Solid-to-solid phase transformations of nanostructured selenium-tin thin films induced by thermal annealing in oxygen atmosphere

The structural and morphological evolution of nanostructured thin films obtained from thermal evaporation of polycrystalline Sn-Se starting charge as a function of the subsequent annealing temperature in an oxygen flow has been analysed. High-resolution transmission electron microscopy, small area electron diffraction, digital image processing, x-ray diffraction and Raman spectroscopy have been employed in order to investigate the structure and the morphology of the obtained films. The results evidenced, in the temperature range from RT to 500°C, the transition of the material from a homogeneous mixture of SnSe and SnSe2 nanocrystals, towards a homogeneous mixture of SnO2 and SeO2 nanocrystals, with an intermediate stage in which only SnSe2 nanocrystals are present.