bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Disorder in the Anion Lattice of Nanocrystalline Zirconia and Hafnia Particles
Authors: Vollath Dieter , Forker Manfred , Hagelstein Michael , Szabó D. Vinga 
Published: April 2011

ABSTRACTNanoparticles of ZrO2 and HfO2 with sizes around 5 nm are – depending on the production route - found in the cubic or tetragonal or monoclinc phase. To shed some light into this difference, an analysis of crystal structure, distances, and symmetry around the cations was performed on alumina coated nanoparticles prepared by the microwave plasma process. Within the range of accuracy, electron-diffraction and -microscopy revealed a possibly cubic cation lattice for both materials. In the case of ZrO2, the evaluation of the amplitude of the modified radial distribution function derived from extended x-ray absorption fine structure (EXAFS) data lead to a structure with a narrow distribution of oxygen ions in the first shell of neighbors. This is expected for the cubic structure. Comparing the imaginary part with model calculations, a distinct similarity with the cubic structure is obvious. In the second shell of neighbors, consisting of metal ions, one radial distribution peak is expected and found experimentally. Perturbed angular correlation measurements indicate a pronounced disorder of the positions of the first neighbors of the metal ions. Together with the EXAFS observation of a narrow radial distribution of the first neighbor oxygen ions, these measurements provide evidence for a randomc distribution of Zr-O bond angles in the vicinity of their crystallographic positions. Above 500°C a partially reversible transformation to almost perfect tetragonal symmetry is observed. Therefore, one has to conclude that the cubic structure with disordered anion lattice is more stable than the tetragonal one at room temperature. Structural relationships like this are unknown in coarse-grained material.
Simulation of Surface Morphology and Defect Structure in Copper Nanoparticles
Authors: Kogure Yoshiaki , Doyama Masao 
Published: April 2011

ABSTRACTMolecular dynamics simulation for the morphology and the defect structure in nanoparticles has been performed. The nanoparticles are consisted of 1300 – 5000 atoms and the EAM potential developed by the present authors is adopted to calculate the interactions between atoms. The atom consisting the surfaces or defects are selected thorough the potential energy of individual atoms and structure is investigated by calculating the local crystalline order. A relation between the cooling rate and the particle morphology is also investigated.
Achieving Superplasticity and Superplastic Forming through Severe Plastic Deformation
Authors: Furukawa Minoru , Horita Zenji , Langdon Terence G. 
Published: April 2011

ABSTRACTThe application of severe plastic deformation to metals provides a convenient procedure for achieving nanometer and submicrometer microstructures. Several different processing methods are available but Equal-Channel Angular Pressing (ECAP) is especially attractive because it provides an opportunity for preparing relatively large bulk samples. This paper describes the use of ECAP in preparing materials with ultrafine grain sizes and the subsequent properties of these materials at elevated temperatures. It is demonstrated that, provided precipitates are present to retain these small grain sizes at the high temperatures where diffusion is reasonably rapid, it is possible to achieve remarkably high superplastic elongations in the as-pressed materials and there is a potential for making use of this processing procedure to develop a superplastic forming capability at very rapid strain rates.
High Spin Mn Molecular Clusters: Spin State Effects On the Outer Core-Level Multiplet Structures
Authors: Nelson A. J. , Reynolds J. G. , Christou George 
Published: April 2011

AbstractOxo-bridged manganese polynuclear complexes have applications in a variety of technologies, such as single-molecule nanomagnets, catalysis and photosynthetic redox chemistry. The reason that these types of compounds are capable of such important and varied technologies is thought to be because they possess ground states with large spin values. However, the electronic, structural and magnetochemical relationships are not well understood and need to be thoroughly investigated to adequately explain why Mn is such an integral part of so many useful processes. X-ray photoemission spectroscopy was used to study the Mn 3p, 3s and valence band electronic behavior as a function of Mn cluster structural properties, where the cluster size and nuclearity are systematically varied. Results show a chemical shift of the Mn 3p3/2,1/2 spin-orbit pair related to the cluster size and nuclearity. Also, the Mn 3s 7S and 5S final state multiplet components shift since they involve the binding energy of a ligand valence electron. In addition, the branching ratio of the 7S:5S states is related to the 3s–3d electron correlation. Specifically, in the 7S state, the remaining 3s electron is well correlated with 3d electrons of parallel spin, while in the 5S state the two spins are antiparallel. Changes in this electron correlation are clearly observed in the 7S:5S branching ratio as a function of cluster size and ligand electronegativity.
Transport Properties of Bi-related Nanowire Systems
Authors: Lin Y. M. , Cronin S. B. , Ying J. Y. , Heremans J. , Dresselhaus M. S. 
Published: April 2011

AbstractWe present here an electrical transport property study of Te-doped Bi nanowires, and Bi1−xSbx alloy nanowires embedded in a dielectric matrix. The crystal structure of the nanowires were characterized by X-ray diffraction measurements, indicating that the nanowires possess the same lattice structure as bulk Bi in the presence of a small amount of Te or Sb atoms. The resistance measurements of 40-nm Te-doped Bi nanowires were performed over a wide range of temperature (2 K≤ T ≤ 300 K), and the results are consistent with theoretical predictions. The 1D-to-3D localization transition and the boundary scattering effect are both observed in magneto-resistance measurements of Bi1−xSbx alloy nanowires at low temperatures (T < 4 K).
Studies of the Dielectric Constant of Thin Film Bismuth Nanowire Samples Using Optical Reectometry
Authors: Blacka M. R. , Lin Y.-M. , Cronin S. B. , Rabin O. , adi M. P , Dresselhaus M. S. 
Published: April 2011

AbstractArrays of 10 to 120 nm diameter single crystalline bismuth nanowires havebeen formed inside amorphous alumina templates. ince bismuth has a small e ective mass compared to other materials, signi cant quantum mechanical con nement is expected to occur in wires with diameter less than 50nm. he subbands formed b yquantum con nement cause in teresting modi cations to the dielectric function of bismuth. his study measures the dielectric function of bismuth nanowires in an energy range where the e ects of quantum con nement are predicted (0.05 to 0.5e). Using F ourier transforminfrared re ectometry, the dielectric constant as a function of energy is obtained for the alumina/bismuth composite system. E ective medium theory is used to subtract the e ect of the alumina template from the measurement of the composite material, thus yielding the dielectric function of bismuth nanowires. A strong absorption peak is observed at ∼1000cm−1 in the frequency dependent dielectric function in the photon energy range measured. he dependence of the frequency and intensity of this oscillator on incident light polarization and wire diameter are reviewed. n addition, the dependence of the optical absorption on antimony and tellurium doping of the nanowires are reported.
Optical Response of Gold Nanoparticles in Dielectric Materials
Authors: Ueda Akira , Bryant Elana M. , Maxwell Carlton B. , Blake Charline M. , Mu Richard R. , Wu Marvin H. , Zavalin Andrey I. , 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.
New Crucible Design for SiC Single Crystal Growth by Sublimation
Authors: Nishizawa Shin-ichi , Yamaguchi Hirotaka , Kato Tomohisa , Khan M. Nasir , Arai Kazuo , Oyanagi Naoki , Kitou Yasuo , Bahng Wook 
Published: April 2011

ABSTRACTSiC bulk single crystal growth by sublimation was investigated. A new crucible design, double-walled crucible, was proposed, and its effect was confirmed numerically and experimentally. On the point of heat transfer in a growth cavity, double-walled crucible is better than conventional crucible. With a double-walled crucible, temperature of seed and source surfaces could be kept constant with better uniformity than that with a conventional crucible. It was deduced that a crystal growth rate could be kept constant with flat surface. Furthermore, in case of a double walled crucible, crystal enlarged rapidly with less inclusion. As the results, a double-walled crucible is useful to grow high quality SiC single crystal by sublimation.
Growth of thick 4H-SiC epilayers in a vertical radiant-heating reactor
Authors: Tsuchida H. , Kamata I. , Jikimoto T. , Izumi K. 
Published: April 2011

ABSTRACTGrowth of very thick 4H-SiC epilayers up to 215 μm has been demonstrated in a vertical radiant-heating reactor. Surface roughness is maintained as small as ˜0.2 nm even for epilayers over 150 μm in thickness, and a regular step structure without macro step bunching is observed from the very thick epilayers indicating a stable step-flow growth. Photoluminescence and secondary ion mass spectroscopy (SIMS) were performed for a 150 μm-thick epilayer. The Photoluminescence showed strong free excitons and comparatively small nitrogen bound excitons, while aluminum-, boron- and titanium-related lines were almost negligible. The SIMS analysis found no impurities exceeding 1 × 1014 cm−3. The influence of growth parameters on thickness uniformity will also be shown.
Hollow defect elimination during solution growth of SiC
Authors: Epelbaum B. M. , Hofmann D. , Müller M. , Winnacker A. 
Published: April 2011

ABSTRACTUsing pure and alloyed silicon melt saturated with carbon we investigated systematically hollow defect elimination during SiC solution growth over a wide temperature range from 1500°C to 2100°C. In the process of solution growth all hollow defects present in a substrate demonstrate an evident tendency to act as growth centers and after an adequate period of treatment they were overgrown. Growth morphologies observed in the vicinity of hollow defects are rather different. A new visualization method is proposed, which reveals crystalline defects associated with hollow cores and allows to detect the quantity and the distribution of HD in a whole SiC wafer. Classification of hollow defects based on these observations is presented and the corresponding closing mechanisms are discussed.
Electronic Properties of Nitrogen Delta-Doped Silicon Carbide Layers
Authors: Yokogawa Toshiya , Takahashi Kunimasa , Uenoyama Takeshi , Kusumoto Osamu , Uchida Masao , Kitabatake Makoto 
Published: April 2011

ABSTRACTNitrogen delta-doped silicon carbide (SiC) layers were grown by a new pulse doping method in a chemical vapor deposition. Doping distribution with high peak concentration (1.×1018 cm−3) and narrow distribution width (12 nm) was fabricated in the nitrogen delta-doped structure of SiC. Mobility enhancement due to spatial separation of electrons and their ionized parent donors was observed for the delta-doped structure. Metal-semiconductor field-effect transistors with a nitrogen delta-doped channel and a recess gate structure were fabricated. The devices had large source-drain breakdown voltages, high drain current capability and easy control of the threshold voltage with a good pinch-off characteristics.
Structural Characterization Of Sic Epitaxial Layers Grown On Porous Sic Substrates
Authors: Saddow S. E. , Melnychuk G. , Mynbaeva M. , Nikitina I. , Vetter W. M. , Jin L. , Dudley M. , Shamsuzzoha M. , Dmitriev V. , Wood C. E. C. 
Published: April 2011

ABSTRACTA layer of porous SiC was fabricated by surface anodization of commercial 4H and 6H-SiC (0001)Si face off-axis wafers. A 8.5 μm 4H–SiC epilayer was grown on porous SiC (PSC) substrates using atmospheric pressure CVD. TEM investigation on cross-sectional specimens of the CVD epitaxial layers revealed that the presence of pores in the substrate does not lead to the formation of any micropipe in the epitaxial layer. The investigation also failed to detect a more than usual dislocation density on the basal plane of the epitaxial layer. Based upon the results of various analytical techniques applied to the CVD deposit we propose that the density of screw dislocations in the epitaxial layer is less than 5–104 cm−3. It should be noted that the density of similar types of dislocations in the initial substrate as determined by the TEM was ∼106 cm−3, so this preliminary investigation indicates that the epitaxial layer grown on PSC may have a reduction in dislocation density of more than an order of magnitude over those grown on conventional SiC substrates that are not porous. Synchrotron white beam x-ray topography (SWBXT) was performed on these layers. Comparison between the dislocation density on the porous and standard epitaxial layers proved to be very similar using this technique.
Traps at the SiC/SiO2-Interface
Authors: Pensl Gerhard , Bassler Michael , Ciobanu Florin , Afanas'ev Valeri , Yano Hiroshi , Kimoto Tsunenobu , Matsunami Hiroyuki 
Published: April 2011

ABSTRACTThe density of interface states Dit at SiC/SiO2 interfaces of different SiC polytypes (4H-, 6H- and 15R-SiC) is monitored and the origin of these states is discussed. The hydrogenation behavior of interface states in the temperature range from 250°C to 1000°C is studied by C-V and G-V investigations. The strong increase of Dit close to the 4H-SiC conduction band is attributed to defects located in the oxide (so-called “Near Interface Traps”).
Micromachining Techniques for Advanced SiC MEMS
Authors: Mehregany Mehran , Zorman Christian A. 
Published: April 2011

ABSTRACTThis paper reviews the development of a multilayer, micromolding-based surface micromachining process for SiC microelectromechanical systems (MEMS). The micromolding process uses polysilicon and SiO2 thin films that are deposited onto polysilicon and SiO2 sacrificial layers, patterned into micromolds by reactive ion etching, filled with polycrystalline SiC (poly-SiC), planarized by mechanical polishing, and eventually dissolved and released in selective wet chemical etchants. In addition, a SiC lift-off technique that exploits the microstructural differences between SiC films deposited on Si, SiO2 and Si3N4 surfaces has been developed. The micromolding and lift-off techniques are being used as the basic patterning processes for a four-layer, poly-SiC surface micromachining process that we call the MUSiC (Multi-User SiC) process.
Point and planar defect formation in SiC during PVT growth
Authors: Khlebnikov Yuri I. , Drachev Roman V. , Rhodes Curtis A. , Cherednichenko Dmitry I. , Khlebnikov Igor I. , Sudarshan Tangali S. 
Published: April 2011

ABSTRACTThe spontaneous nucleation of “negative” crystals from the solute of vacancies in SiC does not appear to be dominant due to the low super-saturation of vacancies. However, clustering of the vacancies is possible due to the energy gain in the system caused by coalescence of any two vacancies. The major reasons for point and planar defect formation in SiC are the liquid phase of free silicon and non-stoichiometry of the vapor.
Epitaxial Growth of SiC on AlN/ Sapphire Using Hexamethyldisilane by MOVPE
Authors: Teker Kasif , Lee Ki Hoon , Jacob Chacko , Nishino Shigehiro , Pirouz Pirouz 
Published: April 2011

ABSTRACTHigh quality SiC and AlN films allow the fabrication of metal/AlN/SiC MIS structures and SiC/AlN heterostructures that require a low lattice mismatch and excellent thermal stability. Epitaxial SiC on AlN/sapphire was grown using hexamethyldisilane (HMDS) by MOVPE. 2HAlN is epitaxially grown on sapphire by MOCVD, and subsequently SiC is deposited on it. The growth of high quality SiC was achieved in a one step process without any nucleation step using dilute hydrogen in argon (12% H2 + Ar) as the carrier gas, which is less explosive than pure H2. The effect of growth temperature and thickness of AlN on the SiC crystal quality and the surface smoothness were studied. All films were analyzed using reflection high energy electron diffraction (RHEED), Nomarski differential interference contrast microscopy (NDIC), X-ray diffraction (XRD), and atomic force microscopy (AFM). Optimum temperature for SiC growth was between 1300°C and 1350°C. At these temperatures, the grown films show strong epitaxial relationship with AlN and very smooth surfaces (RMS ∼ 0.1- 0.75 nm). At temperatures below 1300°C, the film becomes polycrystalline. At 1400°C, the films show highly textured features, observed by XRD. In the RHEED, however, weak rings appear superimposed on the spot pattern, which implies the grown films are polycrystalline but highly textured. In order to evaluate the effect of underlying AlN thickness on the SiC film, layers with various thicknesses (50, 200, 400 nm) have been used at 1350°C. The SiC film on a 50 nm thick AlN layer shows a very smooth surface (RMS ∼ 0.1 nm) compared to the SiC film on a 400 nm (RMS ∼ 0.7 nm) AlN layer. This seems to be caused by the increasing roughness of the underlying AlN, as it becomes thicker. However, all the films show highly epitaxial growth features, which implies that 50 nm is sufficient to relieve the mismatch strain of the underlying AlN/sapphire.
Structural and electrical characterizations of oxynitride films on solid phase epitaxially grown silicon carbide
Authors: Bera L. K. , Choi W. K. , McNeill D. , Ray S. K. , Chatterjee S. , Maiti C. K. 
Published: April 2011

ABSTRACTWe have investigated the structural and electrical properties of as-prepared and rapid thermal oxynitride films on C+ implanted solid phase epitaxially grown SiC. The oxynitride was grown using N2O. The C concentration of the samples was estimated to be 1, 2 and 5 at. %. From the infrared spectra, samples with 1 and 2 at. % carbon showed that the carbon was substitutionally incorporated into the silicon. No precipitation of SiC was detected. However, for the 5 at. % C sample, some precipitation was observed as indicated by a broad peak at ∼800 cm−1. The oxynitride films showed the Si-O-Si stretching mode at ∼1100 cm−1. The shoulder at 980–1067 cm−1 was due to the O-Si-N bond. The peak at 830 cm−1 was due to the Si-N and Si-C bonds and C-O complex vibrational mode was observed at 663 cm−1. Electrical characterization of the oxynitride films was carried out using the MOS capacitor structure. The interface state density was found to range between 5.7×1011 to 3.35×1012 cm−2eV−1 and increased with an increase in the C concentration. The electrical breakdown field was found to be in the range of 5–7 MV cm−1 and reduced with an increase in C concentration. The charge-to-breakdown value was measured and decreased with an increase in C concentration.
One of Many Sources of Defect Generation in SiC
Authors: Khlebnikov Igor I. , Sudarshan Tangali S. , Khlebnikov Yuri I. , Wood Colin 
Published: April 2011

ABSTRACTSilicon carbide is a unique material for the study of process of defect generation and crystallization. In this paper, for the first time, we report the observation of the entrapment of whiskers and dendrites (tree-like defects) within the volume of the growing monocrystalline SiC. The encapsulation of the tree-like defects in the volume of the grown crystal leads to solid state polytype transformation. According to Oswald rule, the most probable transformation sequence is as follows: 2H→3C→xR→4H, 6H until a stable phase is established for the given conditions of crystal growth. We observe that the entrapments of tree-like defects are the source of SiC defects such as micropipes and planar defects. It is very likely that the above process is also the source of dislocations. Practically, every branch of the tree-like structure generates the above mentioned defects (micropipes, planar defects, etc.). Our investigation (by EDAX) shows that the chemical composition of the tree-like defect is the same as that of bulk SiC. In this paper, we will present the mechanism of the entrapment of the tree-like defects in the bulk crystal.
Dislocation Content of Etch Pits in Hexagonal Silicon Carbide
Authors: Khlebnikov Igor I. , Lari Mohsen B. , Khlebnikov Yuri I. , Bondokov Robert T. , Ayyagari Ramakrishna , Muzykov Peter , Sudarshan Tangali S. , Anderson T. , Whitlock J. B. 
Published: April 2011

ABSTRACT6H- and 4H- SiC crystals grown on the Si-face were chemically etched on the as-grown (virgin) surface and the C-face (sliced side). The etching of both the surfaces revealed a strong relationship between a variety of etch pits and the morphological features of the grown boule surface. Several types of etched patterns were revealed. On the Si face, we observed small, medium, and large hexagonal shaped pits and a linear array of small etch pits. However, the C face contained only small pits and a linear array of small pits.We observed individual or group of dislocations that were connected from the Si face to the opposite C face of the wafer. Also, etch pit lines oriented along specific crystallographic directions were seen.Our experimental observations have provided a physical basis to explain the generation of defects in SiC. An analysis of our observations show that a correlation exists between the distribution of different size etch pits and the condition of the crystal growth process.
Multi-Axial Channeling Study of Disorder in Gold Implanted 6H-SiC
Authors: Jiang W. , Weber W. J. , Thevuthasan S. , Shutthanandan V. 
Published: April 2011

ABSTRACTSingle-crystal wafers of 6H-SiC were irradiated at 300 K with 2 MeV Au2+ ions over fluences ranging from 0.029 to 0.8 ions/nm2. The accumulated disorder on both the Si and C sublattices in the irradiated specimens has been studied in situ using 0.94 MeV D+ channeling along <0001>, <1102> and <1011> axes. At low doses, results show that some of the Si and C defects are well aligned with the <0001> axis with more C defects shielded by the <0001> atomic rows; a higher level of C disorder is observed, which is consistent with a smaller threshold displacement energy on the C sublattice. There is only a moderate recovery of disorder, produced at and below 0.058 Au2+/nm2, during the thermal annealing at 570 K; similar behavior is observed in the higher-dose samples annealed between 720 and 870 K. The results suggest the presence of defect clusters and amorphous domains formed during the Au2+ irradiation. Reordering processes at 570 K in the weakly damaged 6H-SiC (0.12 Au2+/nm2, 300 K) appear to occur closely along the <1011> direction.
Defect Structures in Neutron Irradiated 6H-SiC Studied by X-Ray Diffraction Line Profile Analysis
Authors: Seitz C. , Magerl A. , Hock R. , Heissenstein H. , Helbig R. 
Published: April 2011

ABSTRACTWe have investigated by x-ray diffraction defect structures in 6H-SiC after neutron irradiation with different fluences and followed by different annealing procedures. An interpretation along a model of Klimanek [1, 4–6] shows, that higher fluences lead to a stronger than linear reduction of the correlation length, whereas higher annealing temperatures correlate with a better recovery of the correlation length. In addition defects of 1st kind created by irradiation are reduced by annealing. We find that annealing changes the character of the defects and it accentuates a defect structure already present in the original samples.