Study On The Microstructure And Growth Mechanism Of Au Films On Ionic Liquid Substrates

Thin Au films, deposited on ionic liquid substrates by vacuum thermal evaporation method, have been fabricated successfully and their morphologies, microstructures, surface roughening mechanisms and growth processes have been studied systematically.The main results are summarized as follows:(1) The morphologies of the Au thin films evolve with the nominal film thickness d. For d≤0.5 nm, the ramified or net-shaped aggregates can be found. The growth mechanism of them obeys the two-stage growth model. For d> 0.5 nm, the typical coexistent morphology of the quasi-circular and ramified aggregates can be observed. The number density N of the quasi-circular aggregates decreases rapidly with d and then tend to be stable. The average diameterΦm and total surface coverage C of all the quasi-circular aggregates increase with d, and satisfyΦm∞(1-e-d/c) and C∞(1-e-kd) with c= 3.19±0.04 and k= 0.35±0.02. We suggest that the growth of the quasi-circular aggregates results from two kinds of mechanisms, i.e., capturing deposited atoms or small clusters and the coalescing of other aggregates. It can be also found that the branch width of the ramified aggregates increases linearly with d, which indicates the diffusion behaviors of the Au nanograins in the ramified aggregates changes gradually during deposition.(2) The surface morphologies as well as microstructures of the Au films are obtained by atomic force microscopy (AFM). It is found that both the ramified and quasi-circular aggregates are composed of small nanograins with the mean size of the order of 101 nm and remain almost unchanged; The average height h1,h2 of the ramified and quasi-circular aggregates increase linearly with d, and the growth rate of h1 is far greater than it’s of h2, indicating the growth mechanisms of the two aggregates are different. The root-mean-square roughness (wrms) and the one dimensional power spectra density (1DPSD) of the Au films are measured by the AFM software. It is found that the growth exponent β=0.33±0.05, and the roughness exponentαvaries fromα< 1 toα>1 for 0.5 nm≤d≤20.0 nm. Based on the characteristic ofαandβof the Au systems, the surface roughening mechanisms are analyzed.(3) We have also investigated the crystalline nature of the films by transmission electron microscope (TEM) and X-Ray Diffractometer (XRD). It is found that the films exhibit polycrystalline structure. The aggregates are composed of numerous crystal grains with the average size is about 3.7±0.1 nm; as the nominal film thickness increases, higher crystall inity are observed.The thesis is organized as following:In chapterⅠ, A brief review of the growth theories of the thin film systems on solid substrates and the study on thin film systems on various surfaces are given. Then the research progress on dynamic scaling behavior and surface roughening is introduced.In chapterⅡ, The basic principle of the experiment and methods for different specimens are shown in detail.In chapterⅢ, The surface morphology, microstructure and the dynamic scaling behaviors of the Au films deposited on the ionic liquid substrates have been investigated systematically. The growth mechanism of the Au films deposited on the ionic liquid substrates is obtained.In chapterⅣ, Main conclusions and prospect are presented.