| AVS 54th International Symposium | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS+MS-TuA |
| Session: | Characterization of Nanostructures |
| Presenter: | W.A. Mackie, Applied Physics Technologies |
| Authors: | W.A. Mackie, Applied Physics Technologies G.M. Magera, Applied Physics Technologies K.J. Kagarice, Applied Physics Technologies |
| Correspondent: | Click to Email |
An electron source for a high resolution SEM/TEM application should produce a high brightness, have a minimal energy distribution, and should be highly stable. In an application in which the resolution is limited by chromatic aberrations, one can improve the performance over a commonly used thermal field emission source, such as a ZrOW Schottky emitter, by using a cold field emission source (CFE). In CFE, the emitting area of the usable beam is small and understanding surface chemistry and effects are crucial to controlling emission stability. Single crystalline transition metal carbides have electron emission properties making them attractive candidates for CFE applications. We are reporting on field emission from (310) oriented single crystal ZrC and HfC. ZrC(310) has a relatively low work function axial emitting surface (3.4 eV) that has a low evaporation rate, is resistant to ion bombardment and sputtering, has a high melting point (~3800 K), and a very low surface mobility. The robustness of this material allows for repeated cleaning via high temperature flashing without changing the geometry of the emitting end form. These crystals are electrochemically etched and mounted in a mini Vogel mount to enable flash cleaning. Experimental I(V) data were taken from which angular intensity and reduced brightness were calculated. Experimental I(t) data were then taken and analyzed for current stability in both long term drift and short term noise. Results are highlighted from a 160 nm ZrC (310) operating at 0.02 mA/sr. Noise spectra were analyzed by FFT and found to be consistent with step and spike like noise associated with foreign atom migration and ion bombardment. Emission from small areas comprising <100 atom sites are dominated by the mobility of foreign atoms from ion back streaming and surface diffusion both arising from the high electric field. Using an annular area surrounding the beam emission area as a current monitor we were able to control fluctuations in the beam. This control ability results from the overlapping currents from both areas. Data are presented which demonstrate improved stability over a variety of vacuum conditions.