Electrical Appearance Research Articles

Switching Effects, Current Fluctuations and Lateral Photovoltage - The Electrical Appearance of A-Si:H/Metal Multilayers

ABSTRACTMultilayer systems (MLS) consisting of hydrogenated Amorphous silicon (a-Si:II) and a transition Metal (Mo, Ti) were prepared by alternating dual magnetron sputtering. In this study we investigate the electrical performance of multilayer films containing discontinuous metal sublayers separated by a-Si:H sublayers of 80 nm thickness. A voltage of typical 8 V applied to the coplanar electrodes switches the samples from a semiconducting to a metallic state. The switching effect, which is reversible by thermal annealing, is accompanied by chaotic current oscillations. The temperature dependence of the conductivity in the metallic state is described by Inσ α T−1/2. The asymmetric illumination of the interelectrode spacing in coplanar configuration resulted in a generation of a lateral photovoltage.

Interpretation of current-voltage relationships for "active" ion transport systems: II. Nonsteady-state reaction kinetic analysis of class-I mechanisms with one slow time-constant.

The temporal behavior of current through a biological membrane can display more than one time constant. This study represents the reaction kinetic analysis of the nonsteady-state behavior of a class of membrane transporters with one voltage-sensitive reaction step, one dominant (large) time constant, but arbitrary reaction scheme of the voltage-insensitive part of transporter. This class of transporters which shows uniform behavior under steady-state conditions splits into two fundamentally different subclasses, when nonsteady-state behavior is examined: Subclass (Model) A: the slow reaction controls the redistribution of states within the reaction cycle upon an (electrical) perturbation; model B: this redistribution is fast but the transporting cycle can slowly equilibrate with an inactive, "lazy" state. The electrical appearance of model A in a membrane requires specific features of the transporter in the membrane: high densities (10(-8) mol m(-2)), low turnover rates (10(3) sec(-1)) and high stoichiometry (z>1) of transported charges per cycle. The kinetics of both models can formally be described by an equivalent circuit with a steady-state slope conductance (G 0) shunted by a (transporter specific) capacitance (G t ) and a conductance (C t ) in series. The voltage dependence ofC t and ofG t can be used to identify model A or model B. In the range of maximumG 0 in the steady-state current-voltage curve,C t in model A displays a maximum (which may characteristically split into two maxima) and vanishes for larger voltage displacements.C t can be used for the determination of transporter densities in the membrane. In contrast to model A, the appearance of model B in the nonsteady-state behavior of a membrane does not depend on high densities, low turnover rates and high stoichiometry; it can, therefore, be found also in membranes with sparsely distributed, rapidly transporting channels of any stoichiometry. Particular to model B is a change in the signs ofC t andG t at the reversal potential of the steady-state current-voltage relationship. This implies switching from capacitive to inductive behavior (under vanishing amplitudes). Also in model B, the nonsteady-state effects disappear for large voltage displacements from the reversal potential. Model B is expected to occur preferably in transporters subject to metabolic control.