Investigation of fractal properties of nanosized gold, silver and copper films: atomic force and tunnelling microscopy
In this work the surface of thin gold, silver and copper films on the dielectric mica substrate was investigated using the probe microscopy in STM and AFM regimes. It has been found that the metallic films (gold, silver and copper) have the fractal structure. The results obtained using the scanning probe microscope MFP-3D (Asylum Research, USA) in AFM mode (NITU "MISiS", Moscow) allow further verification of the results of the STM "UMKA-02G" (Tver State University, Tver), and also confirm and generalize the conclusion drawn that metallic nanoclusters on dielectric substrates can have a self-similar fractal structure. It was shown that for nano-sized copper films, in contrast to nano-sized gold and silver films, fractal structures on the entire surface of the sample under investigation are not detected, but are found only in certain areas. This indirectly indicates the possibility of selecting such conditions in sample preparation (beam density, temperature substrates), which can ensure the production of fractal structures on the entire surface of a nano-sized copper film. The values of the fractal dimension for the profile and the surface found by us using two alternative methods: atomic force and tunneling microscopy, on the one hand, agree with each other, and on the other, are generally correlated with the results of other studies. The lacunarity (prefactor) for nano-sized gold films was estimated for the first time using the results of STM. Using of two alternative experimental methods allows strictly control the quality of the obtained images in order to exclude artifacts, large-scale discrepancies and takes into account the influence of defects in the surface of the substrate or the possible appearance of oxide films on the film surface. Obviously, having the ability to compare data on mode of vacuum deposition (substrate temperature, beam density, time spraying, etc.), and data on the surface relief, it is possible to develop technologies for «constructing» the surface with a given structure, including fractal structure.