bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoparticles and Nanocomposites in RF Plasma
Authors: Cao Jin , Matsoukas Themis 
Published: April 2011

AbstractThe use of low pressure radio-frequency (rf) plasma for nanoparticle formation and the deposition of thin film on particulate substrates are reported. Plasma polymer particles are synthesized in a capacitively-coupled Ar/monomer discharge at rf power of 15-30 W. A variety of particle structures are observed, including monodispersed nanospheres and liquid-like viscous nano-droplets. Styrene in particular is observed to produce hollow nanospheres. By manipulating the process parameters, films of plasma polymers can be deposited onto suspended submicron particles. We take advantage of the electrostatic trapping of “dusty plasma” to suspend small particles in plasma for extended periods of time until the desired coating thickness is achieved. Sub-micron silica particles introduced into a low pressure rf Ar/monomer plasma are coated with film of thickness ranging from 2 to 70 nm.
Planar Synthesis of Anisotropic Nanoparticles
Authors: Khomutov Gennady B. , Gaynutdinov Radmir V. , Gubin Sergey P. , Obydenov Alexander Yu. , Soldatov Eugene S. , Tolstikhina Alla L. , Trifonov Artem S. 
Published: April 2011

AbstractA novel method of two-dimensional (2-D) synthesis of anisotropic nanoparticles have been developed in which nanoparticle growth is an example of 2-D process where true 2-D diffusion of precursor molecules and active intermediates, metal atoms and its complexes, nucleus and growing nanoparticles, surfactants and additives occurs only in the plain of a monolayer at the gas/liquid interface. Nanoparticles were generated via ultraviolet decomposition of a volatile insoluble metal-organic precursor compound (iron pentacarbonyl) and by chemical reduction of palladium from Pd3(CH3COO)6 molecules in a mixed Langmuir monolayer with stearic acid, arachidic acid or octadecyl amine on the aqueous subphase surface. The properties of such surfactants to form Langmuir monolayer and to prevent aggregation of nanoparticles were here combined successfully. Atomic force microscopy, scanning tunneling microscopy and transmission electron microscopy techniques were used to study morphology of deposited nanoparticulate monolayers. The size and shape of nanoparticles were dependent substantially on the monolayer composition and state during the synthesis process. We demonstrate that planar synthesis in a monolayer at the gas/liquid interface allows to produce anisotropic extremely flat nanoparticles with very high surface to volume ratio and unique morphologies such as iron-containing magnetic nano-rings.
Multi-Layer Coating of Ultrathin Polymer Films on Nanoparticles of Alumina by a Plasma Treatment
Authors: Shi Donglu , Yu Zhou , Wang S. X. , Ooij Wim J. van , Wang L. M. , Zhao J. G. 
Published: April 2011

AbstractMulti-layer ultrathin polymer films have been deposited on the surfaces of nanoparticles of alumina using a plasma polymerization treatment. The nanoparticles ranged from 10-150 nm in spherical shapes. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin film of the pyrrole layer (10-20 Å) was uniformly deposited on the surfaces of the nanoparticles. In particular, the particles of all sizes (10-150 nm) exhibited equally uniform ultrathin films indicating well-dispersed nanoparticles in the fluidized bed during the plasma treatment. After single layer coating, hexamethyldisiloxane (HMDSO) was coated again as a second layer onto the surface of pyrrole. Subsequently, a third layer of pyrrole was coated on the top of HMDSO film completing the multi-layer coating process. Time-of-Flight Secondary ion mass spectroscopy (TOFSIMS) experiments confirmed the deposition of these multi-layer thin films on the nanoparticles. The deposition mechanisms and the effects of plasma treatment parameters are discussed.
High Spatial Resolution Assessment of the Structure, Composition, and Electronic Properties of Nanowire Arrays
Authors: Sander M.S. , Prieto A.L. , Lin Y.M. , Gronsky R. , Stacy A.M. , Sands T.D. , Dresselhaus M.S. 
Published: April 2011

AbstractWe have employed transmission electron microscopy (TEM) and analytical electron microscopy to perform preliminary assessment of the structure, composition and electronic properties of nanowire arrays at high spatial resolution. The two systems studied were bismuth and bismuth telluride nanowire arrays in alumina (wire diameters ~40nm), both of which are promising for thermoelectric applications. Imaging coupled with diffraction in the TEM was employed to determine the grain size in electrodeposited Bi2Te3 nanowires. In addition, a composition gradient was identified along the wires in a short region near the electrode by energy-dispersive x-ray spectroscopy. Electron energy loss spectroscopy combined with energy-filtered imaging in the TEM revealed the excitation energy and spatial variation of plasmons in bismuth nanowire arrays.
Generalized Ellipsometry Using a Rotating Sample
Authors: Xu Weiliang , Wood Lowell T. , Golding Terry D. 
Published: April 2011

AbstractWe propose a generalized ellipsometric technique using a rotating sample. The ellipsometer consists of a polarizer, a rotatable sample holder, an analyzer, and a detector. Fourier coefficients are measured and used to extract the system’s dielectric tensors and film thicknesses. The main advantage of the technique is that all parts of the ellipsometer are fixed except the sample, whose azimuth angle can be modulated. We show calculated responses to isotropic and anisotropic materials as well as superlattices. Potential applications for characterizations of anisotropic nanostructures are discussed.
Effective Medium Theory of DNA-linked Gold Nanoparticle Aggregates:Effect of Aggregate Shape
Authors: Lazarides Anne A. , Kelly K. Lance , Schatz George C. 
Published: April 2011

AbstractWe present a dynamical effective medium theory (EMT) of the dielectric properties of nanoparticle aggregates formed from DNA-linked gold nanoparticles. Experimental measurements show that such aggregateshave reduced UV extinction and plasmon bands that are considerably red-shifted and broadened relative to the plasmon absorption feature observed in spectra of dispersed colloid. The EMT, which can be used to reproduce the observed spectral changes, is tested by comparing aggregate spectra calculated using the EMT dielectric function with spectra from explicit coupled particle calculations, and good agreement is found. The EMT dielectric function is used as well in discrete dipole calculations to calculate extinction spectra for a variety of aggregate shapes not amenable to analytic solution, and the sensitivity of the spectra to aggregate shape is examined. We find that the spectra are only weakly sensitive to aggregate shape, and conclude that, when calculating extinction of the DNA-linked aggregates for comparison with experiment, spherical shapes can be assumed.
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.
Tunable Porous Silicon Photonic Band Gap Structures
Authors: Lugo J. Eduardo , Lopez Herman A. , Chan Selena , Fauchet Philippe M. 
Published: April 2011

AbstractThe tuning of one-dimensional photonic band gap structures based on porous silicon will be presented. The photonic structures are prepared by applying a periodic pulse of current density to form alternating high and low porosity layers. The width and position of the photonic bandgap are determined by the dielectric function of each layer, which depends on porosity, and their thickness. In this work we show that by controlling the oxidation of the porous silicon structures, it is possible to tune the photonic bandgap towards shorter wavelengths. The formation of silicon dioxide during oxidation causes a reduction of the refractive index, which induces the blue shift. The photonic band gap is determined experimentally by taking the total reflection of the structures. In order to understand the tuning of the photonic band gap, we developed a geometrical model using the effective medium approximation to calculate the dielectric function of each of the oxidized porous silicon layers. The two key parameters are the porosity and the parameter β, defined as the ratio between the silicon dioxide thickness and the pore radius before oxidation. Choosing the parameter β, to fit the experimental photonic band gap of the oxidized structures, we extract the fraction of oxide that is present. For example, the measured 240 nm blue shift of a photonic bandgap that was centered at 1.7 microns corresponds to the transformation of 30% of the structure into silicon dioxide. A similar approach can be used for oxidized two-dimensional porous silicon photonic structures.
Inverse-Computation Design of a SiC Bulk Crystal Growth System
Authors: Kulik Alexey V. , Demina Svetlana E. , Kochuguev Sergey K. , Ofengeim Dmitry Kh. , Karpov Sergey Yu. , Vorob'ev Andrey N. , Bogdanov Maxim V. , Ramm Mark S. , Zhmakin Alexander I. , Alonso Anna A. , Gurevich Sergey G. , Makarov Yuri N. 
Published: April 2011

ABSTRACTInverse modeling was applied to the optimization of a crucible design for SiC sublimation growth. We found a crucible shape providing the optimal temperature distribution in terms of the powder source stability during long-term operation and of the convex crystal shape. Considerable improvement of temperature uniformity throughout the powder charge was achieved. The results obtained show selective sensitivity of the thermal field inside the crucible to modification of the crucible design. The inverse problem approach is easy-to-adapt to various optimization criteria and seems to be especially effective in the case of multi-factor optimization.
Surface Morphology of 6H-SiC on various a-plane using Si2Cl6+C3H8+H2 by Chemical Vapor Deposition
Authors: Nishino Shigehiro , Masuda Yasuichi , Ohshima Satoru , Jacob Chacko 
Published: April 2011

ABSTRACTWe have grown epitaxial layer introducing buffer layer using N2 doping on 6H-SiC (1120) and (1100) substrate. The improvement of morphology could be obtained for (1120) and (1100) epilayers. Morphologies of (1120) epilayers were independent on off-orientations, Morphologies of (1100) epilayers were very sensitive to the off-orientations. The quality of epilayer, and impurity incorporation for a-plane were very influenced by the surface treatment before CVD growth compared to (0001) epilayers.
Bonding, Defects, And Defect Dynamics In The Sic-SiO2 System
Authors: Pantelides S. T. , Buczko R. , Ventra M. Di , Wang S. , Kim S.-G. , PennycooK S. J. , Duscher G. , Feldman L. C. , Mcdonald K. , Chanana R. K. , Weller R. A. , Williams J. R. , Chung G. Y. , Tin C. C. , Isaacs-Smith T. 
Published: April 2011

ABSTRACTThis paper presents a review of new results obtained by a combination of first-principles theory, Z-contrast imaging, and electron-energy-loss spectroscopy in the context of a broader experimental/theoretical program to understand and control the atomic-scale structure of SiCSiO2 interfaces. The ultimate purpose is to achieve low interface trap densities for device applications. Results are given for global bonding arrangements in comparison with those of the Si-SiO2 interface, the mechanism of the oxidation process, the nature of possible interface defects and their passivation by N and H, and the formation and dissolution of C clusters in SiO2 during oxidation and reoxidation.
Silicon Carbide bipolar power devices - potentials and limits
Authors: Singh Ranbir 
Published: April 2011

ABSTRACTBipolar devices made with SiC offer 20–50X lower switching losses as compared to conventional semiconductors, and a comparable on-state voltage drop at sufficiently high current densities. To exploit the tremendous advantages offered by SiC for bipolar power devices, it is important to understand the relevant voltage/current range, fundamental limits and technological challenges in order to develop this technology commercially. The opportunity of operating a device at a high current density (>300 A/cm2) to increase total current with reasonable yield, the poor reliability of MOS at high temperatures, and the relatively low channel mobilities obtained in 4H-SiC MOSFETs may make certain bipolar devices more attractive even as low as 1700 V. The total power loss in various bipolar devices is analyzed and compared to fundamental operational limits in order to find the applicability of various devices to advanced applications.
Design and Process Issues for Silicon Carbide Power DiMOSFETS
Authors: Ryu Sei-Hyung , Agarwal Anant K. , Saks Nelson S. , Das Mrinal K. , Lipkin Lori A. , Singh Ranbir , Palmour John W. 
Published: April 2011

ABSTRACTThis paper discusses the design and process issues of high voltage power DiMOSFETs (Double implanted MOSFETs) in 4H-silicon carbide (SiC). Since Critical Field (EC) in 4H-SiC is very high (10X higher than that of a Si), special care is needed to protect the gate oxide. 2D device simulation tool was used to determine the optimal JFET gap, which provides adequate gate oxide protection as well as a reasonable JFET resistance. The other issue in 4H-SiC DiMOSFETs is extremely low effective channel mobility (μeff) in the implanted p-well regions. NO anneal of the gate oxide and buried channel structure are used for increasing μeff. NO anneal, which was reported to be very effective in increasing the μeff of SiC MOSFETS in p-type epilayers, did not produce reasonable μeff of SiC MOSFETs in the implanted p-well. Buried channel (BC) structure with 2.7×1012 cm−2 charge in the channel showed high μeff utilizing bulk buried channel, but resulted in a normally-on device. However, it was shown that by controlling the charge in the BC layer, a normally off device with high μeff can be produced. A 3.3 mm × 3.3 mm DiMOSFET with BC structure showed a drain current of 10 A, which is the highest current reported in SiC power MOSFETs to date, at a forward drop of 4.4 V with a gate bias of only 2.5 V.
Comparison of Current – Voltage Characteristics of N and P Type 6H-SiC Schottky Diodes
Authors: Zhang Q. , Madangarli V. , Gao Y. , Sudarshan T. S. 
Published: April 2011

ABSTRACTForward and reverse current – voltage (I–V) characteristics of N and P-type Schottky diodes on 6H-SiC are compared in a temperature range of room temperature to 550K. While the room temperature I–V characteristics of the N-type Schottky diode after turn-on is more or less linear up to ∼ 100 A/cm2, the I–V characteristics of the P-type Schottky diode shows a non-linear behavior even after turn-on, indicating a variation in the on-state resistance with increase in forward current. For the first time it is shown that at high current densities (> 210 A/cm2) the forward voltage drop across P type Schottky diodes is lower than that across N type Schottky diodes on 6H-SiC. High temperature measurements indicate that while the on-state resistance of N type Schottky diodes increases with increase in temperature, the on-state resistance of P type Schottky diodes decreases with increase in temperature until a certain temperature. While the N-type diodes seem to have soft breakdown characteristics, the P-type diodes exhibit more or less abrupt breakdown characteristics.
Calculation Of Positron Characteristics In Silicon Carbide
Authors: Barbiellini Bernardo , Kuriplach Jan , Anwand Wolfgang , Brauer Gerhard 
Published: April 2011

ABSTRACTPositron affinity calculations performed by a first-principles approach based on density functional theory reveal, contrary to many other semiconductors, that free positrons and positronium atoms can escape from SiC. It is found that the treatment of the electronpositron interaction plays a crucial role when calculating the annihilation characteristics. These characteristics originating from both valence and core electrons, combined with the corresponding measurements, yield a very useful tool for surface studies and point defect identification in the bulk. Calculations will be compared with available experimental data.
Effect of C/B Sequential Implantation on the B Acceptors in 4H-SiC
Authors: Nakano Yoshitaka , Kachi Tetsu , Tadano Hiroshi , Malhan Rajesh Kumar 
Published: April 2011

ABSTRACTWe have systematically investigated the effect of C/B sequential implantation on the B-related acceptors and deep levels in 4H-SiC using thermal admittance spectroscopy. With increasing concentration of co-implanted C, the density of deep levels was found to start decreasing and to be completely suppressed for the C and B ratio of 1:1. Moreover, the density and ionization energy of B acceptors were seen to start increasing and lowering, respectively, with increasing C concentration. However, we found that excess C-content leads to the formation of a new complex defect. The C-V results also support the expected increase in the total hole concentration with increasing concentration of the co-implanted C-atoms, which is followed by a decrease in the concentration under C-rich condition. This is in reasonable agreements with the behavior of the B acceptors and deep defect levels. Therefore, the concentration of co-implanted C-atoms is considered to be very sensitive to the formation of the B acceptor levels.
Comparison of 3C-SiC Films Grown By CVD on Si(111) and Si(211) Substrates
Authors: Grayson B. A. , Wolan J. T. , Graves M. , Bledsoe M. , Kirchner K. , Saddow S. E. 
Published: April 2011

ABSTRACTIn this study, the near-surface region of air-exposed thin 3C-SiC films grown on 50-mm (2-in.) diameter Si(111) and Si(211) substrates have been investigated. Carbonization to create the film in a radio-frequency (RF) induction-heated horizontal atmospheric-pressure chemicalvapor- deposition reactor utilized a propane-hydrogen mix (3% C3H8 in ultra-high purity hydrogen) with a hydrogen carrier. Elemental and chemical-state identification of the thin-films are presented. Several structure sensitive techniques including X-ray diffractaion (XRD) in ω-2θ as well as scanning electron microscopy (SEM) to examine crystal structure, surface morphology and film thickness are included.
Effects of Surface and Interlayer Processing Conditions on Selected Ohmic Contact Metallizations for p-type Silicon Carbide
Authors: Porter L. M. , Jang T. , Worren T. , Chang K. C. , Papanicolaou N. A. , Erickson J. W. 
Published: April 2011

ABSTRACTA comparative study of Pt and Pt/Si contacts to p-type 6H-SiC in terms of various processing conditions and interlayer specifications was performed. Deposition temperature, the thickness of the Si layer, and B-dopant incorporation in the Si were found to significantly affect the specific contact resistivity (SCR) values. In addition, pre-etching of the SiC surface in SF6 + Ar was found to consistently reduce the SCR's. The lowest average SCR values were 3 × 10−5 Ωcm2 for Pt/Si/SiC contacts deposited on pre-etched SiC surfaces (7.0 × 1018 cm−3 doping concentration) and annealed at 1100 °C for 5 min.Aluminum-titanium contacts also showed dependence on the thicknesses of the Al and Ti layers and on the locations of the layers. Differences in both the SCRs and surface morphology are presented.
Decoherence Effects in Arrays of Coupled Quantum Dots
Authors: Cota E. , Rojas F. , Ulloa S. E. 
Published: April 2011

ABSTRACTWe study the dynamics of the charge distribution (polarization) in an array of four quantum dots located at the corners of a square. The array has two extra electrons in a neutralizing background. We take into account electron-phonon interaction effects using a quantum Markovian master equation approach. Results show that dissipative effects are determinant in the dynamical response of a quantum-dot cell close to a nearby driver cell with prescribed polarization varying with time. The response is shown to depend strongly on temperature.
The Assembly of Nano-Materials Using Bio-Scaffolding
Authors: Yun C. Steven , Major Jody L. , Strouse Geoffrey F. 
Published: April 2011

ABSTRACTBio-assembly strategies may allow formation of high-density nano-electronic architectures possessing unique electronic properties. These bio-nanomaterial hybrids should exhibit bio- compatibility and bio-viability. Therefore, contingencies of maintaining tertiary structure in the presence of nanometer-sized particles are a potential fatal flaw in bio-scaffolded assemblies. In this manuscript we investigate the assembly of bio-scaffolded nanomaterial constructs, specifically polypeptides, while probing the issue of bio-compatibility and viability by TEM imaging.
Atomistic Study of Strain Profiles in Semiconductor Quantum Dot Structures
Authors: Shintani K. , Sugii H. , Kikuchi Y. , Kobayashi M. 
Published: April 2011

ABSTRACTThe minimum energy atomic configurations of stacked GaAs/InAs/GaAs quantum dot structures are calculated by using the conjugate gradient energy minimization with the Stillinger-Weber potentials. The islands are assumed to be either of pyramidal shape or of trapezoidal shape. The numerical results for the five-layer stacked structures show that the normal strains exhibit stepwise up-and-down profiles through the vertical centerlines of the islands and intermediate layers. Next, the molecular dynamics method with the Tersoff potential is applied to single Ge/Si and Si/Ge/Si structures with pyramidal islands in order to investigate the effect of temperature. It is found that there is a considerable difference between the normal strain in the direction perpendicular to the island base obtained by the conjugate gradient minimization with the Stillinger-Weber potential and that obtained by the molecular dynamics method at 800 K.
Irreversible Structural Transformation of five fold i-AlPdMn Quasicrystals after Ion Bombardment and Annealing
Authors: Schmithüsen F. , Cappello G. , Decossas S. , Torricelli G. , Lee T.-L. , Boissieu M. de , Calvayrac Y. , Lograsso T. , Comin F. , Chevrier J. 
Published: April 2011

AbstractFive fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses [1]. Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result [2]. We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers.The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained.This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns).