bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomistic Studies of Plasticity in Nanophase Metals
Authors: Swygenhoven H. Van , Derlet P. , Caro A. , Farkas D. , Caturla M. , Rubia T. Díaz de la 
Published: April 2011

ABSTRACTMolecular dynamics computer simulation of nanocrystalline Ni and Cu with mean grain sizes ranging from 5 to 20 nm show that grain boundaries in nanocrystalline metals have structures similar to most grain boundaries found in conventional polycrystalline materials. Moreover, the excess enthalpy density in grain boundaries and triple junctions appears to be independent of grain in both, computer generated and experimental measured samples. Simulations of deformation under constant uniaxial stress demonstrate a change in deformation mechanism as function of grain size: at the smallest grain sizes all deformation is accommodated in the grain boundaries, at higher grain sizes, intragrain deformation is observed
Calculating Surface Energies of Lead Magnesium Niobate Using Density Functional Theory
Authors: Kavarnos George , Richards Roger 
Published: April 2011

ABSTRACTComputations involving density functional theory have been performed on lead magnesium niobate (PMN) single crystal models in an effort to calculate their surface energies, which are believed to play a role in brittle fracture mechanisms. To establish credibility of this approach, test calculations were performed on MgO and SiC single crystal models. The surface energy of MgO was determined to be 1.2 J/m2, which is in close agreement with the experimental value. Similarly, the value for SiC, 8.03 J/m2, supported a level of confidence with this methodology. Surface energies were calculated for several simple perovskites and several PMN models. The calculated values suggest that changes in the A-site ion of PMN do not result in any significant changes in the surface energies.
Atomic Scale Modelling of Supported and Assembled Nanoparticles
Authors: Zhurkin E. , Hou M. , Swygenhoven H.Van , Pauwels B. , Yandouzi M. , Schryvers D. , Tendeloo G.Van , Lievens P. , Verschoren G. , Kuriplach J. , Peteghem S.Van , Segers D. , Dauwe C. 
Published: April 2011

ABSTRACTThe properties of elemental and bimetallic free, supported and assembled nanoclusters are modeled at the atomic scale and the models are discussed on the basis of experimental observations. This way, the memory of some free cluster properties in nanostructured materials may be evaluated.The combination of molecular statics with High Resolution Transmission Electron Microscopy (HRTEM) allows to predict fine detail of the lattice relaxation of a truncated octahedral gold cluster deposited on MgO. Metropolis Monte Carlo (MC) predicts that a lattice mismatch may contribute to disordering in deposited Cu3Au nanoclusters. In both Cu-Au and Ni-Al free clusters, offset of equilibrium stoichiometry may result in segregation of Au or Al at the cluster surface. An ordered stoichiometric core is surrounded by a disordered mantle where the excess species resides. Different modeling methods predict different nanometer scale textures.Therefore, cluster assembled Ni3Al alloys formed by condensation and pressing are modeled in two different ways. Both make use of a combination of Molecular Dynamics and MC. Whatever the model nanostructure, the segregation properties of free clusters remain in the nanostructured material. This segregation is one possible cause that can inhibit the formation of a metastable martensitic phase as observed in bulk Ni-Al alloys.The occurrence of vacancy clusters and voids is hardly identified by HRTEM. On the other hand, their distribution and sizes are sensitive to the nanostructure modeling. Therefore, a new characterization method is developed, which combines positron lifetime spectroscopy with the calculation of positron lifetimes from selected areas of the model samples.
Site-Specific Attachment of Gold Nanoparticles to DNA Templates
Authors: Stevenson Karen A. , Muralidharan Govindarajan , Maya Leon , Wells Jack C. , Barhen Jacob 
Published: April 2011

AbstractDNA was used as a scaffold for the binding of gold nanoparticles using a standard chemical technique. A DNA template was designed with amino-modified thymines located every 3.7 nm, which would allow the attachment of the carboxylic acid functionalized gold nanoparticles. The gold particles were covalently bound to the amino groups on the DNA using standard 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) chemistry in the presence of a competitor to block excess gold binding sites. The products were analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM).
Crystallographic Description for Nanoparticle Asemblies – Application to Cadmium Selenide Clusters
Authors: Vasiliev A L , Aindow M , Lee J , Papadimitrakopoulos F , Jain F 
Published: April 2011

AbstractThe stacking sequence of several layers of self-assembled semiconducting CdSe nanoparticles has been investigated using transmission electron microscopy. FCC, HCP, saddle sites occupation and ring structures were found coexisting in the supercrystals formed by CdSe nanoparticles.
Nanoparticles of Polypyrrole and Their Effect on Mediating Li Ion Transport from Liquid Electrolyte to Cathode
Authors: Pang Yong , Chen Ningpine , Hong Liang 
Published: April 2011

AbsctractNano-scale particles of polypyrrole (PPy) have been synthesized by polymerizing the respect monomer in the presence of its substituted homologue with oxyethylene (POE) oligomers as the substitute groups. The polymerization was carried out by introducing an aqueous solution of oxidant into the tetrahydrofurane (THF) solution of the monomers. The particles obtained possess brush-like architectures in the dispersing medium, and their sizes in dry state fall into the range of 10 to 40 nm according to TEM analysis. When dispersed by a low content (< 0.1 wt %) in an aprotic organic solvent, the nanoparticles synthesized have been foundto affect the conduction of lithium ion. The effect is interpreted as a significant reduction in the electrical resistance at the electrode/electrolyte interface according to gain-phase impedance measurement.This has been attributed to the mediating role of the graft POE chains on the colloidal particles.
Purpose-Built Anisotropic Metal Oxide Nanomaterials
Authors: Vayssieres Lionel , Guo Jinghua , Nordgren Joseph 
Published: April 2011

ABSTRACTLarge arrays of perpendicularly oriented anisotropic nanoparticles of ferric oxyhydroxide (Akaganeite, β-FeOOH) and oxide (Hematite, α-Fe2O3) of typically 3-5 nm in diameter, self-assembled as bundles of about 50 nm in diameter and of up to 1 μm in length have been successfully grown onto polycrystalline substrates without template and/or surfactant by heteronucleation from an aqueous solution of ferric salts and their optical and electronic properties investigated.
Epitaxial Ferroelectric BaTiO3 Thin Films for Microphotonic Applications
Authors: Niu F. , Teren A.R. , Hoerman B.H. , Wessels B.W. 
Published: April 2011

AbstractEpitaxial ferroelectric BaTiO3 thin films have been developed as a material for microphotonics. Efforts have been directed toward developing these materials for thin film electro-optic modulators. Films were deposited by metalorganic chemical vapor deposition (MOCVD) on both MgO and silicon substrates. The electro-optic properties of the thin films were measured. For BaTiO3 thin films grown on (100) MgO substrates, the effective electro-optic coefficient, reff depended on the magnitude and direction of the electric field. Coefficients as high as 260 pm/V have been measured. Investigation of BaTiO3 films on silicon has been undertaken. Epitaxial BaTiO3 thin films were deposited by MOCVD on (100) MgO layers grown on silicon (100) substrates by metal-organic molecular beam epitaxy (MOMBE). The MgO serves as the low index optical cladding layer as well as an insulating layer. X-ray diffraction and transmission electron microscopy (TEM) indicated that BaTiO3 was epitaxial with an orientational relation given by BaTiO3 (100)//Si (100) and BaTiO3[011]//Si [011]. Polarization measurements indicated that the BaTiO3 epitaxial films on Si were in the ferroelectric state.
Enhanced Emission from a Light-Emitting Diode Modified by a Photonic Crystal
Authors: Erchak Alexei A. , Ripin Daniel J. , Fan Shanhui , Joannopoulos John D. , Ippen Erich P. , Petrich Gale S. , Kolodziejski Leslie A. 
Published: April 2011

AbstractEnhanced light output is observed from a light-emitting diode (LED) structure containing a two-dimensional (2D) photonic crystal. The capture of emitted light into planar waveguide modes reduces the extraction efficiency of LEDs. Here, 2D photonic crystals are utilized to: 1) enhance the extraction of light in the vertical direction from an LED and 2) enhance optical pumping by directly coupling light from a pump laser into the LED structure. Spatially and spectrally-resolved photoluminescence (PL) is used to characterize the enhancements. A 100-fold enhancement in extraction for a single wavelength into the vertical direction is obtained without the photonic crystal penetrating the active material.
Investigation of silicon carbide physical vapor transport growth on the C-terminated face of 6H seeds
Authors: Schulz D. , Doerschel J. , Irmscher K. , Rost H.-J. , Siche D. , Wollweber J. 
Published: April 2011

ABSTRACTSublimation growth of 6H-SiC has been studied with respect to surface morphology, growth temperature, supersaturation and growth rate. Growth was performed on the C-terminated face of 6H seeds mainly and for comparison also the Si-terminated face was used. Step bunching is observed dependent on different parameters and is strongly influenced by the seed orientation. The growth rate of 4H on the C-face is found to be higher than the rate of 6H grown on the Siface.
A New Sublimation Etching for Reproducible Growth of Epitaxial Layers of SiC on SiC Substrate in a CVD Reactor
Authors: Wang Rongjun , Bhat Ishwara , Chow Paul 
Published: April 2011

ABSTRACTWe have developed a new and simple method to etch SiC at relatively low temperature with very high rates. This method is particularly useful for cleaning the susceptor after growth. By employing this etching method to clean the susceptor prior to every growth run, we have greatly improved the reproducibility of SiC epitaxial growth and increased the lifetime of the susceptor. The method can also be used to etch SiC wafers at a very fast rate as an alternative to mechanical polishing. An etch rate of over 100μm/hr was obtained at 1600°C using this new method. The surfaces of the etched wafers were examined by atomic force microscope (AFM). Results of epitaxial growth using new etching method are presented.
Epitaxial Growth of SiC on Non-Typical Orientations and MOS Interfaces
Authors: Matsunami Hiroyuki , Kimoto Tsunenobu , Yano Hiroshi 
Published: April 2011

ABSTRACTHigh-quality 4H-SiC has been epitaxially grown on (1120) substrates by chemical vapor deposition. The physical properties of epilayers and MOS interfaces on both (1120) and off-axis (0001) substrates are elucidated. An unintentionally doped 4H-SiC epilayer on (1120) shows a donor concentration of 1×1014 cm−3 with a total trap concentration as low as 3.8×1012 cm−3. Inversion-type planar MOSFETs fabricated on 4H-SiC (1120) exhibit a high channel mobility of 96 cm2/Vs. The channel mobility decreases according to the T−2.2 dependence above 200K, indicating reduced Coulomb scattering and/or electron trapping. The superior MOS interface on (1120) originates from the much lower interface state density near the conduction band edge.
Characterization of Light Emission from 4H and 6H SiC MOSFETs
Authors: Macfarlane P. J. , Stahlbush R. E. 
Published: April 2011

ABSTRACTWhile SiC devices are an attractive alternative to Si in high power applications, interface trap densities measured in SiC-based MOSFETs are significantly larger than in Si-based ones. Here, we study SiC MOSFETs using both spatial images and spectral analysis of light emission due to electron-hole recombination. The light emission is produced by alternately driving the channel between accumulation and inversion using what is essentially a charge-pumping set-up. Emission is due to interface trap and bulk electron-hole recombination. The spatial imaging studies suggest that recombination occurs at both interface traps and bulk defects. Spectral studies of the emission indicate the presence of a narrow band centered at 425 nm and a broad band extending from approximately 500 to 800nm. The former we suggest is due to bulk recombination and the latter to interface trap recombination. The spectral studies of the 500 to 800 nm band are timed to separate light emitted during the inversion-to-accumulation transition from that emitted during the accumulation-to-inversion transition and visa versa. Comparisons of the emission spectra collected during these specific periods are consistent with a larger Dit in the upper half of the bandgap than the lower half in both 4H and 6H devices.
Effect of TMG Addition on the Epitaxial Growth of 3C-SiC on Si(100) and Si(111) Using Hexamethyldisilane
Authors: Lee Ki Hoon , Teker Kasif , Zhang Ming , Chung Juyong , Pirouz Pirouz 
Published: April 2011

ABSTRACTEpitaxial and crack-free 3C-SiC film was successfully grown on Si(100)/(111) by a one step process without separate nucleation or carbonization steps at a low temperature of 1200°C by MOVPE. The growth was achieved by using hexamethyldisilane (HMDS) with the addition of a small amount of trimethylgallium (TMG) (0.5 sccm) with dilute hydrogen (12% H2 + Ar) as a carrier gas. Without the addition of TMG during growth, epitaxial growth of SiC on Si was only possible at temperatures above 1300°C following a nucleation step at 1200∼1250°C. After growth, all the films were analyzed by using cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Nomarski differential interference microscopy (NDIM). It was observed by XPS that the SiC film contained only a small amount of Ga, which means the Ga component of TMG does not much accumulate in SiC, in spite of a relatively high ratio of TMG/HMDS. To investigate the effect of TMG flow rate, various amounts of TMG (0.5 - 5sccm) were added during SiC deposition. Below 0.5 sccm of TMG flow rate, the SiC film showed epitaxial growth, observed by TEM and XRD. However, with an increasing flow rate of TMG above 1 sccm, the XRD peak of 3C-SiC becomes smaller and slightly shifted. At 5 sccm, the film was polycrystalline possibly implying that the SiC lattice is being strained gradually with TMG addition. It is also observed by AFM that, at the initial stages of growth, nucleation is much facilitated with the addition of TMG. The deposition rate with the addition of TMG at 1200°C is about 650 nm/hr, which is much faster than the rate without TMG addition (480 nm/hr). Thus, it is believed that TMG addition has a positive effect on the nucleation and HMDS decomposition during deposition. Also, with the addition of a small amount of Ar+10%HCl during growth, one-step deposition was possible helped by stress release due to void formation at the SiC/Si interface.
Ab Initio Study of SiC/Metal Polar Interfaces: Relation Between Interface Structure and Schottky-Barrier Height
Authors: Tanaka Shingo , Kohyama Masanori 
Published: April 2011

ABSTRACTAb initio calculations of the polar interfaces between thin films of titanium and cubic silicon-carbide (SiC) have been performed by using the first-principles molecular dynamics method. Stable configurations, adhesive energies and Schottky-barrier height (SBH) for the Si-terminated and the C-terminated interfaces are obtained. The C-terminated interface has covalent C-Ti bonds, while the Si-terminated interface has shown metallic nature. Adhesive energy/SBH of the C-terminated interface is larger/smaller than that of the Si-terminated one, respectively. In order to examine a conventional SBH model, work functions of SiC slab with Si and with C surface and Ti slab have been calculated and SBHs have been estimated from the difference of work functions. In estimated SBHs between the interfaces, the relationship depend on the crystal orientation as (111) and (001).
Low Temperature (300°C) Formation of Thermodynamically Stable NiSi2 Contacts to SiC
Authors: Deeb C. , Kahn H. , Milhet X. , Zorman C. , Mehregany M. , Heuer A. H. 
Published: April 2011

ABSTRACTThermodynamically stable, low specific contact resistance electrical contacts to SiC are essential to the application of such devices in high power or high temperature applications. However, thermal budgets impose processing constraints due to interfacial reactions and dopant profiles during device fabrication. Nickel disilicide (NiSi2) is useful for metallization of SiC, as stable contacts can be formed on SiC by reacting a fugitive layer of amorphous silicon (a-Si) with sputtered nickel at 300°C. NiSi2 forms directly upon reacting nickel with a-Si; this is not the case when nickel is reacted with crystalline silicon, where more nickel-rich silicides form first. Specific contact resistances as low as 5.6×10−5 Ωcm2 have been measured using NiSi2 circular TLM contacts so formed on APCVD 3C-SiC thin films deposited on a silicon wafer.
Structural, optical and chemical characterization of 300°C, MeV ion implanted and 1700°C annealed 6H-SiC
Authors: Nipoti R. , Carnera A. , Mattei G. 
Published: April 2011

ABSTRACTThis work deals with the structural, optical and chemical characterization of ion implanted and annealed crystalline SiC. N+ or Al+ ions with various MeV energy and fluence values were implanted at 300°C in 6H-SiC wafers. These processes produced about 1 μm thick doping profiles characterized by a sequence of peaks and valleys across an average plateau value. The annealing process was done in a radio frequency furnace at 1700°C for 30 min in high purity Ar atmosphere. The hot implanted layers show the presence of a weak damage amount, whose profile was estimated by confocal micro-Raman measurements. The annealed samples, in spite of a good crystal recovery, showed the formation of secondary defects as inferred by the Rutherford Back Scattering-Channeling spectrometry. The relative magnitude and position of peaks and valleys in the doping profiles were preserved by the high temperature annealing but the annealed doping profile was displaced towards the surface with respect to the as-implanted profile as shown by the Secondary Ion Mass Spectrometry measurements. No material loss but material densification due to the reordering of the crystalline structure can explain the trend of the chemical profiles.
Interface Effects on the Raman Spectra of Si/3C-SiC Superlattices
Authors: Bezerra E. F. , Filho A. G. Souza , Filho J. Mendes , Lemos V. , Freire V. N. , Ikoma Y. , Watanabe F. , Motooka T. 
Published: April 2011

ABSTRACTTheoretical calculations are performed on the role of smooth interfaces in the Raman spectra of Si/3C-SiC superlattices. The dispersion relations were obtained using a linear chain model with the alloyed interface δ-(3C-SiC)0.5(Si)0.5 described in the virtual crystal approximation. A modified bond-polarizability model was used to calculate the Raman spectra. The main results are the enhancement of the Raman spectra and the appearance of new peaks in between those related to the Si quasi confined and the 3C-SiC-confined modes with increasing number δ?of interfacial monolayers (3C-SiC)0.5(Si)0.5. Some of the smooth interface related Raman peaks have intensity comparable with those of an abrupt Si/3C-SiC superlattice.
Heat and mass transfer modeling for a better knowledge of the large-area growth of homoepitaxial SiC by CVD
Authors: Pons Michel , Mezière Jerome , Dedulle Jean Marc , Kuan Stephane Wan Tang , Blanquet Elisabeth , Bernard Claude , Ferret Pierre , Cioccio Lea Di , Billon Thierry , Madar Roland 
Published: April 2011

ABSTRACTThe growth of thick epitaxial 4H-SiC layers with low defect density is an essential step for the fabrication of SiC based devices. Cold- and hot wall reactors using silane and propane diluted in hydrogen were used in this study. The typical growth temperature range is 1700–1900 K and total pressure range 10–100 kPa. The resulting epilayers exhibit low background doping, low defect density and good thickness uniformity. The main problem is that it is difficult with this first generation of reactors to ensure a constant temperature over large wafer. A 3D simulation approach of heat and mass transfer was used with three objectives. The first one is to have a visualization of the flow, temperature and gaseous species fields in the standard reactor. The second one is to propose solutions for the optimal control of the temperature field and the subsequent uniformity of the epilayers over large dimensions. The third one is to improve the kinetic databases in this temperature range which has been very little investigated.
Investigation of Factors Limiting the High Temperature Stability of W/WC/TaC/SiC Ohmic Contacts to n-type 6H-SiC
Authors: Jang T. , Odekirk B. , Porter L. M. 
Published: April 2011

ABSTRACTThe electrical properties and thermal stability of TaC ohmic contacts with W/WC overlayers were investigated on n-type 6H-SiC (0001) substrates. The specific contact resistance (SCR) was measured after annealing at 600 °C and 1000 °C for 50 ∼ 1000 h. The SCRs (3.0 ∼ 3.6 ×10−5 Ωcm2) of contacts annealed at 600 °C for 1000 h remained constant within the experimental error. Significant increases in the SCR were not observed until the samples were annealed at 1000 °C for several hundred hours.No reaction of the film with the SiC substrate was observed after annealing at 600 °C for 1000 h; however, atomic-scale reactions appeared to be concentrated adjacent to grain boundaries in the reacted film. From Auger depth profiles, it was found that W and WC reacted to form W2C on TaC after annealing.According to SIMS analysis, after annealing at 1000 °C for 600 h, small but measurable changes in the electrical characteristics were associated with O incorporation at the interface between TaC and SiC. Investigation of the W/WC/TaC/SiC interface by TEM indicated that a reaction between the metal layers had occurred, but there was no observed reaction with the SiC substrate. After annealing for 1000 h, substantial changes in the contacts were observed. The findings indicate that both oxidation and metallurgical reactions have important implications on the current operating limits for SiC high temperature devices.
Synthesis of Self-Assembled Metal-Oxide Nanostructures in a Diblock Copolymer Matrix and Integration onto Semiconductor Surfaces
Authors: Mulligan Robert F. , Iliadis Agis A. , Lee U. , Kofinas Peter 
Published: April 2011

ABSTRACTThe synthesis of self-assembled ZnO nanostructures at room temperature using a microphase separated diblock copolymer as a template is reported. Poly(norbornene) / poly(norbornene-dicarboxylic acid) diblock copolymers were synthesized using Ring Opening Metathesis Polymerization (ROMP). The polymers were dissolved and the solutions were doped with ZnCl2. Films were formed from this solution, and subsequently reacted with NH4OH. This converted the ZnCl2 into ZnO contained within the microphase-separated nanodomains of the block copolymer. Fourier Transform Infrared Spectroscopy verified the association of the metal to the second block of the polymer, and X-ray Photoelectron Spectroscopy verified the conversion of the salt to ZnO nanoclusters. The development of such ZnO - block copolymer nanocomposites is targeting the functionalization of nanostructures into device technologies.