Lisa M. Lust

Conductance fluctuations in doped hydrogenated amorphous silicon

Abstract Recent measurements of random telegraph switching noise (RTSN) in n-type doped hydrogenated amorphous silicon (a-Si:H) are described. The discrete two-state switching noise can be changed by light soaking or thermal cycling, which is consistent with the bonded hydrogen microstructure influencing the current filaments believed responsible for the RTSN. Computer simulations of dynamical percolation of a random resistor network also display sharp discrete jumps, similar to that observed in a-Si:H, providing support for the proposal that hydrogen motion underlies the conductance fluctuations.

Langevin simulation of the dynamics of a dense hard sphere liquid

Abstract The dynamic behavior of a dense hard-sphere liquid is studied by numerically integrating a set of Langevin equations which incorporate a free-energy functional of the Ramakrishnan-Yussouff form. Several interesting features of glassy dynamics, such as stretched exponential decay of correlations, two-stage relaxation and Vogel-Fulcher growth of relaxation times, are reproduced and new results on the wavenumber dependence of the kinetics are obtained.

Telegraph noise as a probe of microscopic hydrogen motion in amorphous silicon

Time traces of conductance fluctuations in the co-planar current of hydrogenated amorphous silicon (a-Si:H) display sharp jumps between discrete resistance levels, termed random telegraph switching noise (RTSN). Measurements of the temperature dependence and effects of light soaking of the RTSN in n-type doped a-Si:H are reported. The rise times between the two level fluctuators yield activation energies and attempt to hop frequencies for microscopic hydrogen motion which agree with those obtained from NMR experiments. Computer simulations of a dynamical percolation random resistor network support the suggestion that the RTSN arises from local diffusion processes altering the conductance of inhomogeneous current filaments.

Calculation of electromagnetic constitutive parameters of insulating magnetic materials with conducting inclusions

A Method of Moments (MoM) electromagnetic model of percolating conducting films was applied to calculate the effective parameters of the composite formed by conducting inclusions placed within a dispersive magnetic but nondispersive dielectric matrix. The MoM calculations demonstrate a coupling between the magnetic properties of the matrix and the effective composite permittivity and frequency dispersion of the composite. The coupling of permittivity and permeability is observed near the percolation threshold of the composite and for high conductivity inclusions. The prediction agrees with physical expectations since near percolation the conduction correlation length dominates the effective permittivity of the composite and this correlation length is determined by both the permittivity and permeability of the composite.