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1 Liu, FengTuning nucleation density of metal island with charge doping of graphene substrateWe have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found ...2014-01-01
2 Shetty, Dinesh K.On the effect of birefringence on light transmission in Polycrystalline Magnesium FluorideLight transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot-pressed billets in argon atmosphere at temperatures ranging from 600 to 800°C for 1 hour. The grain-size and grain-orie...2014-01-01
3 Liu, FengSd2 graphene: kagome band in a hexagonal latticeGraphene, made of sp2 hybridized carbon, is characterized with a Dirac band, representative of its underlying 2D hexagonal lattice. The fundamental understanding of graphene has recently spurred a surge in the search for 2D topological quantum phases in solid-state materials. Here, we propose a new ...2014-01-01
4 Tiwari, AshutoshTb2O3 thin films: An alternative candidate for high-k dielectric applicationsWe are reporting the growth and structural, optical, and dielectric properties of Tb2O3, a relatively unexplored high-k dielectric material. A pulsed-laser deposition technique was used to grow Tb2O3 thin-films on four different substrates: Si(100), SrTiO3(100), LaAlO3(100), and MgO(100). High resol...2014-01-01
5 Scarpulla, MichaelTe-rich CdTe surface by pulsed UV laser treatment for ohmic back contact formationPulsed UV laser treatments have recently been applied to polycrystalline CdTe solar cells to create an ohmic back contact. In this work, we investigate the surface stoichiometry variations produced by pulsed laser excitation using X-ray photoelectron spectroscopy (XPS). These results reveal surfaces...2014-01-01
6 Scarpulla, MichaelTemperature dependence of equivalent circuit parameters used to analyze admittance spectroscopy and application to CZTSe devicesWe present a device physics and equivalent circuit model for admittance spectroscopy of CZTSe based photovoltaic devices. The experimental variations of the capacitance and conductance in the depletion width are reproduced for state of the art coevaporated CZTSe devices. We will show that simple Arr...2014-01-01
7 Scarpulla, MichaelThe importance of Se partial pressure in the laser annealing of CuInSe2 electrodeposited precursorsOne method for producing CuInSe2 (CISe) absorber layers is electrodeposition followed by annealing. Replacing the commonly used furnace annealing step with a laser can reduce annealing times by 2-3 orders of magnitude: from 30 minutes to 1 s. However, laser processing has, to date, not resulted in a...2014-01-01
8 Tiwari, AshutoshShape of the Hanle curve in spin-transport structures in the presence of an ac driveResistance between two ferromagnetic electrodes coupled to a normal channel depends on their relative magnetizations. The spin-dependent component, R, of the resistance changes with magnetic field, B, normal to the directions of magnetizations. In the field of spin transport, this change, R(B), orig...2014-01-01
9 Liu, FengPrediction of a Dirac state in monolayer TiB2We predict the existence of a Dirac state in a monolayer TiB2 sheet (m-TiB2), a two-dimensionalmetal diboride, based on first-principles calculations. The band structure of m-TiB2 is found to be characterized with anisotropic Dirac cones with the largest Fermi velocity of 0.57 × 106 m/s, which is a...2014-01-01
10 Liu, FengGiant room-temperature spin caloritronics in spin-semiconducting graphene nanoribbonsSpin caloritronics refers to generating spin current by thermal gradient. Here we report a theoretical study demonstrating giant spin caloritronic effects in a new class of materials, called spin semiconductors, which are characterized with a "spin gap," the energy gap between spin-up and -down chan...2014-01-01
11 Liu, FengEpitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface : The substrate orbital filtering effectFormation of topological quantum phase on conventional semiconductor surface is of both scientific and technological interest. Here, we demonstrate epitaxial growth of 2D topological insulator, i.e. quantum spin Hall (QSH) state, on Si(111) surface with a large energy gap, based on first-principles ...2014-01-01
12 Tiwari, AshutoshManifestation of two-channel nonlocal spin transport in the shapes of Hanle curvesThe dynamics of charge-density fluctuations in a system of two tunnel-coupled wires contains two diffusion modes with dispersion iω = Dq2 and iω = Dq2 + 2τt, where D is the diffusion coefficient and τt is the tunneling time between the wires. The dispersion of corresponding spin-density modes de...2014-01-01
13 Liu, FengElectrochemical measurements on cells, I: Simulation of potential distribution with an embedded probeMeasurements of electric potential in electrochemical devices such as solid oxide fuel cells (SOFC) or solid oxide electrolyzer cells (SOEC) are often made by placing a reference electrode on the surface. Measurement of electric potential with embedded electrodes (probes) has also been reported [1]....2013-01-01
14 Liu, FengExceptional optoelectronic properties of hydrogenated bilayer siliceneSilicon is arguably the best electronic material, but it is not a good optoelectronic material. By employing first-principles calculations and the cluster-expansion approach, we discover that hydrogenated bilayer silicene (BS) shows promising potential as a new kind of optoelectronic material. Most ...2014-01-01
15 Liu, FengExotic electronic states in the world of flat bands: from theory to materialIt has long been noticed that special lattices contain single-electron at bands (FB) without any dispersion. Since the kinetic energy of electrons is quenched in the FB, this highly degenerate energy level becomes an ideal platform to achieve strongly correlated electronic states, such as magnetism,...2014-01-01
16 Liu, FengUnderstanding graphene production by ionic surfactant exfoliation: a molecular dynamics simulation studyWe have simulated sodium dodecyl sulfate (SDS) surfactant/waterþbilayer graphene mixture system to investigate two mechanisms of graphene exfoliation: changing the interlayer distance and sliding away the relative distance. By calculating the total energy as a function of the interlayer (sliding-aw...2014-01-01
17 Scarpulla, MichaelInvestigation of combinatorial coevaporated thin film Cu 2ZnSnS4 (II): Beneficial cation arrangement in Cu-rich growthCu2ZnSn(S,Se)4 (CZTSSe) is an earth-abundant semiconductor with potential for economical photovoltaic power generation at terawatt scales. In this work, we use Raman scattering to investigate phase coexistence in combinatorial CZTS thin films grown at 325 or 470 C. The surface of the samples grown a...2014-01-01
18 Scarpulla, MichaelInvestigation of combinatorial coevaporated thin film Cu 2ZnSnS4. I. Temperature effect, crystalline phases, morphology, and photoluminescenceCu2ZnSnS4 is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 C) and high (475 C) temperatures. Film...2014-01-01
19 Scarpulla, MichaelSurface stoichiometry of pulsed ultraviolet laser treated polycrystalline CdTeThe effects of nanosecond pulsed ultraviolet laser annealing on the surface stoichiometry of close-space sublimated polycrystalline thin films are investigated using angle-resolved x-ray photoemission spectroscopy (XPS). The raw data suggest the formation of a Cd-rich surface layer, but this is coun...2014-01-01
20 Tiwari, AshutoshOxides for spintronics: a review of engineered materials for spin injectionIn this article we have reviewed the role of oxides in spintronics research, and specifically how these materials stand to further improve the efficiencies and capabilities of spin injection for active spintronic device development. The use of oxides in spintronics is advantageous in that they are s...2014-01-01
21 Liu, FengOrbit- and atom-resolved spin textures of intrinsic, extrinsic, and hybridized Dirac cone statesCombining first-principles calculations and spin- and angle-resolved photoemission spectroscopy measurements, we identify the helical spin textures for three different Dirac cone states in the interfaced systems of a two-dimensional (2D) topological insulator (TI) of a Bi(111) bilayer and a three-di...2014-01-01
22 Scarpulla, MichaelEffects of sodium on electrical properties in Cu2ZnSnS4 single crystalWe have studied the effect of sodium on the electrical properties of Cu2ZnSnS4 (CZTS) single crystal by using temperature dependence of Hall effect measurement. The sodium substitution on the cation site in CZTS is observed from the increasing of unit-cell size by powder X-ray diffraction. Sodium in...2014-01-01
23 Scarpulla, MichaelPulsed laser induced ohmic back contact in CdTe solar cellsCreating an ohmic back contact has long been a problem for making efficient CdTe solar cells. Current devices utilize some combination of preferential chemical etching, buffer layer, and Cu doping with additional cost, time, and complexity added for each step. In this Letter, these processes are esc...2014-01-01
24 Tiwari, AshutoshObservation of the inverse spin hall effect in ZnO thin films: an all-electrical approach to spin injection and detectionThe inverse spin Hall effect (ISHE) is a newly discovered, quantum mechanical phenomenon where an applied spin current results in the generation of an electrical voltage in the transverse direction. It is anticipated that the ISHE can provide a more simple way of measuring spin currents in spintroni...2014-01-01
25 Liu, FengA three-layer-mesh bridging domain for coupled atomistic-continuum simulations at finite temperature: formulation and testingAlthough concurrent multiscale methods have been well developed for zero-temperature simulations, improvements are needed to meet challenges pertaining to finite-temperature simulations. Bridging domain method (BDM) is one of the most efficient and widely-used multiscale atomistic-continuum techniqu...2014-01-01
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