Aging and crystallization of evaporated amorphous selenium films

A letter. Influence of ageing on the amorphous--crystalline transition was studied for thermally evaporated Se layers on Al substrates. Three groups of identical samples were aged for 1 week, 7 weeks, and 1 year, respectively at 293 deg K. After ageing, thermograms were obtained at heating rates from 0.5 to 50 deg C min--1 over the temp. range 110-570 deg K. It was found that irrespective of the ageing time the glass transition temp. Tg and crystallization peak temp. Tm increased with the heating rate. Thermograms obtained for the same heating rate but various ageing times showed that as sample age increased Tm decreased. The shift in Tg towards high temp. was marked for ageings of short duration but slowed down for samples older than 2 months. Crystallization energy of about 1 eV was obtained from the kinetics used to explain the results, its value increasing slightly with sample age. The crystallization time constant was 26 days for 293 deg K. Samples aged for 1 year were always amorphous. 16 ref.--E.J.S.