Ž . Diamond and Related Materials 10 2001 960964 A complementary study of bonding and electronic structure of amorphous carbon films by electron spectroscopy and optical techniques  P. Patsalas a,  , M. Handrea b , S. Logothetidis a , M. Gioti a , S. Kennou c , W. Kautek b a Aristotle Uni  ersity of Thessaloniki, Department of Physics, Solid State Physics Section, GR-54006 Thessaloniki, Greece b Laboratory for Thin Film Technology, Federal Institute for Materials Research and Testing, Unter der Eichen 87, 12205 Berlin, Germany c Department of Chemical Engineering, Uni  ersity of Patras and FORTH-ICEHT, Rion Uni  ersity Campus, GR-26500 Patras, Greece Abstract Ž . A complementary study of composition and bonding of sputtered a-C films, deposited on Si 001 substrates with various bias Ž . 3 2 voltages V applied to the substrate during deposition is presented. The sp and sp fractions in the films were calculated by b Ž . deconvolution of the X-ray photoelectron spectroscopy XPS C1s peak and studied by the differential auger electron Ž . 3 spectroscopy AES C peak signal. The results of this analysis are compared with the estimation of sp fraction calculated by KLL Ž . spectroscopic ellipsometry SE and validated using density measurements by X-ray reflectivity. It was observed a considerable increase of sp 3 content in films deposited with negative V . The respective sp 3 and sp 2 fractions and Ar concentration with b respect to the V and the depth profile analysis give valuable information on the deposition mechanism of the sputtered a-C b films. XPS valence band spectra provided the electron density of states in the a-C films’ valence band. The characteristic broad p band of diamond was prominent in most of the films. The valence band structure of the films was correlated with their optical response measured by SE.  2001 Elsevier Science B.V. All rights reserved. Keywords: Amorphous carbon; Electron spectroscopy; Ellipsometry; Sputtering 1. Introduction Ž . Amorphous hydrogen-free carbon a-C films pro- Ž . duced by physical vapour deposition techniques PVD meet a rapidly increasing area of applications in im- proving nanoscale components, in magnetic hard discs, wear-resistant coatings, and they are promising in semi-  conductor devices and optical film applications 1.  Prime novelty of the paper: A thorough study of the bonding and electronic structure of a-C films and a comparison and validation between electron spectroscopy and optical characterization.  Corresponding author. Tel.: 30-31-998129; fax: 30-31-246484. Ž . E-mail address: ppats@skiathos.physics.auth.gr P. Patsalas . Magnetron sputtering has been used to grow amor- Ž . phous carbon a-C films with controllable amount of 3   sp sites which are dense, hard and elastic 2  4 . In sputter process, the ion bombardment creating the sp 3 bonds can be controlled by a negative bias voltage V b  applied to the substrate 3. The study of bonding and electronic structure of Ž . amorphous carbon films a-C is an issue not resolved yet, due to inherent difficulties of most of the charac- terization techniques to describe the disordered struc- ture of a-C with respect to crystalline diamond and graphite. So far, the techniques to estimate the sp 3 sp 2 ratio in a-C were based on electron spectroscopy such Ž .   as X-ray photoelectron spectroscopy XPS 5,6 , auger 0925-963501$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 9 2 5 - 9 6 3 5 00 00480-5