Growth Mechanism And Microstructure Of Al Films Deposited On Ionic Liquid Surfaces

Thin Al films, deposited on ionic liquid substrates by thermal evaporation method, have been fabricated successfully and their morphologies, microstructures and growth processes have been studied systematically.The main results are summarized as follows:(1) A large number of quasi-circular aggregates with different diameters exist in the continuous films. The mean size of the aggregates is about a few microns and it gradually increases with the deposition rate f. For the nominal film thickness d<6.0 nm, the average area of the quasi-circular aggregates, namely Sav, satisfies Sav∝(1-e-Kd); for 6.0 nm 5.0 nm or the deposition rate f> 0.10 nm/s.(2) The surface morphologies as well as microstructures of the Al thin films have been investigated extensively by atomic force microscopy (AFM). Both the quasi-circular aggregates and the region around the aggregates are composed of small grains and the mean sizes of the grains in and out of the aggregates are almost the same. The aggregates grow into compact masses and the granular size distribution is homogenous. Furthermore, it is observed that the surface fluctuation is moderately large in the region out of the quasi-circular aggregates. It is also observed that the outer edges of the aggregates exhibit radial corrugations which mainly result from the relaxation of the compressive stress and the diffusion behaviors of the deposited grains.(3) We have also investigated the crystalline nature of the films by transmission electron microscope (TEM). A typical coexistent microstructure of the crystallized and amorphous states within a sustained film is observed simultaneously. The aggregates are composed of numerous crystal grains, while most of the area outside of the aggregates is nearly amorphous. The average size of the crystal grains is about 5.7±1.7 nm. It is suggested that these characteristic microstructures of the films should be related to the kinetic energy of the deposited atoms and the physicochemical parameters of the ionic liquid surfaces. The experiment indicates that the growth of the quasi-circular aggregates results from two kinds of coalescing mechanisms, i.e., capturing deposited atoms, crystal grains, or amorphous grains and the coalescing of other aggregates.The thesis is organized as following:In chapter I, it is given that a brief review of the basic fabrication methods and detection techniques of the metallic thin films. The growth mechanism of thin film systems on solid and liquid substrates is introduced and the similarities and differences of the metallic thin films on different substrates are compared. Furthermore, the crystallization of the metal is discussed.In chapterⅡ, the basic principle of the experiment, experimental facilities and method are shown in detail.In chapterⅢ, the surface morphology and microstructure of the Al film system deposited on the liquid substrates have been investigated intensively. The growth mechanism of the Al films deposited on the ionic liquid substrates is obtained.In chapterⅣ, main conclusions and prospect are summarized.