Superhard and Elastic Carbon Nitride Thin Films Having Fullerenelike Microstructure

Abstract

${\mathrm{CN}}_{x}$ films were found to have a distorted graphitelike microstructure consisting of buckled and curved basal planes using high-resolution electron microscopy. Nanoindentation showed an elastic recovery of 85%, and a hardness of $\ensuremath{\sim}60$ GPa. Based on detailed quantum chemical calculations and photoelectron spectroscopy, the observed structure is proposed to consist of a network of buckled ${\mathrm{sp}}^{2}$-hybridized ${\mathrm{CN}}_{x}$ planes, cross-linked by ${\mathrm{sp}}^{3}$-hybridized bonds. The buckling is shown to be due to the incorporation of pentagons in the basal planes, giving rise to a fullerenelike microstructure.