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 polymeri c substrates by the glow-discharge decomposition of butane. IR spectro scopy and electron paramagnetic resonance were used for the structural characterization of the films. For a set of samples, produced at diff erent pressures, mechanical properties such as nanohardness and wear r esistance were investigated. It was found that the mechanical properti es of a-C:H films are strongly dependent on the pressure in the reacto r. At a reactor pressure of about 10 Torr, the deposition of polymer-l ike a-C:H films occurs. Such films are characterized by low hardness a nd wear resistance and visco-elastic behaviour at indent reloading. On reducing the pressure in the reactor, an improvement of the mechanica l properties of polymer-like a-C:H films was observed due to ion bomba rdment. Ion bombardment of the growing a-C:H film surface caused drast ic increases of its hardness, the value of elastic recovery of the ind ent depth after unloading and wear resistance. With respect to the mec hanical properties, polymer-like a-C:H films hardened by ion bombardme nt occupy a position between polymer-like and diamond-like a-C:H films . A high wear resistance and adhesion to a polymeric substrate, as wel l as the possibility of being deposited on substrates with a large are a at temperatures below 80 degrees C, make polymer-like a-C:H films, h ardened by ion bombardment, a promising protective coating for polymer ic materials. (C) 1997 Elsevier Science S.A.