UScholar Works
 
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CreatorTitleDescriptionSubjectDate
151 Scarpulla, MichaelEffects of pressure on the band structure of highly mismatched Zn1-yMnyOxTe1-x alloysWe report photomodulation spectroscopy measurements of the pressure dependence of the optical transition in Zn12yMnyOxTe1-x alloys that is associated with the lowest Ѓ conduction band (termed E2 subband). The pressure-induced energy shift of the E2 transition is nonlinear and much weaker as compare...Highly mismatched alloys; Zinc telluride; Anticrossing2004
152 Scarpulla, MichaelSynthesis and optical properties of II-O-VI highly mismatched alloysWe have synthesized ternary and quaternary diluted II-VI oxides using the combination of O ion implantation and pulsed laser melting. CdOxTe12x thin films with x up to 0.015, and the energy gap reduced by 150 meV were formed by O1-implantation in CdTe followed by pulsed laser melting. Quaternary Cd0...Highly mismatched alloys; Cadmium telluride; Zinc telluride; Thermal annealing; Anticrossing; Photomodulation spectroscopy2004
153 Stringfellow, Gerald B.; Rieth, Loren W.Effects of Br and Cl on organometallic vapor phase epitaxial growth and ordering in GaInPCuPt ordering in GaInP has significant effects on the electrical and optical properties. In fact, band gap reductions as large as 160 meV are potentially useful for devices. Thus, control of ordering is important. This has led to the investigation of surfactants that affect the surface processes d...Band gap reductions; Surfactants; Surface processes2004
154 Smith, Grant D.; Bedrov, DmitroNMR experiments and molecular dynamics simulations of the segmental dynamics of polystyreneWe have performed NMR spin?lattice relaxation experiments and molecular dynamics (MD) computer simulations on atactic polystyrene (a-PS). The segmental correlation times of three different molecular weight a-PS (Mn = 1600, 2100, 10 900 g/mol) were extracted from NMR by measuring the 2H spin?lattice ...2004
155 Liu, FengLocal strain-mediated chemical potential control of quantum dot self-organization in heteroepitaxyFrom observations of self-assembly of Ge quantum dots directed by substrate morphology, we propose the concept of control of ordering in heteroepitaxy by a local strain-mediated surface chemical potential. Using quite simple lithography, we demonstrate directed quantum dot ordering. The strain part ...Self-organization; Heteroepitaxy; Chemical potential control; Ge quantum dots2004-01
156 Liu, FengGeometric constant defining shape transitions of carbon nanotubes under pressureWe demonstrate that when a single-walled carbon nanotube is under pressure it undergoes a series of shape transitions, first transforming from a circle to an oval and then from an oval to a peanut. Most remarkably, the ratio of the area of the tube cross sections at the second transition over that ...Geometric constant; Shape transitions; Carbon nanotubes; Pressure2004-03
157 Liu, FengComputational designing of carbon nanotube electromechanical pressure sensorsWe investigate electronic transport properties of single-walled carbon nanotubes (SWNT's) under hydrostatic pressure, using first-principles quantum transport calculations aided by molecular-dynamics simulation and continuum mechanics analysis. We demonstrate a pressure-induced metal-to-semiconduc...Carbon nanotubes; Computational designing; Pressure sensors; Electronic transport2004-04
158 Liu, FengSelf-organized quantum-wire lattice via step flow growth of a short-period superlatticeWe develop a theoretical model for step flow growth of multilayer films, taking into account the interlayer step-step interaction induced by misfit strain.We apply the model to simulate the growth of strain-compensated short-period superlattices. Step-bunch ordering improves in successive layers, le...Quantum-wire lattice; Short-period superlattice; Step flow growth2004-06
159 Bedrov, Dmitro; Smith, Grant D.Anomalous pressure dependence of the structure factor in 1,4-polybutadiene melts: a molecular dynamics simulation studyNeutron scattering has shown the first diffraction peak in the structure factor of a 1,4-polybutadiene melt under compression to move to larger q values as expected but to decrease significantly in intensity. Simulations reveal that this behavior does not result from loss of structure in the polymer...Polymer melts; 1, 4-polybutadiene melts; Pressure; Structure factor2004-07
160 Liu, FengCoulomb sink: a novel Coulomb effect on coarsening of metal nanoclusters on semiconductor surfacesWe propose the concept of a ‘‘Coulomb sink'' to elucidate the effect of Coulomb charging on coarsening of metal mesas grown on semiconductor surfaces.We show that a charged mesa, due to its reduced chemical potential, acts as a Coulomb sink and grows at the expense of neighboring neutral mesas. ...Coulomb sink; Coulomb effect; Metal nanoclusters; Semiconductor surface; Pb mesas2004-09
161 Liu, FengStrain effect on adatom binding and diffusion in homo- and heteroepitaxies of Si and Ge on (001) SurfacesStrain dependence of adatom binding energies and diffusion barriers in homo- and heteroepitaxies of Si and Ge on s001d surface has been studied using first-principles calculations. In general, Si adatom binding energies and diffusion barriers are larger on Sis001d and Ges001d surfaces than a Ge ada...Strain effect; Adatom binding; Adatom diffusion; Adatoms; Heteroepitaxies; Homoepitaxies; (001) surfaces; Si; Ge2004-10
162 Liu, FengPressure-induced hard-to-soft transition of a single carbon nanotubeWe demonstrate a hydrostatic pressure-induced hard-to-soft transition of an isolated single wall carbon nanotube, using classical and ab initio constant-pressure molecular-dynamics simulations and continuum elastic theory analysis. At low pressure, the carbon tube is hard. Above a critical pressur...Carbon nanotubes; Hard-to-soft transition2004-10
163 Liu, FengTheory of equilibrium shape of an anisotropically strained island: thermodynamic limits for growth of nanowiresUsing continuum elastic theory, we show that strain anisotropy removes the shape instability existing for an isotropically strained island. An anistropically strained island has always an anisotropic shape, elongating along the less-strained direction and adopting a narrow width in the more-strain...Strained islands; Equilibrium shape; Growth; Thermodynamic limits2004-11
164 Liu, FengMechanical stability of ultrathin Ge/Si film on SiO2: the effect of Si/SiO2 interfaceWe perform two-dimensional linear elastic finite element analysis to investigate the mechanical stability of ultrathin Ge/Si film grown on or bonded to SiO2, using imperfect interface elements between Si and SiO2 to model Si/SiO2 interfacial slippage. We demonstrate that the overall composite film i...Ultrathin films; Si/SiO2 interface; Mechanical stability2005
165 Scarpulla, MichaelFabrication of GaNxAs1-x quantum structures by focused ion beam patterningA novel approach to the fabrication of GaNxAs1-x quantum dots and wires via ion beam patterning is presented. Photomodulated reflectance spectra confirm that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by amorphization through ion implantation followed by regrowth upon r...Gallium arsenide; Quantum dots; Quantum wires; Thermal annealing2005
166 Liu, FengPattern formation on silicon-on-insulatorThe strain driven self-assembly of faceted Ge nanocrystals during epitaxy on Si(001) to form quantum dots (QDs) is by now well known. We have also recently provided an understanding of the thermodynamic driving force for directed assembly of QDs on bulk Si (extendable to other QD systems) based on ...Pattern formation; Silicon-on-insulator; Strain driven; Faceted Ge nanocrystals; Si(001); Directed assembly2005
167 Tiwari, AshutoshEpitaxial growth and properties of Zn1-xVxO diluted magnetic semiconductor thin filmsHere we report systematic studies on the epitaxial growth and properties of Zn1−xVxO[x=0.001-0.2] thin films deposited onto sapphire c-plane single crystals. The thin films were deposited using pulsed laser deposition technique and were found to be epitaxial in nature. X-ray diffraction and high ...ZnO; Vanadium2005
168 Liu, FengComputational R&D for industrial applicationsRecent advances in high-speed supercomputer and computational algorithms have brought us into a new era of computational materials science. These advances make it possible to investigate many existing materials systems that were previously considered intractable and also predict and design novel mat...Computational materials science2005
169 Scarpulla, MichaelEffect of film thickness on the incorporation of Mn interstitials in Ga1-xMnxAsWe have investigated the effect of film thickness on the distribution of Mn atoms at various lattice sites in Ga1−xMnxAs thin films. We find that the growth surface acts as a sink facilitating the outdiffusion of Mn interstitials sMnId, and thus reducing its concentration in the film. The outdiffu...Interstitials; Gallium arsenide2005
170 Tiwari, AshutoshEpitaxial growth and properties of MoOx(2We report the growth of epitaxial molybdenum oxide (MoOx,2<x<2.75) films on c plane of sapphire substrate using pulsed laser deposition in oxygen environment. The structure was characterized using x-ray diffraction, high resolution transmission electron microscopy and x-ray photoelectron spectroscop...Epitaxy; MoO2005
171 Bedrov, Dmitro; Smith, Grant D.Equilibrium sampling of self-associating polymer solutions: a parallel selective tempering approachWe present a novel simulation algorithm based on tempering a fraction of relaxation-limiting interactions to accelerate the process of obtaining uncorrelated equilibrium configurations of self-associating polymer solutions. This approach consists of tempering (turning off) the attractive interactio...Equilibrium sampling; Self-associating systems; Parallel selective tempering2005
172 Scarpulla, MichaelCarrier concentration dependencies of magnetization & transport in Ga1-xMnxAs1-yTeyWe have investigated the transport and magnetization characteristics of Ga1-xMnxAs intentionally compensated with shallow Te donors. Using ion implantation followed by pulsed-laser melting, we vary the Te compensation and drive the system through a metal-insulator transition (MIT). This MIT is assoc...Gallium arsenide; Ferromagnetic semiconductors; Magnetization; Resistivity2005
173 Liu, FengTowards quantitative understanding of formation and stability of Ge hut islands on Si(001)We analyze Ge hut island formation on Si(001), using first-principles calculations of energies, stresses, and their strain dependence of Ge/Si(105) and Ge/Si(001) surfaces combined with continuum modeling. We give a quantitative assessment on strain stabilization of Ge(105) facets, estimate the cr...Ge hut islands; Si(001); First-principles calculations; Heteroepitaxial growth2005-05
174 Liu, FengBending of nanoscale ultrathin substrates by growth of strained thin films and islandsMechanical bending is ubiquitous in heteroepitaxial growth of thin films where the strained growing film applies effectively an "external" stress to bend the substrate. Conventionally, when the deposited film is much thinner than the substrate, the bending increases linearly with increasing film th...Nanoscale ultrathin substrates; Strained thin films; Islands; Heteroepitaxial growth; Si substrate; Ge film2005-08
175 Liu, FengFirst-principles study of strain stabilization of Ge(105) facet on Si(001)Using the first-principles total energy method, we calculate surface energies, surface stresses, and their strain dependence of the Ge-covered Si (001) and (105) surfaces. The surface energy of the Si(105) surface is shown to be higher than that of Si(001), but it can be reduced by the Ge deposition...First-principles calculation; Strain stabilization; Ge(105); Si(001); Strained thin films; Epitaxial growth2005-09
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