Study On The Formation Mechanism And Microstructure Of Ag Films On Silicone Oil Surfaces

The nature of the substrates influence greatly on the diffusion and aggregation behavior of the deposited atoms. Although the films on solid substrates can control and keep stably the film microstructures and modify the physical properties of the films, the physical properties of the films deposited on solid substrates, such as the microstructure, the critical temperature of superconductivity, the phonon spectrum and so on, may obviously be affected by the characteristic internal stresses, owing to the lattice mismatch and the strong interactions between the films and the solid substrates. Based on the fact that the liquid surfaces can make up for the deficiencies for the solid surfaces, a nearly free sustained silver film systems on silicone oil surfaces are made by thermal evaporation method and the formation mechanism and microstructures of the Ag films are studied systematically in this thesis.A silver film system which is deposited on silicone oil surfaces by vapor phase deposition method has successfully been fabricated. It can be proved that, the growth mechanism of the silver film approximately obey the two-stage growth model. It is found that if the deposition rate is fixed and the nominal film thickness increases, the number of the atoms deposited on the surface increase, so that the stable ramified aggregates can capture more atoms in a unit time, and the average width of the ramified aggregates shows the trend of increasing. Meanwhile, the increase of the number of the atoms deposited on the surface results in the increase of the density of the ramified aggregates, therefore the average width of the ramified aggregates shows the trend of decreasing. For a fixed deposition rate, these two tendencies counteract each other, which results in the stable average width of the ramified aggregates, i.e.,0.5μm, according with which of the other metallic aggregates on liquid surfaces.We also take photos for the silver film by AFM, discovering that the ramified aggregates are composed of smaller atomic clusters, the average diameter of the clusters exhibits a Gaussian distribution. For a fixed deposition rate, the average diameter shows no significant change with d. Its principle is similar to the principle that the change of the average width of ramified aggregates doesn't follow the change of the d. In order to study the influence of the thickness(d) on coverage(σ), we produce a series of samples with different thicknesses under a fixed temperature. The results of the change behavior ofσwith d are presented. In the center of the sample, It is found that, within the interval of 020 A, however,σincreases slowly with the increase in d, then gradually tends to a saturation value. In our analysis, this phenomenon is caused by the competition between two trends:the probability of nucleation of the silver atoms deposited on silicone oil substrates increases with the deposition time, the numerical density of atomic clusters andσincrease with d. On the other hand, the continuous diffusion of the silver atomic clusters towards the sample edge results in the decrease of the coverage ratio in the central region of the sample. When the quantity of silver atomic clusters diffusing towards the sample edge balance with the new clusters generated during the deposition,σapproaches a saturation value.This thesis is divided into three chapters and organized as following:In chapterⅠ, we describe three film growth patterns on two-dimensional solid surfaces, and present a brief review of the previous and recent studies on the atomic clusters and thin film systems on liquid surfaces.In chapterⅡ, we study on the preparation method of the Ag film and describe the theory of the thermal evaporation method.In chapterⅢ, the formation mechanism and microstructures of the silver film system deposited on silicone oil surfaces are studied systematically.