An XPS study of the early stages of silver photodiffusion in Ag/a-As 2 S 3 films Himanshu Jain * , Andriy Kovalskiy, Alfred Miller Materials Science and Engineering Department, Lehigh University, 5 East Packer Avenue, Whitaker Lab. 5, Bethlehem, 18015 PA, USA Available online 21 February 2006 Abstract X-ray induced structural changes at the Ag/As 2 S 3 interface are investigated using X-ray photoelectron spectroscopy on the samples prepared within the spectrometer. The as-prepared film consists of stable heteropolar As–S bonds as well as 16% S (and As) atoms in lower (higher) electron density configurations such as the –S–S– (–As–As–) segments with ‘wrong’ homopolar bonds. Two distinct stages of the X-ray induced diffusion are revealed. At first, silver reacts with atoms within –S–S– like segments to form Ag–S bonds. In the second stage, the Ag–S bonds decompose due to the reaction of S with As atoms within the –As–As– ‘wrong’ segments to form As–S heteropolar bonds, and silver diffuses away from the interface into the film. The results provide guideline for enhancing silver photodiffusion in chalcogenide glass. The irradiation of the (Ag–Te)/As 2 S 3 sample with X-rays shows that not only Ag, but Te also diffuses away from the surface. Ó 2006 Elsevier B.V. All rights reserved. PACS: 79.60.Ht; 68.35.Fx; 61.43.Fs Keywords: Diffusion and transport; Chalcogenides; Photoinduced effects; XPS 1. Introduction It is well known that the diffusion of silver into chalco- genide glass (ChG) matrix is enhanced by increasing the temperature, or by exposure to visible light (photodoping) [1,2], X-rays [3,4], electrons [5] and ions [6]. The unusual radiation enhanced diffusion, accompanied by the change in chemical reactivity, is very useful in modern lithography, programmable metallization cell devices, as well as in the development of holographic materials, relief images, dif- fractive optical elements, MEMS structures, submicron patterns, etc. [7–10]. In spite of numerous investigations during the past three decades [1,2,7,11–17], the mechanisms of irradiation induced silver diffusion in ChG matrix remain unclear, especially with regard to ionizing radiation (X-rays, electrons and ions). There is a disagreement in the literature even about the number and characteristics of the stages of silver photodiffusion. Very few investigations are devoted to the compositional features of this phenomenon. Therefore, in the present work we have employed X-ray photoelectron spectroscopy (XPS) to characterize in situ the early stages of X-ray induced diffusion as well as corresponding changes of electronic structure at the Ag/As 2 S 3 interface. Similar observations are also made at the (Ag–Te)/As 2 S 3 interface. 2. Experimental As 2 S 3 films (500 A ˚ thick) were deposited on Si sub- strate (Wacker Siltronic Corp., 525 ± 20 lm thickness) by thermal evaporation of the bulk glass (Amorphous Materi- als Inc.) of same composition, followed by the deposition of an 70 A ˚ thick film of silver metal (Puratronic, 99.9999%) on top of the ChG film. In a few samples the film of silver–tellurium alloy (86% Ag + 14% Te, as mea- sured by XPS) was deposited, in place of pure silver, on top of the As 2 S 3 layer. 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.11.044 * Corresponding author. Tel.: +1 610 758 4217; fax: +1 610 758 4244. E-mail address: h.jain@lehigh.edu (H. Jain). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 562–566