Amorphous thin-film growth: Theory compared with experiment

– Experimental results on amorphous ZrAlCu thin-film growth and the dynamics of the surface morphology as predicted from a minimal nonlinear stochastic deposition equation are analysed and compared. Key points of this study are: i) an estimation procedure for coefficients entering into the growth equation and ii) a detailed analysis and interpretation of the time evolution of the correlation length and the surface roughness. The results corroborate the usefulness of the deposition equation as a tool for studying amorphous growth processes. Introduction. – During the last decade the study of the kinetics of surface growth processes has attracted considerable interest (cf. the reviews [1]). The dynamics of the surface morphology, e.g. in amorphous thin-film growth is dominated by the interplay of roughening, smoothening, and pattern forming processes. On the microscopic level, these processes are governed by the highly complex and only partly understood interaction of the depositing particles with the already condensed surface atoms. Despite the complexity of the growth processes on the atomic scale, experiments on the slightly coarser mesoscopic scale typically reveal some sort of regularity of the surface morphology with some superimposed small-scale stochastics [2,3]. This, in turn, indicates that the machinery of coarse-grained continuum models based on phenomenologically motivated stochastic growth equations [1] is a useful tool for the understanding and interpretation of the growth dynamics. In particular, amorphous thinfilm growth represents an attractive testing ground for the validation of such phenomenological models; this is mainly due to the spatially isotropic nature of the amorphous structure at this scale and the lack of long-range ordering. Our objective is a detailed comparison between a stochastic nonlinear evolution equation for amorphous thin-film growth [4] and experimental results on the surface morphology of ZrAlCu films prepared by physical vapor deposition that are analysed using scanning tunneling microscopy (STM). Using the aforementioned theoretical approach, we develop a method to estimate the phenomenological parameters that is based on the evolution for short times. (∗) Present address: I. Physikalisches Institut, Universität Göttingen Bunsenstr. 9, D-37073 Göttingen, Germany. (∗∗) Present address: Research center caesar Friedensplatz 16, D-53111 Bonn, Germany.