Filtered saddle field fast atom beam deposition of diamondlike carbon films

Abstract

An innovation to separate out ionic and neutral radicals from the beam coming out of a saddle field fast atom beam (FAB) source is reported. Diamondlike carbon (DLC) films were grown simultaneously by these ionic and filtered neutral radicals using methane (CH4) as the source gas in the FAB source, on to the substrates placed at different positions inside the deposition chamber. Faraday cup measurements carried out on the two beams confirm the separation of ionic and neutral radicals. It was found that the DLC films deposited by neutral radicals have higher hardness values (980–1070 kg/mm2) than those deposited by ionic radicals (810–970 kg/mm2), whereas, the values of optical band gap and refractive index are found to be higher in DLC films deposited by ionic radicals than those deposited by neutral radicals. It is emphasized that during normal operation of a saddle field source, to grow DLC films, one essentially has a mixed deposition with contributions both from neutral and ionized radicals. Higher hardness values (1050–1150 kg/mm2) of films grown this way may, perhaps, be due to an ion assisted process of network compaction leading to higher degree of overstraining.