RADIATION HARDNESS OF DLC FILMS PRODUCED BY ION-ASSISTED DEPOSITION

DLC coatings are prepared by a novel technique in which a stream of lo w vapour pressure oil is condensed onto a substrate whilst simultaneou sly a 40 keV N+ beam impinges on the target. The films produced, are h ard and wear resistant, but quite electrically conducting (1-10 ohm-cm ) when compared to DLCs produced by many other methods. The modificati on of the electrical and structural properties of these unusual films following ion bombardment with inert (Xe) and potentially electrically active dopants (B and P) are studied, and compared with the response to ion irradiation of other DLCs and hard amorphous carbon films. In c ontrast with other DLCs which show a dramatic rise in conductivity upo n ion impact, the material produced by the method described above prov es to be relatively radiation hard. For ion beam irradiation at or bel ow room temperature, in-situ measurements of the resistance, R, of the films as a function of Xe ion dose, D, reveals an unusual non-monoton ic behaviour in which the resistance first dropped and then rose to a value equal to or greater than that of the pristine films. Measurement s of the temperature dependence of the resistivity indicate the conduc tion mechanism to be the result of variable range hopping, both before and after ion irradiation. The films were found to be stable up to a temperature of about 470K, but heating above this temperature leads to a permanent degradation of the films as reflected in an observed irre versible decrease in the film resistance. The results provide basic in formation relevant to the possible uses of such films for electrical a nd electronic applications in radiation harsh environments.