Much has been written about the structure of a-Se [1-5]. Selenium-based glasses have been the subject of renewed interest in the field of materials research. Recently Kotkata [6] has described, in detail, phase properties of the semiconductor Se in singleand double-phase systems. In this letter we have tried to examine vapour-grown Se on different substrates under activated and non-activated conditions. Amorphous-Se film inhibits structural changes due to (i) the temperature of the substrate, (ii) the vapour temperature, and (iii) the deposition rate. Subsequent heat treatment and ageing transformed the a-Se films into its stable crystalline configuration. It has been seen by Beltov and Belan and others [7, 8] that the substrate plays a crucial role in interpreting the physical processes which lead to structural modifications under suitable conditions. It has been seen by the present authors [9] that deposition of an a-Se film (110 nm) on z-cut quartz after heat treatment just above the transition temperature results in a characteristic dendritic growth which is absent even when in glassy and metallic substrates. The present letter deals with a-Se films on glassy and quartz substrates which were heat treated stepwise and allowed to age for a period of one year (activated). Another batch of films were simply aged without any prior heat treatment (nonactivated). The structural changes which occurred after ageing are studied selectively. Pellets of Se (99.999%, obtained from Johnson Matthey & Company) were melted in a filamentwound molybdenum boat slowly under a vacuum of 2.6 x 10 .3 Pa when a particular substrate at room temperature was placed 5 cm above the heat source (Polaron-150 Vacuum coating unit). Substrates of mirror-polished pure soda glass and z-cut quartz single crystal were cleaned using trichloroethylene, acetone and ethyl alcohol and exposed to the atmosphere prior to deposition. Several specimens of a-Se films grouped into thicknesses of 123 and 223 nm were prepared on the substrates under identical conditions of the vacuum and the vapour temperature (350 °C), and at a uniform deposition rate of 8 nm s -1. The thicknesses of the films were measured by an in-house FTM-5 Edwards monitor and further verified by an ellipsometry technique. The prepared samples of a-Se on glass, S-I 223 nm and quartz, S-II 123 nm, were heat treated between 50 and 100 °C for 40 min in steps of 10 °C, and then returned to room temperature at a rate of 1 °C min-1. Samples S-I, S-II and an untreated specimen on