Dept. of Applied Physics
Oregon Graduate Center
A thermal field emission (TFE) electron source has been incorporated into a microprobe with two magnetic lenses to produce a 0.10 Âµm beam spot with 0.11 ÂµA current at 12 kV and a working distance of 13 cm, in agreement with calculated performance assuming a source angular intensity of 1 mA sr [superscript -1]. Experience with cold field emitters has discouraged their use in many applications because of noise problems, instability, short life, and extreme vacuum requirements. The TFE mode of operation allows a relaxation of vacuum requirements by rapid thermal annealing of sputter-induced surface deformation, thereby minimizing the probability of emitter destruction by a regenerative vacuum arc. Additionally, the high emitter temperature maintains a low and constant coverage of adsorbed gases on the emitter surface thereby eliminating time dependent work function change. The emitter used was <100> oriented W coated with Zr, operated at 1800 K. The microprobe was used to construct a scanning Auger microscope which produced submicron resolution Auger elemental maps with scan times of 5 min or less. The high voltage Zr/W<100> TF emitter not only exhibits long life (~ 5000 h on several tests), but sufficiently low noise (e.g., 0.23%) to be used in SAM applications without the need for sophisticated beam current stabilization schemes. Specimen current densities which far exceed SAM requirements can be obtained at 0.1 Âµm spot size with relatively simple gun optics. At present a current density of 1300 A/cm2 or power density of 1.6 x 10[superscript 7] W/cm2 has been achieved in a 0.1 Âµm beam spot. This corresponds to an image plane brightness of 5.5 x 10[superscript 7] A cm [superscript -2] sr [superscript -1] at 12 kV. The geometric stability of the emitter structure is excellent once it achieves equilibrium temperature. Measurements show the emitter drift over 16 h periods to be < 0.05 Âµm/h for a TFE emitter operating at 1800 K.
Tuggle, David William, "Application of a thermal field emission source for scanning Auger microscopy" (1981). Scholar Archive. 221.