NANOSCALE ENGINEERING OF ALUMINIUM SURFACES

The development of regular, finely spaced, arrays of metal ridges and troughs, i.e. nanotex tures, by surface treatment of aluminium has been probed by atomic force microscopy (AFM) and transmission electron microscopy (TEM), assisted by radio frequency glow discharge optical emission spectrometry (rf GDOES). AFM reveals the grain orientation dependence of the tex ture and its increased dimensions with increased metal purity. TEM reveals atomic number contrast effects at the centres of metal ridges comprising the boundaries of the cells, thus implicating the composition and structure of the substrate. Enrichment of copper in the alloy immediately beneath the residual alumina film is evident in rf GDOES depth profiles; conversely, iron and silicon, present at similar levels as copper, are not detected. This suggests strongly that crucial impurities, i.e. silicon, are present as fine segregates in the alloy with a grain orientation dependent distribution originating from casting. The distribution of segregates controls the dissolution of the adjacent aluminium matrix in surface pretreatment, thus generating nanotex tures of regular arrangements of metal ridges and troughs with an amorphous alumina film developed over the macroscopic aluminium surface.