bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTElectrical 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

ABSTRACTIII-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

ABSTRACTAlN 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

ABSTRACTLow-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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTMechanical 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

ABSTRACTThe 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

ABSTRACTCopper 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTArrays 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

ABSTRACTA 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

ABSTRACTPulsed 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

ABSTRACTIon 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

ABSTRACTOblique 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

ABSTRACTOrganic 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

ABSTRACTWe 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.
Oxygen Nonstoichiometry of Various Functional Layered Oxides
Authors: Shimoyama Jun-ichi , Yokota Yuui , Shiraki Masahiro , Sugiura Yuuki , Horii Shigeru , Kishio Kohji 
Published: April 2011

ABSTRACTThe mixed metal oxides having layered crystal structure have been of much interest because of their various new and excellent functions. Precise phase diagrams on the oxygen content have not been clarified for most of these layered oxides, while oxygen nonstoichiometry often plays a crucial role for determining functions of oxide materials. In this paper, we report oxygen nonstoichiometry and related physical properties mainly on the manganese-based and cobalt-based layered oxides. In the La2–2xSr1+2xMn2Oy (x = 0.3, 0.4), dramatic change in magnetization properties with oxygen content were observed in spite of its small oxygen nonstoichiometry. For (Ca2CoO3-δ)0.62CoO2 systems, high valence metal substitution was found to be effective for suppression of oxygen nonstoichiometry, increase of decomposition temperature and thermoelectric properties.