Studies On Growth Mechanism Of Metal Surface Film Using In Situ Spectroscopic Ellipsometry

Metal surface thin films can change the surface properties of materials, producestructural or functional properties, which greatly broaden the application area ofmetallic materials. For example, TiO2, ZrO2nanotubes and polyaniline nanostructuredfilms, which have large surface-tovolume ratio that can dramatically improve thematerial performances and reduce the component size and weight, have wideapplication in optical, electrical, magnetic, thermal and catalytic fields. However, thegrowth mechanism of these metal surface films is still unclear so far, employing thehighly sensitive and non-destructive in situ techniques to monitor the growth process ofmetal surface film is exactly desirable.In this thesis, in situ spectroscopic ellipsometry (SE) technique was employed toinvestigate the initial stage growth of anodic TiO2nanotubes in organic electrolyte. Theinfluences of the water concentration in electrolyte and anodization voltage on thegrowth process of anodic TiO2nanotubes were also studied by in situ SE. Combinedwith the FE-SEM results, the evolution of the characteristic parameters of anodic TiO2film upon anodization was obtained by deconvoluting the ellipsometric spectra withappropriate models (one-layer, two-layer and three-layer optical models). It is found thatthe rate of anodic oxidation reaction increases with the water concentration inelectrolyte and anodization voltage increasing; anodic TiO2film grown slowly inorganic electrolyte, each layer of the anodic film was in an unstable stage within thefirst80s anodization.The highly sensitive SE was also employed to in situ monitor the growth of anodicZrO2nanotubes in inorganic electrolyte. The influences of the F-concentration inelectrolyte, anodization voltage and temperature on the growth process of anodic ZrO2nanotubes were also studied. Combined with the FE-SEM results, the in situ SE spectraof porous layer can be interpreted better with anisotropic EMA optical model. Foursuccessive phases, namely, formation of compact barrier layer, formation of pores, poreevolution to nanotubes and the nanotube steady-growth, were clearly distinguishedduring the initial stage of anodization. The growth dynamics of the anodic ZrO2filmwas mainly dependent on that of the porous layer, obeying the linear growth kineticswith a maximum rate of25.6nm/s under20℃,20V and0.15M F-. Improving the F-concentration in electrolyte, anodization voltage and temperature can increase the rate of anodic oxidation reaction while which should not be too large. The F-concentrationin electrolyte is likely to be the decisive factor in the formation of porous layer.The electrodeposition processes of polyaniline (PANI) in0.2M aniline+0.5MH2SO4electrolyte on Ti through potentiostatic method (PM), pulse potentiostaticmethod (PPM) and cyclic voltammetry (CV) were investigated by in situ SE. Based onthe FE-SEM results, Cauchy optical model can accurately describe the structure andcharacteristic of the PANI film. It is found that the electrodeposition processes of PANIcan be clearly divided into three successive phases, namely, the nucleation phase, lineargrowth phase and steady-growth phase. By comparing the growth kinetics results, wefind that the linear growth rate of PANI deposited by PPM was the highest of1.1nm/s,and coverage of the electrode surface was the also the largest. The linear growth rate ofPANI by PM was0.7nm/s, and the coverage of the electrode surface was smaller thanthat by PPM. In addition, PANI deposited by CV has a growth-dissolve cyclical growthrhythm with the lowest net growth rate of only0.2nm/s, and has the smallest coverageof the electrode surface.