Frequency-independent parameters of an equivalent circuit of two dimensional island gold films

Abstract

This paper deals with the outcome of a follow-up of our erlier work that tackled the ac measurements on two-dimensional island gold films [2D-I(Au)Fs] prepared by the thermal evaporation technique and identified by their stabilized surface resistivity (ρs) (23 MΩ/□ to 37.5 GΩ/□). In that work, the ac parallel resistance (rp) of the different 2D-I(Au)Fs was deduced, with the aid of a lock-in amplifier, as a function of the frequency (f) [0.1 to 80 kHz] of the voltage imposed on the films at six temperature points over the range 100 to 300 K. Here, the follow-up is intended to exploit the known values of rp at different frequencies in finding the magnitudes of the frequency-independent parameters of an equivalent circiut of 2D-I(Au)Fs. These parameters are Rb, Rg and Cg, where Rb is the resistance associated with the conduction within the bulk (interior) of islands, Rg is the resistance that accompanies the conduction across the gaps between islands and Cg is the capacitance due to the presence of metallic islands and gaps. The equation that relates rp to Rb, Rg, Cg and f is known and thus the experimental values of rp and the corresponding frequencies were inserted into it; then via a computerized analysis the least squares values of Rb, Rg und Cg were eventually deduced. It was found that: (i) Rb and Rg increase while Cg decreases with the increase in ρs. (ii) Rb and Cg increases but Rg decreases with the increase in T. (iii) The activation energy of charge carrier generation increases as ρs does. (iv) The magnitude of the temperature coefficient of gap resistance increases with the increase in ρs and the decrease in T. The present results were interpreted, qualitatively, by assuming that the transfer of charge carriers, across the gaps between the islands, takes place via the thermally activated tunneling mechanism. To the best of our knowledge, the present results are the first to be reported for 2D-I(Au)Fs. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)