Y. Yamamoto et T. Miyokawa, EMISSION CHARACTERISTICS OF A CONICAL FIELD-EMISSION GUN, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 16(5), 1998, pp. 2871-2875
Characteristics of a conical field emission gun (FEG) are measured and
discussed. The field emission current from a W emitter is found to ob
ey the Fowler-Nordheim (FN) equation. An expression was given describi
ng the dependence of the mean work function on the curvature radius at
the vertex of the emitter. Using scanning electron microscopy, a radi
us of 1500 Angstrom was measured with which the slope of the FN plot y
ielded a mean work function of 4.8 eV. The initial value of the emissi
on current, obtained after cleaning the tip by flashing, decays with t
ime due to an increase of the work function caused by the adsorption o
f residual gases. The measured time dependent mean emission current wa
s interpreted as a weighted superposition of local field emissions fro
m the W(310), (100), (110), (111), and (112) planes. This interpretati
on resulted in a mean work function of 4.6 eV in good agreement with t
he value determined from the EN plot. For an accelerating voltage of 1
5 keV and an emission current of 8 mu A after flashing, the dependence
of the probe current on the extraction voltage was measured. For V-ac
c/V-ex = 1, an angular current density of (41 +/- 4) mu A/sr was found
. Similar measurements of the dependence of the probe current on the r
atio V-acc/V-ex (accelerating voltage/extraction voltage) made 3 h aft
er flashing yielded (20 +/- 6) mu A/sr for V-acc = V-ex. The transfer
efficiency defined as the ratio between probe current and emission cur
rent was found to be 0.4%-0.3%. (C) 1998 American Vacuum Society.