Effects of oxygen and hydrogen on electron field emission from microwave plasma chemically vapor deposited microcrystalline diamond, nanocrystalline diamond, and glassy carbon coatings

Abstract

Electron field emission from chemically vapor deposited polycrystalline diamond, nanocrystalline diamond, and glassy carbon coatings are reported. Effects of hydrogen-rich or oxygen-containing CVD precursors on electron field emission from CVD carbon coatings are presented. Surface conductivity and negative electron affinity resulting from hydrogen termination of crystalline diamond were found to promote electron field emission for discrete diamond particles and non-continuous diamond films but not for high quality and continuous diamond films as well as nanocrystalline diamond and glassy carbon coatings containing conductive graphitic carbon. Graphitic carbon in nanocrystalline diamond coatings and glassy carbon coatings provided additional conduction paths for electrons and allowed more effective injection of electrons into electron emitters. Nanocrystalline diamond coatings deposited by methanol/ethanol plasmas contained more graphitic carbon than that deposited by hydrogen/methane plasmas resulting in lower turn-on electric field and higher electron field emission current. Glassy carbon coatings deposited by both processes exhibited excellent electron emission characteristics. Low turn-on electric field, i.e., 1 V/μm, for electron field emission was achieved for diamond and glassy carbon coatings deposited under optimized conditions. Among these three classes of carbon coatings, glassy carbon deposited at elevated substrate temperatures were found to exhibit the best electron field emission properties.