Vacuum 77 (2004) 63–68 Chemical bonding of a-Ge 1x C x :H films grown by RF reactive sputtering C.Q. Hu a , W.T. Zheng a,Ã , B. Zheng a , J.J. Li a , Z.S. Jin a , X.M. Bai a , H.W. Tian a , Q. Jiang a , X.Y. Wang a , J.Q. Zhu b , S.H. Meng b , X.D. He b , J.C. Han b a Department of Materials Science, Key Lab of Automobile Materials of MOE and State Key Laboratory of Superhard Materials, Jilin University, Qianwei Road 10 Changchun 130023, PR China b Composite Research Center, Harbin Institute of Technology, Harbin 150001, PR China Received 4 January 2004; accepted 3 August 2004 Abstract Amorphous hydrogenated germanium-carbon (a-Ge 1x C x :H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH 4 /(CH 4 +Ar) in a discharge Ar/CH 4 , and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH 4 /(Ar+CH 4 ), and the Ge–C, Ge–H, C–H bonds were formed in the films. The fraction of Ge–C, Ge–H, and C–H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge–Ge and C–C bonding. Based on the change of the chemical bonding of a-Ge 1x C x :H films with the flow rate ratio CH 4 /(CH 4 +Ar), an optimal experimental condition for the application of infrared windows was obtained. r 2004 Elsevier Ltd. All rights reserved. Keywords: a-Ge 1x C x :H films; RF reactive sputtering; Chemical bonding 1. Introduction Amorphous hydrogenated germanium–carbon (a-Ge 1x C x :H) films have numerous attractive properties, such as low stress and light absorption, good adhesion on many infrared substrates as ZnS and Ge. In particular, the refractive index can be widely varied with composition within the range of 2–4, these excellent performances make the a-Ge 1x C x :H films applicable for design and preparation of multilayer anti-reflection and pro- tection coatings of IR windows [1,2]. In addition, a-Ge 1x C x :H films may provide the apparent tunability of the band gap over a very wide range and thermostability, which may be important for ARTICLE IN PRESS www.elsevier.com/locate/vacuum 0042-207X/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2004.08.004 Ã Corresponding author. Tel./fax: +86-431-516-8246. E-mail address: wtzheng@mail.jlu.edu.cn (W.T. Zheng).