Current-voltage (I-V) and electron emission characteristics of two types of diamond particles deposited on Mo tips were measured by using another Mo probe in a scanning electron microscopy chamber. The I-V and field emission characteristics of the diamond particles strongly depend on their quality. Ohmic current and no electron emission are observed in a high quality diamond particle, while Pool-Frenkel current and electron emission are observed in a cauliflowerlike particle. Furthermore, to make use of structural and electrical properties of a polycrystalline diamond film, a novel gated diamond cathode with a plane diode structure was fabricated. (c) 2007 American Vacuum Society