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  • 1
    Electronic Resource
    Electronic Resource
    Numerical simulation of field emission and tunneling: A comparison of the Wigner function and transmission coefficient approaches (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4409-4427 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum transport through one-dimensional potential barriers is usually analyzed using either the transmission coefficient (TC) or the Wigner distribution function (WDF) approach. Fast, accurate, and efficient numerical algorithms are developed for each and are compared for (a) calculating current-field relationships for field-emission potentials with silicon parameters (and current-voltage relationships for resonant tunneling diodes), (b) their ability to accommodate scattering, self-consistency, and time dependence, and for (c) the behavior of their "particle trajectory'' interpretations. In making the comparisons, the concern will be on the ability of each method to be incorporated into a larger ensemble-particle Monte Carlo simulation; it is argued that, in this regard, the WDF approach has significant advantages. Since the TC calculations rely on the Airy function approach, a detailed comparison of this method is made with the widely used Wentzel–Kramers–Brillouin and Fowler–Nordheim approaches for the general problem of field emission from a material into the vacuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352779
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  • 2
    Electronic Resource
    Electronic Resource
    Erratum: "Exchange-correlation, dipole, and image charge potentials for electron sources: Temperature and field variation of the barrier height" [J. Appl. Phys. 85, 2667 (1999)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4455-4456 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289819
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  • 3
    Electronic Resource
    Electronic Resource
    Field emitter arrays for plasma and microwave source applications : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2241-2253 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Field emitter arrays (FEAs) stand to strongly impact device performance when physical size, weight, power consumption, beam current, and/or high pulse repetition frequencies are an issue. FEAs are capable of instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, and low voltage operation characteristics. Advanced microwave power tubes, and in particular, inductive output amplifiers, are by far the most technically challenging use to date. Other important uses include, e.g., electron sources for micropropulsion systems–Hall thrusters–and tethers for satellites, and (the most widely pursued application) field emission displays. The characteristics of field emitters that make them attractive to such applications shall be surveyed. A thorough analytical model of a field emitter array, beginning with a review of the nature of field emission and continuing with an analytical model of a single emitter and the operation of an array of emitters, shall be presented. In particular, attention shall be directed towards those features of FEAs that render them attractive as cold cathode candidates for electron beam generation. Tip characteristics, such as emission distribution, and array operation, such as space charge effects, will be analyzed in the context of the model. Finally, restricting attention to microwave applications, the performance of a tapered-helix inductive output amplifier to highlight the advantages of high frequency emission gating of the electron beam in a power tube shall be investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873502
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  • 4
    Electronic Resource
    Electronic Resource
    Analytic expressions for emission in sharp field emitter diodes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3569-3571 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a complete analytical treatment of elliptical field emitting structures in a diode geometry which correctly includes image charge effects off axis and the variation of field along the tip. The methodology may be extended to other geometries. The angular distribution of electron emission along the tip, the total emitted current, and the area factor may all be calculated as a function of emitter to anode distance, tip radius, tip height, and the anode-tip voltage difference. We show not only where errors arise if the planar Fowler–Nordheim (FN) equation is used to govern electron emission, but also how the FN equation may be modified to correctly address the complications due to atomically sharp tips. Finally, we present an analytic form of the area factor and compare it to the exact calculation and the various approximations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358591
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  • 5
    Electronic Resource
    Electronic Resource
    An analytical model of an emission-gated Twystrode using a field emitter array (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7982-7992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical model of a unit cell and of an array of field emitters with a distribution of tip radii is used to estimate the total current and current characteristics on the basis of geometry and materials. Based on the unit cell modeling, analytical estimates of ring cathode inductance, resistance, and capacitance are made to estimate the drive power required to sinusoidally modulate the array in order to produce a bunched electron beam. For a configuration of parameters indicative of a next generation field emitter array (FEA) ring cathode, the characteristics of the array are used to estimate the gain, efficiency, power output, and optimized length of an emission-gated Twystrode (TWT) using a simple model of the beam-wave interaction. The integrated analytical approach and its numerical implementation ("Cassandra") are validated by comparison to a 1D TWT code (CHRISTINE) which estimates the output power and the optimized length of a TWT. Using "Cassandra," it is shown that with next generation FEA parameters, interesting and significant levels of performance may be anticipated for a compact, broadband rf inductive output amplifier; in particular, an electronic efficiency of 32% with 15 dB gain may be possible from an array producing 260 mA peak and 71 mA average current at 10 GHz modulation using a helix 1.51 cm long.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367980
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical calculation of particle trajectories and tunneling times for resonant tunneling barrier structures (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 669-671 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Wigner particle trajectories in phase space for double-barrier semiconductor quantum well structures are investigated by numerically calculating the Wigner distribution function. The determination of the particle dynamics of the phase points allows for an estimation of tunneling times, particle currents, and particle energies associated with the statistics of bound and open trajectories across the double-barrier structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101817
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  • 7
    Electronic Resource
    Electronic Resource
    Space charge effects on the current-voltage characteristics of gated field emitter arrays (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 845-854 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microfabricated field emitter arrays (FEAs) can provide the very high electron current densities required for rf amplifier applications, typically on the order of 100 A/cm2. Determining the dependence of emission current on gate voltage is important for the prediction of emitter performance for device applications. Field emitters use high applied fields to extract current, and therefore, unlike thermionic emitters, the current densities can exceed 103 A/cm2 when averaged over an array. At such high current densities, space charge effects (i.e., the influence of charge between cathode and collector on emission) affect the emission process or initiate conditions which can lead to failure mechanisms for field emitters. A simple model of a field emitter will be used to calculate the one-dimensional space charge effects on the emission characteristics by examining two components: charge between the gate and anode, which leads to Child's law, and charge within the FEA unit cell, which gives rise to a field suppression effect which can exist for a single field emitter. The predictions of the analytical model are compared with recent experimental measurements designed to assess space charge effects and predict the onset of gate current. It is shown that negative convexity on a Fowler–Nordheim plot of Ianode(Vgate) data can be explained in terms of field depression at the emitter tip in addition to reflection of electrons by a virtual cathode created when the anode field is insufficient to extract all of the current; in particular, the effects present within the unit cell constitute a newly described effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365783
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  • 8
    Electronic Resource
    Electronic Resource
    Numerical simulation of transient response and resonant-tunneling characteristics of double-barrier semiconductor structures as a function of experimental parameters (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 5248-5250 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The tunneling current characteristics and transient response of double-barrier semiconductor structures are simulated for different barrier and quantum-well widths, barrier heights, operating bias voltage, and ambient temperatures, using the equation for the Wigner distribution function. The numerical results suggest the following: (a) There is a particle buildup inside the quantum well prior to the resonant current peak as the applied bias is varied: (b) the number of resonant energy levels seen in the simulation agrees with its proportionality to the square root of the product of the barrier height and quantum-well width: (c) the resonant peak width is larger for higher resonant energy levels than for the lower resonant energy levels in agreement with the different degree of localization of these levels; (d) at T=77 K, the current slowly increases with bias at lower bias than for T=300 K, with higher peak-to-valley ratio at T=77 K, presumably due to a much sharper convolution of the tunneling density and resonant energy level width; and (e) a higher degree of localization and existence of numerically resolved resonant energy level, in the case of asymmetrical barrier widths, occurs when the thicker barrier is located in the side with lower electron potential or higher voltage bias; no negative differential resistance was observed when these barrier widths were interchanged in our simulation. The superior accuracy of an alternative finite difference scheme, coupled with the Cayley form for the time evolution operator, in this type of numerical simulation is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343120
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  • 9
    Electronic Resource
    Electronic Resource
    Modeling of pyrolytic laser-assisted chemical vapor deposition: Mass transfer and kinetic effects influencing the shape of the deposit (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 198-206 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The laser-assisted chemical vapor deposition of metals is modeled. The case of pyrolytic deposition induced by a continuous laser source is considered. The heat transfer in the solid substrate is considered to be transient, while the gas-phase heat and mass transfer are assumed to be in the quasi-steady state. The model accommodates the use of temperature-dependent physical properties and the occurrence of irregularly shaped deposits. The modeling equations are solved by a finite element approach which is briefly described. Volcanolike deposits are predicted under certain conditions of gas pressure and laser intensity. Model predictions show that depletion effects and adsorption-desorption phenomena are major factors in influencing the occurrence of volcanolike deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340490
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  • 10
    Electronic Resource
    Electronic Resource
    A SQUID-based ac susceptometer (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2644-2652 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed a high-resolution ac susceptometer that uses a rf superconducting quantum interference device to directly measure the flux coupled into a superconducting detection coil from a sample's changing magnetic moment in an applied ac field. The system operates in a frequency range from 0.01 to 1500 Hz and an applied ac field range of 0.1–400 μT with a sensitivity of about 5×10−12 A m2 for magnetic moment measurement, and at a reduced sensitivity down to 0.001 Hz. The instrument is based on an existing dc magnetometer system and uses that system's temperature control and dc superconducting magnet to allow operation over a temperature range from 2 to 400 K and in applied dc fields of ±5.0 T. During a measurement all operations are controlled automatically by computer from a menu-driven software system, with user input required only on initiation of a measurement sequence. Both real and imaginary components of the ac susceptibility can be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144664
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