Metal-insulator transition in amorphous Si(1-x)Ni(x): Evidence for Mott's minimum metallic conductivity

We study the metal-insulator transition in two sets of amorphous Sil-x Nix films. The sets were prepared by different, electron-beam-evaporation- based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, energy dispersive x-ray analysis, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w = d ln s / d ln T, we observe that, for insulating samples, w(T) shows a minimum, increasing at both low and high T. Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of w (T,x) leads to the conclusion that the transition in Si 1-xNix is very likely discontinuous at zero temperature in agreement with Mott's original views.