bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coherency Strain and a New Yield Criterion
Authors: Jayaweera N.B. , Downes J.R. , Dunstan D.J. , Bushby A.J. , Kidd P. , Kelly A. 
Published: April 2011

ABSTRACTWe have studied the onset of plasticity in coherently-strained semiconductor superlattices, using nano-indentation with spherical indenter tips to observe the full stress-strain curve. The yield pressure is reduced by as much as a factor of two by the presence of the coherency strain. By varying the thicknesses and strains of the superlattice layers, we provide a proof that yield commences over a finite volume. It is properties averaged or summed over this volume which determine the yield pressure. We show that the relevant yield criterion for our experimental data is the rate of change of elastic strain energy with plastic relaxation, integrated over a volume of the order of a micron across. This result is expected to be valid for other systems with highly inhomogenous strain fields, and hence to be applicable to modelling of point contact, and to the design and understanding of structural materials which have coherently-strained microstructure.
Correlations of Microstructure and TEM Observations of Plasticity in Metallic Nanolaminates
Authors: Kramer Donald E. , Foecke Tim 
Published: April 2011

ABSTRACTNanolaminate materials exhibit increases in hardness and yield strength beyond those expected according to rule of mixtures calculations. Several models have been proposed to explain this enhancement of strength, but conclusive experimental verification is hindered by the complex interaction between ingrown defects, in-plane microstructure and compositional modulation. In this study, mechanisms of plastic deformation in nanolaminates are investigated by in situ TEM straining of epitaxial Cu/Ni nanolaminates grown on Cu (001) single crystal substrates. Two distinct types of deformation are observed. Initial plastic deformation is accommodated by motion of “Orowan” and threading dislocations in a uniform and random fashion. As the stress levels increase, fracture occurs creating a mixed mode crack. Subsequent observations suggest that intense plastic deformation occurs over many bilayers in the direction of crack growth, but is contained to within one or two bilayers in a direction normal to the crack faces.
Interaction Between Dislocations and Misfit Interface
Authors: Kuronen A. , Kaski K. , Perondi L. F. , Rintala J. 
Published: April 2011

ABSTRACTMechanisms responsible for the formation of a misfit dislocation in a lattice-mismatched system have been studied using Molecular Dynamics simulations of a two-dimensional Lennard-Jones system. Results show clearly how the strain due to the lattice-mismatched interface acts as a driving force for migration of dislocations in the substrate and the overlayer and nucleation of dislocations in the overlayer edges. Moreover, we observe dislocation reactions in which the gliding planes of dislocations change such that they can migrate to the interface.
New Ceramic Composite from a Multioxide Eutectic Melt
Authors: Calderon-Moreno Jose M. , Yoshimura Masahiro 
Published: April 2011

ABSTRACTNew high temperature ceramic eutectic composites have been obtained. The composite is self-assembled in one quick step by rapid supercooling of the multioxide alumina-YAG-zirconia eutectic in an arc-image lamp furnace. The new material will find applications as in-situ coating and component for use at ultra-high temperature. Periodic self-assembled layered structures kinetically forced to solidify with interspacing in the submicron range will result in very interesting properties and applications for high temperature multioxide oxide eutectic composites, offering the challenge of design of layered nanostructures tailored to specific applications by kinetic control during solidification.
Structural and Optical Properties of Gold In MgO: Effects of Shape And The Interface
Authors: Bryant Elana M. , Ueda Akira , Mu Richard R. , Wu Marvin H. , Meldrum Alkiviathes , Henderson Don O. 
Published: April 2011

AbstractThe fundamental studies of metallic nanoparticles embedded in various host materials have been made. The host-guest interaction causes the shapes of embedded nanoparticles, and the surface plasmon resonances of the metallic nanoparticles are affected by the host materials. The control of the surface plasmon resonance condition is a challenging question. We will discuss the interface effect of the systems where gold nanoparticles were fabricated between materials of MgO and SiO2.
Matrix-Assisted Synthesis of Palladium Nanocage and Nanowires
Authors: Cheon Jinwoo , Lee Kyung-Bok , Kang Hongkyu , Oh S. J. , Ri H.-C. 
Published: April 2011

AbstractOur study describes the synthesis of novel nanoscale Pd cage and wires whose sizes and shapes are templated by mesoporous matrices. The templates used are cubic phase MCM-48 and hexagonal phase CnMCM-41 (n = 16, and 22), SBA-15, which have pore diameters of ∼3, ∼3.8, ∼4.7, and ∼9 nm, respectively. For Pd@MCM-48, the Pd metal forms spherical domains (∼38 nm) consisting of three dimensionally interconnected into Pd arrays; for Pd@SBA-15 and Pd@MCM-41, the Pd metal forms of one-dimensional wires. Etching out the matrix produces porous Pd cages (pore sizes of ∼1.5 - 2.0 nm) with retaining original domain sizes of ∼38 nm; similarly Pd@SBA-15 and Pd@MCM-41 afford freestanding Pd nanowires. All the materials are examined by TEM, XRD, BET, and EDAX analysis. Furthermore, the thermal behavior of Pd nanowire is briefly described.
Nanosphere Lithography: Synthesis and Application of Nanoparticles with Inherently Anisotropic Structures and Surface Chemistry
Authors: Haynes Christy L. , Haes Amanda J. , Duyne Richard P. Van 
Published: April 2011

AbstractEarly work with size-tunable periodic particle arrays (PPAs) fabricated by nanospherelithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the spectrum. The LSPR is sensitive to changes in nanoparticle aspect ratio and local dielectric environment. This property has recently been exploited to develop a novel method of measuring surface-enhanced Raman scattering (SERS) excitation profiles. Single layer PPAs consist of size-tunable anisotropic nanoparticles that can be modified to exhibit anisotropic surface chemistry. This work demonstrates multiple schemes for PPA modification using self-assembled monolayers and colloid decoration. Nanoparticle anisotropy can be further exploited with the recent combination of NSL and reactive ion etching (RIE); this extends the two-dimensional PPA structure into the third dimension.
Microstructural and Magnetic Properties of Core-Shell Ni-Ce Nanocomposite Particles Assemblies
Authors: Sun Xiang-Cheng , Toledo J. A. , Yacaman M. Jose 
Published: April 2011

AbstractNovel magnetic core-shell Ni-Ce nanocomposite particles (15-50 nm) are presented. SEM observation indicates a strongly ferromagnetic interacting order with chain-like features among Ni-Ce nanocomposite particle assemblies. Typical HREM image demonstrates that many planar defects (i. e. stacking faults) exist in large Ni core zone (10-45 nm ); the innermost NiCe alloy and outermost NiO oxide exist in the thin shell layers ( 3-5 nm ). Nano-diffraction patterns show an indication of well-defined spots characteristic and confirm the nature of this core-shell nanocomposite particles. Superparamagnetic relaxation behavior above average blocking temperature (TB =170K) for Ni-Ce nanocomposite particles assemblies have been exhibited, this superparamagnetic behavior is found to be modified by interparticle interactions, which depending on the applied field; size distribution and coupling with the strong interparticle interaction. In addition, an antiferromagnetic order occurs with a Neél temperature TN of about 11K due to Ce ion magnetic order fuction. A spin-flop transition is also observed below TN at a certain applied field and low temperature.
Nonlinear Optical Responses of Spin-Coated Vanadium Oxide Films
Authors: Ando Masanori , Kadono Kohei , Kamada Kenji , Ohta Koji , Delouis Jean-François , Nakatani Keitaro , Delaire Jacques 
Published: April 2011

AbstractWe report on the third-order nonlinear optical responses of V2O5 films prepared by pyrolysis of spin-coated films of vanadium 2-ethylhexanoate. Temporal behavior of third-order optical nonlinearity of the spin-coated V2O5 films was examined at a wavelength of 532 nm by the degenerate four-wave mixing (DFWM) technique using a mode locked Nd/YAG laser (35 ps fwhm). Fast relaxation with a lifetime of 25 ps and slow relaxation with a lifetime of 150 ps were observed. The nonlinear transmission experiment on the spin-coated V2O5 films using the same laser source showed that the transmittance decreased with increasing intensity of the incident light. The intensity-dependent absorption coefficients (β) were roughly estimated to be 3.5×10−5 cm/W. Transient absorption properties of the V2O5 film were measured by use of the second and third harmonics of a Q switched Nd/YAG laser (10 ns fwhm). The results observed for the nonlinear transmission and the transient absorption suggest that induced absorption would contribute to the third-order optical nonlinearity of the V2O5 films with fast response times, and also suggest that the V2O5 films have potentiality for use as optical power limiting materials.
SiC Crystal Growth from the Vapor and Liquid Phase
Authors: Hofmann Dieter , Bickermann Matthias , Ebling Dirk , Epelbaum Boris , Kadinski Lev , Selder Markus , Straubinger Thomas , Weingaertner Roland , Wellmann Peter , Winnacker Albrecht 
Published: April 2011

ABSTRACTThe status of SiC vapor growth technique (PVT) is reviewed and related innovative aspects are introduced. Problems of the preparation of SiC crystals with uniform electronic properties are addressed, especially the growth of semiinsulating SiC. An overview about the performance of numerical modeling is given as tool for the optimization of the PVT process. Development activities in the field of liquid phase processing for the preparation of SiC bulk crystals and micropipe healing are presented. Finally recent results on the present understanding of filamentary void formation/elimination (micropipes, macrodefects) are summarized.
Heat and mass transfer simulation of SiC boule growth by sublimation
Authors: Pons Michel , Moulin Cecile , Dedulle Jean-Marc , Pisch Alexandre , Pelissier Bernard , Blanquet Elisabeth , Anikin Michail , Pernot Etienne , Madar Roland , Bernard Claude , Faure Christian , Billon Thierry , Feuillet Guy 
Published: April 2011

ABSTRACTAn accurate modelling and simulation of the sublimation growth process needs a software taking into account a multitude of highly coupled phenomena: fluid mechanics, convective, conductive and radiative heat transfer, electromagnetic, multicomponent species transport, homogeneous and heterogeneous reactivity and finally thermal and transport databases. The objective of this paper is to combine modelling trends with experimental results to propose explanations and solutions to growth problems. Finally, a simple and generic mechanical approach will show the relations between the density of dislocations and the temperature field.
Challenges and State-of-the-Art of Oxides on SiC
Authors: Lipkin Lori , Das Mrinal , Palmour John 
Published: April 2011

ABSTRACTSingle crystal SiC is a wide band-gap semiconductor with material characteristics that make it quite suitable for high voltage and high current applications. However, these devices are currently limited by their passivation. Significant improvements have been made with oxides on SiC. The most notable oxide processes are the re-oxidation anneal, a stacked ONO dielectric, and nitridation using an NO or N2O anneal. Additional improvements in lateral MOSFET mobility have been achieved using a surface channel implant, and lower temperature implant activation anneals. However, the passivation remains a significant limitation for SiC power devices.
Nitrogen Passivation of the Interface States Near the Conduction Band Edge in 4H-Silicon Carbide
Authors: Williams J. R. , Chung G. Y. , Tin C. C. , McDonald K. , Farmer D. , Chanana R. K. , Weller R. A. , Pantelides S. T. , Holland O. W. , Das M. K. , Lipkin L. A. , Feldman L. C. 
Published: April 2011

ABSTRACTThis paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec)] in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200–400sccm for 2hr reduces the interface state density at Ec-E ≅0.1eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm−2eV−1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30–35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm−2eV−1 (compared to approximately 1010cm−2eV−1 for passivated Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap – one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.
Profiling of the SiO2 - SiC Interface Using X-ray Photoelectron Spectroscopy
Authors: Ghosh R. N. , Ezhilvalavan S. , Golding B. , Mukhopadhyay S. M. , Mahadev N. , Joshi P. , Das M. K. , Jr J. A. Cooper 
Published: April 2011

ABSTRACTThe implementation of SiC based sensors and electronics for operation in chemically harsh, high temperature environments depends on understanding the SiO2/SiC interface in field effect devices. We have developed a technique to fabricate wedge polished samples (angle ∼ 1×10−4 rad) that provides access to the SiO2/SiC interface via a surface sensitive probe such as xray photoelectron spectroscopy (XPS). Lateral scanning along the wedge is equivalent to depth profiling. Spatially resolved XPS images of the O 1s and Si 2p core levels were obtained of the interfacial region. Samples consist of device-quality thermally grown oxides on 4H-SiC single crystal substrates. The C 1s spectrum suggests the presence of a graphitic layer on the nominally bare SiC surface following thermal oxidation.
Influence of Interface States on Output Characteristics of 4H-SiC MESFETs on Semi–Insulating Substrates
Authors: Sghaier Nabil , Souifi Abdel K. , Bluet Jean-Marie , Berenguer Manuel , Guillot Gérard , Noblanc Olivier , Brylinski Christian 
Published: April 2011

ABSTRACTThe aim of this work is to study the origin of parasitic phenomena in the output characteristics of 4H-SiC MESFETs on semi-insulating (SI) substrates with various buffer layers. Ids-Vds measurements as a function of temperature have first been performed. Different parasitic effects such as kink effect, hysteresis effect when the gate voltage is successively increased or decreased, or changes in the output characteristics after a high drain polarization are presented. Random Telegraph Signal (RTS) measurements and frequency dispersion of the output conductance have next been realized. From the obtained results, we propose that the parasitic effect on the output characteristics are correlated with the presence of deep levels located near the semi -insulating substrate interface. The main observed trap is tentatively attributed to the presence of Vanadium in the SI substrate.
Short-Channel Effect Suppression In Silicon Carbide Power Mesfets
Authors: Konstantinov A. , Saroukhan A-M. , Karlsson S. , Harris C. , Litwin A. 
Published: April 2011

ABSTRACTWe demonstrate that the performance of silicon carbide MESFETs is largely determined by short-channel effects. Parasitic bipolar transistor turn-on limits the operation voltage to a small fraction of the theoretically expected value for an ideal device. Tradeoffs are shown to exist between optimum gate length and on-state current on one hand, and the maximum blocking voltage on the other hand. Composite p-buffers with an elevated doping in the vicinity of the active layer considerably increase the operation voltage. Silicon carbide MESFETs utilizing composite buffers are reported.
Quality of Thermally Grown Oxides in 4H-SiC over Nitrogen or Phosphorus Implanted Regions
Authors: Khan I. A. , Um B. , Matin M. , Capano M. A. , Cooper J. A. 
Published: April 2011

ABSTRACTCurrent SiC metal-oxide-semiconductor-field-effect-transistors (MOSFETs) have regions of the gate electrode that overlaps the source/drain contact implant. The source/drain region is electrically isolated from this gate electrode extension by the gate insulator. Typically, the gate insulator is established through a controlled thermal oxidation step. The performance of the electrical isolation between the gate electrode and the source/drain implant region is studied using MOS systems for the nitrogen and phosphorus implant species. The dielectric strength of thermal oxide grown over a phosphorus implanted region is about four times lower than a non-implanted region and about two times lower than the nitrogen implanted region for the same implant and anneal conditions.
Al/Ni And Al/Ti Ohmic Contact To P-type SiC Diffused Layer
Authors: Wang Xaiobin , Soloviev Stanislav , Gao Ying , Straty G. , Sudarshan Tangali , Williams John R. , Crofton John 
Published: April 2011

ABSTRACTOhmic contacts to p-type SiC were fabricated by depositing Al/Ni and Al/Ti followed by high temperature annealing. A p-type layer was fabricated by Al or B diffusion from vapor phase into both p-type and n-type substrates. The thickness of the diffused layer was about 0.1–0.2 μm with surface carrier concentration of about 1.0×1019cm−3. Metal contacts to a p-type substrate with a background doping concentration of 1.2×1018cm−3, without a diffusion layer, were also formed. The values of specific contact resistance obtained by Circular Transmission Line Method (CTLM) and Transfer Length Method (TLM) for the n-type substrate, and by Cox & Strack method for p-type substrate, respectively, varied from 1.3×10−4Ωcm2 to 8.8×10−3 Ωcm2. The results indicate that the specific contact resistance could be significantly reduced by creating a highly doped diffused surface layer.
Optical Absorption of Doped and Undoped Bulk SiC
Authors: Miller K. , Zhou Q. , Chen J. , Manasreh M. O. , Feng Z. C. , Ferguson I. 
Published: April 2011

ABSTRACTOptical absorption spectra of undoped, n-type, and semi-insulating 6H and 4H bulk silicon carbide (SiC) were obtained in the spectral region of 200 – 3200 nm (6.20 – 0.3875 eV). Several features were observed in the absorption spectra collected for various samples. A sharp peak below the band gap was observed in 4H SiC. The intensity of this peak was observed to increase in samples that exhibit larger absorption due to free carriers, which leads us to conclude that the defect responsible for this peak is also the source of the free carriers in the materials. Additionally, a series of optical absorption peaks separated by approximately 21 meV were observed around 0.9185 eV (1350 nm). These peaks are zero phonon lines of intraband transitions in the VSi 3d shell. The optical absorption near the band edge was observed to be sample dependent. The variation of the band gap as a function of temperature is also observed to be sample dependent.
Annealing Study of Ga Implanted p-Type 6H-SiC for Ohmic Contact Metallizations
Authors: Prenatt M. , Iliadis A. A. , Vispute R. D. , Wood M. C. , Derenge M. , Geil B. , Jones K. A. 
Published: April 2011

ABSTRACTShallow implantations of Ga ions were performed on p-type 6H-SiC by conventional broad area implantation, and the physical and electrical properties of the Ga-SiC system upon high temperature annealing were examined, in order to understand the role of Ga in ohmic contact formation. The shallow implantation depth (30 nm) and high Ga doses ranging between 1×1015 and 1×1016 cm−2, resulted in heavy surface damage as observed by atomic force microscopy surveys. Samples annealed using a sacrificial SiC wafer as a capping layer, showed no improvement in surface roughness for annealing up to 1300 °C, while at 1500 °C, surface roughness was markedly changed. At 1600 °C the surface re-crystallized back to the stepped terraced morphology of the un-implanted surface but with significantly larger step and terrace size. At this annealing temperature, heavy Ga loss from the surface was observed. Samples annealed at 1500 °C using an AlN capping layer, showed significant outdiffusion of Si into the AlN layer, and redistribution of Ga within the SiC surface. The contact resistance of as-implanted and annealed samples using the sacrificial SiC wafer, were measured by the TLM method. Although contact resistance was found to decrease with increasing annealing temperature, sheet resistance increased, and contact resistance values were higher than expected, indicating that the heavy loss of Ga atoms contributed to the increased levels of contact resistance.
Physical Characterization of Residual Implant Damage in 4H-SiC Double Implanted Bipolar Technology
Authors: Wright N. G. , Johnson C. M. , O'Neill A. G. , Horsfall A. , Ortolland S. , Adachi K. , Phelps G. J. , Knights A. P. , Coleman P. G. , Burrows C. P. 
Published: April 2011

ABSTRACTThe effects of post-implant anneal conditions on the level of residual damage resulting from nitrogen and boron implants after different anneal processes are investigated using the Positron Annihilation Spectroscopy (PAS) technique. It is shown that after implantation there is a substantial defect concentration significantly below the range of the implants. However such damage is almost completely recovered after anneal in contrast with the damage close to the implant range point. Such residual damage has a strong effect on the electrical characteristics of double implanted bipolar transistors - principally though reduction in carrier mobility and lifetime. It is shown that the precise implant and anneal conditions play a strong role in the level of such damage and the subsequent electrical performance of bipolar devices.