Order in nickel films deposited at low temperatures and its effect on their electronic properties

Abstract

Atomic structure and electronic properties of Ni films condensed on the Mo(011) substrate at low temperature ( T= 5 K) with and without subsequent annealing are studied by low-energy electron diffraction (LEED), electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), and contact potential difference (CPD) within the coverage range of 5 monolayers. The near-monolayer and duolayer films show surprisingly high adatom mobility at low temperatures which is sufficient for formation of an ordered close-packed Ni structure. Abnormal adatom mobility can be explained from the consideration of interstitial relaxation through formation of a soliton structure. This mobility is, however, insufficient to provide perfect monolayer fillup. Work function changes taking place under low-temperature deposition within the 5 monolayer coverage range are consistent with the overall enhancement of surface roughness, excluding the regions near a monolayer and duolayer. The multilayer film deposited at T < 78 K acquires an amorphous structure characterised by the correlation radius of about 1.5 interatomic distances ( a). The EEL spectrum taken from such an amorphous multilayer shows no fine structure peculiar to the annealed well ordered film. The fine structure emerges at the very early stage of ordering under annealing, when the film continues to be amorphous with the correlation radius of about 1.6 a. The emerging fine structure corresponds to the entire set of losses including those for transitions between narrow d bands. So such bands may be formed not only in perfect Ni crystals, but also in amorphous material.