Ageing of Ge24.9Sb11.6S63.5 thin films under various conditions

Amorphous Ge24.9Sb11.6S63.5 thin films prepared by thermal evaporation were aged for more than 1 year under various conditions: in the dark in a desiccator, in a dark and humid atmosphere and under laboratory conditions under daylight. The bleaching of thin films (the blue shift of the optical band gap) was observed with the magnitude depending on the storage conditions. The overall kinetics of ageing (bleaching) follows well the stretch exponential function with the formal rate depending on the storage conditions and the stretch exponent slightly varying in the region of 0.54-0.6. The photo-sensitivity of the aged thin films was significantly affected by storage conditions and was found to decrease with the increasing time of ageing. The changes in thin films during the ageing were monitored with respect to the chemical composition, the structure, the surface wettability, the surface topology and information about the depth and optical parameters of the formed over-layer and were finally correlated with the storage conditions.