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  • 1
    Electronic Resource
    Electronic Resource
    Energy broadening due to photoion space charge in a high resolution laser photoelectron source (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 4098-4105 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The results of experimental and theoretical studies, aiming at a quantitative characterization of photoion-induced energy broadening effects in a laser photoelectron source, are reported. The electron source is based on two-step cw laser photoionization of potassium atoms in a collimated beam. In the experimental studies, the attachment spectra for the formation of (N2O)9O− cluster ions through a narrow vibrational Feshbach resonance (full width at half maximum 2.3 meV) were measured as a function of the photocurrent. The theoretical studies involved Monte Carlo simulations of the broadening effects and were based on potential distributions caused by realistic spatial distributions of the photoions. Using the corresponding electric field distribution, trajectories were calculated for a representative ensemble of electrons, and effective electron energy distributions were obtained from averages over the electron trajectories in the volume relevant for electron attachment. Furthermore, the effects of additional weak electric fields, applied along the atomic beam direction, have been simulated. For our geometry (ionization volume about 2 mm3) the effective space charge related energy width is found to be about 16 μeV/pA. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412861
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  • 2
    Electronic Resource
    Electronic Resource
    Aero-acoustic levitation: A method for containerless liquid-phase processing at high temperatures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 456-465 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for containerless liquid-phase processing was developed which has practical application in process and property research on virtually any material which is involatile at the melting point. It combines aerodynamic and acoustic forces to support and position the levitated material. The design provides forced convection control of the thermal boundary in the gas surrounding beam-heated specimens, which stabilizes the acoustic forces and allows acoustic positioning necessary to stabilize the aerodynamic levitation forces on molten materials. Beam heating and melting at very high temperatures was achieved. Experiments were conducted on specimens with diameters in the range 0.25–0.4 cm, of density up to 9 g/cm3, at temperatures up to 2700 K, and in oxygen, air, or argon atmospheres. Unique liquid-phase processing results included deep undercooling of aluminum oxide, glass formation at exceptionally small cooling rates, complete melting and undercooling of YBa2Cu3Ox superconductor materials, direct formation of the YBa2Cu3Ox from the liquid phase, and the vaporization of volatile constituents from a low-liquefaction point glass to form a refractory, high melting material. The application of rapid containerless batch processing operations to materials synthesis is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145157
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  • 3
    Electronic Resource
    Electronic Resource
    Deep level transient spectroscopy on focused ion beam written in-plane capacitances (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6088-6093 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss defects created by focused Ga ion beam implantation in GaAs or AlGaAs/GaAs heterostructures using deep level transient spectroscopy (DLTS). A novel contact configuration which is sensitive to defects located at the boundary between implanted and unperturbed regions at a well-defined depth is presented. The DLTS spectra for these samples are dominated by a peak with an activation energy of Ea=0.38 eV. The results show that this peak is associated with implantation-induced damage independent of the ion species. The defect is also found in a sample with Schottky contacts on top of a Ga-implanted GaAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355193
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  • 4
    Electronic Resource
    Electronic Resource
    Evidence of an off-center position of thulium in GaAs and excitonic excitation of the Tm3+ emission (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6457-6459 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By photoluminescence and by Zeeman spectroscopy we study the characteristic 4f luminescence transition 3H5 → 3H6 at 1.0 eV of thulium in gallium arsenide which has been reported recently. It turns out that optically active Tm3+, which is present in mainly one specific type of center, does not occupy a simple substitutional lattice site. The results show a considerable tetragonal crystal field. The excitation mechanism of the 1.0-eV luminescence is investigated by photoluminescence excitation. The 3H5 → 3H6 is pumped most efficiently by trapping of free excitons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355133
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  • 5
    Electronic Resource
    Electronic Resource
    Influences of a high excitation frequency (70 MHz) in the glow discharge technique on the process plasma and the properties of hydrogenated amorphous silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5665-5674 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very-high-frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50 °C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional frequency of 13.56 MHz considerable differences concerning the electronic and structural properties are observed as the substrate temperature is decreased from 280 to 50 °C. Down to a substrate temperature of 150 °C the electronic film properties change only a little and the total hydrogen content cH and the degree of microstructure that can be directly correlated to cH increase only moderately. Below 150 °C the electronic properties deteriorate in the usual manner but still the total hydrogen content does not exceed 21 at. % even at a substrate temperature of 50 °C. It is argued that the influence of the higher excitation frequency on the plasma and on the growth kinetics plays a key role in this context by allowing a highly effective dissociation of the process gas with the maximum ion energies remaining at low levels. It is concluded that deposition processes at higher excitation frequencies can have important technological implications by allowing a decrease of the deposition temperature without losses in the material quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350500
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  • 6
    Electronic Resource
    Electronic Resource
    Erratum: "Photoluminescence study of impurity states in aluminum antimonide'' [J. Appl. Phys. 67, 1478 (1990)] (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1944-1944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347200
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  • 7
    Electronic Resource
    Electronic Resource
    Implantation and diffusion of noble gas atoms during ion-beam etching of silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6179-6186 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The excessive damage and high defect density generated during ion-beam etching of crystalline Si is characterized by Rutherford backscattering, photoluminescence, and transmission electron microscopy. In samples etched at room temperature, a highly damaged surface layer (d≈5 nm) with a large concentration of noble gas atoms is detected and analyzed using Rutherford backscattering in axial channeling geometry. Point defects due to the low-energy noble gas ion implantation are produced within a depth of 100 nm and deeper, and are monitored by their characteristic photoluminescence. The intensity of the noble-gas-defect photoluminescence is studied for different ion-beam energies (200–2000 eV) and crystal orientations. A threshold to produce the defects can then be determined, leading to an estimate of the number of vacancies contained in the noble gas defect. Annealing of etched samples at 650 °C causes the formation of different new photoluminescent centers. Although little is known about the structure of these defects, it is observed that the defects effectively getter copper. Further annealing of the Ar-etched samples at 1050 °C causes the formation of Ar bubbles with an average diameter of about 5 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346908
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  • 8
    Electronic Resource
    Electronic Resource
    Electronic properties of semiconducting FeSi2 films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1726-1734 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline iron disilicide thin films are prepared by furnace annealing of electron-beam deposited iron layers. As substrates we use single-crystal silicon wafers, epitaxial silicon thin films on sapphire substrates, and low-pressure chemical vapor deposited polycrystalline silicon thin films on oxidized silicon wafers. X-ray diffraction indicates that orthorhombic β-FeSi2 is obtained for growth temperatures in the range 800–900 °C. Photothermal deflection spectroscopy reveals a direct band-gap of 0.85 eV. Optical transitions at energies above 1.4 eV are investigated by spectroscopic ellipsometry. Measurements of the subgap defect absorption, photoluminescence, conductivity, and of the Hall mobility suggest that lower growth temperatures yield material of better quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346601
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  • 9
    Electronic Resource
    Electronic Resource
    Optically detected microwave-induced impact ionization of ytterbium bound excitons in InP (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2237-2239 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optically detected microwave-induced impact ionization of excitons and shallow donors is studied in Yb-doped InP grown by metalorganic chemical vapor deposition. The experimental results directly confirm that Yb3+ intrashell emission is induced by nonradiative recombination of Yb bound excitons due to an impurity Auger effect. Yb3+ ions in InP are found to bind excitons with the electron being localized first, followed by subsequent hole capture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104937
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  • 10
    Electronic Resource
    Electronic Resource
    Intermolecular interaction energies from the total energy bifunctional: A case study of carbazole complexes (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6411-6421 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An approach in which the total energy of interacting subsystems is expressed as a bifunctional depending explicitly on two functions: electron densities of the two molecules forming a complex (ρ1 and ρ2) was used to determine the equilibrium geometry and the binding energy of several weak intermolecular complexes involving carbazole and such atoms or molecules as Ne, Ar, CH4, CO, and N2. For these complexes, the experimental dissociation energies fall within the range from 0.48 to 2.06 kcal/mol. Since the effect of the intermolecular vibrations on the dissociation energy is rather small, the experimental measurements provide an excellent reference set. The obtained interaction energies are in a good agreement with experiment and are superior to the ones derived from conventional Kohn–Sham calculations. A detailed analysis of relative contribution of the terms which are expressed using approximate functionals (i.e., exchange-correlation Exc[ρ1+ρ2] and nonadditive kinetic energy Tsnad[ρ1,ρ2]=Ts[ρ1+ρ2]−Ts[ρ1]−Ts[ρ2]) is made. The nonvariational version of the applied formalism is also discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1462613
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