Role of carbon in the formation of hard Ge sub(1-x)C sub(x) thin films by reactive magnetron sputtering

• Published in: Physica. B, Condensed matter Condensed matter, 2011-07, Vol.406 (13), p.2658-2662
• Main Authors: Hu, Chaoquan, Qiao, Liang, Tian, Hongwei, Lu, Xianyi, Jiang, Qing, Zheng, Weitao
• Format: Article
• Language: English
• Subjects: Bonding; Carbon; Chemical bonds; Condensed matter; Expenses; Hardness; Magnetron sputtering; Networks; Thin films
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2011.01.077

We have deposited germanium carbide (Ge sub(1-x)C sub(x)) films on Si(1 0 0) substrate via radio-frequency (RF) reactive magnetron sputtering in a CH sub(4)/Ar mixture discharge, and explored the effects of carbon content (x) on the chemical bonding and hardness for the obtained films. We find that x significantly influences the chemical bonding, which leads to a pronounced change in the hardness of the film. To reveal the relationship between the chemical bonding and hardness, first-principles calculations have been carried out. It is shown that as x increases from 0 to 0.33, the fraction of sp[super]3 C-Ge bonds in the film increases at the expense of Ge-Ge bonds, which promotes formation of a strong covalently bonded network, and thus enhances the hardness of the film. However, as x further increases from 0.33 to 0.59, the fraction of sp[super]3 C-Ge bonds in the film gradually reduces, while that of sp[super]3 C-H and graphite-like sp[super]2 C-C bonds increases, which damages the compact network structure, resulting in a sharp decrease in the hardness. This investigation suggests that the medium x (0.17x0.40) is most favorable to the preparation of hard Ge sub(1-x)C sub(x) films due to the formation of dominant sp[super]3 C-Ge bonds.