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  • American Institute of Physics (AIP)  (219)
  • 2015-2019  (36)
  • 2010-2014  (9)
  • 1995-1999  (174)
  • 1
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    Structural and electronic properties of GaN nanowires with embedded InxGa1−xN nanodisks (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-07-16
    Description: In the present study, the effects of various types of strain and indium concentration on the total energy and optoelectronic properties of GaN nanowires (NWs) with embedded In x Ga 1− x N nanodisks (NDs) are examined. In particular, the bi-axial, hydrostatic, and uniaxial strain states of the embedded In x Ga 1− x N NDs are investigated for multiple In concentrations. Density functional theory is employed to calculate the band structure of the NWs. The theoretical analysis finds that the supercell-size-dependent characteristics calculated for our 972-atom NW models are very close to the infinite supercell-size limit. It is established that the embedded In x Ga 1− x N NDs do not induce deep states in the band gap of the NWs. A bowing parameter of 1.82 eV is derived from our analysis in the quadratic Vegard's formula for the band gaps at the various In concentrations of the investigated In x Ga 1− x N NDs in GaN NW structures. It is concluded that up to ∼10% of In, the hydrostatic strain state is competitive with the bi-axial due to the radial absorption of the strain on the surfaces. Above this value, the dominant strain state is the bi-axial one. Thus, hydrostatic and bi-axial strain components coexist in the embedded NDs, and they are of different physical origin. The bi-axial strain comes from growth on lattice mismatched substrates, while the hydrostatic strain originates from the lateral relaxation of the surfaces.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-17
    Description: We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
    Electronic Resource
    Electronic Resource
    Two-temperature relaxation in nonideal partially ionized plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1241-1249 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evolution equations for the coupled relaxation of densities and temperatures for the components in nonideal partially ionized plasmas are given. In these equations many-body effects, such as screening, self-energy, and lowering of the binding energy, are included. The coupled equations are solved numerically for a hydrogen plasma consisting of electrons, protons, and atoms. Impact ionization, three-body recombination, and elastic processes are taken into account. Thermal relaxation times are determined and the results are compared with those from the literature. The influence of many-body effects on the evolution process are discussed. In some cases, a significantly increased lifetime of the two-temperature regime is found. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871748
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  • 4
    Electronic Resource
    Electronic Resource
    Relaxation of temperature and chemical composition in nonideal plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3214-3221 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rate equations for the coupled evolution of density and temperature in nonideal partially ionized plasmas are presented. The equations are derived from generalized quantum kinetic equations that include many-particle effects, such as screening, self-energy and lowering of the binding energy. The equations are solved for a three-component plasma. The influence of many-body effects on the density–temperature relaxation is demonstrated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871152
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  • 5
    Electronic Resource
    Electronic Resource
    Domain structure and anisotropy of exchange coupled Co/Cr/Fe multilayers (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4531-4531 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the magnetic properties of Co/Cr/Fe multilayers by means of magneto-optic methods. These multilayers are of special interest because they combine different anisotropies and exchange coupling through the nonmagnetic Cr-spacer layer which was found to oscillate from ferromagnetic to antiferromagnetic coupling. The samples were grown by MBE methods on MgO(100) substrates at temperatures of about 300 °C. The fourfold crystalline symmetry is also obtained in the magnetic easy axis structure of Fe and Co. From the results of magneto-optic Kerr hysteresis loops we were able to distinguish between crystalline anisotropy and exchange coupling contributions. Additional monitoring of the domain structure by applying longitudinal Kerr microscopy was necessary to identify the regime were magnetization reversal occurs via domain wall motion or coherent rotation of the magnetization of the entire layer, respectively. From these results we were able to perform numerical simulations of the micromagnetic properties of trilayer samples. We discuss the results in terms of bilinear and biquadratic coupling. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361713
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  • 6
    Electronic Resource
    Electronic Resource
    Hole-trapping sites and the mechanism of the photostimulated luminescence of the x-ray storage phosphor RbI:Tl+ (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2430-2435 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Radiation damage centers generated by x irradiation at 80 and 300 K in the storage phosphor RbI:Tl+ were investigated with optically detected magnetic resonance and optical measurements. It is shown that the intensity of the photostimulated luminescence depends on the concentration of Tl2+ centers. Bleaching into any of the seven identified Tl2+ absorption bands destroys the Tl2+ centers and leads to a Tl+ emission as well as to VK centers. Proportionally to photodestruction of Tl2+ centers, the photostimulated luminescence is decreased. The traps for information storage in RbI:Tl+ are F centers and Tl2+ centers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363078
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  • 7
    Electronic Resource
    Electronic Resource
    Structural and magnetic studies of FexCo1−x(001) alloy films on MgO(001) substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1055-1060 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin epitaxial FexCo1−x alloy films sputtered on MgO(001) substrates were studied by x-ray scattering and by the magneto-optical Kerr effect in order to investigate the structural phase stability induced by the substrate and to relate the magnetic properties to the alloy film structure. Alloy films with a thickness of about 20 nm and concentrations from x=1 to x=0.3 exhibit a bcc (001) growth with the in-plane [100] axis parallel to the MgO[110] axis. For pure Co (x=0) a fcc (001) structure with the Co[100] axis parallel to the MgO[100] axis was obtained. For x=0.15 no out-of-plane or in-plane Bragg peak could be observed, possibly due to the bcc-fcc structural phase transition. Kerr rotation angles in saturation as a function of x reveal a shape similar to the Slater–Pauling curve. Magnetic hysteresis measurements reveal a fourfold anisotropy with easy axes parallel to the FexCo1−x[100] crystal axis for 1≥x≥0.8, and parallel to the FexCo1−x[110] crystal axis for 0.7≥x≥0.3. In pure Co the easy axis lies parallel to the fcc-Co[110] crystal axis. Finally, for x=0.28 a step in the magnetic hysteresis in the FexCo1−x[11¯0] direction indicates an overlap of a fourfold and twofold magnetic anisotropy. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358965
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of the heterointerface on the spin splitting in modulation doped InxGa1−xAs/InP quantum wells for B→0 (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 4324-4333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin splitting of conduction band electrons in In0.53Ga0.47As/In0.77Ga0.23As/InP heterostructures due to spin-orbit coupling is studied by performing Shubnikov–de Haas measurements on nongated and gated Hall bars. From an analysis of the beating pattern in the Shubnikov–de Haas oscillations, the spin-orbit coupling constant is determined. For a symmetric sample no beating pattern and thus no spin splitting is observed. This demonstrates that the k3 contribution to the spin-orbit coupling constant can be neglected. By applying an envelope function theory it is shown that the major contribution to the Rashba spin-orbit coupling originates from the band offset at the interface of the quantum well. Using gated Hall bar structures it is possible to alter the spin-orbit coupling by application of an appropriate gate voltage. A more negative gate voltage leads to a more pronounced asymmetry of the quantum well, which gives rise to a stronger spin-orbit coupling. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367192
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  • 9
    Electronic Resource
    Electronic Resource
    Field mapping characterization for axially magnetized, superconducting cylinders in the remanent critical state: theory and experiment (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3035-3041 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on the Bean model with a constant critical current density jc, novel and very precise, analytical approximations for the axial induction component Bz(r) inside and outside of a finite, axially magnetized, circular cylinder with arbitrary aspect ratio in the fully penetrated, remanent critical state are presented. Starting from any mapped field profile the possibility to determine the material parameter jc by means of a global optimum fit procedure is demonstrated. Some characteristic results for melt-textured yttrium barium copper oxide material are outlined. We found that jc determined by vibrating sample magnetometry (VSM) exceeds that from mapping at least by about 50%. This systematic discrepancy is discussed on the basis of two independent effects resulting in a local, space-dependent critical current density: the B-dependence of jc and material inhomogeneities. The first effect becomes important for sample radii in the 1-cm-range, although the Bz-profile remains axially symmetric and well fitted by the Bean model. The second one may lead to asymmetric Bz-profile deformations connected with a decreasing fitting significance. For the first and second effect we estimate the considerable ratio of the absolute maximum to absolute minimum of the local, critical current density of 2 and 4, respectively, which explains the observed discrepancies between the effective jc from mapping and VSM measurements. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366141
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  • 10
    Electronic Resource
    Electronic Resource
    High-sensitivity quantitative Kelvin probe microscopy by noncontact ultra-high-vacuum atomic force microscopy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 286-288 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present quantitative measurements of the work function of semiconductor and metal surfaces prepared in ultrahigh vacuum (UHV) using a combination of UHV noncontact atomic force microscopy and Kelvin probe force microscopy. High energetic and lateral resolution is achieved by using the second resonance frequency of the cantilever to measure the electrostatic forces, while the first resonance frequency is used to simultaneously obtain topographic images by the frequency modulation technique. Spatially resolved work-function measurements reveal a reduced work function in the vicinity of steps on highly oriented pyrolytic graphite. On the GaAs(110) surface it could be demonstrated that defect states in the forbidden band gap cause a local pinning of the Fermi level along monolayer steps. On p-WSe2(0001) work-function variations due to the Coulomb potential of single dopant sites were resolved. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124357
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