An in situ scanning tunneling microscope (STM) was used to observe the morphological changes accompanying the selective dissolution of Ag h m low-Ag content Ag-Au alloys in dilute perchloric acid This study was undertaken to explore the role of surface diffusion in alloy corrosion pmcesses. These d t s are interpreted within the h e w o r k of the kink-ledge-terrace model of a aystal surface and a recent model of alloy corrosion based on a variant of percolation theory. The corrosion process leads to roughenhg of the surface by dissolution of Ag atoms h m terrace sites. h e a l i n g or smootheniug of the surface occurs by vacancy migration through dusters and the subsequent annihilation of dusters at terrace ledges.
Crystallographic and surface morphological characteristics of polycrystalline hcp Ti and Zr thin films were studied as a function of the homologous substrate temperature TS/TM and the thickness t of the films (28 nm ≤ t ≤ 380 nm). TS is the substrate temperature during deposition and TM is the melting point of the film's material. For the whole range of considered temperatures (0.14 ≤ TS/TM ≤ 0.48) Zr films presented a {0002} crystallographic orientation. As TS/TM increased, Ti films suffered a transition from a columnar grain structure with {0002} preferential crystallographic orientation to a cone-like-shape grain structure with {1011} preferential crystallographic orientation. Our results suggest that Zr films suffer a structural transition from Zone T to Zone II at temperatures similar to those predicted by Thornton's Structure Zone Model for thick films while Ti films do not have a microstructure typical of Zone II even for relatively high values of TS/TM, presenting a transition from Zone I to Zone T in the studied range of temperatures.
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