Investigation of possible roles of plasma processes in field induced electron emission from polycrystalline diamond films

Abstract

Summary form only given, as follows. Polycrystalline diamond films from vapor deposition methods have properties similar to those of single crystal diamond and have the potential for large-scale applications. Investigation of the electronic and thermal properties of the as-deposited films is presently a very active research area. During an electronic properties investigation, it was observed that substantial electron emission was produced from 15 mm diameter 5 micron thick undoped polycrystalline diamond film coated molybdenum electrodes at fields as low as 5 MV/m, which is approximately three orders of magnitude lower than expected from a field emission (tunneling) mechanism. This low-field emission will be referred to as field-induced cold electron emission. The experiments took place in ultrahigh vacuum at room temperature. Electron emission took the form of about 50-60 localized emission sites roughly evenly distributed over the film surface. The switch-on field was in the 3-5 MV/m range. Emission increased with applied field up to about 20 MV/m at which point vacuum breakdown occurred. Breakdown was often initiated at an emission site and consisted of sequential multiple arcs. We are investigating the possible role of plasma processes in the above experimental results. Possible plasma process include instabilities due to inter-valley electron transfer, avalanche instabilities, recombination instabilities, and plasma streaming. We are particularly investigating whether instability criteria could have been met for instabilities due to inter-valley electron transfer.