bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly-Si TFTs From Glass to Plastic Substrates: Process and Manufacturing Challenges
Authors: Lemmi F. , Lin S. , Drews B.C. , Hua A. , Stern J.R. , Chung W. , Smith P.M. , Chen J.Y.
Published: April 2011

Poly-Si Thin-Film Transistors (TFTs) are currently used in commercial active-matrix displays. They provide superior performance with respect to their amorphous silicon counterparts and allow integration of driving electronics directly on the display glass plates.

For several applications, it can be desirable to have active-matrix displays made on flexible substrates. However, a direct application of a standard TFT process to plastic substrates is not in general possible, mostly because of temperature limits and related dimensional stability issues. In addition, standard flat-panel manufacturing tools are not capable of automatically handling non-rigid floppy substrates.

Therefore, a new process has to be developed, compatible with a suitable way of handling plastic substrates. A process was developed in which plastic sheets are laminated on glass carrier wafers and run through all the automated tools. A low-temperature process using excimer laser annealing is developed and optimized. High-quality TFT backplanes are manufactured with a pixel layout designed for active-matrix OLED (AMOLED) displays. Field-effect mobility in excess of 70 cm2Vs on p-channel TFTs are achieved, together with leakage currents lower than 2 pA per micron gate width.

Challenges include low-temperature gate dielectric development, reduction of intrinsic film stress, protection of plastic from laser damage, and contact formation. Solutions to these challenges are discussed and TFT transfer characteristics on glass and plastic substrates are presented. Finally, images from prototype monochrome AMOLED displays are presented, with 64 × 64 pixels and 80-dpi resolution.
Photosensitive Carbazolylethylmethacrylate Copolymers on Flexible Substrate for Optical Information Registration
Authors: Robu S. , Dementiev I. , Dmitriev S.
Published: April 2011

This 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

This 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

The 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

This 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

In 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

The 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

Grain 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

Crystallographic 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

The 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

Intersubband 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

The 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

Gratings 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

High-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

Significant 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

Short 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

We 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

Ongoing 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

We 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

An 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.
Non-Polar GaN/AlN Superlattices on A-plane AlN (500nm) Buffer Layers Grown by RF-MBE
Authors: Morita Takayuki , Kikuchi Akihiko , Kishino Katsumi
Published: April 2011

The growth conditions of A-plane AlN and GaN epitaxial layers by radio-frequency plasma assisted molecular beam epitaxy on R-plane sapphire substrates were investigated. The growth temperature and V/III supply ratio dependency on structural quality and surface roughness was described. The optimum V/III ratio for A-plane GaN and AlN layers was shifted to nitrogen rich side compared to the C-plane layers. A-plane GaN/AlN superlattices (SLs) were also grown on R-plane sapphire substrates. The X-ray diffraction peaks from a primary and a 1st satellite were observed. From a comparison of low temperature photoluminescence peak wavelength between A-plane and C-plane SLs, the built-in electrostatic field originated from spontaneous and piezoelectric polarization is negligible for A-plane SLs.
Electrical Characterization of As and [As+Si] doped GaN Grown by Metalorganic Chemical Vapor Deposition
Authors: Ahoujja M. , Elhamri S. , Berney R. , Yeo Y.K. , Hengehold R. L.
Published: April 2011

Electrical properties of As, Si, and [As+Si] doped GaN films grown on sapphire substrates by low temperature metalorganic chemical vapor deposition have been investigated using temperature dependent Hall-effect and deep level transient spectroscopy measurements. The Hall measurements from the GaN layers show that the concentration decreases with arsine flow (4, 40, and 400 sccm) at all temperatures. The carrier concentration of the Si-doped GaN, on the other hand, increases with the incorporation of arsine flow. This behavior is attributed to the formation of AsGa antisites which act as double donors. A deep level at around 0.82 eV below the conduction in the band gap of As doped GaN is measured by DLTS and is tentatively assigned to arsenic on gallium antisite.
Growth and Characterization of InGaN/GaN LEDs on Corrugated Interface Substrate Using MOCVD
Authors: Kim Sunwoon , Oh Jeong Tak , Lee Kyu Han , Kim Dong Joon , Kim Je Won , Kim Yong Chun , Lee Jeong Wook , Cho Hyung-Koun
Published: April 2011

III-nitride films were grown on the corrugated interface substrate using a metalorganic chemical vapor deposition system to increase the optical power of white LEDs. The patterning of a substrate for enhancing the extraction efficiency was processed using an inductively coupled plasma reactive ion etching system and the surface morphology of the etched sapphire wafer and that of the non-etched one were investigated using an atomic force microscope. The structural and optical properties of GaN on CIS were characterized by a high-resolution x-ray diffraction, transmission electron microscopy, AFM and photoluminescence. The roughness of the etched sapphire wafer was higher than that of the non-etched one. The GaN layer didn't grow locally over the surface of the cone shape pattern. The reason is that (0001) c-plane which is favor for GaN growth doesn't exist on the cone shape patterned region. The lateral growth of the GaN layer that was initially grown on the (0001) c-plane among pattern regions, was enhanced by raising the growth temperature and lowering the reactor pressure, resulting in the smooth surface over the pattern region. The (102) FWHM of GaN layer on the patterned substrate was better than that of GaN on the conventional substrate and no defect was detected at the interface of the cone shape pattern. The optical power of the LED on the patterned substrate was 20% higher than that on the conventional substrate due to the increased extraction efficiency.
Mechanism of Metalorganic MBE Growth of High Quality AlN on Si (111).
Authors: Gherasoiu I. , Nikishin S. , Kipshidze G. , Borisov B. , Chandolu A. , Holtz M. , Temkin H.
Published: April 2011

AlN constitutes the buffer layer of choice for the growth of GaN on all common substrates and its crystalline quality and surface morphology determine many of the properties of the overgrown epitaxial structure. This work systematically investigates the MOMBE growth of high quality AlN on Si (111) using trimethylaluminum and ammonia as sources of aluminum and nitrogen, respectively. Metalorganic MBE represents a hybrid growth technique that offers a combination of growth precision, in-situ monitoring and ease of source management with the promise of high material quality. We demonstrate very efficient growth, with the growth rate in excess of 500 nm/h and low ammonia consumption of less than 1 sccm. Over the entire domain of growth parameters, the surface roughness remained in the range from 12 to 53 Å rms for AlN layers up to 1000 nm thick. Here, the low values of the roughness are associated to the low growth temperature (760 °C), behavior that contrasts with that usually observed in gas source MBE with elemental Al source. X-ray diffraction linewidth as narrow as 141 arcsec has been demonstrated for samples grown under stoichiometric conditions. High temperature of the ammonia injector promotes the transition to the two-dimensional growth, while reducing the growth rate, pointing out the importance of surface hydrogen. We demonstrate that hydrogen plays an important role in the MOMBE process acting as a surfactant and passivating surface nitrogen bonds.
Low-Frequency Noise Characterization in AlGaN/GaN HEMTs with Varying Gate Recess Depths
Authors: Jha Shrawan. K. , Leung Bun. H. , Surya Charles C. , Schweizer Heins , Pilkhuhn Manfred. H.
Published: April 2011

Low-frequency noise measurements were performed on a number of AlGaN/GaN HEMTs with different gate recess depths, which were formed by dry etching. Detailed characterizations of the low-frequency noise properties were performed on the devices as a function of as a function of hot-electron stressing conducted at VD = 10 V and VG = -1.5 V. The room temperature voltage noise power spectral density, SV(ƒ), of the devices were found to show 1/ƒ dependence. A comparison of SV(ƒ) measured from different devices clearly indicate increase in the noise levels for the devices with large recess depths, reflecting the degradation caused by ion-impact induced damage during recess formation. Furthermore, the results of low-frequency noise measurements showed fast degradations for the devices with larger gate recess depths. Our experimental data clearly show that the dry etching process has induced damages in gates.
Progress in the Growth and Characterization of Ge Quantum Dots and Islands
Authors: Baribeau J.-M. , Rowell N.L. , Lockwood D.J.
Published: April 2011

We review progress in the growth of Si1-xGex islands and Ge dots on (001) Si. We discuss the evolution of the island morphology with Si1-xGex coverage, and the effect of growth parameters or post-growth annealing on the shape of the islands and dots. We outline some of the structural, and optical properties of Si1-xGex islands and review recent progress in the determination of their composition and strain distribution. We discuss various approaches currently being investigated to engineer Si1-xGex quantum dots and in particular control their size, density and spatial distribution. For example, we show how C pre-deposition on Si (001) can influence nucleation and growth of Ge islands.
Fabrication of a Regular Array of Atomic Silicon Wires on Silicon
Authors: Sekiguchi Takeharu , Yoshida Shunji , Itoh Kohei M.
Published: April 2011

We report on the experimental realization of atomically straight, single wires of Si atoms on a Si surface. The Si wires were formed by solid-source molecular beam epitaxy (MBE) on a specific substrate prepared by a thermal treatment of a vicinal Si(111) wafer. The structures of the substrate and the atomic wire were investigated by scanning tunneling microscopy (STM). The substrate consists of an array of atomically straight step edges with a uniform structure serendipitously suitable for self-assembly of the atomic wires. The isotopic version of this structure —single lines of29Si on28Si— is expected to be the most basic building block for the all-silicon quantum computer [1], which utilizes the nuclear spins of individual29Si isotopes as quantum bits (qubits).
Nucleation and growth processes of silicon nanowires
Authors: Takeda Seiji , Ozaki Nobuhiko , Ueda Kohei , Kohno Hideo , Kikkawa Jun , Ohno Yutaka
Published: April 2011

We have studied the nucleation and growth processes of silicon nanowires (SiNWs) by means of transmission electron microscopy and scanning tunneling microscopy. SiNWs are grown on hydrogen-terminated Si surface via the VLS (Vapor-Liquid-Solid) mechanism using silane (SiH4) as source gas. We have classified the growth process of SiNWs into three stages: the formation of nanocatalysts on a substrate, the nucleation of SiNWs in nanocatalysts, followed by the growth of SiNWs. We have shown that the structures of SiNWs are varied in several ways in each stage, and accordingly the structural properties of grown SiNWs can be modified to great extents. At the present moment, the phenomena at the each stage are not fully controlled, and this prevents us utilizing silicon nanowires more effectively.
First-Principles Study of Mechanical Properties of Alumina-Copper Nano-Coating Interfaces
Authors: Tanaka Shingo , Yang Rui , Kohyama Masanori
Published: April 2011

Mechanical properties of alumina-copper nano-coating interfaces have been studied by the first-principles calculations. We have applied the rigid-type first-principles tensile tests for O-rich (O-terminated) and stoichiometric (Al-terminated) interfaces and for back Cu1st-Cu2nd interlayers. The O-terminated interface is twice as strong as the Cu1st-Cu2nd interlayer whereas the Al-terminated interface is twice as weak as the Cu1st-Cu2nd interlayer. We have performed the fitting of interlayer potentials by universal binding-energy relation (UBER). The interlayer potential of the Cu-Al interface is well reproduced by UBER in whole region, although those of Cu-O interface and Cu1st-Cu2nd interlayer are partially reproduced.
Photochemical Adhesion of Fused Silica Glass Lens by Silicone Oil
Authors: Funatsu Takayuki , Kobayashi Masanori , Okamoto Yoshiaki , Murahara Masataka
Published: April 2011

The optical system that is pervious to ultraviolet light of 200nm and under in the wavelength has been developed by putting one silica glass to another with the silicone oil photo-oxidized in oxygen atmosphere.

Quartz has siloxane bonds, while silicone oil (dimethyl siloxane) is composed of siloxane bonds of the main chain and methyl groups of the side chain. Therefore, the organic silicone oil has been photo-oxidized by irradiating UV rays in oxygen atmosphere to change into inorganic glass. That is, the silicone oil was poured into the thin gap between the two pieces of silica glass in oxygen atmosphere and was irradiated with the Xe2 excimer lamp while heating at temperature above 150°C. Consequently, the siloxane of the silicone oil was linked with the O atoms that had been absorbed on the glass surface to form SiO2.

The UV and IR spectrum analysis was conducted on the silicone oil before and after lamp irradiation. The results revealed that as the time of lamp irradiation increased, the absorption peak of the CH3 group in the region of 2960 cm−1 decreased but the transmittance of the light in the 190nm wavelength conversely became high. The UV transmittance of the silicone oil was 50% before the lamp irradiation; which improved to 87% after the irradiation for 60 minutes. Furthermore, the tensile strength of the bonded sample was measured. It confirmed that the adhesive strength of the silicone oil was enhanced from 0 kgf/cm2 of before-irradiation to 180 kgf/cm2 of after- irradiation.
Copper Pattern Formation on Fluorocarbon Film by Single Shot of ArF Laser
Authors: Mochizuki T. , Murahara M.
Published: April 2011

Copper nuclei have been photo-chemically patterned on the fluorocarbon film surface in copper sulfate atmosphere via the reticle with just one shot of the ArF laser. Previously, we have reported that it required more than 3, 000 shots of the ArF laser to substitute the Cu atoms on the fluorocarbon surface.

Fluorocarbon is regarded as promising as a printed wiring board material in the high- frequency band. However, the fluorocarbon is chemically stable making it difficult to bond to copper foil. Generally, a copper foil is formed on the fluorocarbon surface by electroless plating with a catalyst core. In this method, however, the surface is made rough in pretreatment, which impairs its characteristics. Using the catalysts also causes differences in the dielectric constant, generating a high frequency noise. Thus, we demonstrated the direct formation of copper nuclei on the fluorocarbon surface photo-chemically by using the Xe2 excimer lamp and the ArF excimer laser.

The sample surface was first irradiated by Xe2 excimer lamplight to ma ke it hydrophilic. The surface was then irradiated with circuit patterned ArF laser light in the presence of copper-sulfate (CuSO4) aqueous solution to substitute the Cu atom. The modified sample was immersed in the electroless plating solution at 60 degrees Celsius for 15 minutes, and the copper foil was locally formed on the areas exposed to light.
Effects of High-Speed Deformation on the Phase Stability and Interdiffusion in Ultrasonically Joined Aluminum and Zinc Foils
Authors: Gunduz Ibrahim Emre , Shattuck Emily D. , Ando Teiichi , Wong Peter Y. , Doumanidis Charalabos C.
Published: April 2011

The effects of high strain-rate deformation on the phase stability and interdiffusion were investigated for Al-Zn welds produced by ultrasonic welding at 513 K. The welds exhibited three distinct regions: a featureless region indicative of local melting on the zinc side, a solidified mushy layer and a layer of fcc grains enriched with zinc. Al-Zn phase diagrams calculated from vacancy-modified Gibbs free energy curves indicate that local melting at the weld interface may result even at 513 K if the vacancy concentrations in the fcc and hcp solutions approach 0.07 as a result of high strain-rate deformation. EDS analysis of the weld interface yielded an interdiffusivity of 1.9 μm2/s, which is five orders of magnitude larger than the normal diffusivity of zinc in aluminum at 513 K. Application of the mono-vacancy diffusion mechanism to the diffusion data also yields a vacancy concentration of 0.07, indicating that such a high vacancy concentration may indeed resulted during the ultrasonic welding at 513 K.
Improved Fatigue Properties of 316L Stainless Steel Using Glass-Forming Coatings
Authors: Liu F. X. , Chiang C. L. , Wu L. , Hsieh Y. Y. , Yuan W. , Chu J. P. , Liaw P. K. , Brooks C. R. , Buchanan R. A.
Published: April 2011

The effects of the glass-forming coatings on the fatigue behavior of 316L stainless steel were investigated. Films consisting of 47%Zr, 31%Cu, 13%Al and 9%Ni (atomic percent) were deposited onto the stainless steel by magnetron sputtering. The influences of the substrate condition, the surface roughness, the adhesion, and the compressive residual stresses on the fatigue behavior were studied. The applications of the glass-forming coating gave rise to significant improvements in both the fatigue life and the fatigue limit, in comparison with the uncoated steel. Depending on the maximum stress applied to the steel, the fatigue life can be increased by at least 30 times, and the fatigue limit can be elevated by 30%.
The Use of Closely Spaced Vickers Indentations to Model Erosion of Polycrystalline α-Al2O3
Authors: Júnior Adolfo Franco , Roberts Steve G.
Published: April 2011

Arrays of closely spaced quasi-static indentation were made on specimens of polycrystalline α-Al2O3, mean grain size G=1.2, 3.8 and 14.1 μm. The critical indentation spacing to produce crack coalescence between indentations, and thus significant loss of material from the surface, was determined. These data are compared to results for low-impact-velocity wet erosive wear on the same materials; a good correspondence is found. The indentation data can be used to produce “wear maps”, which provide a guideline for predicting the low-impact-velocity erosive wear resistance of brittle materials.
A Surface Coating for Silicon Carbide Whiskers
Authors: Zhang Heng. , Xiao T. D. , Reisner D. E. , Santiago P.
Published: April 2011

A mullite coating process has been conducted to form an electrically insulating layer on the surface of the silicon carbide whiskers for whisker reinforcement application by a chemical deposition and hydrolysis. The phase, structure, morphology and electrically insulating property of the coated silicon carbide whiskers have been investigated by using x-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrical measurement. The study indicates that a crystalline mullite coating layer is formed after heat-treating the precursor coating at elevated temperature. The formed mullite coating significantly increases the electrical resistance of the silicon carbide whiskers.
Limiting Catalytic Coke Formation by the Application of Adherent SiC Coatings via Pulsed Laser Deposition to the Inner Diameter of Tube Material Traditionally Used for Ethylene Pyrolysis Service
Authors: Chauhan Alok , Moran Wilton , Casey Elizabeth , Si Weidong , White Henry
Published: April 2011

Pulsed laser deposited coatings can be used to enhance the corrosion resistant of materials traditionally used for industrial applications. In this paper, we describe our initial results on coating HK40 (a material used for ethylene heater tubing) with silicon carbide (a carburization resistant coating) to increase tube life. A 1 um thick film of silicon carbide was successfully deposited onto a heated HK40 substrate. An array of characterization techniques (scanning electron microscopy, atomic force microscopy, and scratch tests) demonstrated that the processing conditions were suitable for good coverage and promising adhesion behavior.
Simultaneous Effects on Topography, Composition and Texture in Ion Assisted Deposition of Thin Films
Authors: Harper James M.E.
Published: April 2011

Ion bombardment during deposition may simultaneously affect thin film topography, composition and crystallographic texture. Ion etching can produce periodic ripples that depend on the angle of ion incidence and surface temperature. When applied during deposition, ion bombardment can produce in-plane crystallographic orientation in polycrystalline materials for specific angles of incidence. In addition, ion bombardment changes the composition of multicomponent thin films according to the local angles of ion incidence and ion/atom ratios. Therefore, these three mechanisms may be linked under certain deposition conditions to generate novel topographically patterned materials with locally controlled composition and texture. Examples include metal alloys, oxides and nitrides, and recommendations for specific nanoscale structures are given.
Low Damage Smoothing of Magnetic Materials using Oblique Irradiation of Gas Cluster Ion Beam
Authors: Kakuta Shigeru , Sasaki Shinji , Furusawa Kenji , Seki Toshio , Aoki Takaaki , Matsuo Jiro
Published: April 2011

Oblique irradiation using a gas cluster ion beam (GCIB) has been studied in order to achieve low-damage smoothing of magnetic materials. We investigated how the surface morphology and surface roughness depended on the angle of incidence. Quite smooth surfaces could be obtained using both normal and grazing-incidence irradiation. At incident angles larger than 45?, periodic ripples were formed. The orientation of the ripples changed from perpendicular to parallel with respect to the GCIB when the incident angle exceeded a critical value. Surface roughening resulting from the formation of ripples was observed at incident angles between 45° and 65°. Fluctuations in the Ni/Fe component ratio and the intermixing of oxygen from the native oxide were evaluated. As the angle of incidence increased, both the thickness of the layer in which the component ratio was fluctuating and the depth of oxygen intermixing decreased. As a result, it was determined that low-damage smoothing of magnetic materials could be performed by using grazing-incidence irradiation from a GCIB.
Helical Rosette Nanotubes as a Potentially More Effective Orthopaedic Implant Material
Authors: Chun Ai Lin , Fenniri Hicham , Webster Thomas J.
Published: April 2011

Organic nanotubes called helical rosette nanotubes (HRN) have been synthesized in this study for bone tissue engineering applications. They possess intriguing properties for various bionanotechnology applications since they can be designed to mimic the nanostructured constituent components in bone such as collagen fibers and hydroxyapatite (Ca5(PO4)3(OH)) which bone cells are naturally accustomed to interacting with. This is in contrast to currently used orthopaedic materials such as titanium which do not possess desirable nanometer surface roughness. The objective of this in vitro study was to determine bone-forming cell (osteoblasts) interactions on titanium coated with HRNs. Results of this study showed for the first time increased osteoblast adhesion on titanium coated with HRNs compared to those not coated with HRNs. In this manner, this study provided evidence that HRNs should be further considered for orthopaedic applications.
A Hybrid Laser/Aerosol Method for the Synthesis of Porous Nanostructured Calcium Phosphate Materials for Bone Tissue Engineering Applications
Authors: Brown Shatoya , Kim Hyunbin , Camata Renato P.
Published: April 2011

We present a new synthesis method based on laser generation and processing of aerosol particles that can produce calcium phosphate coatings in a porous nanostructured configuration. The process uses laser ablation of crystalline hydroxyapatite targets to produce a calcium phosphate aerosol comprising micro- and nanoparticles that are processed and deposited on metallic substrates under well-controlled temperature and ambient conditions, creating a microporous calcium phosphate network suitable for growth of biogenic calcium phosphate materials. Laser ablation is carried out using a KrF excimer laser at fluences between 0.4 J/cm2 and 2.8 J/cm2 and temperatures ranging from 500°C to 760°C. X-ray diffraction and scanning electron microscopy measurements on samples deposited above 750°C show that the obtained material is crystalline hydroxyapatite with good mechanical stability. Its microstructure features a porous framework of partially sintered microparticles surrounded by nanoparticulate material.