Influence of deposition pressure on hydrogenated amorphous carbon films prepared by d.c.-pulse plasma chemical vapor deposition

Hydrogenated amorphous carbon films (a-C : H) were prepared by d.c.-pulse plasma chemical vapor deposition using CH4 and H-2 gases. The microstructure and hardness of the resulting films were investigated at different deposition pressures (6, 8, 11, 15, and 20 Pa). The growth rate increased sharply from 3.2 to 10.3 nm/min with increasing the pressure from 6 to 20 Pa. According to Raman spectra, XPS, and Fourier transform infrared analysis, the films deposited at the pressure of 6 and 8 Pa have high sp(3) content and show typical diamond-like character. However, the microstructures and bond configuration of the films deposited at 11, 15, and 20 Pa have high sp(2) content and favored fullerene-like nanostructure. The hardness and sp(2) content were shown to reach their minimum values simultaneously at a deposition pressure of 8 Pa and then increased continuously. The film with fullerene-like nanostructure obtained at 20 Pa displays a high Raman I-D/I-G ratio (similar to 1.6), and low XPS C 1s binding energy (284.4 eV). The microstructural analysis indicates that the films are composed of a hard and locally dense fullerene-like network, i.e. a predominantly sp(2)-bonded material. The rigidity of the films is basically provided by a matrix of dispersed cross-linked sp(2) sites. Copyright (C) 2012 John Wiley & Sons, Ltd.