Physical aging effects on the structural and optical properties of nano As-Se-Tl films

As20Se65Tl15 films of thickness of 400 nm as a candidate of As-Se-Tl films were prepared by thermal evaporation technique under a vacuum of 10(-6) Torr. The aging of these films for 4 and 8 months and were studied. The as deposited films have amorphous nature and the aged films have (170) and (432) preferred nanocrystalline orientations. The crystallite size of 8 months aged films are 22 and 43 nm respectively. Within the wavelength range (200-1100) nm, optical parameters were measured and the optical constants were calculated within the visible range. Indirect electronic transition was dominated. The value of the optical energy gap, E-gi(opt) increases with aging from 1.68 to 1.82 eV. The dispersion parameters were studied by single oscillator model. Aging process increases the values of N/m* and E-o while decreases the values of n, epsilon(infinity), epsilon(L) and E-d. The obtained changes were attributed to structural enhancement and ordering due to aging process. The single oscillator model is used to describe spectrum of refractive index. Free carriers concentration makes a difference between epsilon(infinity) and epsilon(L) values. The calculated values of epsilon(1) are higher than the values of epsilon(2). The Optical conductivity as well as VELF and SELF were also studied. (C) 2016 Elsevier B.V. All rights reserved.