bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Near-Threshold Gain Mechanisms in MOCVD-Grown GaN Epilayers and InGaN/GaN Heterostructures
Authors: Bidnyk S. , Schmidt T. J. , Little B. D. , Song J. J. 
Published: April 2011

ABSTRACTWe report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers and InGaN/GaN heterostructures at temperatures as high as 700 K. We show that the dominant near-threshold gain mechanism in GaN epilayers is inelastic excitonexciton scattering for temperatures below ∼ 150 K, characterized by band-filling phenomena and a relatively low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge related emission indicates electron-hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. The dominant mechanism for SE in InGaN epilayers and InGaN/GaN multiple quantum wells was found to be the recombination of carriers localized at potential fluctuations resulting from nonuniform indium incorporation. The SE spectra from InGaN epilayers and multiple quantum wells were comprised of extremely narrow emission lines and no spectral broadening of the lines was observed as the temperature was raised from 10 K to over 550 K. Based on the presented results, we suggest a method for significantly reducing the carrier densities needed to achieve population inversion in GaN, allowing for the development of GaNactive-medium laser diodes.
Annealing of Ion Implantation Damage in SiC Using a Graphite Mask
Authors: Thomas Chris , Taylor Crawford , Griffin James , Rose William L. , Spencer M. G. , Capano Mike , Rendakova S. , Kornegay Kevin 
Published: April 2011

ABSTRACTFor p-type ion implanted SiC, temperatures in excess of 1600 °C are required to activate the dopant atoms and to reduce the crystal damage inherent in the implantation process. At these high temperatures, however, macrosteps (periodic welts) develop on the SiC surface. In this work, we investigate the use of a graphite mask as an anneal cap to eliminate the formation of macrosteps. N-type 4H- and 6H-SiC epilayers, both ion implanted with low energy (keV) Boron (B) schedules at 600 °C, and 6H-SiC substrates, ion implanted with Aluminum (Al), were annealed using a Graphite mask as a cap. The anneals were done at 1660 °C for 20 and 40 minutes. Atomic force microscopy (AFM), capacitance-voltage (C-V) and secondary ion mass spectrometry (SIMS) measurements were then taken to investigate the effects of the anneal on the surface morphology and the substitutional activation of the samples. It is shown that, by using the Graphite cap for the 1660 °C anneals, neither polytype developed macrosteps for any of the dopant elements or anneal times. The substitutional activation of Boron in 6H-SiC was about 15%.
Photo-Assisted RIE of GaN in BCl3/Cl2/N2
Authors: Medelci N. , Tempez A. , Berishev I. , Starikov D. , Bensaoula A. 
Published: April 2011

ABSTRACTGallium nitride (GaN) has been under intense investigation due to its unique qualities (wide band gap, chemical and temperature stability) for optoelectronic and high temperature/high power applications. To this end, reactive ion etching (RIE) experiments were performed on GaN thin films using BCl3/Cl2/Ar. These resulted in etch rates of 1400 Å/min at −400 V dc bias. However, rough etched surfaces, nitrogen surface depletion and high chlorine content were observed. In order to remedy these shortcomings, a photo-assisted RIE process using a filtered Xe lamp beam was developed, resulting in higher etch rates but again in nitrogen depleted surfaces. Preliminary results on using nitrogen instead of argon in the process chemistry show a big improvement in photo-asssisted etch rates (50%) and Ga/N ratio (0.78 versus 1.25). In this paper, the effects of epilayer doping, dc bias, nitrogen flow rate and photo-irradiation flux on GaN etch rates, surface morphology and composition are presented. Finally, preliminary results on the use of a KrF excimer laser beam in the GaN photo-assisted RIE process are presented.
Full Band Monte Carlo Simulation of Short Channel MOSFETs in 4H and 6H-SiC
Authors: Hjelm M. , Nilssoni H-E. , Dubaric E. , Persson C. , Käckell P. , Petersson C. S. 
Published: April 2011

ABSTRACTThis is a presentation of a full band Monte Carlo (MC) study, which compares electron transport and device performance for 4H and 6H-SiC 100 nm n-channel MOSFETs. The model used for the electrons is based on data from a full potential band structure calculation using the Local Density Approximation (LDA) to the Density Functional Theory (DFT). For the holes the transport is based on a three band k-p model including spin orbit interaction. The two polytypes are compared regarding surface mobilities obtained with the program, as well as transconductance, unit current gain frequency, carrier velocity, I-V characteristics and energy distribution in the channel for the MOSFETs.
Selective Dry Etching of the GaN/InN/AlN, GaAs/AlGaAs and GaAs/InGaP Systems
Authors: Hays D. C. , Abernathy C. R. , Hobson W. S. , Pearton S. J. , Han J. , Shul R. J. , Cho H. , Jung K. B. , Ren F. , Hahn Y. B. 
Published: April 2011

ABSTRACTSelective etching of InN over GaN and AlN, and of GaAs over both AlGaAs and InGaP was examined with a number of different plasma chemistries under inductively coupled plasma conditions. Selectivities up to 55 for InN/GaN and 20 for InN/AlN were achieved in IC1/Ar discharges. For GaAs/AlGaAs, maximum selectivities of 75(with BCl3/SF6) were obtained while for GaAs/InGaP values of 80(with BCl3/SF6) and 25(with BCl3/NF3) were achieved. Selective etching of InGaP over GaAs is possible with either CH4/H2 or BI3. The selectivity is a strong function of ion flux and ion energy, and can result from two factors – either formation of a nonvolatile etch product, or a difference in bond strength between the two materials.
A Novel Surface Pivation Structure for III-V Compound Semiconductors Utilizing a Silicon Interface Control Layer and its Application
Authors: Hashizume Tamotsu , Hasegawa Hideki 
Published: April 2011

ABSTRACTThe present status of surface passivation research for III-V compound semiconductors utilizing a novel unique structure including a silicon interface control layer (Si ICL) is presented and discussed. The basic principle of passivation is to insert an ultrathin MBE-grown Si layer between the III-V compound semiconductor and a Si-based thick insulator so as to terminate the surface bonds of the III-V material with Si atoms and then to transfer Si-bonds smoothly to those of the Si based insulator. Based on the calculation of quantized levels in strained Si ICL, the passivation structure was optimized. Such a structure was realized by partial nitridation of Si ICL surface. In-situ surface characterization techniques including newly developed UHV contactless C-V technique, were used for optimization of each passivation step. Surface reconstruction of initial semiconductor surface was found to have a great influence on passivation. In the case of GaAs, the c(4×4) surface is preferable to the (2×4) surface. The novel process has realized the oxide-free surface passivation of InP with a Nssmin value of 2 × 1010 cm−2 eV−1. Furthermore, the novel passivation technique has been successfully applied to the fabrication of MISFETs and IGHEMTs, and the passivation of quantum structures.
Degradation Reactions in SONY-Type Li-Ion Batteries
Authors: Roth E. Peter , Nagasubramanian G. 
Published: April 2011

ABSTRACTThermal instabilities were identified in SONY-type lithium-ion cells and correlated with interactions of cell constituents and reaction products. Three temperature regions of interaction were identified and associated with the state of charge (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 100°C involving the solid electrolyte interface (SEI) layer and the LiPF6 salt in the electrolyte (EC:PC:DEC/LiPF6). These reactions could account for the thermal runaway observed in these cells beginning at 100°C. Exothermic reactions were also observed in the 200°C-300°C region between the intercalated lithium anodes, the LiPF6 salt, and the PVDF. These reactions were followed by a hightemperature reaction region, 300°C-400°C, also involving the PVDF binder and the intercalated lithium anodes. The solvent was not directly involved in these reactions but served as a moderator and transport medium. Cathode exothermic reactions with the PVDF binder were observed above 200°C and increased with the state of charge (decreasing Li content). This offers an explanation for the observed lower thermal runaway temperatures for charged cells.
Development and Characterization of Nanostructure Tin alloys as Anodes in Lithium - Ion Batteries
Authors: Peled E. , Ulus A. , Rosenberga Y. 
Published: April 2011

ABSTRACTSeveral tin-antimony and tin-zinc nanostructure alloys were electroplated from an acid bath, on a copper foil, at current densities higher by an order of magnitude than the limiting current density. They have been characterized as potential high-capacity anodes for lithium-ion battery applications. SEM micrographs of the tin-based alloys reveal nanosize particles, which aggregate into larger agglomerates of fractal shapes. On the nanoscale, the zinc-tin alloys have house-of-cards or honeycomb morphology. The composition of one series of tin based alloys was Sn:Sb (atomic ratio) 1.4:1 to 9:1; another alloy consisted of Sn:Sb:Cu in the ratio 34:10:4. All contained about 5% carbon and about 20% oxygen. The zinc-rich tin alloys contain at least 80 atomic percent zinc (their electrochemical characterization will be reported elsewhere). Tin-based alloys with low antimony content, have high reversible capacity (up to 700mAh/g), low irreversible capacity (about 24%), a better rate capability, and a lower average working potential vs. Li. On the other hand, alloys rich in antimony have a longer cycle life, but poor rate capability and a high average working potential vs. Li. The addition of copper to the tin-based alloys improved cycle life and slightly reduced irreversible capacity.
Effect of Alloy Composition on the Structure of Zr Based Metal Alloys
Authors: Chao B. S. , YOUNG R. C. , Ovshinsky S. R. , Pawlik D. A. , Huang B. , Im J. S. , CHAKOUMAKOS B. C. 
Published: April 2011

ABSTRACTThe structures of Ovonic multi-element, multi-phase Zr-based transition metal alloys for hydrogen storage are studied. The alloys are designed to be multi-phase materials. The hexagonal and diamond cubic structures, known as C14 and C15 Laves structures respectively, are the two major hydrogen storage phases in the alloys. In both C14 and C 15 structures, Zr and Ti are the elements typically occupying the hydride former (A) sites and V, Cr, Mn, Fe, Co and Ni the catalytic (B) sites. Based on the application of Ovshinsky's design principles for disordered materials, both A and B sites are compositionally disordered by the corresponding elements in cubic (C15) structure. However, the hexagonal (C14) structure has two distinct B sites, B(I) and B(Il) with a 1:3 ratio. Preliminary neutron diffraction studies indicate that the B(I) sites are predominantly occupied by Ni and the B(ll) sites are randomly mixed with V, Cr, Mn, Fe, and Ni. It is then proposed that the formula of the hexagonal structure should become A2B(I)IB(II) 3 in the current multi-element Zr-based alloys. Minor phases close to the structures of Zr7Ni10, Zr9Ni11, and ZrO2 are also present in some alloys. The average electron concentration factor (e/a) derived from the alloy composition dictates the alloy structures. The alloys with higher electron concentration factor (> 7.1) favor the diamond cubic structure. On the other hand, the hexagonal structure is associated with the alloys with lower electron concentration factor (< 6.5). The alloys having electron concentration factors in between are mixtures of the diamond cubic and hexagonal structures.
Lithium Nickelate with Cadmium Iodide Structure
Authors: Arai Hanime , Sakurai Yoji 
Published: April 2011

ABSTRACTWe obtained a highly delithiated sample of Li0.04NiO2using acid leaching. The Rietveld analysis of its X-ray diffraction pattern indicated that the sample was a mixture of three phases. Two of them maintained the pristine structure with cubic close-packing layers while the other phase had a cadmium iodide structure with hexagonal close-packing layers. We examined the electrochemical behavior of this sample as a positive electrode material for lithium batteries. The discharge capacity was smaller than that of a Li0.10NiO2sample obtained by acid leaching, suggesting that the capacity loss is due to the formation of the phase with the cadmium iodide structure.
Porous Thin-Film Anode Materials for Solid-Oxide fuel Cells
Authors: Morse Jeffrey D. , Graff Robert T. , Hayes Jeffrey P. , Jankowski Alan F. 
Published: April 2011

ABSTRACTThin film, solid-oxide fuel cells (TFSOFCs) synthesized from an electrolyte and conductive material are developed using photolithographic patterning and physical vapor deposition. The anode layer must enable combination of the reactive gases, be conductive to pass the electric current, and provide mechanical support to the electrolyte and cathode layers. The microstructure and morphology desired for the anode layer should facilitate generation of maximum current density from the fuel cell. For these purposes, the parameters of the deposition process and post-deposition patterning are developed to optimize a continuous porosity across the anode layer. The anode microstructure is characterized using scanning electron microscopy and the power ouput generated through current-voltage measurement.
A Study on Oxidized Glassy Carbon sheets for Bipolar Supercapacitor Electrodes
Authors: Braun A. , Bärtsch M. , Geiger F. , Schnyder B. , Kötz R. , Haas O. , Carlen M. , Christen T. , Ohler C. , Unterinahrer P. , Krause E. 
Published: April 2011

ABSTRACTElectrochemical Double Layer Capacitors (EDLC) for high energy and power density applications, based on glassy carbon (GO) electrodes, are being developed in our laboratory. In the context of this project, GC sheets were oxidized and investigated with Small Angle X-ray Scattering (SAXS), Electrochemical Impedance Spectroscopy (EIS) and Nitrogen Gas Adsorption (BET). During oxidation an active film with open pores is built on the surface of the GC. Upon oxidation, the internal volumetric surface area of the active film decreases, whereas the volumetric electrochemical double layer capacitance increases. We show that this effect is correlated with the opening, the growth and the coalescence of the pores.
New Conducting Polymers for Electrochemical Ultracapacitors
Authors: Naoi K. , SUEMATSU S. 
Published: April 2011

ABSTRACTRedox reactions and structural changes of a poly(2,2′-dithiodianiline) [poly(DTDA)], a conducting polymer interconnected with disulfide (S-S) bonds, in acid aqueous solution of various pH values are discussed. We proposed the poly(DTDA) as a proton-exchange type of energy storage material. The cyclic voltammograms (CVs) for poly(DTDA) showed a reproducible redox couples for repeated (10,3-104cycles. To investigate the structure of the poly(DTDA) for each potential and the pH value, a plot of E° vs. pH values obtained from the results of CVs (Pourbaix diagram) was formed and discussed.
Stability of Self-Assembled Organic-Inorganic Layered Perovskite
Authors: Kitazawa Nobuaki , Yamamoto Takafumi , Watanabe Yoshihisa , Nakamura Yoshikazu 
Published: April 2011

ABSTRACTPhoto-stability of (C6H5C2H4NH3)2PbX4 (X; Br and I) films was studied and the degradation processes were discussed. The prepared films were not stable against the UV-light irradiation. The PhE-PbX4 films were readily oxidized by the UV-light irradiation in air. In vacuum, the PhE-PbI4 films changed to β-phenethylamine intercalated PbI2 due to the elimination of halogen species. On the contrary, no degradation was observed for the PhE-PbBr4 films. These results suggested that the photo-irradiation induced photochemical reaction was one of the possible reasons for the degradation. To suppress the oxidation and halogen elimination induced by the photochemical reaction, PMMA-coated PhE-PbX4 films were also fabricated and their photo-stability was examined.
Nanostructural Lithography via Photo-Initiated Phase Transformation of Silica-Surfactant Assemblies
Authors: Doshi D. A. , HÜsing N. , Fan H. , Hurd A. J. , Brinker C. J. 
Published: April 2011

ABSTRACTCooperative self-assembly processes of inorganic species and amphiphilic molecules have experienced major advances over the past six years. The ability to design these materials with spatially controlled combinations of different mesophases or compositions, and therefore different properties, would greatly enhance their utility as nanofunctional surfaces.We present a simple lithographic procedure, which allows a deliberate control of structure and properties of a meso-ordered silica film through optical mediation. This nanostructural lithography process exploits the pH sensitivity of supra-molecular self-assembly which allows spatial control over mesophases in the thin film and a selective etching capability. Through the addition of a photoacid generator in the coating sol along with surfactant and silica source, dip coating results in continuous, ordered photosensitive films. Exposure to UV light through a mask produces local pH changes, inducing mesostructural phase transitions and an increase in the acidcatalyzed siloxane condensation rate in the exposed regions. Two surfactant systems, CTAB (CH3(CH2)15N+(CH3)3Br–) and Brij 56 (CH3(CH2)15(OCH2CH2)10OH) have been studied. X-ray diffraction, transmission and scanning electron microscopy, optical microscopy, ellipsometry, MAS-NMR and atomic force microscopy are used to characterize the patterned nanostructured surfaces.
Storage Stability of Solvent-Free Condensates of Functionalized Trialkoxysilanes
Authors: Stein S. , Clausbruch St. Cramer V. , Moszner N. , Ag V. Rheinberger Ivoclar 
Published: April 2011

ABSTRACTThe lack of storage stability of organic-inorganic solvent-free sols is a well-known problem. We investigated the influence of different solvents in the acid catalyzed hydrolysis of various sols on their storage stability. Our experiments were based on two different silanes, 3-methacryloxypropyltrimethoxysilane (MPTS) and 1,1,1-tris(allyloxymethyl)-l-[[[3-(triethoxysilyl)propyl]aminocarbonyl]oxymethyl]methane (silane 31), synthesized by reaction of pentaerythritol triallyl ether and 3-isocyanatopropyltriethoxysilane. The employed solvents were alcohol, tetrahydofuran and tert-butyl methyl ether in a range of 95 wt% to 30 wt% in solution. In order to get comparable chemical conditions the degree of condensation of the various sols were adjusted between 75% and 85%. Furthermore, the sols were modified by silylation with trimethylchlorosilane. A comparison of silylated and not silylated silane 31 clearly showed that a decrease in residual silanol groups increase the storage stability. The results of the investigations demonstrated that both the kind and the amount of solvent used in hydrolysis affects the initial viscosity of solvent-free condensates of silane 31 and MPTS.
Optical Characteristics Of Silica-Poly(Ethylene Oxide) Hybrid Thin Films
Authors: Park O. H. , Eo Y. J. , Choi Y. K. , Bae B. S. 
Published: April 2011

ABSTRACTSilica-PEO hybrid materials which have both silica network and polymer network are synthesized from hydrolysis, condensation and polymerization of γ -glycidoxypropyltrimethoxysilane(GPTS). Polymerization of the epoxy groups to poly(ethylene oxide) units is achieved by using mixed triarylsulfonium hexafluorophosphate salt as a UV curing agent. The structural change of the hybrid solution is investigated by using NMR spectroscopy. The microstructure of silica hybrid film can be changed according to the degree of polymerization controlled by the UV curing conditions. The epoxide polymerization is confirmed by using FT-IR. The hybrid material is densified due to the epoxide polymerization as well as silica condensation with UV curing. The optical properties such as optcial absorbance and refractive index of the silica hybrid thin films are measured as functions of curing conditions. These optical properties are then correlated to the epoxide polymerization.
Influence Of Hybridation With A Silicate Network On The Properties Of An Eu 3+ Complex Derived From Dipicolinic Acid
Authors: Franville A. C. , Zambon D. , Mahiou R. , Troin Y. , Cousseins J. C. 
Published: April 2011

ABSTRACTIn this paper, the preparation, the characterization and the optical features of organicinorganic materials incorporating a trivalent europium organic chelate into a silicate network are described. The covalent grafting and the sol-gel process allow to obtain monophasic hybrid gels in which the structure and the activity of the organic molecules were retained. The Eu3+ coordination mode is not sensitive to the sol-gel processing conditions whereas the morphology of materials, their thermal resistance and their luminescence properties may be adjusted. Characteristics of hybrid compounds are compared to those of the corresponding organic species.
Thermosetting Mechanism Study of Organosilicon Polymer Containing Carborane by Solid-State NMR Spectroscopy
Authors: Kimura H. , Okita K. , Ichitani M. , Yonezawa M. , Sugimoto T. 
Published: April 2011

ABSTRACTThe thermosetting mechanism of an organosilicon polymer containing carborane has been studied utilizing the 13and 29Si solid-state NMR method. The polymer having C≡C bonds in the main chain and CH═CH2, Si-H bonds, and carborane in the bulky side chain, shows a very highly thermal stability in air by curing. From 13C and 29Si NMR spectra of the polymer, it was found that the intermolecular cross-linking reactions of the polymer was due to (1) the diene reaction between Ph-C≡C and C≡C and (2) the addition reaction between side chain terminal and Ph-C≡C and between CH═CH2 and Si–H, and a very highly thermal stable structure is formed.
Magnetic Anisotropy in Rare-Earth - Transition Metal Intermetallic Compounds
Authors: Luong Nguyen Hoang , Thuy Nguyen Phu , Quang Pham Hong , Thang Pham Duc 
Published: April 2011

ABSTRACTIn this work the rare-earth anisotropy in the rare-earth - transition metal intermetallic compounds is investigated by studying the temperature-induced spin reorientation phenomena on aligned powder samples and by analyzing the temperature dependence of the magnetization measured along different principal axes of single crystals. From such investigations the crystalline-electric-field parameters of the rare-earth ions in these compounds have been derived. The results on different hard magnetic materials of the compositions R2Fe14B, RFe11 and their substituted compounds as well as R2Co17 are summarized.
Novel Permanent Magnets and Their Uses
Authors: Constantinides S. 
Published: April 2011

ABSTRACTTwo changes have gone hand in hand during the 20th century. First, applications were conceived that required new or greatly improved materials. Need being the mother of invention, materials were then developed to satisfy the application needs. Permanent magnets are today used in devices that could only have been dreamed about 25 years ago. Who could have foreseen, for example, the advances in data storage that have occurred over the last 15 years? Hard disk drives of under 10 megabytes in size and with random access times of over 65 milliseconds were the norm in 1984. Today, the standard drive is over 8 gigabytes, is smaller in size and costs less than a fourth of the old drives, with an access time of 10 milliseconds and more than 33 mbps burst throughput. Novel has two interpretations: first it may refer to the magnetic material or it may refer to the application of a material. Several examples of each are presented.