Growth mechanism of ordered stress-induced patterns in Al films deposited on silicone oil surfaces

An optical microscope study of large spatially ordered patterns in an aluminium (Al) film system deposited on silicone oil surfaces is presented in this letter. The ordered patterns, namely bands, are composed of a large number of rectangle-shaped domains, which are evolved from small triangle-shaped domains with size less than 1??m in vacuum conditions. The bands start from the film edge and then extend towards the central region of the sample. Both the length and width of the rectangle-shaped domains in each band decrease approximately linearly as the band extends. It is pointed out that the appearance of the bands represents the distribution of the internal stress in the Al films. The theoretical analysis shows that due to the characteristic boundary condition and interactions between the metallic films and the liquid substrates, the nearly free sustained Al films may contain a series of sinusoidal stress distributions with different amplitudes and frequencies, and their composition results in the formation of the ordered stress-induced patterns.