bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photosensitive Carbazolylethylmethacrylate Copolymers on Flexible Substrate for Optical Information Registration
Authors: Robu S. , Dementiev I. , Dmitriev S. 
Published: April 2011

AbstractThis report present results of study of some organic materials suitable for creation of photothermoplastic media (on flexible base) for optical information recording. In particular, speech is about donor-acceptor systems on the base of carbazolyl containing polymers, in particular, carbzolylethylmethacrylates (CEM) with oktylmethacrylates (OMA) and polyepoxypropylcarbazolyl (PEPC) copolymers sensibilization of which was made by means of 5-20% of trinitrofluorenone (TNF), N-fenylamino-2,4,7-trinitrofluorenone (FNF) and ditianomethylen-2,4,7-trinitrofluorenone (DTF) (containing donor-acceptor group) and additives of photochromic substances of indolynospirobenspyran series.There were studied the dependencies of photosensitivity on sensibilizer's concentration and temperature of heating of polymeric material and also the spectral diapason of photosensitivity. It was established that maximum of photosensitivity is observed at the concentration of sensibilizing agent 12-14%. Heating above 60°C leads to sharp decrease of photosensitivity of developed organic materials.It was established that donor-acceptor systems as photoplastic layers possess photosensitivity on the level 10−3-10−4 J/cm2. The introduction of PP layers of 6-10% photochromic additives leads to 2-3 times increasing of the photosensitivity of the given donor- acceptor system. At that the essential growth of photosensitivity is observed in the blue-green part of visible spectrum. Also, it was established that 8'-nitro-1,3,3- trimethylindolynospirobenzopyrane possess the greatest effect of sensibilization. The fact that adsorption band (500-600 nm) is in the visible part of spectrum confirms the amplification of concentration of donor-acceptor group in PP layers and, as result, considerable growth of photosensitivity. The received results are discussed.Thus, donor-acceptor systems, developed on the base of photopolymer CEM:OMA, demonstrate photosensitivity of 10−6 J/cm2. at 80-85°C that 2-3 times higher than in case of usual donor-acceptor systems.
100-nm Channel Length a-Si:H Vertical Thin Film Transistors
Authors: Chan Isaac , Nathan Arokia 
Published: April 2011

AbstractThis paper reports on hydrogenated amorphous silicon (a-Si:H) vertical thin film transistors (VTFTs) with channel length of 100 nm, using conventional planar TFT processing technology. The device has a fully self-aligned vertical channel structure, which is highly insensitive to the non-uniformity of reactive ion etching (RIE). Therefore, the VTFT process is very suitable for large-area electronics. Presently, we can demonstrate VTFTs with remarkable ON/OFF current ratio of more than 108, low leakage current down to 1 fA, and good subthreshold slope of 0.8 V/dec at Vd = 1.5 V. The impacts of contemporary device issues, such as short-channel effects and contact resistance, on the performance of short-channel VTFTs and suggested avenues for improvement are discussed.
Top Gate Tft for Large Area Electronics
Authors: Meitine Mark , Sazonov Andrei 
Published: April 2011

AbstractThe TFT fabrication by PECVD at low processing temperature (<100°C) is of great importance due to its compatibility with low-cost plastic foil substrates. The first bottom gate amorphous silicon TFTs fabricated at 75°C in our lab demonstrated the leakage current of 10−12A, the threshold voltage of 15V and the field effect mobility of 10−2cm2/(Vs). To increase the field-effect mobility, reduce the threshold voltage, and reduce the mask count, nanocrystalline silicon based top gate TFT was designed.The TFT fabrication process was done at maximum processing temperature of 75°C. The direct PECVD SiNxand SiOx/SiNxstack were used as gate dielectrics. Nanocrystalline silicon was used as the channel layer. The SiNxgate dielectric TFTs demonstrated the leakage current about 10−13A, the threshold voltage of 8..10V, the field effect mobility of ∼10−4cm2/(Vs), the subthreshold slope of 4..8V/decade, and Ion/Ioffratio of about 102. High source and drain contact resistance were attributed to low efficiency of phosphorous doping in amorphous silicon at 75°C, which also limited the Ionvalue. Using n+nc-Si for the source and drain contacts, the Ion/Ioffratio was increased to 106, and the field effect mobility was increased to ∼0.1cm2/(Vs). The threshold voltage, however, increased, which was attributed to higher fixed charge.
Mechanically strained a-Si:H AMOLED driver circuits
Authors: Servati P. , Tao S. , Horne E. , Striakhilev D. , Sakariya K. , Nathan A. 
Published: April 2011

AbstractThis paper examines the variations in performance of amorphous silicon (a-Si:H) thin-film transistor (TFT) pixel driver circuits for active-matrix organic light-emitting diode (AMOLED) displays, which are subject to compressive or tensile mechanical strain. The external strain is induced by bending of the TFT substrate, and is measured by the observed changes in resistance of in-situ strain gauges. Mechanical strain impacts the performance of the circuit in terms of its drive current, which may be attributed to mobility and Fermi energy shifts in the individual TFTs. The effect of strain-induced shifts in the TFTs as a function of strain orientation (longitudinal or transverse) with respect to direction of current flow is also examined. Our measurements show that the variation in the drain current of a longitudinally oriented TFT can be as much as ∼ 1.5% for strains as high as 10−3. Proper layout and circuit design can suppress the effect of strain-induced shifts, and should be taken into consideration when designing stable TFT driver circuits for mechanically flexible AMOLED displays.
Micro-Scale Metallization of Cu and Au on Flexible Polyimide Substrate by Electroplating Using SU-8 Photoresist Mask
Authors: Cho Suhyeon , Kim Soohong , Lee Nae-eung 
Published: April 2011

AbstractIn order to fabricate flexible microelectronic devices, fabrication of metallization lines and metal electrodes on the flexible substrate is essential. Cu lines are often used as interconnect lines in electronic devices and Au as microelectrodes in organic transistors and bioelectronics devices due to its good electrochemical stability and biocompatibility. For minimizing the size of device, the realization of metallization lines and microelectrodes with the scale of a few micrometers on the flexible substrate is very important. In this work, micro-scale metallization lines of Cu and Au were fabricated on the flexible polyimide (PI) substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Surface of PI substrate was treated by O2 inductively coupled plasma for improvement in the adhesion between the Cr layer and the PI and in-situ sputter-deposition of 100-nm-thick Cu seed layers on the sputter-deposited 50-nm- thick Cr adhesion layer was followed. Electroplating of Cu and Au lines using a sulfuric acid and a noncyanide solution with the patterned SU-8 mask, respectively, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Micro-scale Au electrode lines were successfully fabricated on the PI substrate. Micro-scale gap-filled Cu lines with spin- coated polyimide on the PI substrate with the thickness of 6 ∼ 12 νm and the aspect ratio of 1~3 were successfully fabricated.
Role of the α/β Interface in the Plastic Anisotropy of Single Colony Crystals in Titanium Alloys
Authors: Savage M. F. , Tatalovich J. , Mills M. J. 
Published: April 2011

AbstractThe anisotropy in room temperature plastic deformation has been investigated in single α(HCP)/β(BCC) colonies of a commercial α/β titanium alloy (Ti-6Al-2Sn-4Zr-2Mo-0.1Si) oriented for activation of individual basal slip systems. Detailed transmission electron microscopy (TEM) studies of the slip transmission mechanisms through the α/β interfaces have been performed to elucidate the role of these interfaces in determining yield and strain hardening behavior. Significant anisotropy in the yield strengths and hardening rates for the 3 unique basal slip systems is measured, and is attributed to the different slip transmission mechanisms active due to the near-Burgers orientation relationship existing between α- and β-phases. These results are should be transferable to other alloy systems exhibiting this orientation relationship.
Linking Grain Boundary Structure and Composition to Intergranular Stress Corrosion Cracking of Austenitic Stainless Steels
Authors: Bruemmer S. M. 
Published: April 2011

AbstractGrain boundary structure and composition is assessed in austenitic stainless steels along with its influence on intergranular stress corrosion cracking (IGSCC) in high-temperature water. Brief examples are presented illustrating effects of grain boundary character and segregation on behavior in specific light-water-reactor environments. Although grain boundary engineering can produce an increased fraction of “special” boundaries in austenitic stainless alloys, practical benefits depend on the boundary orientation distribution. It is critical to recognize that only ∑3s appear to be more resistant to SCC and the behavior of other low ∑ boundaries is uncertain. Grain boundary composition can have a dominant effect on IGSCC under certain conditions, but altered interfacial chemistry is not required for cracking. In high-potential oxidizing environments, IGSCC susceptibility is a direct function of the boundary Cr concentration. Non- equilibrium thermal segregation of Cr and Mo is often present in mill-annealed stainless steels and may influence cracking susceptibility. This initial grain boundary composition alters subsequent radiation-induced segregation and delays irradiation-assisted SCC susceptibility to higher doses. Other alloying elements and impurities in 300-series stainless steels have been seen to enrich grain boundaries, but few have any significant impact on IGSCC susceptibility. One exception is Si that strongly segregates during irradiation. Recent results suggest that Si may accelerate crack propagation in both low- and high-potential water environments. Critical research is still needed to isolate individual grain boundary characteristics and quantitatively link them to IGSCC.
Crystallographically-Necessary Constraints at Triple Junctions in Grain Boundary Engineered Alloys
Authors: Randle Valerie 
Published: April 2011

AbstractCrystallographic characteristics of a large number of Σ3 boundaries have been investigated in a nickel superalloy. The results indicated that {111}, vicinal-to-{111} (within 10° of {111} planes) and not-{111} Σ3s were all present in the sample population. At Σ3/Σ3/Σ9 junctions a combination of one {111} and one vicinal-to-{111} Σ3 was more likely to occur than two {111} or two not-{111} Σ3s, and an explanation is proposed. An analysis of the interface planes for the not-{111} Σ3s indicated that more than half the boundaries in this category could not have {211}{211}, {774}{855}, {111}{511}, {001}{221} or {110}{411} planes.
(110) InAs Quantum Dots: Growth, Single-Dot Luminescence and Cleaved Edge Alignment
Authors: Wasserman D. , Shaner E. A. , Lyon S. A. , Hadjipanayi M. , Maciel A. C. , Ryan J. F. 
Published: April 2011

ABSTRACTThe formation of InAs self-assembled quantum dots on (110) GaAs substrates is demonstrated. These dots form with significantly lower densities than InAs dots grown on (100) GaAs. The low density growth mode of these InAs nanostructures allows for the fabrication of devices capable of electroluminescence from individual quantum dots. Such a device has been fabricated with conventional photolithography and its emission spectra characterized. Additionally, because GaAs cleaves naturally along the (110) crystal plane, the ability to grow InAs quantum dots on (110) GaAs substrates allows for the growth of these dots on the cleaved edges of GaAs first growth samples containing InGaAs strain layers of varying thickness and In fraction. 100% linear alignment of InAs quantum dots over these InGaAs strain layers is demonstrated.
Intersubband Transitions in GaN/AlxGa1-xN Multi Quantum Wells
Authors: DeCuir E. A. , Chua Y. C. , Passmore B. S. , Liang J. , Manasreh M. O. , Xie J. , Morkoc H. , Asghar A. , Ferguson I. T. , Payne A. 
Published: April 2011

ABSTRACTIntersubband transitions (ISTs) in GaN/AlxGa1-xN multiple quantum wells (MQWs) were investigated using an optical absorption technique. Several samples were grown by either Molecular Beam Epitaxy (MBE) or Metal-Organic Chemical Vapor Deposition (MOCVD) and were investigated using both normal incident and waveguide configurations. The waveguides were fabricated by dicing each sample into 2 mm wide by 5 mm long pieces with two facets polished at 45 degrees with respect to the surface such that light propagates across the sample's width. Preliminary results indicate that ISTs are observable in Si-doped and undoped GaN/AlxGa1-xN MQWs. The source of these charge carriers in the undoped samples are explained as being due to the spontaneous polarization effect which exists at the GaN/AlxGa1-xN interfaces where the GaN surface has Ga-polarity. Scanning Electron Microscopy indicates that a sample containing what appeared to be a large number of cracks and or hexagonal voids lacked the presence of ISTs.
Electric Field Enhancement of Dark Current Generation in Detectors
Authors: Lavine James P. 
Published: April 2011

ABSTRACTThe performance of detectors and sensors is degraded by dark current generation, which is due to defects and impurities in the materials. Electric fields enhance the generation from the resulting deep levels. When the electric field is in the mid-105 V/cm range, the present work finds enhancements of the order of 100 or more for iron and gold in silicon. The activation energy of the generation rate as a function of temperature is seen to decrease when the electric field increases. Many detectors have pixels that form a charge packet before the detectors are read out. Since the presence of charge decreases the electric field, the electric field enhancement varies with time. This is modeled for iron in silicon with an illustrative charge versus electric field relation. The resulting activation energy is found to be barely affected.
Processing of deeply etched GaAs/AlGaAs quantum cascade lasers with grating structures
Authors: Golka S. , Austerer M. , Pflügl C. , Schrenk W. , Strasser G. 
Published: April 2011

ABSTRACTGratings in GaAs/AlGaAs mid-infrared quantum cascade lasers (QCLs) are fabricated with a structure depth of more than 10 μm. A N2/SiCl4 inductively coupled plasma reactive ion etching (ICP-RIE) process was employed to achieve extremely smooth sidewalls and selectivities to the SiNX etch mask of up to 70:1. EDX spectra measured on as-etched samples show that sidewall etch inhibition is caused by a thin Si containing layer on the sidewalls that is formed simultaneously with ICP etching of GaAs at the bottom of the trenches. To demonstrate device application gratings with a pitch of 1.72 μm are applied to long rib waveguide -based QCLs emitting at λ = 10.7 μm. When etched laterally together with the rib the grating gives rise to stable single mode emission up to 295K from these QCLs. The respective grating coupling coefficient is determined to be κ = 29 cm-1.
Roughness Analysis of Episurfaces Grown on Ion-Beam Processed GaSb Substrates
Authors: Krishnaswami K. , Fenner D. B. , Vangala S. R. , Santeufemio C. , Grzesik M. , Allen L. P. , Dallas G. , Goodhue W. D. 
Published: April 2011

ABSTRACTHigh-quality GaSb substrates with minimal surface roughness and thin, uniform oxide layers are critical for developing low-power, epitaxy-based, electronic and optoelectronic devices. Ion-beam processing techniques of gas-cluster ion beam (GCIB) and bromine ion-beam assisted etching (Br-IBAE) were investigated as to their potential for improving the suitability of substrate surfaces for molecular beam epitaxial (MBE) growth. Statistical analysis of the residual surface roughness provides insight into ion-beam processing and its impact on epitaxial growth. Images of episurfaces grown on chemical mechanical polished (CMP), Br-IBAE, and GCIB finished substrates were obtained using atomic force microscopy (AFM) and these were statistically analyzed to characterize their surface roughness properties. Autocorrelation analysis of the first two types of episurfaces showed a quick loss of correlation within ∼100 nm. The episurface with Br-IBAE also showed isotropic mound roughness with sharp point-like protrusions. The GCIB prepared episurfaces exhibited the formation of uniform step-terrace patterns with monatomic steps and wide terraces as indicated by the strong, long range (>0.5 μm) correlations. Statistical analysis of the GCIB episurfaces showed self-similar random fractal behavior over eight orders of magnitude in the power spectral density (PSD) with a fractal dimension of ∼2.5.
Study of Germanium Diffusion in HfO2 Gate Dielectric of MOS Device Application
Authors: Zhang Qingchun , Wu Nan , Bera L.K. , Zhu Chunxiang 
Published: April 2011

ABSTRACTSignificant germanium incorporation into HfO2 gate dielectrics has been found after thermal annealing in germanium MOS device. The dependences of germanium incorporation in HfO2 with dielectric deposition method, annealing temperature and annealing ambient were extensively studied by means of physical analytical methods such as SIMS and XPS. MOCVD (metal organic chemical vapor deposition) technique shows stronger germanium incorporation than PVD (physics vapor deposition) while surface nitridation of germanium can effectively suppress the Ge-incorporation. In addition, the results indicate that a thermal budget higher than 500°C in device fabrication results in apparent Ge out-diffusion. And the germanium out-diffusion is found to be enhanced under oxygen environment.
Fabrication of LED Based on III-V Nitride and its Applications
Authors: Shibata Naoki 
Published: April 2011

ABSTRACTShort wavelength LED (TG Purple) based on III-V nitride semiconductors is established in addition to blue and green. This short wavelength LED is realized by adjusting “Indium” chemical content of the well layer. Light output power of “TG Purple” is high and FWHM is narrow. “TG Purple” is applied to light source of white LED. Combination of “TG Purple” and various phosphors can generate white light with high luminous intensity and good color rendering. “TG Purple” is also applied to light source of air-purifier. This air-purifier was equipped in a car and several applications of this system are widely utilized in room air conditioners and refrigerators.
Electro-optic and thermal studies of multi-quantum well light emitting diodes in InGaN/GaN/sapphire structure.
Authors: Park Jeong , Shin Moo Whan , Lee Chin C. 
Published: April 2011

ABSTRACTWe present an electrical model for quantum-well light emitting diodes (LEDs) with a current spreading layer. The LEDs studied have a Multi-Quantum Well (MQW) between p-GaN and the n-GaN grown on sapphire. The model consists of a diode connected with a series resistor resulting from the current spreading layer. Using the model, the I-V curve of the diode itself is extracted from the measured LED I-V curve. The model also includes a current equation for the diode itself which was subsequently sought to match the extracted I-V curve. In the seeking process, junction temperature (Tj) rather than case temperature (Tc) was used in the equation. The diode model allows one to calculate the reduction on conversion efficiency caused by the current spreading layer. Results show that the current spreading layer causes 20% of the efficiency reduction at Tj = 107°C. The model can be used to optimize the conversion efficiency by balancing the transparency and the resistance of current spreading layer.
Grain Expansion and Subsequent Seeded Growth of AlN Single Crystals
Authors: Zhuang Dejin , Schlesser Raoul , Sitar Zlatko 
Published: April 2011

ABSTRACTOngoing efforts of growing large AlN single crystals at NCSU using an induction-heated, high-temperature reactor are based on (1) engineered expansion of single crystalline grains with increasing boule length, as well as (2) the development of a growth process that enables seeded growth on AlN surfaces previously exposed to air. The growth process is based on physical vapor transport (PVT), where AlN powder is sublimed in a high purity nitrogen atmosphere. The growth temperature was typically in the range of 2250 to 2300 °C. In this study, tungsten crucibles were used in combination with graphite insulation and were found to be durable for AlN growth. Boule growth was interrupted several times in order to refill the AlN powder source and the growth surface was subjected to surface preparation to facilitate epitaxial re-growth. Grain expansion was studied as a function of process parameters. Crystalline quality of large single crystalline grains was correlated with their surface morphology.
Modeling of elastic, piezoelectric and optical properties of vertically correlated GaN/AlN quantum dots
Authors: Łepkowski Sławomir P. , Jurczak Grzegorz , Dłużewski Paweł , Suski Tadeusz 
Published: April 2011

ABSTRACTWe theoretically investigate elastic, piezoelectric and optical properties of wurtzite GaN/AlN quantum dots, having hexagonal pyramid-shape, stacked in a multilayer. We show that the strain existing in quantum dots and barriers depends significantly on the distance between the dots i.e. on the width of AlN barriers. For typical QDs, having the base diameter of 19.5nm, the drop of the electrostatic potential in the quantum dot region slightly decreases with decreasing of the barrier width. This decrease is however much smaller for QDs than for superlattice of GaN/AlGaN quantum wells, with thickness similar to the height of QDs. Consequently, the band-to-band transition energies in the vertically correlated GaN/AlN QDs show unexpected, rather weak dependence on the width of AlN barriers. Increasing the QD base diameter leads to stronger decreasing dependence of the band-to-band transition energies vs. the width of AlN barriers, similar to that observed for superlattieces of QWs.
Transmission Electron Microscopy Study of an Epitaxial Gate Oxide on III-N Semiconductor Structures
Authors: Saripalli Yoga. N. , Liu X-Q , Barlage D.W. , Johnson M.A.L. , Braddock D. , Stoddard N.A. , Chugh A. 
Published: April 2011

ABSTRACTAn effective gate insulator for compound semiconductors has been a challenging goal for the materials research community for nearly 40 years. Recent developments on the epitaxial deposition of complex gate oxides as gate insulators have shown promise with the demonstration of enhancement mode high electron mobility transistors (e-mode HEMTs). In this work, gate oxide epilayers deposited on III-V semiconductors for field effect transistors (III-V MOSFETs) are examined using transmission electron microscopy (TEM) to identify the structure of the oxide/semiconductor interface. The high resolution images of the cross-sectional structures for the first time reveal a crystalline nature of the interface between the oxide and the III-V semiconductor. The composition of the oxide layers are determined by Z-contrast Electron Energy Loss Spectroscopy (EELS). The surface morphology of the FET structures is investigated by atomic force microscopy (AFM) both before and after gate oxide deposition, and the structural results are related to device DC electrical characteristics. With an underlying GaN/InGaN heterojunction grown by metal-organic chemical vapor deposition (MOCVD) on sapphire, the MOSFET devices exhibit the characteristics of a substantially unpinned interface, including the capacity for significant charge accumulation and transconductance at positive gate voltages.