bluuebunny/crossref_metadata_2025_split huggingface dataset:
DNA-Directed Assembly of Anisotropic Nanoparticles on Lithographically Defined Surfaces and in Solution
Authors: Reiss Brian D. , Mbindyo Jeremiah N. K. , Martin Benjamin R. , Nicewarner Sheila R. , Mallouk Thomas E. , Natan Michael J. , Keating Christine D. 
Published: April 2011

AbstractAnisotropic, noble metal nanoparticles have been synthesized using a template synthesis strategy. In short, metallic salts are reduced in the nanometer scale pores of either an alumina or polycarbonate membrane. The particles can then been released from the template to form suspensions of anisotropic nanoparticles. These nanoparticles have been modified with deoxyribonucleic acid (DNA) oligomers of varying length using several different attachment chemistries. The thermodynamics and kinetics of modifying these particles with DNA has been explored. DNA has also been used to assemble the particles on planar Au surfaces as well as lithographically defined Au pads on Si wafers. In addition to surface assembly, DNA has been used to assemble the nanowires into simple, yet deterministic structures in solution.
The Effect of Surface Finish on the Dislocation Density in Sublimation grown SiC Layers
Authors: Sanchez E. K. , Liu J. , Vetter W. M. , Dudley M. , Bertke R. , Mitchel W. C. , Skowronski M. 
Published: April 2011

ABSTRACTThe effect of the seed surface finish on the dislocation density of sublimation grown silicon carbide was investigated. Growth on seeds that were polished down to 1 μm diamond paste resulted in the nucleation of threading screw dislocations in a density of 106 cm−2 and threading edge dislocations in densities of 107 cm−2. Following the mechanical polish of the seeds with a hydrogen etch or chemo-mechanical polish prior to growth resulted in the screw dislocation density decreasing by four orders of magnitude and the threading edge dislocation density dropping two orders of magnitude. Using the dislocations density and the hydrogen etch rate, the depth of damage in mechanically damaged seeds was determined to be between 400 and 1000 Å.
Defect Evolution in 4H-SiC Sublimation Epi-Layers Grown on LPE Buffers with Reduced Micropipe Density
Authors: Yakimova R. , Syväjärvi M. , Jacobsson H. , Kakanakova-Georgieva A. , Tuomi T. , Rendakova S. , Dmitriev V. , Janzén E. 
Published: April 2011

ABSTRACTThe objective of this work is to study defect occurrence and appearance in thick sublimation epitaxial layers grown on top of LPE layers with different thickness and substrates with reduced micropipe density. Data from growth on C-terminated surfaces are also presented. The results were analyzed with the aid of optical microscopy, SEM images, HRXRD and synchrotron white beam X-ray topography. A pronounced effect of the LPE (buffer) layer surface roughness on formation of dislocations and micropipes is observed in the sublimation epitaxy layers. While with increasing the thickness of the buffer layer the efficiency of the micropipe reduction increases, the structure quality of the top sublimation epilayer degrades. LPE layers with a thickness of 0.1 μm appear to be the best compromise.
Investigation of Lo-Hi-Lo and Delta-Doped Silicon Carbide Structures
Authors: Konstantinov A. , Karlsson S. , Adås C. , Harris C. , Linnarsson M. 
Published: April 2011

ABSTRACTFeasibility of lo-hi-lo and delta-doped structures for evaluation of high-field silicon carbide material properties is investigated. Delta-doped structures are grown using the hot-wall CVD technique. Aluminum and nitrogen doping profiles are demonstrated with FWHM below 10 nm. Nitrogen doping transients are found to be slower than those for aluminum. The growth interrupt technique has been developed for achieving narrow nitrogen doping peaks. Lo-hi-lo structures were fabricated using the implantation-and-regrowth technique. Structures with confined avalanche multiplication are demonstrated using the lo-hi-lo and delta doping techniques. The effect of substrate imperfections on early avalanche breakdown is investigated using confined avalanche multiplication devices.
Electroluminescence from 4H-SiC Schottky Diodes
Authors: Carlsson F. H. C. , ul-Wahab Q. , Bergman J. P. , Janzén E. 
Published: April 2011

ABSTRACTWe have observed electroluminescence from 4H-SiC Ni-Schottky diodes on 1015cm−3 nitrogen doped n-type epilayers. A high barrier Schottky contact will form an inversion layer close to it. This creates minority carriers that can be injected into the epi and recombine to emit light. The spectral composition and its temperature dependence have been investigated from liquid He temperatures to room temperature. Band edge luminescence, Al related luminescence and DI bound exciton have been observed. To study the electroluminescence from Schottky diodes provides an easy and additional technique for defect characterization of epitaxial layers.
The Growth and Characterization of Large Diameter Silicon Carbide Substrates
Authors: Gupta A. , Yoganathan M. , Burton J. , Byrd N. , Dimondi A. , Edwards S. , Giordana A. , Glesener J. , Harding J. , Long F. , Mitchel W. , Saxler A. , Sostak R. , Whitlock J. , Thomas R. N. , Anderson T. 
Published: April 2011

ABSTRACTAffordable, high quality SiC wafers are very desirable for a variety of new technologies including GaN based lighting, RF, and high-power electronics based on wide band gap materials. At Litton Airtron we have a major effort in the growth and characterization of SiC. We will present data on 35, 50 and 75-mm diameter crystals. We are growing both n-type, semiinsulating 4H, 6H, and 15R material. A variety of characterization techniques are being used at Litton Airtron to determine wafer quality. These include Raman microscopy, digital wafer photography, and crossed polarizer images. Raman spectroscopy is an excellent probe of polytype and carrier concentration for n-type materials; in addition it can be done at room temperature and is sufficiently fast that it can be used in an industrial environment. The use of digital photography allows for the collection of images that can be quantitatively analyzed and archived.
Ordinary and Extra-Ordinary Dielectric Function of 4h- and 6H-SiC in the 0.7 to 9.0 eV Photon Energy Range
Authors: Lindquist O. P. A , Järrendahl K. , Arwin H. , Peters S. , Zettler J.-T. , Cobet C. , Esser N. , Aspnes D. E. , Henry A. , Edwards N. V. 
Published: April 2011

ABSTRACTWe report ordinary <ε┴> and extra-ordinary <ε║> dielectric function data of 4H- and 6H-SiC from 0.7 to 9.0 eV. These data, which were obtained by with spectroscopic ellipsometry, are in good qualitative agreement with trends recently reported in ab initio calculations.
Sublimation Growth of 6H-SiC Boule on Various a-Plane Substrates
Authors: Nishino S. , Nishiguchi T. , Masuda Y. , Sasaki M. , Ohshima S. 
Published: April 2011

ABSTRACTSublimation growth of 6H-SiC was performed on {1100} and {1120} substrates. The difference between the growth on {1100} plane and {1120} plane was observed. {1100} facet was almost flat and there were grooves oriented toward <1120> direction. The step bunching was observed on {1100} plane 5° off-axis. A lot of pits were introduced on {1120} plane of the crystal grown both on {1100} and {1120} substrates. Step flow growth toward <1120> direction created the pits on {1120} plane. It was important to grow crystal by layer by layer growth on {1120} plane. By changing the growth mode from step flow growth to layer by layer growth, pit on the {1120} plane may be reduced as same as CVD growth on {1120} plane. Growth temperature and C/Si ratio should be optimized to keep layer by layer growth.
Titanium Tungsten (TiW) for Ohmic contacts to n-and p-type 4H-SiC
Authors: Lee S.-K. , Zetterling C.-M. , Östling M. 
Published: April 2011

ABSTRACTIn the present work, we investigated sputtered titanium tungsten (TiW) contacts for Ohmic contacts to both n- and p-type 4H-SiC with long-term stability under high temperature (500°C).. Epitaxial layers with a doping concentration of 1.3×1019 and 6×1018 cm−3 were used. After high temperature annealing (>950°C) sputtered TiW contacts showed Ohmic behavior with good uniform distribution of the specific contact resistance. We obtained an average specific contact resistance (pc) of 4×10−5 Ωcm2 and 1.2 ∼ 1.7×10−4 Ωcm2 for p- and n-type, respectively from linear TLM measurement. We also found some variation of the specific contact resistance and the sheet resistance from our TLM measurement for p-type contacts. We will discuss this behavior with the measurement of SIMS. Long-term stability with a top-cap layer is also discussed
A Single-Band Constant-Confining-Potential Model for Self-Assembled InAs/GaAs Quantum Dots
Authors: Califano M. , Harrison P. 
Published: April 2011

ABSTRACTA simple and versatile numerical method for electronic structure calculations in InAs pyramidal dots is presented, and its predictions compared with both theoretical and experimental data. The calculated ground state energy eigenvalues agree well with those of more sophisticated treatments which take into account band mixing and the microscopic effects of the strain distribution. The number of electron bound states predicted is in excellent agreement with very recent calculations for strained quantum dots performed in the framework of the 8-band k · p theory. Very good agreement is obtained with both the number and the energy of the peaks in several experimental photoluminescence spectra. Furthermore our ca agreement with that deduced from capacitance and photoluminescence measurements.
Quantum Dot Cell Coupled to a Single Mode Quantum Cavity
Authors: Rojas F. , Cota E. , Ulloa S. E. 
Published: April 2011

ABSTRACTWe study the properties of the charge distribution (polarization) of a 4-quantum dot square cell with two electrons, induced or modified by the coupling to a single quantized mode field. The effect of the relevant parameters (tunneling between dots, the amplitude of the electron-cavity interaction, cavity frequency) is investigated in the properties of polarization of the two-electron fundamental states. We further investigate the effects of asymmetry in the electron-cavity interaction in each dot and evaluate the modification to the dynamic evolution of the polarization. We find that there is a range of values of the asymmetry for which the polarization is improved. This suggests that an optimization of the coupling of the quantum dot cell with its environment may yield more reliable and stable operation.
The Enhancement of Band Edge Emission from ZnS/Zn(OH)2 Quantum Dots
Authors: El-Khair Hatim Mohamed , Xu Ling , Huang Xinfan , Li Minghai , Gu Xiaofeng , Chen Kunji 
Published: April 2011

ABSTRACTWurtzite structure monodisperse ZnS quantum dots (QDs) of 1 to 5 nm diameter, synthesized by colloidal chemical method, were confirmed by transmission electron microscopy (TEM) images and electron diffraction (ED) patterns. Enhanced blue shifted band edge emission from Zn(OH)2 capped ZnS QDs with decreasing size has been observed, which indicates the role of inorganic surface passivation and hence supports the quantum size effect. Detectable far-red shifted emission from bare ZnS QDs has been observed when QDs precursors and stabilizer dispersed in solvents with different polarities. This emission is attributed to the surface trap states of different energies.
Observation of CdSe Colloidal Nano-Dot Films by Scanning Probe Microscopy
Authors: Tanaka Ichiro , Kawasaki Eri , Ohtsuki O. , Saita S. , Kamiya I. 
Published: April 2011

ABSTRACTWe observed the surface topography of CdSe colloidal nano-dot film by cyclic contact mode atomic force microscopy. The observed structure changes with cantilever oscillation amplitude, and non-uniform images with long-range corrugations are obtained with relatively large oscillation amplitude while fine structures are revealed with smaller oscillation amplitude. When the amplitude is larger and the surface is weakly ‘tapped’, the topography of the soft organic matrix of the film dominates, and when the tapping force is increased, the hard CdSe dots begin to reveal.
Phase Diagram and Electrostatic Levitation Undercooling Studies of Polytetrahedral Phases in Ti-Fe-Si-O and Ti-Zr-Ni Alloys
Authors: Croat T.K. , Davis J.P. , Gangopadhyay A.K. , Kelton K.F. , Lee G.W. , Simmons J. , Hyers Robert W. , Robinson Michael B. , Rathz Thomas J. 
Published: April 2011

AbstractNew information on the phase diagrams of Ti-Fe-Si-O and Ti-Zr-Ni alloys near the quasicrystal and rational approximant compositions is presented. α(TiFeSiO), the 1/1 rational approximant, is shown to form in a peritectic mode from the liquid, indicating the possibility to produce single-crystal samples. Very long duration annealing studies demonstrate unambiguously that the TiZrNi i-phase and 1/1 approximant form at low temperatures by a solid-state transformation; their phase fields do not extend to the liquidus temperatures. The first undercooling measurements of electrostatically-levitated droplets of the Ti-Zr-Ni alloys are presented. These nucleation studies provide new information on the structural relations between polytetrahedral phases and the undercooled liquid, and on the phase transformation processes. The reduced undercooling for the polytetrahedral phases in these alloys is less than for crystal phases of a similar composition, demonstrating a low interfacial energy between the polytetrahedral phase and the liquid.
Classification of Icosahedral Quasicrystals and their Approximants by the Electronic Conduction Mechanisms
Authors: Takeuchi Tsunehiro , Banno Eiichi , Onogi Tomohide , Mizunol Takayuki , Sato Takuya , Vincent Fournée , Mizutani Uichiro 
Published: April 2011

AbstractIn this paper, two independent factors, electronic structure at the Fermi energy and electron scattering, both of which determine the electrical resistivity, are clearly separated by using a plot of ρ4K versus RRR (RRR = ρ4K/ρ300K) for icosahedral quasicrystals and their approximants. Each contribution of the electronic structure and the electron scattering on the electrical resistivity was systematically revealed, and the origin for the high resistivities observed in the quasicrystals and approximants is well understood by taking each effect into account. We found that the quasicrystals and approximants are classified into three groups in terms of the electron scattering mechanism, which dominates the temperature dependence of the resistivity. The temperature dependence of the electrical resistivity in the first group is well understood in terms of the Boltzmann transport mechanism, and those in the second and the third groups are in terms of the weak localization and the Anderson localization, respectively.
Electron Transport Properties and Thermoelectric Effect of Al-Pd-Mn Single Quasicrystals Doped with M=Au or Re by ion Implantation and its Comparison with Quaternary Quasicrystalline Samples.
Authors: Fournée V. , Mizutani U. , Takeuchi T. , Saitoh K. , Ikeyama M. , Guo J.Q. , Tsai A.P. 
Published: April 2011

AbstractIon implantation experiments were carried out on a single grain Al-Pd-Mn icosahedral quasicrystal. The influence of Re or Au dopant on the thermopower and the electrical resistivity has been measured. Comparison with ternary and quaternary alloys produced by usual metallurgical techniques is made. The results indicate that the efficiency of this quasicrystalline alloy as a thermoelectric material can be improved by adjusting composition and structural quality, as well as by the addition of a small amount of Re, whereas Au implantation is inefficient in that respect.
Decagonal Model Based on Periodic Structures in the Al-Pd-Mn System
Authors: Boudard Michel 
Published: April 2011

AbstractThe structure of periodic phases, in the Al-Pd-Mn system, showing the importance of chemical ordering is reviewed as well as their description in term of pentagonal chains of transition metals. These features are discussed in relation with structural models for AlPdMn decagonal quasicrystals.
Processing and Mechanical Properties of Quasicrystal-Reinforced Al-Alloys
Authors: Schurack F. , Eckert J. , Schultz L. 
Published: April 2011

AbstractWe investigated the suitability of powder metallurgy as well as die casting for the fabrication of light-weight Al-based composites with quasicrystalline particles embedded in an aluminum matrix. Al-Mn-Ce and Al-Cu-Fe quasicrystalline powders were synthesized by milling of elemental powder mixtures or arc-melted prealloys using a planetary ball mill. The mixture of the quasicrystalline phase and the Al-matrix phase with an appropriate ratio was realized by an initial aluminum excess or by blending of quasicrystalline powder with pure aluminum. The powders were consolidated by hot extrusion. Bulk samples of Ø3mm diameter and 50mm length were also directly prepared by squeezing the melt into a copper mold. CCRT-compression tests revealed a yield strength of about 400 MPa, an ultimate strength of 565 MPa and a ductility of up to 19 % fracture strain as optimum mechanical properties.
γ-Brass Crystallization in a Simple Monotomic Liquid
Authors: Zetterling Fredrik H.M. , Dzugutov Mikhail , Lidin Sven 
Published: April 2011

AbstractWe present a molecular dynamics simulation investigating the crystallization pattern of a simple monatomic liquid model which utilize an interatomic interaction potential. The shape of the potential imitates effective interionic interaction in metallic systems. The potentials is constructed to favour icosahedral arrangement in the first coordination shell. We observe that, the system forms a thermodynamically stable solid phase exhibiting cubic symmetry. Its diffraction pattern can be identified as that of γ-brass phase, a terahedrally packed crystalline structure with 52 atoms in the unit cell. We conclude that the monatomic version of γ-brass structure generated in this simultion can be regarded as a new archetype for the γ-base structures observed in many intemetllic compounds.
Refinement of d-AlNico Quasicrystal Structures
Authors: Takakura Hiroyuki , Yamamoto Akiji , Tsai An Pang 
Published: April 2011

AbstractThe models of decagonal Al72Ni20Co8quasicrystal with the space group ofP105/mmcwere refined on the basis of single crystal x-ray diffraction data set using the 5D description. The results of a structure model derived from Al13Fe4-type approximant crystal and Burkov model are compared. The former gives ωR=0.045 andR=0.063 for 449 reflections with 103 parameters and a resonable chemical composition of Al71.2TM28.8(TM=transition metals). The projected structure in consistent with high resolution images of this material. On the other hand, the latter gives ωR=0.161 andR=0.193 for 55 parameters and a compositon of Al64.6TM35.1.
Effects of Hydrogen on the Internal Time Scales in Zr-Ti-Ni-Cu-Be Bulk Metallic Glasses
Authors: Suh Daewoong , Dauskardt Reinhold H. 
Published: April 2011

AbstractThe effects of pre-charged hydrogen on various kinetic processes in a Zr-Ti-Ni-Cu-Be bulk metallic glass alloy were investigated. Hydrogen charging induced longer internal time scales for structural relaxation and viscous flow. Crystallization was retarded by hydrogen charging leading to enhanced glass stability. Positron annihilation spectroscopy indicated reduced average free volume size after hydrogen charging. The reduced free volume and higher viscosity caused by hydrogen retard the plastic deformation and are believed to be responsible for hydrogen embrittlement.
Elastic Properties of Three Bulk Metallic Glasses. Evolution Versus Temperature in the Glass Transition Region and Influence of Crystallisation.
Authors: Van De Moortele B. , Pelletier J.M. , Soubeyroux J.L. , Lu I.R. 
Published: April 2011

AbstractThree bulk metallic glasses, with different resistance against crystallisation, were investigated using DSC experiments, X-ray diffraction, transmission electron microscopy and mechanical spectroscopy. Like in other non-crystalline materials, the elastic modulus exhibits a large decrease above the glass transition temperature. In materials with a large supercooled region (Pd-Ni-Cu-P for instance), this decrease can reach three decades, leading to an attractive glass forming ability. In contrast, in bulk metallic glasses in which onset of crystallisation occurs very rapidly above Tg, this decrease is on less than one decade. A correlation is made with the microstructure evolution revealed by X-Ray diffraction and transmission electron microscopy.
Fracture Mechanisms of Bulk Amorphous Metal under Impact Loading
Authors: Kobayashi Takao , Shockey Donald A. 
Published: April 2011

AbstractAdvanced diagnostic instruments and analyses applied to failure surfaces and cross sections of bulk metallic glasses (BMGs) can provide insight into the deformation and failure of these materials and assist in prototyping new materials with improved failure resistance. Confocal- optics scanning laser microscopic analysis of conjugate fracture surface topographs suggests that the formation and stretching of ligaments are likely keys to the high impact toughness of Vitreloy.
Production of Zr-based Amorphous Wires by Rotating Disk Casting Method
Authors: Zhang Tao , Inoue Akihisa 
Published: April 2011

AbstractContinuous amorphous wires with high strength and good ductility have been produced for the Zr55Al10Ni5Cu30and Zr55Ti5Al10Ni10Cu20alloys by a rotating disk casting technique. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous wires have a nearly circular cross-section, smooth peripheral surfaces and diameters in the range from 0.5 to 1.5mm. The amorphous alloy wires have good bending ductility. The maximum tensile strength, μf, is 1600 MPa for Zr55Al10Ni5Cu30 amorphous wire and 1900 MPa for Zr55Ti5Al10Ni10Cu20 amorphous wire, respectively. The success of forming amorphous alloy wires in a continuously long form by the present casting method is important for the further extension of application fields of amorphous alloys.
The Glasses Transition and Low Energy Excitations in Supercooled Metallic Liquid and Glasses
Authors: Kanazawa I. 
Published: April 2011

AbstractWe have introduced the theory of three-dimensional supercooled metallic liquids and glasses, which is based on the gauge invariant agrangian with spontaneous breaking, and discussed the viscosity of the three-dimensional supercooled metallic liquids. n the basis of the present theoretical formula, a qualitative picture of low energy excitations (the boson peak) is proposed.
Investigation on the Thermal Stability of Bulk Glass Forming Alloy Pd-Cu-Ni-P
Authors: Lu I.-R. , Görler G. P. , Willnecker R. , Fecht H. J. 
Published: April 2011

AbstractThe metallic glass former Pd-Ni-P is well known for its pronounced stability against crystallization. Samples of this alloy vitrify completely at low cooling rates down to 0.1 K/s. The addition of copper to this alloy system reduces further the crystallization kinetics significantly. Investigations on critical cooling rates were performed on Pd-Cu-Ni-P alloy by means of isothermal nucleation experiments. The results indicate a critical cooling rate in the order of 5.10−3 K/s, which is the lowest one presently known for metallic glass-formers. The high stability against crystallization during cooling allows for simultaneous measurements of its thermodynamic properties within the entire temperature range from the regime of the liquid to the glassy state. Heat capacity measurements were carried out by differential heat-flow calorimetry and the coefficient of thermal expansion was determined by applying sessile drop technique. The results can be described within the free-volume model.