Field emission site density studies of amorphous carbon films

Abstract

Amorphous carbon (a-C) films have been deposited by radio frequency (RF) plasma chemical vapor deposition (CVD) using CH 4 gas mixtures at a DC bias of –300 V, and their field emission characteristics investigated, particularly with regard to the turn on/off behavior of emission sites. A phosphor-coated indium tin oxide (ITO) anode in a parallel-plate configuration was used for observing and characterizing the field emission sites. The field emission properties of a-C films annealed at 200 °C in vacuum for 48 h were also studied. Both the as-deposited and annealed films exhibit an exponential relationship between the emission current and the number of emissive spots on the phosphor screen (i.e. emission sites on the film). A new term, ‘emission site conductance', the average emission current per site, in units of nA site −1, is introduced to characterize the emission characteristics of an individual site. Thermal annealing of a-C films is shown to enhance both the density and the uniformity of emission sites, thereby reducing the current load per site. Such benefits are most likely attributable to an increase in the number and efficiency of conducting pathways in the bulk of the films.