Amorphous tin oxide films deposited on carbon substrates have been studied by high-resolution transmission electron microscopy. As-deposited film was composed of a mixture of microcrystallites of SnO, SnO2 and SnO3 with size of 2 nm. Crystallization took place above 450°C. SnO crystals appeared between 450°C and 500°C, whereas SnO2 crystals appeared above 550°C. The appearance of β-tin crystals with the reduction of tin oxide has been verified using the heating stage of the electron microscope. A drop of liquid tin was recognized upon heating above 500°C. The difference in crystallization upon applying an electron beam, synchrotron radiation and heating in vacuum has been summarized and discussed with respect to the problem of the excitation of crystallites.
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