Comparative study of electron- and photo-induced structural transformations on the surface of As 35 S 65 amorphous thin films A. Kovalskiy a, ⁎ , J.R. Neilson a , A.C. Miller a , F.C. Miller b , M. Vlcek c , H. Jain a a Materials Science and Engineering Department, Lehigh University, 5 East Packer Ave., Bethlehem, PA 18015, USA b Sherman Fairchild Laboratory, Lehigh University, Bethlehem, PA 18015, USA c Faculty of Chemical Technology, University of Pardubice, nam Cs. legii 565, Pardubice, 53210, Czech Republic Received 9 January 2008; received in revised form 13 March 2008; accepted 7 April 2008 Available online 15 April 2008 Abstract Change of electronic structure and chemical composition on the surface of freshly prepared As 35 S 65 thin films caused by electron- and light irradiation have been studied by high-resolution X-ray photoelectron spectroscopy. The mechanisms of the induced transformations are compared. It is shown that light irradiation causes redistribution of chemical bonds without change in chemical composition. The products of such light- induced structural transformations were also identified by Raman spectroscopy in the volume of thin films. Electron irradiation changes chemical composition of the surface by creating an As-enriched layer due to the formation of As–O bonds. Anomalous increase of the ~10 eV band associated with non-bonding As 4s electrons was observed after light- and low dose e-beam irradiation. © 2008 Elsevier B.V. All rights reserved. Keywords: Glass; X-ray photoelectron spectroscopy (XPS); Photo-induced effects; Electron-induced effects 1. Introduction Photo- and electron lithography [1–4] are two of the most promising applications of thin films of chalcogenide glasses (ChG), which are non-oxide vitreous compounds of chalcogen atoms (S, Se or Te) with elements of IVA and VA groups of Periodic Table (Ge, As, Bi, P, etc.). Photo-induced effects in ChG have been widely studied by different authors [5–7], being explained within photodarkening, photo-induced volume change, photo-induced defect creation and photorelaxation mechanisms. However, the mechanism of the photo-induced effects and, especially, the kinetics of photostructural changes are still the exciting topics in the physics of disordered solids. At the same time, lithography applications of high-energy electrons, such as from a scanning electron microscope (SEM), have been reported to be based on a thermal expansion through the thickness of films [8], as well as increasing the refractive index of the glass [9]. Several authors have offered also such explanations as electron trapping within the film causing electrostatic repulsion between layers [8,10] and homopolar bonds breaking, akin to that proposed for explaining photo-induced effects [8]. We utilized earlier the electron- induced change in ChG to fabricate by wet etching parallel nanolines 80 to 250 nm in height, 27 nm in widths and separated only by 7 nm [4]. Such fine motives can be obtained by electron beam irradiation of As 35 S 65 thin films due to the amorphous nature of their structure and small size of structural building blocks. Chalcogenide layers of this composition have been effectively used also for direct laser writing of complex patterns with hexagonal air holes [11]. However, the atomic and electronic origin of the induced structural transformations, as well as the role of surface oxidation, if any, remains unclear. The aim of this paper is to compare the mechanisms of photo- and electron-induced structural effects of the surface layers in thin ChG film using high-resolution X-ray photoelectron spectro- scopy (XPS). Additionally, we have compared these photo- induced structural changes in the very top part of ChG film with Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 7511 – 7518 ⁎ Corresponding author. Tel.: +1 610 758 6879; fax: +1 610 758 4244. E-mail addresses: ank304@lehigh.edu (A. Kovalskiy), fcm1@lehigh.edu (F.C. Miller), miroslav.vlcek@upce.cz (M. Vlcek), h.jain@lehigh.edu (H. Jain). www.elsevier.com/locate/tsf 0040-6090/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.04.054