bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel Solid State Hybrid QM/MM Embedding Investigation into Methanol Synthesis over Cu Supported on ZnO Catalysts
Authors: French Samuel A. , Bromley S. T. , Sokol A. A. , Catlow C. R. A. , Kendrick J. , Rogers S. , Sherwood P. 
Published: April 2011

ABSTRACTA new solid-state embedding approach has been developed which focuses on modelling the surfaces of polar materials. The method is applied to investigate the chemisorption of pre- methanol species on the polar (000-1) surface of zincite (a major phase of zinc oxide having the wurtzite structure). Initial results include the geometries of active sites and adsorbates in different charge states.
Multiscale Modeling of Stress-Mediated Diffusion in Silicon - Volume Tensors
Authors: Windl W. , Daw M. S. , Carlson N. N. , Laudon M. 
Published: April 2011

ABSTRACTIn a previous paper, we presented a general theoretical treatment of the effect of stress on defect diffusion in Si (M. S. Daw, W. Windl, N. N. Carlson, M. Laudon, and M. P. Masquelier, to be published in Phys. Rev. B). In this paper, we discuss the calculation of the parameters governing the stress dependence of the diffusivity, which are volume quantities, and present the fully anisotropic volume tensor for vacancy formation in Si.
Stress Distribution and Tomographic Profiling with Energy Dispersive X-Ray Scattering
Authors: Croft Mark , Zakharchenko Igor , Zhong Zhong , Tsakalakos Thomas , Gulak Yuriy , Kalman Zwi. , Hastings Jerome , Hu Jingzhu , Holtz Ronald , Sadananda Kuntimaddi 
Published: April 2011

AbstractTwo novel and potentially powerful, x-ray scattering techniques for tomographic profiling of composite materials and for profiling residual strain variation, versus depth, in a specimen are presented. The techniques utilize a high intensity/energy “white” beam synchrotron source and monitor the energy dispersive scattering from a fixed micro-volume as the specimen is scanned through it. The tomographic profiles based on the net scattered intensity and exploiting absorption coefficient/scattering-power variations, can be contrast enhanced by selectively monitoring scattering from specific crystal structures in a composite material. The strain profiling technique is shown to chronicle the detailed internal the stress variation over several mm's of steel. The initial state residual stresses, the effect of a cantilever spring imposed external stress, and their interplay in elastic/plastic deformation are discussed.
Synchrotron X-ray Diffraction Measurement of Reinforcement Strains in Uniaxially Stressed Bulk Metallic Glass Composites
Authors: Balch Dorian K. , Üstündag Ersan , Dunand David C. 
Published: April 2011

AbstractHigh-energy synchrotron x-rays were used to measure internal reinforcement strains in bulk metallic glass composites containing tungsten or tantalum particles during in-situ uniaxial tensile loading. Load transfer from the matrix to the stiffer but weaker particles was characterized in both their elastic and plastic regimes and compared to theoretical predictions.
Grazing incidence small-angle x-ray scattering applied to the characterization of nanocomposite thin films
Authors: Babonneau David , Suárez-García Amelia , Gonzalo José , Videnovic Ivan R. , Garnier Michael G. , Oelhafen Peter , Jaouen Michel , Naudon André 
Published: April 2011

AbstractGrazing incidence small-angle x-ray scattering (GISAXS) allows to investigate precisely the microstructure of nanocomposite thin films containing metal nanocrystals produced using different synthesis techniques. We present results on the size, size distribution, shape, and correlation length of metallic nanoparticles embedded in different matrices fabricated by sequential pulsed laser deposition, magnetron sputtering, and ion-beam sputtering co-deposition. The morphology of the nanoparticles is discussed in terms of the different growth process that takes place in each case.
Analysis of Residual Stress Gradients Below the Surface of a Material Using a Multi-Energy Method
Authors: Xiao Yanan , Graber Tim , Lee Myungae , Wittmer Dale E. , Mini Susan M. 
Published: April 2011

AbstractThe residual-stress-gradient distribution just below the surface of a material is an important factor to consider during the engineering and design of a component. With the availability of an intense energy-tunable synchrotron x-ray source, it becomes easier to analyze the stress gradient below the surface, using a multi-energy x-ray diffraction method. A program was developed to efficiently determine possible experimental parameters using a sample with a known stress gradient distribution. In addition, this program can also calculate the stress gradient distribution below the surface taking into account experimental results. It also includes a subroutine for calculating the x-ray absorption coefficients of all of the elements, generalizing it for use with any material. As an example, in the present study, the relationship between x-ray energy and the residual stress gradient is discussed according to the calculated result for a silicon nitride composition.
Investigations of Buried Interfaces Using High Energy X-Ray Reflectivity
Authors: Rieutord F. , Eymery J. , Plantevin O. , Bataillou B. , Buttard D. , Fournel F. 
Published: April 2011

AbstractX-ray reflectivity using high-energy X-rays allows one to characterize interfaces between thick materials at nanometer scale. The technique combines the high penetration of X-rays allowing the crossing of the radiation through large thicknesses of material with the interface sensitivity of grazing angle techniques. In the case of a buried interface between two thick materials, the beam enters the sample through the side of one material and contributions of external surfaces are suppressed. Then, the technique is sensitive to the interface structure only. Examples are given using wafer bonding interfaces, both in the hydrophilic case (as used e.g. in Silicon-On-Insulator substrate fabrication) and in the hydrophobic case (Silicon/Silicon bonding).
Analysis of the Use of Molecular Resonant Tunneling Diodes for Local Refresh of Dynamic Random Access Memory Cells
Authors: Berg Jonas , Bengtsson Stefan , Lundgren Per 
Published: April 2011

ABSTRACTSimulations have been made to analyze the use of molecular resonant tunneling diodes for local refresh of DRAM (Dynamic Random Access Memory) cells. Local refresh can be provided by a latch consisting of a pair of resonant tunneling diodes connected to the storage capacitor of the cell. Such a solution would significantly reduce the standby power consumption of the DRAM cell. We have compared the requirements on the resonant tunneling diodes for proper refresh operation with the electrical properties of published molecules with resonant IV-curves. The simulations show that no molecules with resonant electrical properties published so far in the literature have properties making them useful for this particular application. This is true also for low temperature operation. The issues of maximum tolerable series resistance and of maximum tolerable fluctuations in the number of attached molecules have also been addressed. Our results show that the focus for development of molecules with resonant electrical properties should be to find molecules with resonance for lower applied voltages and lower current levels than the molecules published so far. If the synthesis of new molecules with attractive properties is successful the merging of silicon technology and molecular electronics, for instance for new generations of DRAM cells, is a realistic future path of microelectronics.
Supramolecular Ultrathin Film Strategies for DNA Assemblies: Substrates for Optobioelectronics, Gene Therapy, and Microarrays
Authors: Advincula Rigoberto C. , Wang Yingfan , Park Mi-Kyoung , Bhatia Gautam , Stepleton Seth , Monroe Cara , Shelton Iman , Blanton Wally , Fan Xiaowu 
Published: April 2011

ABSTRACTWe describe our strategies and results in the preparation of supramolecularly ordered ultrathin films of DNA assemblies using the layer-by-layer (LbL) alternate polyelectrolyte adsorption technique. The properties of DNA are intimately associated with their polyelectrolyte behavior in solution. Deposition at interfaces is governed by conformation, orientation, and charge density of these biomolecules in relation to the physisorption phenomena in oppositely charged surfaces. Thus, controlling the nature of surfaces (polymer charge density, ionic strength, other non-covalent interactions, etc.) is important in modifying the adsorption phenomena. In this work, differences in adsorption and incorporation of DNA with dyes, linear polymers and dendrimers are highlighted. A number of surface sensitive spectroscopic and microscopic techniques were used to probe the adsorption and multilayer assembly phenomena, e.g. surface plasmon resonance spectroscopy (SPS), AFM, quartz crystal microbalance (QCM) and ellipsometry. These studies are important for future applications such as the use of polycations as non-viral gene transfection vectors for drug-delivery and DNA adsorption on microarray surfaces. By combining with the alternate assembly of azobenzene and phthalocyanine dyes, we have been able to prepare optobiolelectronic substrates where the phenomena of irradiation and electrochemistry can be used to probe the ordering and response of these films.
Modeling of a Breakdown Voltage in GaN Rectifiers and SiC Rectifiers
Authors: Lee You-Sang , Han Min-Koo , Choi Yearn-Ik 
Published: April 2011

ABSTRACTThe breakdown voltage of wurtzite and zinc-blende GaN rectifiers as function of a doping concentration and the width of epitaxial layer were successfully modeled in the reach-through case. The breakdown voltage was derived by the impact ionization integral employing the effective impact ionization coefficient and an accurate approximation. Our model shows that the breakdown voltage of wurtzite GaN rectifier was larger than those of zinc-blende GaN rectifier and SiC rectifiers including 4H-SiC and 6H-SiC in the condition that both the thickness and doping concentration of epitaxial layer are identical.
X-band Silicon Carbide IMPATT Oscillator
Authors: Vassilevski Konstantin V. , Zorenko Alexandr V. , Zekentes Konstantinos 
Published: April 2011

ABSTRACTPulsed X-band (8.2 - 12.4 GHz) IMPATT oscillators have been fabricated and characterized. They utilized 4H-SiC diodes with single drift p+-n-n+ structures and avalanche breakdown voltages of about 290 V. The microwave oscillations appeared at a threshold current of 0.3 A. The maximum measured output power was about 300 mW at input pulse current of 0.35 A and pulse duration of 40 ns.
High Spatial Resolution Thermal Conductivity investigation of SiC Wafers
Authors: Florescu D.I. , Pollak Fred H. , Brande G.R. , Landini B.E. , Salant A.D. 
Published: April 2011

ABSTRACTSilicon carbide (SiC) is a material with very attractive properties for high power/high temperature electronic devices. Its mechanical strength, high thermal conductivity ( κ), large bandgap, and extreme chemical inertness are a few of the characteristics making SiC interesting for semiconductor electronics. Due to the significant head load generated over large areas in high power devices, it is desirable forthe thermal properties of the substrate to be uniform and optimal. Scanning thermal microscopy (SThM), which provides nondestructive, absolute measurements of the thermal conductivity with a spatial/depth resolution in the 2-3 μm range, was used to examine the room temperature κ as a function of position of four 2” diameter SiC wafers. Wafers of 4H and 6H polytype were fabricated with carrier concentrations in the(1-3)×1018 cm−3 and (6-9)×1017 cm−3 ranges, respectively. A radial distribution of the thermal conductivity was determined for all the investigated samples. For a radius r < r1 (r1 ∼ 0.3”) and r > r2 (r2 ∼ 0.7”) highest thermal conductivity values were measured in the range of (3.8-3.9) W/cm-K, comparable to the highest κ reported for this material [D. Morelli et al., Inst. Phys. Conf. Ser. 137, 313 (1993); E.A. Burgemeister,.et al., J. Appl. Phys. 50, 5790 (1979)]. For r1 < r < r2 the thermal conductivity drops to about (2.85-3.25) W/cm-κinterval. Atomic force microscopy (AFM) investigation revealsthat the influence of surface roughness effects on κ is negligible. The κ dip may arise from a higher basal plane defect density in this region that could be associated with the presence of super screw dislocations, or “micropipes” [M. Dudley et al., J. Phys. D: Appl. Phys. 28, A63 (1995)]. The implications of these findings for device applications and design are considered.
Single-Crystal Aluminum Nitride Substrate Preparation from Bulk Crystals
Authors: Rojo J. Carlos , Schowalter Leo J. , Morgan Kenneth , Florescu Doru I. , Pollak Fred H. , Raghothamachar Balaji , Dudley Michael 
Published: April 2011

ABSTRACTLarge (15mm diameter) single-crystal AlN boules have been prepared using sublimationrecondensation growth. X-ray topography shows that the dislocation density averages less than 103 cm2 in some of the substrates but also that the dislocations are not uniformly distributed. Also, strain due to the differential expansion with the crucible walls seems to cause severe cracking in the periphery of the crystal and high-strain regions. Thermal analysis using the Scanning Thermal Microscopy (SThM) reveals a thermal conductivity of 3.4 ± 0.2 W/K-cm, which is the largest value ever reported for AlN.
Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition
Authors: Forsberg U. , Henry A. , Danielsson Ö. , Linnarsson M.K. , Janzén E. 
Published: April 2011

ABSTRACTWe have investigated the nitrogen incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor. The incorporation mechanism for 4H- and 6H-SiC both for Si- and C-face material is presented. A comparison with previously published results in a cold-wall reactor is also made.
Frequency Response of Trap States in an AlxGa1−xN/GaN Heterostructure Field-Effect Transistor Measured at the Nanoscale by dC/dV Spectroscopy
Authors: Schaadt Daniel M. , Yu Edward T. 
Published: April 2011

ABSTRACTScanning capacitance spectroscopy has been used to characterize, at the nanoscale, the frequency-dependent response of surface charge and of charge in the two-dimensional electron gas of an AlxGa1−xN/GaN heterostructure field-effect transistor structure. dC/dV spectra were measured in a scanning capacitance microscope with a voltage signal consisting of a triangle wave at frequencies of 1 – 50 Hz applied to the sample. The spectra were obtained in the dark (except for 600 nm laser light from the scanning capacitance apparatus) and under illumination. Measurements were performed in the vicinity of and away from charged threading dislocations visible in scanning capacitance images. In the absence of illumination, the dC/dV data indicate that electrons are trapped at or near the AlxGa1−xN surface, consistent with suggestions in the literature that a high density of surface states exists on the free AlxGa1−xN surface. Frequency-dependent measurements show that emission times for these traps can be as long as several hundred ms. In the presence of illumination, reduced electron trapping is observed. The nature and behavior of trap states in the vicinity of threading dislocations is found to differ significantly from that in regions between dislocations for measurements in the dark, and suggest that the electrostatic potential due to the charged threading dislocation is negligible at the surface.
Effects of Beam Current Density on Ion Beam Synthesis OF SiC
Authors: Chen D.H. , Wong S.P. , Lindner J.K.N. 
Published: April 2011

ABSTRACTThin SiC layers were synthesized by high dose C implantation into silicon using a metal vapor vacuum arc ion source at various conditions. Characterization of the ion beam synthesized SiC layers was performed using various techniques including x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) absorption, and Raman spectroscopy. The XPS results showed that for samples with over-stoichiometric implant doses, if the implant beam current density was not high enough, even after prolonged thermal annealing at high temperatures, the as-implanted gaussian-like carbon depth profile remained unchanged. However, if the implant beam current density was sufficiently high, there was significant carbon redistribution during annealing, so that a thicker stoichiometric SiC layer can be formed after annealing. The XPS and Raman results also showed that there were carbon clusters formed in the as-implanted layers for the low beam current density implanted samples, while the formation of such carbon clusters was minimal in the high beam current density as-implanted samples. The effect of beam current density on the fraction of different bonding states of the implanted carbon atoms was studied.
Carrier-Density Fluctuation Noise and the Interface Trap Density in GaN/AlGaN HFETs
Authors: Kotchetkov Dmitri , Balandin Alexander A. 
Published: April 2011

ABSTRACTThe interface trap density NT is extracted from the experimental low-frequency noise data for GaN/AlGaN heterostructure field-effect transistors (HFETs). The trap density is determined based on the carrier-density fluctuation formalism. We show that the value of NT approximately defines the noise response of different GaN/AlGaN HFETs fabricated on the same wafer and it weakly depends on the gate bias. The dependence is due to the non-uniformity of the trap distribution. A model for computer simulation of the low-frequency noise in GaN devices is proposed.
Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature
Authors: Kalabukhova E.N. , Lukin S.N. , Saxler A. , Mitchel W.C. , Smith S R. , Solomon J.S. , Evwaraye A.O. 
Published: April 2011

ABSTRACTPhoto-Electron Paramagnetic Resonance (photo-EPR) measurements of semi-insulating (s.-i.) 4H SiC have been made at 37 GHz including photo excitation and photo quenching techniques in the temperature interval from 77 K to 50 K. At T = 77 K in the dark the EPR spectrum consists of a low intensity line due to boron on the cubic lattice site and a single line with isotropic g∥ = g⊥ = 2.0025 due to a carbon-related surface defect. During illumination with ultraviolet light the EPR lines of hexagonal boron and cubic nitrogen appear in the EPR spectrum and persist after the illumination is removed. Subsequent illumination of the sample with sub-band gap, visible, light resulted in the quenching of the EPR lines from nitrogen and appearance of the IP1EPR line with g∥ = 2.0048, g⊥ = 2.0030 caused by direct transfer of electrons from nitrogen donor to the P1 center. The lifetime of the photo-generated carriers trapped by the P1 centers is found to be more than 15- 20 hours after the photo-excitation was turned off. The deep donor P1 local center is suggested to be the as yet unidentified deep level located at EC – 1.1 eV which pins the Fermi level in this sample at this energy in the dark. As the temperature is lowered from 77K and the quasi Fermi level positions reach shallow donor and acceptor states, an additional EPR line, ID, with g∥ = 2.0063, g⊥ = 2.0006, appears at 50 K in the excitation EPR spectrum and is attributed to the antisite defect Si−c with an energy level shallower than nitrogen. At the same time the ratio of the photo-excited EPR line intensities responsible for boron on the cubic and hexagonal sites, IkB:IhB, returns to the value observed at 77 K and becomes equal to 0.4 at 50 K, showing that the concentration of boron in the hexagonal site is higher than on the cubic site.
Raman scattering spectra in C-implanted GaN epilayers
Authors: Sun W. H. , Chua S. J. , Zhang J. , Wang L. S. , Hao M. S. , Chen K. M. , Qin G.G. 
Published: April 2011

ABSTRACTWe have investigated the Raman scattering spectra in C-implanted GaN epilayers. (a) In as-implanted GaN, new Raman bands at 293, 376, 669, 1027, 1094 and 1053 cm−1 appeared. From phonon-dispersion curves for hexagonal GaN, the 293 cm−1 and 669 cm−1 bands were tentatively assigned to the highest acoustic-phonon branch and the optical-phonon branch at the Brillouin zone boundaries, respectively; the 1027 and 1094 cm−1 peaks might be caused by two-phonon scattering involving the 376 and 669 cm−1 phonons, and the 376 cm−1and A1(LO) phonons respectively. (b) Two sharp bands at ∼1350 and ∼1600 cm−1 were observed in the Raman spectra of carbon- implanted GaN after post-implantation annealing treatments. The intensities of these two bands increased while their full widths at half maximum decreased with increasing annealing temperature. We assigned them, respectively, to the D and G bands of small graphite crystallites arising from C implantation and post-implantation annealing. The observation of these two bands indicates the formation of small graphite crystallites in C-implanted GaN.
Underfill Encapsulant Flow Measured using Capacitance Measurement Techniques
Authors: Driscoll T. E. , Lehmann G. L. , Cotts E. J. 
Published: April 2011

ABSTRACTCapillary flows of dense, model suspensions and industrial underfill encapsulants are investigated. Flow behavior is characterized by measuring the infiltration rate of an encapsulant or model suspension into a channel formed by parallel surfaces. A capacitance measurement technique is used to track the advancement of the front. Significantly this technique allows the channel surfaces to be formed from opaque materials such as those that found in the principal industrial application of electronics packaging. A scaling law to describe the functional dependence of the front position on channel spacing, surface tension and viscosity is presented.
Simultaneous Measurements of Electrical Resistivity and Raman Scattering from Conductive Die Attach Adhesives
Authors: Miragliotta Joseph , Benson Richard C. , Phillips Terry E. , Emerson John A. 
Published: April 2011

ABSTRACTThe development of electrical conductivity in silver (Ag)-filled conductive polymer adhesives is dependent on the thermal profile of the curing process. Previous studies of polymer adhesive systems have shown that chemical reactions at the interface of the micronsized Ag filler are a key factor in determining the subsequent performance of the conductive system. In an attempt to correlate the behavior of electrical conductivity with the chemical nature of the Ag particle interface, we have simultaneously performed electrical resistivity and surface enhanced Raman scattering (SERS) measurements on a commercial conductive adhesive. At room temperature in the low conductance state (∼10−9 ohms−1), the SERS spectrum from the uncured adhesive exhibited peaks that were identified with a molecular species bound to Ag surface via the carboxylate functionality of the adsorbate. During the thermal cure processing, the SERS data showed a partial decomposition of the carboxylate species and the formation of an amorphous carbon layer at the Ag surface. A comparison of the simultaneously recorded electrical resistance and SERS data showed a strong correlation between the development of high conductance (∼ 1 ohm−1) in the adhesive and the formation of the amorphous carbon layer.