THERMOEFFUSION OF HYDROGEN IN A-C-H FILMS PREPARED BY GLOW-DISCHARGE

The structure and properties of hydrogen-doped amorphous carbon (a-C:H) films are determined by the hydrogen content and the structure of the hydrogen bonding with the lattice. Study of the thermal effusion of hydrogen (TEH) provides information concerning both the thermal stability of the films and the chemical bonding of hydrogen. Wild and Koidl [1] measured the TEH in a-C:H films as a function of the bias potential V(b). They found that as V(b) was increased from 50 to 500 V, the TEH threshold temperature increased from 300 to 600-degrees-C. In a study of the thermal stability of a-C:H films prepared by glow discharge, Watanabe and Okumura [2] observed that on heating to 350-degrees-C the thickness and optical gap of the films decreased and at still higher temperatures the films decomposed. Nadler et al. [3] investigated the thermal annealing effect in films prepared by the decomposition of hydrocarbons. On annealing at 500-degrees-C, they observed hydrogen effusion from sp3 states and formation of C = C bonds, accompanied by a decreased transparency of the films. In an investigation of a-C:H films prepared by r.f. glow discharge, we observed changes in the structure of the amorphous network and of the hydrogen bonding with the lattice as well as in the electronic properties of such films [4]. The data obtained suggest that TEH occurs differently in a-C:H films of different structures. Therefore it would be of interest to experiment on the TEH in a-C:H films.