Substrate Temperature Effects On The Microstructure And Growth Mechanism Of Silver Films On Ionic Liquid Surfaces

Silver (Ag) thin films have been fabricated successfully on ionic liquid ([bmim]BF4) surfaces under different substrate temperatures (Ts) by thermal evaporation method. We have systematically studied the surface morphology, microstructure, crystalline and formation mechanism of the films and obtained the main results as follows:(1) When the substrate temperature Ts>275K, the Ag films exhibit a typical coexistent morphology of the quasi-circular compact and ramified aggregates, both of which are constituted by numerous nanoparticles. As Ts decreases, the density of the quasi-circular aggregates increases, while the average diameter Φm and total surface coverage C of all quasi-circular aggregates decrease, which satisfies C∝(1-e-kTs). Meanwhile, the coverage of the ramified aggregates increases, while its width remains almost unchanged.(2) When Ts reaches near273K, the shape of the aggregates gradually changes from quasi-circular to irregular compact morphology and then a coexistent morphology of the irregular and ramified aggregates is found. As Ts further decreases, the size of the irregular aggregates decreases and its number density Ni increases, which satisfies lgNi∝1/TS. We suggest that the change of the aggregate morphology due to the viscosity coefficient of ionic liquid and diffusion coefficient of the nanoparticles on liquid surface varying with Ts.(3) The microstructure studies show that the diameter of the nanoparticles in Ag aggregates is of the order of101nm. The average height of aggregates linearly increases with decreasing Ts. Meanwhile, the average diameter of the nanoparticles inside the aggregates has no significant change with the lowering of substrate temperature. The above phenomena imply that the geometrical shape of the nanoparticles transfers gradually from flat to spherical structures. The possible reason is that the surface and interface energy of aggregates change with Ts. On the other hand, the kinetic scaling and rough mechanism analysis show that the roughness wrms increases with the decreasing of Ts, and the roughness exponent a remains a>1. By transmission electron microscope experiment, it is found that the Ag films exhibit polycrystalline structure and no obvious changes of the crystallization are observed with Ts.The contents of this thesis are organized as follows:In chapter1, the basic theory of the thin film formation, surface roughening mechanism and the deposition conditions of the thin film growth are briefly described. The study of the metallic thin films on the liquid surfaces is also summarized.In chapter2, the preparation of the Ag aggregates on the ionic liquid surfaces is detailed.In chapter3, we systematically study the surface morphology, microstructure, kinetic scaling behavior and crystallization of the Ag aggregates with the substrate temperature. And the reasonable interpretation has been given.In chapter4, the main conclusions and prospects are presented.