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  • 1
    Electronic Resource
    Electronic Resource
    Production and evolution of composition, morphology, and luminescence of microcrystalline arsenic oxides produced during the anodic processing of (100) GaAs (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4997-5003 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs when exposed to a 7 V anodic bias in aqueous HCl, forms pitted structures from which visible photoluminescence has been observed. Previous work in our laboratory identified the source of the luminescence to be arsenic oxide microcrystals, formed during the electrochemical oxidation, which evolve in composition and morphology during the course of the anodic processing. The density and size of pits is dependent on the solution conditions as well as the applied potential program (stepped vs swept to 7 V. At early times (t〈30 min) the pits are composed of a mixture of small (∼1 μm) and larger (10's of μm) faceted microcrystals identified by x-ray photoelectron spectroscopy and energy-dispersive x-ray analysis to be a combination of As(III) and As(V) oxides. At longer times As(III) oxides predominate, and the smaller microcrystals are no longer observed, suggesting that the smaller microcrystals are As(V) oxide, and that they evolve chemically into As(III) oxide over the course of the oxidation. A suitable reaction pathway which explains the observed predominance of As(III) species is suggested. The luminescence properties of these electrochemically produced structures were investigated by near-field excitation. The luminescent properties evolve in parallel with the morphology and composition although the form of the spectrum is invariant in time and consistent with that obtained from bulk As2O3 and As2O5. The similarity of emission obtained from the two types of microcrystals suggests an impurity-related origin. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371470
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetoresistance and Hall effect of chromium dioxide epitaxial thin films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5585-5587 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial CrO2 thin films have been grown on TiO2(100) and Al2O3(0001) substrates by atmospheric pressure chemical vapor deposition. The films have a Curie temperature (Tc) of around 393 K with the ones grown on TiO2 exhibiting in-plane uniaxial magnetic anisotropy. They also display metallic characteristics, with room temperature resistivity of about 285 μΩ cm, dropping by about two orders of magnitude upon cooling down to 5 K. Magnetoresistance (MR) properties of the films have been measured with the magnetic field in the plane. For a field of 40 kOe, a positive transverse MR of about 25% at 5 K and a negative MR of about 7% at near Tc have been observed. In addition, Hall resistivity has been measured with magnetic field up to 40 kOe. A positive ordinary Hall effect is found at low temperatures, indicating the conduction carriers are holes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369807
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  • 3
    Electronic Resource
    Electronic Resource
    Theory of laser wakes in plasma channels (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 591-602 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these "quasi-modes" is studied by constructing and analytically continuing the causal Green's function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying frequencies. Characteristic decay rate is given by the mixing time τm, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels analytic expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873204
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  • 4
    Electronic Resource
    Electronic Resource
    An 18-cm-diam intense beam current broad beam ion source for surface modifications (abstract) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1217-1217 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large diameter intense beam current broad beam ion source used for surface modifications is described. It consists of a discharge chamber and a three-grid extraction system. The discharge chamber has two anodes (front and rear) and a specially designed cusped magnetic field is used for forming a large field free region in the chamber so that a very uniform and intense ion beam has been extracted from this source. Beam currents of more than 900 mA for hydrogen and 750 mA for argon at 2.5 kV extraction voltage have been obtained. The highest beam current density is over 2.5 mA/cm2, measured at a location 25 cm downstream of the source. The density uniformity changes from +5% to +15% over a 15-cm-diam circle. The feature and the performance of this source will be described in this paper. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146736
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  • 5
    Electronic Resource
    Electronic Resource
    State selection of O+(4So,2Do,2Po) using resonance dissociative charge transfer of He+(Ne+, Ar+)+O2 and radio frequency multipole ion guide techniques (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2871-2878 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By controlling the collision energies for dissociative charge transfer collisions of He+(Ne+,Ar+) +O2 in a rf octopole ion guide gas cell, and by applying appropriate effective ion trapping potentials to the rf octopole ion guide, we show that state-selected O+(4So), O+(2Do), and O+(2Po) reactant ion beams with high purities and usable intensities can be prepared for scattering experiments. This experimental scheme, which makes possible the enrichment of an ionic species with a lower kinetic energy distribution in a rf multipole ion guide, should be useful for state selection of other excited atomic ions by using appropriate dissociative charge transfer or dissociative photoionization processes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145571
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  • 6
    Electronic Resource
    Electronic Resource
    Electron beam evaporation broad beam metal ion source for material modifications : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 924-926 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a new type of electron beam evaporation intense beam current broad beam metal ion source. In this ion source, a focusing electron beam is used to bombard and vaporize the metal and other solid elements within the same chamber where the metal and solid element atoms are ionized by arc discharge. It can operate with gaseous and solid elements. Both pure or mixed ions with single or multiple charge states can also be extracted from this source. The performance and the characteristics of this source have tested. Ion beams of a series of elements, which include C, W, Ta, Mo, Cr, Ti, B, Cu, Ni, AI, Ar, N, etc., have been extracted, and the highest beam current is up to 90 mA. By using this ion beam bombardment, a good mixture between substrate and film was observed. Deposition rates as high as 25 A(ring)/s for Mo, 30 A(ring)/s for Ti, and 80 A(ring)/s for C have been obtained. The structure of the ion source and the experimental results will be presented in this paper. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146773
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  • 7
    Electronic Resource
    Electronic Resource
    Epitaxial La0.67Sr0.33MnO3 magnetic tunnel junctions : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5509-5511 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of a large magnetoresistance (83%) at low magnetic fields of tens of Oe at 4.2 K in the epitaxial trilayer junction structure, La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. The spin-polarization parameter of the manganite has been determined from the magnetoresistance value. The switching fields of the two magnetic layers were designed by using the magnetic shape anisotropy. By limiting the sweeping field in a low field range (∼100 Oe), we have achieved bistable resistive states at zero field, which is of potential interest for magnetoelectronic applications. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364585
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  • 8
    Electronic Resource
    Electronic Resource
    Temperature dependence of infrared photocurrent in Pb(Zr,Ti)O3 on YBa2Cu3O7−x (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4780-4783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) (001) thin films, integrated to high Tc superconducting YBa2Cu3O7−x (YBCO) films used as electrodes, have been studied for their photocurrent response and permittivity as a function of temperature. A stable photocurrent was observed to increase with increasing the temperature over the range of 25–350 °C. This increase was found to be strongly polarization dependent and due to the change of the pyroelectric coefficient of PZT thin film with temperature. The pyroelectric coefficient for a PZT sample was measured as ∼30 nC/cm2 K at room temperature, and ∼80 nC/cm2 K at 320 °C. The YBCO electrode showed a stable metallic resistance behavior in this temperature range. There was no detectable photocurrent from YBCO layer. No poling is required until 350 °C for the PZT/YBCO heterostructure detector because the PZT film is oriented when grown on c-axis oriented YBCO. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359825
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  • 9
    Electronic Resource
    Electronic Resource
    Optical and electrical investigation of semiconducting amorphous Si:P alloy thin films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 301-307 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements are reported on the infrared (IR) absorption, the optical band gap, and the dark conductivity of amorphous silicon-phosphorus alloy thin films (a-Si:P) with 20–44 at. % P prepared by coevaporation of Si and P. The results show that the optical band gap can be tailored in a range of 1.5–2.15 eV by varying the P concentration and the annealing temperature. The band gap for the sample with 20 at % P is the widest (1.70–1.82 eV) when annealed at temperatures ≤600 °C. From the IR-absorption study, a stretching mode associated with Si—P bonds at 465–474 cm−1 has been found for all alloy films. An evolution (shift or sharpening) of the Si—P absorption band with annealing temperature and P concentration have also been observed. Based on the IR-absorption study the change of bonding structures in the alloy films is discussed. Conductivity measurements show that two electron conduction processes mainly exist in the investigated temperature range: extended-state conduction in the conduction band at high temperatures and hopping conduction in the band tail at low temperatures. The transition temperature is around room temperature (14–55 °C), indicating that the carriers may mainly drift by hopping even at room temperature. The correlation between the optical band gap and the bonding structure is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359392
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of e-beam irradiation on a p-n junction GaN light emitting diode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2687-2690 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A GaN p-n junction structure was grown on a (0001) sapphire substrate by atmospheric pressure metalorganic chemical vapor deposition using a double buffer layer. The resulting light emitting diode (LED) was further exposed to a low-energy electron beam source. The effect of e-beam exposure on the room-temperature electroluminescence spectra of the LED is reported. It is found that the electroluminescence spectral features change dramatically as a function of the electron-beam exposure time and current density. This is attributed to changes in active Mg concentration. The origin of each electroluminescence band is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363131
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