Effect of 4MeV electron beam irradiation on carbon films

Pulsed KrF excimer laser is used to deposit tetrahedral amorphous carbon (ta-C) thin films on Si (1 1 1) single crystal substrates at room temperature under vacuum ∼10−6 mbars. The pristine deposited films are then irradiated by 4 MeV electron beam at doses varying from 1000 to 4000 cGy. Analysis through AFM illustrates that the irradiation of electron has induced cluster formation on the film surface and increased the surface roughness. Optical properties (n, α and Tauc optical band gap) measured by spectroscopic ellipsometry and electrical resistivity measured by four probe technique are found to depend strongly on electron dose. High electron doses cause significant alteration in order/disorder or sp2 states in the film which is the main cause of modifying band gap in the carbon films. The electrical conductivity of the films also increases by increasing electron dose which is due to tunneling of charge carriers through neighbouring conductive chains. The present electron irradiation process at varying electron doses proved to be successful to modulate the optical and electrical properties of carbon films.