Study On The Microstructure And Growth Mechanism Of Cu Films On [Bmim]BF₄Surfaces

A copper film system with characteristic morphology deposited on ionic liquid ([bmim] BF4) surface was successfully fabricated by thermal evaporation method. And its surface morphology, microstructure, formation mechanism and roughening mechanisms were analyzed and studied. The results are summarized as below:(1) When the nominal film thickness d=0.5nm, the copper atoms deposited on [bmim] BF4surface compose ramified or reticular aggregates, then many quasi-circular aggregates were found in the reticular aggregates when d is greater or equal to1.0nm. The surfaces were observed to exhibit the coexistent morphology of the quasi-circular and ramified aggregates when the deposition rate f is in the range of0.05nm/s-1.8nm/s. We suggest that the different diffusion behaviors of Cu nanoparticles composing the aggregates during and after deposition lead to the formation of the quasi-circular aggregates. Further studies show that when the deposition rate is0.05nm/s, the most probable diameter of the quasi-circular aggregates Φm rises up with the increasing nominal thickness d, the number density N declines with d, the total coverage of the quasi-circular aggregates C is positively correlated with the nominal thickness d and meeting the exponential relationship C∝(1-e-kd)well; When the nominal film thickness d=6.0nm, the most probable diameter of the quasi-circular aggregates Φm decreases with increasing deposition rate f, the number density of quasi-circular aggregates N remains the same with the increasing f, the total coverage of the quasi-circular aggregates C drops with the rise off. We suggest that the two main growth mechanics of the quasi-circular aggregates are the coalescence of the quasi-circular aggregates and capturing depositing atoms or atom clusters.(2) The microstructures of the copper film are observed by atomic force microscope (AFM). The experimental results show that both the ramified and quasi-circular aggregates are composed of particles of copper atoms with the mean size of70nm, and the mean size is independent of d. The average heights of the ramified and quasi-circular aggregates are almost the same and increase linearly with d. It’s found that the growth exponent β=0.42±0.02. And the roughness exponent a increases with thickness d from0.75and reaches1.0when d=4.0nm. It then tends to stabilize. Researches show that because of the changing of shadowing effect, the growth mechanism of Cu film transforms from balanced roughening mechanism to irregular roughening mechanism.This thesis is divided into four chapters and organized as following:In chapter I, a brief review of the methods for fabricating film and the growth theories of thin film systems, and a summary of the study on dynamic scaling behavior and surface roughening mechanism are given. Then the research progress of thin metal film systems on liquid surfaces is introduced.In chapter II, the methods for fabricating films deposited on [bmim] BF4substrates are given.In chapter III, the typical morphology, microstructures, formation mechanism and the dynamic scaling behaviors of the Cu films deposited on [bmim] BF4substrates have been investigated systematically.In chapter IV, the main conclusions and prospect are given.