Effect of phosphorus content on structural properties of phosphorus incorporated tetrahedral amorphous carbon films

Abstract

With phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films prepared using filtered cathodic vacuum arc technique with PH3 as the dopant source, we investigate the effect of phosphorus content on the structural properties of the films by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS analysis indicates that a function is established between the atomic fraction of phosphorus in the samples and the flow rate of PH3 during deposition, and that phosphorus implantation increases the graphite-like trihedral sp2 bonds deduced from fitted C 1s and P 2p core level spectra. Raman spectra of a broad range show that there are two notable features for all ta-C:P films: the first-order band centered at about 1560 cm-1 and the second-order band between 2400 and 3400 cm-1. The broad first-order band demonstrates that the amorphous structure of all samples does not remarkably change when a lower flow rate of PH3 is implanted, while a higher concentration of phosphorus impurity enhances the clustering of sp2 sites dispersed in sp3 skeleton and the evolution of structural ordering. Furthermore, the second-order Raman spectra confirm the formation of small graphitic crystallites in size due to a finite-crystal-size effect.