NITROGEN AND IODINE DOPING IN AMORPHOUS DIAMOND-LIKE CARBON-FILMS

Thin films of amorphous diamondlike carbon (a:DLC) were deposited by p lasma decomposition of hydrocarbon gas, such as methane gas (CH4). The plasma was produced using a r.f. generator. These thin films of a:DLC were doped by incorporation of nitrogen (a:N-DLC) and iodine (a:I-DLC ) gases during the deposition process. Microhardness tests showed high hardness of about 4700-4900 kg mm(-2) for a:DLC films. The microhardn ess of the films was reduced by the doping process (3400 kg mm(-2) for 10% nitrogen and 3200 kg mm(-2) for 10% iodine partial pressure). Fro m optical measurements at visible light (400-800 nm), optical energy b and gaps of about 1.1 eV for a:DLC film, 1.39 eV for a:N-DLC and 0.78 eV for a:I-DLC were determined. From measurements of d.c. conductivity as a function of temperature, the electrical activation energies were determined and found to be 0.34 eV for undoped a:DLC films, 0.20 eV f or nitrogen-doped films and 0.23 eV for iodine-doped films. The electr ical resistivity at room temperature was reduced by almost three and t wo orders of magnitude with the doping processes, from 10(8)W cm for u ndoped film to 5.10(5)W cm for nitrogen- and iodine-doped films. (C) 1 997 Elsevier Science S.A.