Preparation and properties of highly tetrahedral hydrogenated amorphous carbon

Abstract

A highly tetrahedrally bonded, hydrogenated amorphous carbon (ta-C:H) has been deposited from an acetylene-fed plasma beam source. The plasma beam source is operated to provide a highly ionized, monoenergetic plasma beam of ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}^{+}$ ions. The resulting films are characterized in terms of their ${\mathit{sp}}^{3}$ content, mass density, intrinsic stress, surface roughness, radial distribution function, C---H bonding, Raman spectra, optical gap, electrical conductivity, gap states, Youngs modulus, and hardness. The ${\mathit{sp}}^{3}$ content reaches a maximum value of 75% at an ion energy of 200 eV, or 92 eV per C ion. The density and stress also reach a maximum at this ion energy. The formation of ta-C:H is interpreted in terms of the subplantation of ${\mathrm{C}}^{+}$ ions, which produces a densified, ${\mathit{sp}}^{3}$ bonded network. The C-H vibration spectra suggest that C ${\mathit{sp}}^{2}$ sites form C=C alkene groups. The optical gap ${\mathit{E}}_{04}$ reaches a maximum of 2.85 eV and increases with the ${\mathit{sp}}^{3}$ fraction. The spin density due to defects is high and decreases with increasing ion energy. The Youngs modulus and hardness measured by microindenter reach maximum values of 290 and 61 GPa, consistent with the highly ${\mathit{sp}}^{3}$ bonding. The variation of hardness with ${\mathit{sp}}^{3}$ fraction is consistent with the constraint model of network rigidity. \textcopyright{} 1996 The American Physical Society.