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Browsing by Author "Yang, Z. Q."

Now showing 1 - 3 of 3
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    Effects of geometry and doping on the operation of molecular transistors
    Yang, Z. Q.; Lang, N. D.; Di Ventra, M. (AIP Publishing, 2003-03)
    We report first-principles calculations of current versus gate voltage characteristics of a molecular transistor with a phenyldithiolate molecule as active element. We show that (i) when the molecule is placed in proximity to the gate electrode, current modulation and resonant tunneling can occur at very small gate voltages. This is due to the first-order perturbation of the electronic states induced by the electrostatic potential of the gate in the molecular region. Such perturbation is present even if the molecule does not have an intrinsic dipole moment. (ii) The molecular transistor can be converted from n-type to p-type by the simple co-adsorption of a single oxygen atom placed near the molecule. While the latter finding suggests that the character of molecular transistors can be easily changed by doping the electrode surfaces, it also puts severe constraints on the experimental control of such structures for molecular electronics applications. (C) 2003 American Institute of Physics.
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    Nonlinear current-induced forces in Si atomic wires
    Yang, Z. Q.; Di Ventra, M. (American Physical Society, 2003-04)
    We report first-principles calculations of current-induced forces in Si atomic wires as a function of bias and wire length. We find that these forces are strongly nonlinear as a function of bias due to the competition between the force originating from the scattering states and the force due to bound states. We also find that the shorter the wire, the larger the average force in the wire, suggesting that the wires are more difficult to break under current flow with increasing length. The last finding is in agreement with recent experimental data.
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    Variational and nonvariational principles in quantum transport calculations
    Yang, Z. Q.; Tackett, A.; Di Ventra, M. (American Physical Society, 2002-07)
    A variational principle is not generally satisfied in steady-state quantum transport as opposed to the case of ground-state problems. We show that for a short-range potential, a functional for the scattering amplitude can be introduced that is stationary for arbitrary variations about the exact scattering wave function. However, except for the special case of spherically symmetric potentials, the functional does not satisfy any minimum principle even in linear response and for single-channel scattering. The absence of a minimum principle puts severe limitations on the choice of trial wave functions in transport calculations. Examples of electronic transport in selected quantum wires will be presented to illustrate the problem.