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  • 1
    Digitale Medien
    Digitale Medien
    A transmission electron microscope investigation of the dose dependence of the microstructure of silicon-on-insulator structures formed by nitrogen implantation of silicon (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3503-3511 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Transmission electron microscope studies have been made of (100) silicon wafers implanted at 500 °C with 200-keV 14N+ ions to doses of either 0.25, 0.75, or 1.4×1018 cm−2. For all of these specimens, the as-implanted wafers contained a buried amorphous layer with a damaged upper single-crystal silicon layer. For the 1.4×1018 cm−2 specimen, the amorphous layer contained bubbles. Wafers subsequently annealed at 1200 °C in order to form silicon-on-insulator structures showed the following. For the 0.25×1018 cm−2 specimen, there was a buried discontinuous polycrystalline α-Si3N4 layer, and an upper silicon layer with no observable defects. For the 0.75×1018 cm−2 specimen, there was a buried continuous polycrystalline α-Si3N4 layer containing small silicon islands, and an upper silicon layer either without defects or with microtwins adjacent to the nitride/silicon interface. For the 1.4×1018 cm−2 specimen, there was a buried multilayer structure with the middle layer consisting of substantially single-crystal α-Si3N4 free from silicon islands but containing bubbles; and an upper silicon layer with microtwins and threading dislocations. For the 0.25 and 0.75×1018 cm−2 specimens, the α-Si3N4 had often grown epitaxially in the single-crystal silicon. For the 0.75×1018 cm−2 specimen, such epitaxy had less often occurred. For the 1.4×1018 cm−2 specimen, such epitaxy was not observed. These structural results are correlated with the implantation conditions and nitrogen depth profiles obtained by secondary ion mass spectrometry. The mechanisms responsible for producing the structures are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348491
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  • 2
    Digitale Medien
    Digitale Medien
    Electronic properties of silicon δ-doped InSb (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 671-675 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated magneto-transport and cyclotron resonance (CR) of two-dimensional electron gas in silicon δ-doped p-InSb under a magnetic field of up to 12 T at 4.2 K. Because there are multiple subbands occupied, Shubnikov–de Haas oscillations show a beating behavior. The CR spectra also display several peaks originating from different subbands. Effective masses of electrons associated with the lowest three subbands can therefore be directly determined, and they are in excellent agreement with a self-consistent calculation, which takes into account the electrostatic Poisson equation, the Schrödinger equation, and realistic sample parameters. Furthermore, we observed an absorption peak, whose resonance position has anomalous angle dependence. It is attributed to impurity CR where donors are in the vicinity of the δ-doped sheet.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351850
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  • 3
    Digitale Medien
    Digitale Medien
    Design considerations for z-pinch driven photoresonant x-ray lasing in neonlike krypton (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4671-4677 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A neonlike x-ray laser photoresonant pumping scheme is explored. An attractive design is a coaxial z-pinch consisting of an inner krypton lasant plasma surrounded by a carbon shell that itself is surrounded by a stagnated krypton plasma. The photoresonant radiation emitted from the outer plasma passes inwardly through the carbon shell and photoexcites lasant electrons to the 3s, 3d, and 4d levels. It is calculated that monochromatic pump powers of 30 GW/cm eV can be achieved for the 4d neonlike resonance line while powers of 100–200 GW/cm eV are attainable for the 3s and 3d resonance lines. The gain in several neonlike 3s-3p transitions is calculated as a function of temperature and density of the lasant plasma. Reasonable gain in only the 3p-3s (J=0–1) transition is obtained for high-density, high-temperature lasant conditions. This gain, which is driven by monopole excitation from the ground state to the 3p (J=0) level, is nearly independent of the presence of pump radiation. For low-density, low-temperature lasants, optimal gain is obtained in the 3p-3s (J=2–1) transitions. Under these conditions, the pump radiation is necessary to photoionize and photoexcite the lasant plasma to the neonlike stage while radiative decay from the resonantly pumped 4d level to the 3p (J=2) states provides the major upper lasing level pump mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350657
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  • 4
    Digitale Medien
    Digitale Medien
    Generation of high-energy x-radiation using a plasma flow switch (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1999-2007 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high-voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x-radiation pulse occurs substantially after the high-voltage pulse suggesting that high-energy electrons are generated by dynamic processes in a very high speed ((approximately-greater-than)106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low-density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force-u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30-keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348773
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  • 5
    Digitale Medien
    Digitale Medien
    Use of atomic layer epitaxy buffer for the growth of InSb on GaAs by molecular beam epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7166-7172 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A 300 A(ring) buffer layer of InSb grown by atomic layer epitaxy at a substrate temperature of 300 °C at the GaAs/InSb interface has been employed to grow epitaxial films of InSb having bulk-like properties. The reduction of the defects in the top InSb film has been observed with cross-sectional transmission electron microscopy and channeling Rutherford backscattering spectroscopy. The optimum substrate temperature for the primary InSb layer growth was 420 °C with an atomic flux ratio of Sb to In of 1.4 and a growth rate of 1 μm/h. The best 5-μm-thick InSb layers had x-ray rocking curve widths of 100 s, 77 K n-type carrier concentrations in the low 1015/cm3 range, and 77 K carrier mobilities greater than 105 cm2/V s. Mesa isolated photodiodes had carrier lifetimes of 20 ns, in comparison to 200 ns observed in bulk InSb having a similar carrier concentration. An unexplained, weak free-electron spin resonance transition has been observed in these films.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347608
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  • 6
    Digitale Medien
    Digitale Medien
    An efficient tabulated collisional radiative equilibrium radiation transport model suitable for multidimensional hydrodynamics calculations (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3480-3489 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A computationally efficient method for transporting radiation in multidimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multidimensional radiation transport problem. This method is superior to diffusion methods because (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent nonlocal thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multidimensional calculations. Given the internal energy and ion density, and by calculating the line probability of escape from a zone of the multidimensional plasma, the equation of state, including emissivities and absorption coefficients, of the zone is determined from the table. Total radiative power, K-shell radiative power, total radiative yield, K-shell radiative yield, and plasma density and temperature profiles obtained from 1D Z-pinch calculations employing this method are in good agreement with the same powers, yields, and profiles calculated using a full radiation transport model. This method has been implemented in the 2D plasma radiating imploding source model code [F. L. Cochran et al., Phys. Plasmas 2, 2765 (1995)] to determine the influence of radiation transport in argon Z-pinch experiments performed on the Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1373415
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  • 7
    Digitale Medien
    Digitale Medien
    Trends in plasma conditions inferred from an analysis of x-ray data from high wire-number, Z-pinch load implosions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3708-3717 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An analysis of x-ray data from two series of Z-pinch shots taken on the short current-risetime Saturn accelerator at Sandia National Laboratories [Proceedings of 6th International IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] is presented. In one series, the array radius was held constant and the array mass was varied; in the other series, the array mass was held constant and its radius varied. In both sets of experiments, large wire-number loads (N≥93) of aluminum were used in contrast to earlier small wire-number aluminum array experiments on Saturn where N≤42. Average electron temperatures and ion densities were inferred from the data. In addition, from the measured size of the emission region of K-shell x rays and from the inferred ion density, a fraction of the total array mass that participated in the K-shell emission was inferred and found to be directly correlated to the K-shell yields that were measured. This paper also demonstrates that the yields varied as a function of array mass and radius in much closer agreement with predictions [J. Appl. Phys. 67, 1725 (1990)] than had been observed in the earlier small wire-number experiments. Thus, a serious misperception that the reason for the early disagreement was in the calculations and not in the experiments is corrected. These predictions were made using one-dimensional (1D) magnetohydrodynamics calculations. The density and temperature trends inferred from the data analysis are well-behaved and consistent with the 1D calculations. This data analysis confirms the importance of achieving uniform plasma initial conditions and implosion symmetry when comparing computer code calculations with experiment. When the wire number of an array load is increased, a more uniform shell of plasma is calculated initially as the wires explode and, as the plasma stagnates on axis, the x-ray powers and yields are found experimentally to approach the powers and yields predicted by 1D calculations. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1380695
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  • 8
    Digitale Medien
    Digitale Medien
    High energy photon radiation from a Z-pinch plasma (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4509-4517 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new approach to the generation of kilovolt x ray radiation in Z-pinch plasma radiation sources is proposed. In cases where the pulse power machine has insufficient energy to efficiently produce K-shell emission from the atomic number element that emits in the required kilovolt energy range, it may be advantageous to produce x rays by recombination radiation emitted from a lower atomic number plasma. The optimal load conditions for maximizing the high energy free–bound continuum radiation that can be produced in a given spectral range are analyzed. The largest yield is expected from a highest-atomic-number element that could efficiently produce K-shell yield on a given pulse power machine. Two options available for the choice of a wire array material to generate x rays with photon energies above 7–8 keV are identified and discussed, aluminum and titanium. The analytical estimates and simulation results for "Z" machine implosions show that continuum radiation from an aluminum plasma in this spectral range could exceed the K-shell output from nickel. If a titanium plasma could be ionized to a H-like state on "Z," then its yield above 7 keV should be higher compared to that of aluminum by a factor of 3 to 4. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1398572
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  • 9
    Digitale Medien
    Digitale Medien
    Comparative analysis of time-resolved and time-integrated x-ray data from long pulse Z-pinch implosions on Saturn (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3799-3809 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Two series of Al:Mg wire array Z-pinch implosions were performed on the Saturn pulsed-power generator [R. B. Spielman et al., in Proceedings of the 2nd International Conference on Dense Z-Pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3]. In one series, the wire number was varied, in the other, the load mass was varied. In all cases an initial array diameter of 40 mm was maintained. Sufficient x-ray data were obtained in these experiments to allow the plasma conditions to be inferred by matching x-ray data to that calculated by a collisional-radiative equilibrium (CRE) model. In fitting the data, the plasma has been assumed to be either uniform [zero dimension (0D)] or to vary one-dimensionally (1D) with radius. On one shot, a comparison of these two methods of data analysis performed with both time-resolved and time-integrated data has been carried out. While the same trends in plasma conditions as a function of load mass and wire number are seen, the uniform plasma assumption yields higher electron temperatures, lower core densities, but higher K-shell radiating mass fractions than those obtained from the 1D assumption. When comparing time-resolved and time-integrated spectroscopic data, a pronounced difference is seen in a density-sensitive line ratio whose time-resolved values corroborate experimental evidence that much of the K-shell radiation is emitted from a high density core plasma of spatial extent less than about 300 μm. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1381565
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  • 10
    Digitale Medien
    Digitale Medien
    Model of enhanced energy deposition in a Z-pinch plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3265-3277 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In numerous experiments, magnetic energy coupled to strongly radiating Z-pinch plasmas exceeds the thermalized kinetic energy, sometimes by a factor of 2–3. An analytical model describing this additional energy deposition based on the concept of macroscopic magnetohydrodynamic (MHD) turbulent pinch heating proposed by Rudakov and Sudan [Phys. Reports 283, 253 (1997)] is presented. The pinch plasma is modeled as a foam-like medium saturated with toroidal "magnetic bubbles" produced by the development of surface m=0 Rayleigh-Taylor and MHD instabilities. As the bubbles converge to the pinch axis, their magnetic energy is converted to thermal energy of the plasma through pdV work. Explicit formulas for the average dissipation rate of this process and the corresponding contribution to the resistance of the load, which compare favorably to the experimental data and simulation results, are presented. The possibility of using this enhanced (relative to Ohmic heating) dissipation mechanism to power novel plasma radiation sources and produce high K-shell yields using long current rise time machines is discussed. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874192
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