Surface and in-depth distribution of sp2 and sp3 coordinated carbon atoms in diamond-like carbon films modified by argon ion beam bombardment during growth

Abstract

Carbon atom coordination at diamond-like carbon (DLC) film surfaces and in sub-surface regions has been determined nondestructively from high-energy resolved C 1s photoelectron spectra, X-ray induced C KVV Auger electron spectra, and angular-resolved C 1s spectra (ARXPS) aided by maximum entropy method (MEM). The spectra were recorded from hydrogen-free DLC films prepared by a pulsed laser deposition under medium energy Ar ion beam assisted growth. The sp3 and sp2 fractions determined from C 1s and C KVV spectra recorded at the normal emission angle differ substantially. This indicates an inhomogeneous depth-resolved distribution of the fractions. The result is validated by the analysis of angular-resolved C 1s spectra using the MEM approach. In-depth reconstructions of the carbon bonding states show that sp2 coordination is dominant at the surfaces. We found that Ar ion beam assisted growth induces a C sp2 peak beneath the surface. The peak shifts towards the surface and is growing with Ar ion energy. C sp3 hybridization is dominant in deeper layers. The in-depth reconstruction is further supported by the depth-dependent mass density determined from the low-loss electron spectra excited at various primary electron energy. The results are discussed within the subplantation model.