Electroplating and direct brushing technique were used to deposit commercial HTHP diamond powder on W needles and Si substrates to form cold cathodes.These cold cathodes combined with phosphor anodes constructed testing vacuum diodes.By measuring current-voltage characteristics and observing light emission of these diodes

electron emission feature of these diamond powder cold cathodes were investigated.Experiments show that

these cold cathodes have good electron emission ability

the minimum threshold field is 3.25V/μm.Thermal-electric positive feed back and conductivity modulation effects were proposed to interpret the phenomenon of random distribution of electron emission sites.