Nitrogen and iodine doping in amorphous diamond-like carbon films

Abstract

Abstract Thin films of amorphous diamondlike carbon (a:DLC) were deposited by plasma decomposition of hydrocarbon gas, such as methane gas (CH 4 ). 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.