguchi analysis. Through the sensitivity of these easy-to-optimize parameters, LCLE lithography processes can be effectively predicted.
Optimization of Ge–Sb–Sn–O Films for Thermal Lithography of Submicron Structures
Authors: Chen Jhewn-Kuang , Lin Jing-Wen , Chen Jung-Po , Chiu Kuo-Chi
Published: June 2012

Ge–Sb–Sn inorganic resist materials are developed to fabricate submicron structures that have a pattern size smaller than 150 nm and a depth over 100 nm via thermal lithography. The materials are sputtered under Ar:O2 atmospheres by varying O2 flow rate and Ge level. Both increasing O2 flow rate and Ge level can decrease the extinction coefficient, k, at 405 nm wavelength to within a range of 0.58–0.89. Films with appropriate absorption of laser power are chosen to optimize exposure and development processes. A continuous 2.0 mW laser power is used to crystallize the Ge–Sb–Sn–O films. 175-nm-wide and 107-nm-deep grooves are formed after development using alkaline solutions. The 175 nm width is well below half of the 380 nm diffraction limit. A laser pulse strategy is also developed to fabricate discrete dot patterns. By shortening the write 1 time to 0.5 T (7.8 ns), the dot patterns change from oval to round shape. A pit pattern as small as 140 nm diameter and 100 nm depth is achieved.
Study of Development Processes for ZEP-520 as a High-Resolution Positive and Negative Tone Electron Beam Lithography Resist
Authors: Mohammad Mohammad Ali , Koshelev Kirill , Fito Taras , Zheng David Ai Zhi , Stepanova Maria , Dew Steven
Published: June 2012

ZEP brand electron beam resists are well-known for their high sensitivity and etch durability. The various performance metrics such as sensitivity, contrast, and resolution of ZEP resist depend strongly on the development process. In this work, we investigate the development of ZEP-520 resist through contrast curves, dense gratings, and surface roughness measurements using three different classes of developer systems of varying solvation strength, ZED-N50, methyl isobutyl ketone (MIBK) : isopropyl alcohol (IPA) 1:3, and IPA : H2O 7:3, at the ambient temperature (22 °C) and cold (-15 °C) development conditions. In order to provide a deeper insight into the ZEP development process, we propose a novel kinetic model of dissolution for ZEP, and develop an efficient analytical method that allows determining the microscopic parameters of ZEP dissolution based on experimental contrast curves. We also observe experimentally and characterize the negative tone behavior of ZEP for dense grating patterning and compare its performance with positive tone behavior.
Graphene Growth from Spin-Coated Polymers without a Gas
Authors: Suzuki Satoru , Takei Yusuke , Furukawa Kazuaki , Webber Gregory , Tanabe Shinichi , Hibino Hiroki
Published: June 2012

We grew graphene films on polycrystalline metal substrates using spin-coated polystyrene or polyaniline films as a carbon source by heating the films in an Ar atmosphere or in a vacuum. In an Ar atmosphere of 6.7×104 Pa, precise control of the initial polymer film thickness is crucial for few-layer graphene growth. In a vacuum, few-layer graphene films were obtained regardless of the initial polymer film thickness, because excess carbon atoms are removed from the surface when the polymer is thermally decomposed. This latter method does not require any gas and is thus a very simple and easy way to grow few-layer graphene.
Three-Dimensional Force Sensing Device Using Carbon Nanofiber Polymer Composites: Design and Fabrication
Authors: Chang Fuh-Yu , Liu Chia-Ming , Chen Tse-Min , Chen Chia-Ming , Lin Yu-Hsien , Huang Shu-Jiuan
Published: June 2012

We propose an innovative three-dimensional force sensing device fabricated with carbon nanofiber (CNF) polymer composites. The device has four piezoresistive strain sensors made onto a polyimide substrate using surface patterning treatment and tilted-drop process with CNF polymer solutions. The proposed design and fabrication process is simpler than that of other three-dimensional force sensors and the device is suitable for mass production. The fabricated strain sensor properties using CNF polymer solutions with different composition ratios were investigated. An equation was derived using simple percolation theory to predict the conductivity of CNF polymer composites. The measured gauge factors were in the 4.84 to 17.68 range for CNF polymer composites with CNF 8.85–45.2 wt %. A programmable system on chip (PSoC) with built-in operational (OP) amplifier, analog-to-digital (AD) converter and multiplexer was used to develop a scanning and analyzing circuit for the three-dimensional force sensing device. The proposed integrated system was successfully applied to control a computer screen cursor.
Amorphous Carbon Deposited by a Novel Aerosol-Assisted Chemical Vapor Deposition for Photovoltaic Solar Cells
Authors: Ahmad Nurfadzilah , Kamaruzzaman Dayana , Rusop Mohamad
Published: June 2012

Amorphous carbon (a-C) solar cells were successfully prepared using a novel and self-designed aerosol-assisted chemical vapor deposition (AACVD) method using camphor oil as a precursor. The fabricated solar cell with the configuration of Au/p-C/n-Si/Au achieved an efficiency of 0.008% with a fill factor of 0.15 for the device deposited at 0.5 h. The current–voltage (I–V) graph emphasized on the linear graph (ohmic) for the a-C thin films, whereas for the p–n device structure, a rectifying curve was obtained. The rectifying curves signify the heterojunction between the p-type a-C film and the n-Si substrate and designate the generation of electron–hole pair of the samples under illumination. Photoresponse characteristics of the deposited a-C was highlighted when being illuminated (AM 1.5 illumination: 100 mW/cm2, 25 °C). Transmittance spectrum exhibit a large transmittance value (>85%) and absorption coefficient value of 103–104 cm-1 at the visible range of 390 to 790 nm. The atomization of a liquid precursor solution into fine sub-micrometre-sized aerosol droplets in AACVD induced the smooth surface of a-C films. To the best of our knowledge, fabrication of a-C solar cell using this AACVD method has not yet been reported.
Microscopic Raman Mapping of Epitaxial Graphene on 4H-SiC(0001)
Authors: O Ryong-Sok , Iwamoto Atsushi , Nishi Yuki , Funase Yuya , Yuasa Takahiro , Tomita Takuro , Nagase Masao , Hibino Hiroki , Yamaguchi Hiroshi
Published: June 2012

We propose a quality control method for wafer-scale epitaxial graphene grown on SiC substrates. The peak position of Raman spectra of epitaxial graphene is an excellent indicator of film quality and reveals irregularities, such as graphene thickness inhomogeneity and SiC substrate defects. A comparison of microscopic Raman maps and scanning probe microscopy images of the same position of the sample revealed that wave numbers of Raman peaks (G and 2D band peaks) were strongly correlated with the strain in the graphene film. The increase in number of graphene layers (2 to 3–4 layers) induced phonon softening (∼6 cm-1) and broadening (∼6 cm-1) of the 2D band peak. Significant phonon softening and abnormal broadening of the Raman peaks were observed at residual scratches on the SiC substrate. The quantitative layer number distribution of graphene on SiC is successfully estimated from the wave number distribution of the 2D band peak.
Thermal Durability of Diamond Like Carbon Films Containing Tungsten Fabricated by Focused-Ion-Beam Chemical Vapor Deposition
Authors: Fujimoto Akihiro , Okada Makoto , Kang Yuji , Niibe Masahito , Matsui Shinji , Suzuki Tsuneo , Kanda Kazuhiro
Published: June 2012

Diamond like carbon film containing tungsten (W-DLC) was fabricated by focused-ion-beam chemical-vapor deposition (FIB-CVD), and its thermal durability was investigated using near the carbon K-edge X-ray absorption fine structure (C-K NEXAFS) spectroscopy and a combination of Rutherford backscattering and elastic recoil detection analysis, in comparison with those of commercial DLC and W-DLC films. The concentration of W in the films did not decrease when the annealing temperature was increased, while the concentration of H did. The sp2/(sp2+sp3) ratio of carbon atoms in the films increased with annealing temperature. The W-DLC film fabricated by FIB-CVD unchanged after annealing for 32 h at 873 K in vacuum. Its thermal durability was comparable to that of commercially available films.
Identification of Graphene Layer Numbers from Color Combination Contrast Image for Wide-Area Characterization
Authors: Rahman Shaharin Fadzli Abd , Hashim Abdul Manaf , Kasai Seiya
Published: June 2012

Identification of the number of graphene layers using an optical microscope images taken at various magnifications is investigated from the viewpoint of simple wide-area inspection. For graphene on 300-nm-thick SiO2, combination of red and green color contrast gives more accurate contrast value and provides better contrast even at the low magnification as compared with the single color channel contrast. The color combination with suitable weighting factors taking account of light wavelength and intensity dependences of the system response results in the contrast that agrees well with the theoretical values from Fresnel's law. Simple image processing is also investigated to improve the signal-to-noise ratio (SNR) of the image. Median filtering improves the SNR of the image having high pixel density, whereas dithering is effective for the low magnification image having block noise due to low pixel density.
Improvement in Film Quality of Epitaxial Graphene on SiC(111)/Si(111) by SiH4 Pretreatment
Authors: Sanbonsuge Shota , Abe Shunsuke , Handa Hiroyuki , Takahashi Ryota , Imaizumi Kei , Fukidome Hirokazu , Suemitsu Maki
Published: June 2012

The epitaxy of graphene on 3C-SiC/Si (GOS) has attracted much attention owing to its viability to fuse graphene with Si-based technologies. It is known that the surface condition of the 3C-SiC thin film before graphitization plays a decisive role in determining the quality of the GOS film. We have investigated the effect of the pretreatment of the 3C-SiC thin film in vacuo at a SiH4 partial pressure of 6.7 ×10-4 Pa on the subsequent formation of graphene. As a result, it is revealed that the SiH4 pretreatment restores the defects on the SiC surface, such as the Si vacancy and point defects formed by the presence of native oxides, and improves the quality of graphene. The effect is found to be highest when the substrate temperature is 1173 K.
Fine Patterning of Inkjet-Printed Single-Walled Carbon-Nanotube Thin-Film Transistors
Authors: Nobusa Yuki , Takagi Yuki , Gocho Shota , Matsuzaki Satoki , Yanagi Kazuhiro , Takenobu Taishi
Published: June 2012

We fabricated single-walled carbon nanotube (SWCNT) thin-films via the combination of inkjet printing and site-selective deposition based on the patterning of self-assembled monolayers (SAMs) through an optical lithography mask. Previously, we patterned SWCNT films by ultraviolet light irradiation onto SAMs through metal masks, and the minimum film size achieved was 90 µm wide. In this study, we succeeded in achieving a width of 13 µm using SAMs and optical lithography masks, thus improving the performance limit of SWCNT printed electronics.
Formation of Graphene Nanofin Networks on Graphene/SiC(0001) by Molecular Beam Epitaxy
Authors: Maeda Fumihiko , Hibino Hiroki
Published: June 2012

A graphene nanofin consists of few-layer graphene and sticks out from the surface like a fin. To understand what graphene nanofin is and gain insight into its formation mechanism, we grew graphene at various substrate temperatures by gas-source molecular beam epitaxy (MBE) on previously prepared epitaxial graphene formed on a SiC(0001). Then, the surfaces were observed using atomic force microscopy, transmission electron microscopy, and low-energy electron microscopy (LEEM). We found the graphene nanofin formation at the growth temperature from 600 to 915 °C. The LEEM and low-energy electron diffraction observations reveal that the crystal axes of the graphene layer are completely random, although their (0001) axes are aligned. This experimentally supports a formation mechanism where the nanofins are formed by the collision between incommensurate domains of graphene at their boundaries.
Graphene Converted from the Photoresist Material on Polycrystalline Nickel Substrate
Authors: Lee Hyonik , Lee Seulah , Hong Juree , Lee Sang Geun , Lee Jae-Hong , Lee Taeyoon
Published: June 2012

Graphene has attracted attention from both academia and industry owing to its fascinating properties and a wide range of potential applications. Methods for graphene synthesis from solid and liquid carbon sources, including poly(methyl methacrylate) (PMMA), benzene, and other carbon sources, have been reported due to the potential use of a wide variety of carbon feedstocks. In this study, high quality graphene was grown from SU-8-2002 photoresist materials on Ni foil with annealing at 1000 °C for 20 min in an ambient mixture of He and H2 gas. Scanning electron microscopy image of the as-synthesized graphene on Ni foil indicated that graphene covered the whole area of the Ni foil with various numbers of layers due to the different carbon segregation rate depending on the underlying Ni grain orientation. To unambiguously distinguish the thickness variation of the synthesized graphene layers, they were transferred onto SiO2 (300 nm)/Si substrate and were analyzed using optical microscopy, and Raman spectroscopy, which confirmed that the synthesized graphene is composed of various numbers of layers. The thickness dependent G/2D peak intensity ratio (I
G/I
2D) of Raman spectra and their full width at half maximum values obtained from the transferred graphene layers were examined, which were in good accordance with atomic force microscopy analyses.
Continuous Electron Doping of Single-Walled Carbon Nanotube Films Using Inkjet Technique
Authors: Matsuzaki Satoki , Nobusa Yuki , Shimizu Ryo , Yanagi Kazuhiro , Kataura Hiromichi , Takenobu Taishi
Published: June 2012

The fabrication of logic circuits using the inkjet technique has attracted especially strong interest owing to wide range applications such as flexible and printed electronics. Although logic circuits fabricated using the inkjet method have already been accomplished, the precise control of gate threshold voltages has not been realized yet. In this study, we have demonstrated electron doping of single-walled carbon nanotube (SWCNT) films by inkjet printing of dilute poly(ethylene imine) (PEI) ink. We have successfully obtained the continuous threshold voltage shift by varying the number of doping steps, indicating that the carrier concentration in PEI ink is much lower than that of our previous work.
In-situ Observation of Current-Pulse-Induced Curling of Graphene Edges and Carbon-Cages Production
Authors: Nishijima Takuya , Ueki Ryuichi , Kano Emi , Fujita Jun-ichi
Published: June 2012

We found a new cage transformation process where Joule heating with a cyclic current pulse strongly triggered the curling of graphene edge, and enhanced the transformation of the cages feeding with a source of amorphous carbon that adhered on the graphene sheet. Here the cyclic thermal stress seems to play an important role to induce the curling of the graphene edges. We also found that internal stress induced by a mechanical vibration strongly enhanced the transformation to larger carbon-cages and multi-walled graphitic onions that was never appeared in the current pulse induction.
Recovery Force of Carbon Nanotube Shape Memory
Authors: Itaya Shotaro , Hirahara Kaori , Nakayama Yoshikazu
Published: June 2012

We measured the recovery forces generated by a shape memory effect of plastically bent carbon nanotubes (CNTs) using a manipulator installed in a transmission electron microscope. The recovery force as estimated with the moment is as high as 120 aN m for a curvature of 0.025 nm-1 of the plastic bend. It is indicated that recovery force depends on bending curvature: a larger curvature generates a larger recovery force. This result is discussed in terms of the gliding rate of topological defects to be repaired.
Electric Field Enhancement by Laser Light Focused at Electrode Edges for Controlled Positioning of Carbon Nanotubes
Authors: Takahashi Toru , Yabumoto Takuya , Inori Ryuji , Okada Takako , Akita Seiji , Arie Takayuki
Published: June 2012

We demonstrated single-walled carbon nanotube aggregation at electrode edges by local electric field enhancement by a focused laser irradiation. It was revealed that the formation of nanobubbles and their induced fluid motion play an important role in carrying nanotubes to the electric field enhancement region around the laser irradiation spot from the laser power dependence of the aggregation on electrode edges. Furthermore, we found that metallic nanotubes preferentially aggregated near irradiation spots by the investigation of the laser irradiation time dependence of the aggregation. This technique is useful for manipulating and bridging nanotubes between electrodes for device applications.
In-situ Observation of Surface Graphitization of Gallium Droplet and Concentration of Carbon in Liquid Gallium
Authors: Ueki Ryuichi , Nishijima Takuya , Hikata Takeshi , Ookubo Soichiro , Utsunomiya Risa , Matsuba Teruaki , Fujita Jun-ichi
Published: June 2012

Although carbon has been recognized to be insoluble in gallium, we found that the outermost surface of gallium has unexpectedly high carbon solubility, particularly the limited region of about a few nanometers in depth. Our in-situ transmission electron microscope observations revealed that a graphene layer was precipitated at the surface of a gallium droplet simultaneously with gallium evaporation, and some of the droplets created an internal graphitic layer. On the basis of these experimental data, we evaluated a substantial carbon solubility that seemed to exceed about 50 at. %, but was realized in a very thin surface region of about 4 nm in depth. We believe that this high carbon solubility at the gallium surface is the key mechanism for the catalytic ability of gallium that was observed at the interface between liquid gallium and solid amorphous carbon.
Single-Photon Detection by a Simple Silicon-on-Insulator Metal–Oxide–Semiconductor Field-Effect Transistor
Authors: Du Wei , Inokawa Hiroshi , Satoh Hiroaki , Ono Atsushi
Published: June 2012

We demonstrate that a simple silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistor (MOSFET) which can be found in ordinary integrated circuits could operate as a single-photon detector at room temperature. A potential well created by n+p-n+ junctions is used to trap photo-generated holes, which is detected as increased electron current in the bottom channel with a single-hole sensitivity. Although peaks in histograms of drain current are overlapped due to relatively small sensitivity to the holes, signal-to-noise ratio (SNR) is large enough to determine the position and height of each peak corresponding to the discrete number of trapped holes. In addition to this single-photon detection capability, the simple MOSFET structure could also benefit from the potentially high quantum efficiency (QE) since it includes fewer absorbing electrodes to the incident light.
Characteristics of Gate-All-Around Hetero-Gate-Dielectric Tunneling Field-Effect Transistors
Authors: Lee Jae Sung , Choi Woo Young , Kang In Man
Published: June 2012

In this paper, gate-all-around (GAA) tunneling field-effect transistors (TFETs) with hetero-gate dielectric (HG) materials have been simulated and their characteristics have been optimized as a function of the high-k dielectric length (L
highk
). For the optimization of L
highk
, simulation results have been analyzed in terms of on- and off-current (I
on, I
off), subthreshold swing (SS), on/off current ratio, intrinsic delay time (τ), and RF performances. In the device simulations, the on-current characteristics were optimized when L
highk
is 8 nm. The optimized GAA HG TFET had ∼100 times higher I
on and ∼2 times improved SS than a GAA SiO2-only TFET. It has also been shown that the RF performances of TFETs can be improved by introducing an HG structure.
Fabrication of Stacked Organic Electroluminescence Devices with a Combination of Spin Coating and Electrospray Deposition
Authors: Anzai Hideaki , Watanabe Yuuki , Sakamoto Tetsuo
Published: June 2012

A combination of spin coating and electrospray deposition (ESD) was applied for the fabrication of an organic light-emitting diode (OLED) with a stacked structure. Two kinds of polymer materials were used to fabricate a multilayered structure. One was poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV; Sigma-Aldrich) and the other was poly[2,5-di(hexyloxy)cyanoterephthalylidene] (CN-PPV; Sigma-Aldrich). With the addition of acetone to polymer material (MEH-PPV and CN-PPV) solution, smaller droplets were produced at the emitter resulting in thin-film fabrication under a dry condition. This condition was adopted for CN-PPV film deposition on MEH-PPV surface made by the spin coating method. The double-layered OLED obtained successfully emitted light at a bias voltage of 15 V. Layer-by-layer stacking of CN-PPV and MEH-PPV was confirmed by the UV-induced fluorescence spectrum. In case of the layer-by-layer structure, the obtained spectrum showed a linear combination of spectrum from MEH-PPV and CN-PPV.
Regression Analysis for Transport Electron Scattering Caused by Structural Defects in InSb Quantum Wells: Application of Matthiessen's Formula
Authors: Mishima Tetsuya D. , Santos Michael B.
Published: June 2012

The graphical representation and numerical interpretation of the results obtained by a regression analysis for Matthiessen's formula have been investigated for the electron scattering due to micro-twins (MTs) and threading dislocations (TDs) in InSb quantum wells (QWs) at room temperature. By plotting the reciprocal of the total mobility vs the summation of the linear terms due to MTs and TDs, a two-dimensional graphical representation that clearly exhibits the “goodness of fit” of the regression analysis was depicted. The usefulness of numerical indexes, “effective defect density” and “equivalent defect scattering”, was discussed: “effective defect density” made it possible to evaluate the electron scattering in InSb QWs by using one type of structural defects, either MTs or TDs. “Equivalent defect scattering” enables one to intuitively grasp the difference in magnitude of electron scattering between MTs and TDs in InSb QWs.
Channel Recessed One Transistor Dynamic Random Access Memory with SiO2/Si3N4/SiO2 Gate Dielectric
Authors: Park Jin-Kwon , Yang Jong-Heon , Cho Won-Ju
Published: June 2012

A fully depleted (FD) single-transistor dynamic random-access memory (1T-DRAM) cell with SiO2–Si3N4–SiO2 (ONO) stacked gate dielectric was fabricated on a recessed silicon channel. The electrical and memory characteristics of a 1T-DRAM with a stacked ONO gate dielectric were compared with those of 1T-DRAM cell with a single SiO2 gate insulator. As a result, the FD channel recessed 1T-DRAM cell with an ONO gate insulator provides excellent electrical characteristics such as a high on/off ratio of nearly 109 and a low leakage current (<10-14 A). Further, the sensing margin of channel recessed 1T-DRAM cells was largely enhanced by the ONO stacked gate insulator compared to a single SiO2 layer at the same operation condition.
Collision-Based Computing Using Single-Electron Circuits
Authors: Hayashi Shunsuke , Oya Takahide
Published: June 2012

A single-electron (SE) device based on “collision-based computing (CBC)” is proposed for information processing. CBC is an analog computing in which input signals behave like billiard balls, and the goals of moving balls are regarded as output positions. The proposed SE device consists of arrayed SE oscillators with coupling capacitor between each pair. An SE oscillator is a threshold decision device which can be used as a reaction-diffusion (RD) model, a kind of the analog computation model. The RD model can express the various behaviors of an excited wave, e.g., “moving at a constant velocity” and “disappearing due to collision”. These behaviors are also important for CBC. We designed basic SE-CBC circuits and a full adder as an application, and evaluated their operation by Monte-Carlo computer simulation. The results indicate that this circuit is useful for configuring various types of logical circuits.
Photocurrent Measurements on a Quantum Cascade Laser Device by Fourier Transform Infrared Microscope
Authors: Enobio Eli Christopher I. , Sato Hiroki , Ohtani Keita , Ohno Yuzo , Ohno Hideo
Published: June 2012

Intersubband photocurrent in the InAs/AlSb mid-infrared quantum cascade laser (QCL) device is measured. To characterize subband energies in a fabricated and functioning QCL laser device, Fourier-transform infrared (FTIR) microscope is used to focus the probe light on the cleaved mirror of QCL. Photocurrent associated with intersubband transitions in the active layer are observed up to room temperature and the origin of peaks is identified by numerical simulation, which demonstrates the potential as a characterization tool for QCL devices.
Design and Characterization of Plasmonic Terahertz Wave Detectors Based on Silicon Field-Effect Transistors
Authors: Hwang Hee Cheol , Park Kibog , Park Wook-Ki , Han Seong-Tae , Kim Kyung Rok
Published: June 2012

We report the first implementation of a modeling and simulation environment for the plasmonic terahertz (THz) detector based on the silicon (Si) field-effect transistor (FET) with a technology computer-aided-design (TCAD) platform. The nonresonant plasmonic behavior has been modeled by introducing a quasi-plasma electron box as a two-dimensional electron gas (2DEG) in the channel region. The alternate-current (AC) signal as an incoming THz wave radiation successfully induced a direct-current (DC) drain-to-source voltage as a detection signal in the broadband sub-THz frequency regime. The simulated dependences of photoinduced DC detection signals on structural parameters such as gate length and dielectric thickness confirmed the operation principle of the nonresonant plasmonic THz detector in the Si FET structure. We evaluated the design specifications of THz detectors considering both responsivity and noise equivalent power (NEP) as the typical performance metrics. The proposed methodologies provide the physical design platform for developing novel plasmonic THz detectors operating in the nonresonant detection mode.
Characterization of Low-Frequency Noise in Etched GaAs Nanowire Field-Effect Transistors Having SiNxGate Insulator
Authors: Muramatsu Toru , Miura Kensuke , Shiratori Yuta , Yatabe Zenji , Kasai Seiya
Published: June 2012

Low-frequency noise in SiNxinsulator–gate GaAs-based etched nanowire field-effect transistors (FETs) is investigated, focusing on the device size dependence and the effect of electron traps in the insulator. Intensity of the drain current noise is found to systematically increase when the nanowire width and gate length decrease, as indicated by the conventional FET noise model. Noise spectrum also changes continuously from 1/fto 1/f2with the decrease of the device size, which is not observed in Schottky-gate nanowire FETs. Theoretical analysis shows that traps having short time constants mainly affect on the spectrum slope, whereas those having long time constants only shift the spectrum and do not affect on the slope. Observed size dependence of the spectrum slope is explained by broadening of the distribution of the time constant rather than the change in the combination of discrete traps having different time constants.