Role of hydrogen on field emission from chemical vapor deposited diamond and nanocrystalline diamond powder

The field emission properties of diamond-graphite composites were investigated as a function of composition both for oxidized and hydrogen covered diamond. The composites consist of mixtures of nanocrystalline diamond and graphite particles. In this way their composition could be varied at will while the field enhancement factor of the individual crystallites remained unchanged. The measurements prove that graphite is the phase responsible for low threshold field emission. The apparent emission threshold is strongly influenced by the conductivity of the composites. Hydrogenation has two beneficial effects. It provides a conducting path to the emission sites via the hydrogen induced surface conductivity of diamond. It also lowers the effective emission threshold of graphite in contact with diamond that exhibits negative electron affinity after hydrogenation. The latter effect was experimentally verified by photoelectron yield spectroscopy.