THICKNESS DEPENDENCE OF THE PHASE-TRANSITION TEMPERATURE IN AG2SE THIN-FILMS

Thin films of silver selenide (Ag2Se) between thicknesses of about 700 and 2200 Å have been prepared on glass substrates at room temperature in a vacuum of 5×10-5 Torr. After vacuum annealing the films (at about 373 K for 3 h) electrical resistivity measurements on these films have been carried out in vacuum. From the increase in the rate of decrease of resistance with temperature, the phase transition temperatures (orthorhombic to body-centered cubic) of the different films have been located. It is found that the phase transition temperature of the thin films is a function of thickness increasing with a decrease in the thickness. This observation has been explained by a recently developed theory [V. Damodara Das and D. Karunakaran, J. Phys. Chem Solids 46, 551 (1985)] of phase transitions in thin films modified further. Also, an order-of-magnitude value of the difference in the function of specific surface and interfacial energies of the two phases has also been determined using the theory.