Reactive pulsed laser deposition of hydrogenated carbon thin films: The effect of hydrogen pressure

Abstract

Diamondlike properties of amorphous carbon films can be enhanced by applying reactive hydrogen atmosphere during pulsed laser deposition (PLD) as shown by recent studies. The complex phenomena occurring during carbon plume expansion has not been examined yet thoroughly. Therefore we deposited amorphous hydrogenated carbon thin films in hydrogen ambient atmosphere (4×10−4–25Pa) by PLD at room temperature. The deposited films were characterized by Rutherford backscattering spectrometry, elastic recoil detection analysis, Raman spectroscopy, infrared spectroscopy, variable angle spectroscopic ellipsometry, and nanoindentation measurements. At low hydrogen pressures (below ∼0.1Pa), when the mean free path of plasma constituents in the background gas is larger than the target substrate distance, the deposited films show diamondlike properties. At higher pressures (above ∼0.1Pa) the deposited films change their diamondlike carbon character towards to a structure which contains increasing amount of sp2 bonded carbon sites. Further increase in pressure (above ∼2Pa) results in hydrogenated carbon films with increasing hydrogen content. Principally these changes are caused by the energy decrease of the plume when plasma is decelerated by the background gas. Chemical reactions also effect the composition of the films especially in the highest pressure domain.