Electron emission characteristics of needle type semiconductor diamond electron emitters by pulsed bias operation and X-ray generation

Abstract

Electron emission characteristics of needle-type semiconductor diamond electron emitters with pulsed bias operation were evaluated. An X-ray generation experiment was performed. Fowler–Nordheim plotting confirmed that field emission completely governed the electron emission. Maximum emission current of 4.2 mA was achieved using an n-type diamond needle. The needle tip, with area smaller than 1 μm 2, had estimated electron emission density greater than 4.2 × 10 5 A/cm 2. The effective emission area obtained from the Fowler–Nordheim plot was several 10 − 13 cm 2. For adopting and emission area of 1 × 10 − 12 cm 2, the estimated electron emission density was higher than 4.2 × 10 9 A/cm 2. Furthermore, the average emission current was 0.5–0.6 mA. This large electron emission was continued for several seconds and repeatable. A threshold electric field existed for electron emission higher than 50 kV/mm; pulsed electron emissions of less than 30 ms were created by slow triangular waveform shaped bias voltage supplied at frequencies of 5–10 Hz. An improved vacuum level and pulsed bias operation prevented damage to diamond electron emitters and steady electron emission better than with thermoelectronic emission and high bias voltage supply in DC mode; continuous X-ray generation of 1 h was achieved.