Field emission property of chemical vapor deposited diamond overlayer films

The effect of diamond overlayer films on field emission properties has been studied. When conductive diamond layers are deposited on high quality diamond films, the non-diamond carbon contents in the films are increased with increasing overlayer thickness. The increase of overlayer thickness improves significantly both the electron emission currents and the number of emission sites. The threshold field of the diamond films grown at 2% CH₄/H₂ decreases from 12.0 to 7.7 μm^-1 with post-growth at 10% CH₄/H₂ for 5 min. The enhancement of field emission is explained by the improvement of electron transport through the high quality diamond layer by the field enhancement across the diamond layer. On the contrary, when the non- conductive diamond layers are grown on the conductive diamond films, both the electron emission currents and the number of emission sites degrade markedly with the increase of overlayer thickness while there is no substantial change in structure and morphology of the films. These degradations are attributed to both the electron transport through the overlayer and the reduction of the triple junction effect.