Metallic transport properties of amorphous nickel - silicon films

Abstract

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.

Metal-insulator transition in amorphousSi1−xNix:Evidence for Mott’s minimum metallic conductivity

“…This method uses the varying incidence angles and distances to the sources to produce a composition gradient along a substrate. The film is then cut into narrow samples with their axes (the direction of current flow) perpendicular to the composition gradient [55]. This technique has two advantages: Composition determination is related to a geometrical measurement, and neighboring samples are prepared under almost identical conditions.…”

“…The conditions were as follows: residual gas pressure during deposition ≈ 1 · 10 −5 mbar, and, for the samples close to the MIT, rate ≈ 0.8 nm/s; for more details see Ref. [55].…”

“…Energy dispersive X-ray analysis (EDX) by means of a LINK AN10000 EDS system attached to a JSM-840 SEM was used in determining the composition for sample set B in Witwatersrand, South Africa, within Refs. [55,56]. The results of these analyses are given in Tables I and II. In order to compare both x scales, we performed additional EDX analyses for samples 3, 6, f, h, and i by means of a Tracor/Noran spectrometer Voyager IIa, attached to a transmission electron microscope (TEM) Philips CM20FEG, in Dresden.…”

“…Moreover, for sample j, the Witwatersrand EDX result was checked by an RBS analysis performed in Faure, South Africa, within Ref. [55].…”

“…For a-Si 1−x Ni x :H, a structure study [51], optical conductivity measurements [52], also under pressure [53], and electronic structure investigations by XPS and XES [54] were reported in the literature. Last but not least, some of the authors have gained detailed experience in trying fits of σ(T ) by conventional theories for a-Si 1−x Ni x samples prepared by electron-beam evaporation in Tel Aviv [55,56]. The present paper is organized as follows: Section II describes the sample preparation.…”