High Resolution Electron Microscopic Observation of Crystallization and Decomposition of Amorphous Selenium Films

The crystallization and decomposition process of amorphous Se films, which takes place by electron beam irradiation in an electron microscope, has been investigated by high resolution electron microscopy. A vacuum-deposited film 5 nm thick has the structure unit of Se molecules composed of as few as three or four atoms. It transforms to the hexagonal crystal, through an amorphous structure whose unit is long-chain molecules. An amorphous layer covering the crystallized layer has been observed in the film before the complete crystallization. It has been found that Se atoms, which are a segment of a chain, are removed from the crystal surface in the early stage of the decomposition.