We study the metal-insulator transition in two sets of amorphous Si 1−x Ni x 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 σ/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−x Ni x is very likely discontinuous at zero temperature in agreement with Mott's original views. 71.30.+h,71.23.Cq, Typeset using REVT E X

Useful and simple 3D crossover expressions are presented for the resistance versus temperature behaviour in highly insulating 3D films. At high temperatures, this theory extrapolates to the Mott variable-range hopping law, and at low temperatures to the Efros - Shklovskii variable-range hopping law. Good agreement is found between the crossover theory and resistance measurements.

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Transport properties including conductivity and magnetoconductance have been measured for amorphous nickel-silicon films. This study focuses on metallic amorphous a-Ni x Si 1−x films, located just above the metal-insulator transition (MIT). Using various techniques, the MIT was identified. Electron-electron interactions dominated the conductivity, where σ ≈ σ (0) + CT 0.55. Strong spin-orbit scattering was important in the weak-localization contribution to the magnetoconductance data for the metallic films. The inelastic scattering time was extracted from the magnetoconductance data. The low-temperature magnetoconductance data versus Ni content x exhibited a negative maximum just above the critical concentration x c , suggesting another technique for identifying the MIT.