Mechanism of field emission from chemical vapor deposited undoped poly crystalline diamond films

Field emission characteristics of undoped polycrystalline diamond films with different structural properties have been investigated. By introducing positive bias voltage and/or increasing CH₄/H₂ ratio, the film quality is significantly deteriorated together with the increase of nondiamond carbon component and the surface morphologies of the films lost their unique facet shape. The reason for the increase of nondiamond carbon content is described in terms of both the increase of substrate temperature and the excessive generation of CH_n radicals. It is confirmed that an increase in the nondiamond carbon content markedly enhances field emission properties of diamond films. From the spatial distribution of emission sites, it is suggested that the transport path of field-emitted electrons depends on the nondiamond carbon content: for the film with a large amount of nondiamond carbon, electrons transport preferentially through the conducting mediums such as grain boundaries while for the film with a relatively small amount of nondiamond carbon, electron transport occurs mainly through the diamond surface.