Study On The Growth Mechanism And Microstruc-Ture Of Iron Aggregates On Silicone Oil Surfaces

The study on the fabrication and characteristic physical phenomena of various nanos-tructures, such as quantum dots, nanoribbons, nanorods and branched atomic clusters etc., is one of the most important topics in modern scientific research field. During the last two decades, due to the characteristic physical properties, metallic films and, in particu-lar, nanostructures grown on liquid substrates have attracted much attention and fruitful results have been obtained.In this dissertation, the ramified iron (Fe) aggregates grown on silicone oil surfaces are successfully fabricated by vacuum thermal evaporation method. The microstructure and evolution behaviour of the aggregates are studied by atomic force microscopy (AFM). The experimental results show that the growth mechanism of the Fe aggregates can be traced to the two-stage growth model, which is similar to that of the Au and Ag aggregates on silicone oil surfaces.The experimental measurement shows that the branch width of the ramified Fe ag-gregates is almost independent of the nominal film thickness h. The high resolution AFM images exhibit that the ramified aggregates are composed of numerous Fe nanoparticles. The diameter of each nanoparticle in the aggregates is measured and its distribution is pre-sented. The Gaussian fitting of the distribution shows that the mean size of the nanoparticles Φc≈34nm. As the nominal film thickness increases, the mean size Φc remains unchanged. Meanwhile, the height of the nanoparticles in the aggregates is also measured. The statistic distribution of the heights reveals that the mean height of the nanoparticles is also inde-pendent of the thickness h. Hence, we suggest that, during the growth process, the material density of the Fe nanoparticles increases gradually with h, mirroring the existence of the condensation process in the nanoparticles.The high resolution field emission scanning electron microscopy is used and the results show that the nanoparticles observed by AFM are further consisted of particles with the average size around7-8nm and a large amount of vacancies exist among the particles, indicating the incompact structure of the nanoparticles. This finding again provides a strong evidence for the condensation behaviour of the nanoparticles.Since the dynamic scaling analysis can be performed to characterize the growth mode of the surface, the dynamic scaling behaviour of the ramified Fe aggregates is studied. The analysis shows that, as the nominal film thickness h increases, the growth exponent β=0.23±0.02remains unchanged. For h<0.80nm, the roughness exponent a reads0.66, which is greatly decreased to0.42as h>0.80nm. This phenomenon indicates that, as h increases, the growth mode of the ramified Fe aggregates transforms from the LDS growth mode to the traditional KPZ growth mode. The theoretical analysis reveals that, due to the nearly free diffusion character, the aggregates formed in the early growth stage exhibit large diffusion coefficient, which may be greatly suppressed as the nominal film thick-ness increases. This decrease of the diffusion coefficient finally results in the growth mode transformation of the aggregates.The contents of the dissertation are organized as follows:In Chapter1, firstly, the history of the thin film, ultrathin film and nanosystem is summarized. Then a brief review about the fabrication condition, growth mechanism and microstructure of the nanosystems on solid substrates is presented. The dynamic scaling analysis is introduced to describe the surface roughening. Finally, the research process on the preparation and growth mechanism of the ramified aggregates deposited on liquid sur-faces is detailed.In Chapter2, we systematically study the fabrication, microstructure and self-assembly of the Fe aggregates grown on silicone oil substrates and the growth mode of the aggregates is studied.In Chapter3, the microstructure and surface evolution of the ramified Fe aggregates are studied by atomic force microscopy and the material condensation behaviour of the nanoparticles is explained theoretically. In Chapter4, the dynamic scaling analysis of the surface roughening of the aggregates is performed and the transformation of the growth mode is analyzed.In Chapter5, based on the present work, the main conclusions and prospects are pre-sented.