Nitrogen and iodine doping in amorphous diamond-like carbon films

Thin films of amorphous diamondlike carbon (a:DLC) were deposited by plasma 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 microhardness 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). From optical measurements at visible light (400-800 nm), optical energy band 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 for nitrogen-doped films and 0.23 eV for iodine-doped films. The electrical resistivity at room temperature was reduced by almost three and two orders of magnitude with the doping processes, from 10(8)W cm for undoped film to 5.10(5)W cm for nitrogen- and iodine-doped films. (C) 1997 Elsevier Science S.A.