Diamond-like carbon films: electron spin resonance (ESR) and Raman spectroscopy

Abstract

Tetrahedral diamond-like carbon (ta-C) films and hydrogenated a-C:H films were deposited onto Si substrates using filtered cathodic vacuum arc (FCVA) process and direct ion beam deposition from CH 4/C 2H 4 plasma, respectively. Stress of deposited films was varied in the range 2.8–8.5 GPa depending on deposition conditions. Stationary and pulse electron spin resonance (ESR), and Raman spectroscopy techniques were used to analyze sp 2 related defects in pseudo-gap of undoped as deposited and annealed 20–100 nm thick films. 1 1 The preliminary results of this study were reported on the MRS 1999 Fall Meeting. Symposium U: Amorphous and Nanostructures Carbon. Boston, USA, November 1999. Mat. Res. Soc. Symp. Proc., Vol. 593, p. 249 (2000). High density of ESR active paramagnetic centers (PC) N s=(1.0–4.5)×10 21 cm −3 at g=2.0025 was observed in the films. The dependence of ESR line width and line shape vs. deposition conditions and internal film stress were investigated. The several actual mechanisms for ESR line width broadening were considered: spin–spin dipole–dipole and exchange interactions, super-hyperfine interaction (SHFI) with 1H (for a-C:H), averaging of SHFI due to electron jumps between PC positions with different SHFI values, and broadening due to Mott's electron hopping process. Three types of samples were revealed depending on relative contribution of these mechanisms. Effects of annealing on mechanical and paramagnetic properties of films were studied. An electrical resistance anisotropy at room temperature for ta-C films and g-value anisotropy at low temperature ( T<77 K) for both ta-C and a-C:H films were found for the first time. Nature and distribution details of paramagnetic defects in DLC films, anisotropy effects and Raman spectroscopy data are discussed.