Temperature dependence of the mechanical properties of amorphous carbon films deposited by magnetron sputtering

Abstract

Amorphous carbon (a-C) films were deposited by d.c. magnetron sputtering with a graphite target in an argon plasma. We studied the dependence of the hardness and modulus of elasticity of the films on the deposition and annealing temperature in the range 20–650 °C by the indentation method, and we studied the structure of the films by electron diffraction and Raman spectroscopy. We have established that increasing the substrate temperature during condensation leads to a decrease in both the hardness and the modulus of elasticity of the a-C films. With annealing of the a-C films deposited at room temperature, these parameters vary insignificantly with temperature. The results obtained allow us to hypothesize that the structure of the films is formed predominantly by sp2-bonded carbon atoms. In the condensation temperature range of 50–450 °C, ordered formation of aromatic rings and graphite-like clusters occurs, and the degree of their ordering increases as the condensation temperature increases. At condensation temperatures T > 450 °C, the mechanism for growth of the C-film changes, and nuclei of graphite phase form directly on the substrate and grow. Annealing the C-films in the range 50–300 °C causes rapid transformation of distorted pentagonal and hexagonal aromatic rings to regular rings and ordering of the rings in the plane of the substrate without formation of graphite fragments. Further raising the annealing temperature has a weak effect on the structural changes in the film. The indicated changes in the film structure are the reason for the changes in hardness and modulus of elasticity in the studied temperature range.