Transition from polymer-like to diamond-like a-C:H films - Structure and mechanical properties

Amorphous hydrogenated carbon (a-C:H) films were deposited on polymeric substrates by the glow-discharge decomposition of butane. IR spectroscopy and electron paramagnetic resonance were used for the structural characterization of the films. For a set of samples, produced at different pressures, mechanical properties such as nanohardness and wear resistance were investigated. It was found that the mechanical properties of a-C:H films are strongly dependent on the pressure in the reactor. At a reactor pressure of about 10 Torr, the deposition of polymer-like a-C:H films occurs. Such films are characterized by low hardness and wear resistance and visco-elastic behaviour at indent reloading. On reducing the pressure in the reactor, an improvement of the mechanical properties of polymer-like a-C:H films was observed due to ion bombardment. Ion bombardment of the growing a-C:H film surface caused drastic increases of its hardness, the value of elastic recovery of the indent depth after unloading and wear resistance. With respect to the mechanical properties, polymer-like a-C:H films hardened by ion bombardment occupy a position between polymer-like and diamond-like a-C:H films. A high wear resistance and adhesion to a polymeric substrate, as well as the possibility of being deposited on substrates with a large area at temperatures below 80 degrees C, make polymer-like a-C:H films, hardened by ion bombardment, a promising protective coating for polymeric materials. (C) 1997 Elsevier Science S.A.