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  • 11
    Electronic Resource
    Electronic Resource
    Core excitons in silicon and silicon oxides : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1480-1482 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Using a newly developed reflectometer we have measured the reflectivity at the silicon K edge for different silicon compounds. Combining these measurements with silicon L edge reflectivity measurements carried out on a different reflectometer we determined the binding energy of core excitons at the L edge. The results show that it is possible to carry out reflectivity measurements with the resolution necessary for the determination of the exciton parameters. Comparison with literature values shows that a rigid Kramers–Kronig analysis is not needed when the angle of incidence is well below the critical angle of total external reflection. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146471
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  • 12
    Electronic Resource
    Electronic Resource
    A new high-resolution two-dimensional micropositioning device for scanning probe microscopy applications (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3216-3219 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the development of a new two-dimensional micropositioning device, or walker, which is capable of moving across very large distances (in principle unlimited) and with a very small step size (as small as 100 A(ring)/step) in both directions. Based on a unique tracking design, the motion is extremely orthogonal with very little crosstalk between the two directions. Additionally, there is no detectable backlash in either direction. The walker performance has been extensively tested by using a position-sensitive proximitor probe. Tests have been done between 77 and 300 K. However, we project that the walker will be able to operate at temperatures as low as 4 K. This walker system has shown extremely reliable performance in a UHV environment for use with scanning tunneling microscopy and has been especially useful for cross-sectional scanning tunneling microscopy and spectroscopy studies of semiconductor hetero- and homostructures. We show one example of results on the (AlGa)As/GaAs heterostructure system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144552
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  • 13
    Electronic Resource
    Electronic Resource
    The effects of CdCl2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 881-889 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature (J-V-T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10−7 A/cm2 to 2.6×10−9 A/cm2 and, (c) an increase in cell Voc from 385 to 720 mV. The CdCl2 also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl2-treated structures indicate that the CdCl2 treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl2-treated devices at Ev + 0.64 eV which is attributed to the formation of VCd-related defects during the annealing process after the CdCl2 dip. J-V-T analysis demonstrated that this trap is the probable source of dominant recombination in the CdCl2-treated cells. An inverse correlation was found between the density of the Ev + 0.64 eV trap and cell Voc, suggesting that the heat treatment with CdCl2 may eventually limit the CdTe/CdS cell performance unless the formation of this defect complex is controlled or eliminated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349652
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  • 14
    Electronic Resource
    Electronic Resource
    Spin cast thin films of fullerenes and fluorinated fullerenes: Preparation and characterization by x-ray reflectivity and surface diffuse x-ray scattering (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5248-5250 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that high quality thin films of fullerenes (C60) and fluorinated fullerenes can be prepared from solution by the spin coating technique on float glass or silicon wafers. The films were characterized by x-ray reflectivity and diffuse x-ray scattering. A systematic study of films of different thicknesses allows estimation of the distance between the fullerenes spheres to be 10.9±1 A(ring) in our C60 films. The C60 film-air surface is very smooth. Annealing in air above 90 °C leads to an irreversible increase of the film thickness, which is attributed, at present, to oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350583
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  • 15
    Electronic Resource
    Electronic Resource
    Re-evaluation of the derivatives of the half order Fermi integrals (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7030-7034 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Fermi integrals of half orders are important in the simulation of semiconductor transport processes. Several of these integrals (−1/2, 1/2, 3/2, 5/2) have been recently retabulated since the 1938 study by McDougall and Stoner [Phil. Trans. Roy. Soc. A 237, 67 (1938)], but the derivatives were not re-evaluated. The original integral values were calculated without the aid of high speed computers by using approximate series evaluation and tabulations of exponentials and zeta functions. In addition, a discrepancy was found in the literature since the original study in 1938. The second derivative of F1/2 has been mistakenly represented as being proportional to a Fermi integral of another order. This article tabulates the half order Fermi integrals from −1/2 to 5/2 over the reduced energy range −5 to 20 in 0.25 increments. The first two derivatives of F−1/2 are also calculated by numerical integration and tabulated to aid in interpolation. It is shown that the second derivative of F1/2 is not proportional to another Fermi integral. A suitable interpolation scheme is proposed to calculate the values of the Fermi integrals of various order to high accuracy over the total reduced energy range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352420
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  • 16
    Electronic Resource
    Electronic Resource
    A new device for injection of iron atoms into plasmas : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 568-570 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Reduction of indigenous metal impurities in tokamak plasmas and impurity requirements for the x-ray diagnosis of central plasma parameters necessitates artificial introduction of metal atoms. A new inexpensive method is described using ferrocene, Fe(C5H5)2, a substance which sublimes. A prototype device was tested at the Atomic-Beam Facility at PPPL. Ferrocene was injected into a pulsed helium plasma with an electron density of 2×1013 cm−3 and an electron temperature of 5 eV. The injected amount of ferrocene was controlled by varying the sublimation temperature in the range from 70 to 150 °C and adjusting the pulse length of a solenoid valve; the resulting iron atom concentration in the plasma was determined by monitoring the intensity of the Fe line at 5269 A(ring). The device and the test results are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146287
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  • 17
    Electronic Resource
    Electronic Resource
    Studies of He-like krypton for use in determining electron and ion temperatures in very-high-temperature plasmas : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 761-763 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-resolution measurements of the He-like Kr K-shell radiation are presented showing the direct excitation lines as well as Li- and Be-like dielectronic recombination lines appearing in the KLL resonance. The measurements were performed on the Electron Beam Ion Trap (EBIT) facility and motivated by the need for accurate atomic data of high-Z He-like K-shell transitions for diagnostic applications in determining the central ion and electron temperature of very-high-temperature plasmas produced in next-generation tokamaks, such as the International Thermonuclear Experimental Reactor (ITER). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146281
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  • 18
    Electronic Resource
    Electronic Resource
    Molecular orientational dynamics in solid C70: Investigation by one- and two-dimensional magic angle spinning nuclear magnetic resonance (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7554-7564 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of 13C nuclear magnetic resonance (NMR) measurements that probe molecular orientational dynamics in solid C70 in the temperature range 223–343 K. Orientational dynamics affect the NMR line shapes and spin–lattice relaxation rates by modulating the 13C chemical shift anisotropy (CSA). Motionally averaged CSA line shapes, determined from both one-dimensional and two-dimensional magic angle spinning NMR spectra, and relaxation rates are determined for each of the five inequivalent carbon sites in the C70 molecule. Comparisons of the results for the five sites provide evidence for rapid uniaxial molecular reorientation in the monoclinic (T≤280 K) and rhombohedral (280≤T≤330 K) phases and rapid isotropic reorientation in the face-centered cubic (T≥330 K) phase. The orientational correlation time is roughly 2 ns at 250 K and of the order of 5 ps at 340 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465685
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  • 19
    Electronic Resource
    Electronic Resource
    Rotational dynamics and orientational melting of C60: A neutron scattering study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8631-8633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Well-defined librational excitations have been observed at energies of 2–3 meV in the low temperature ordered phase of solid C60. These relatively high energies imply a stiff orientational potential below the transition. The sharpness of the peaks indicates that this potential does not depend strongly on the axis of the angular displacement. The modes soften and broaden as the temperature approaches that of the orientational melting transition which occurs when the librational amplitude is a considerable fraction of nearest-neighbor interatomic angles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462876
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  • 20
    Electronic Resource
    Electronic Resource
    A new asymptotic form for the Laguerre polynomials (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 1666-1671 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A new asymptotic formula in terms of elementary functions is demonstrated for the Laguerre polynomials Lαn(x) in the limit when all three parameters (n,α,x) become large. This asymptotic limit appears in the problem of obtaining the low-field semiclassical approximation from the full quantum mechanical behavior of a two-dimensional electron gas in a magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529694
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