화학공학소재연구정보센터
Journal of Vacuum Science & Technology B, Vol.12, No.5, 2889-2893, 1994
Electrostatic Removal of Lithium-Fluoride from Field-Emitter Tips at Elevated-Temperatures
The electrostatic removal of lithium fluoride (LiF) from field-emitter tips has been visualized at elevated temperatures in the transmission electron microscope (TEM). The apex of a field-emitter tip coated with similar to 1500 Angstrom of LiF provides a unique substrate for observing the removal process in the TEM in real time, and its curvature generates the required electrostatic field strength. The influence of the imaging electron beam on coating morphology has been visually assessed. A LiF coating can tolerate an electron dose of similar to 2000 e(-)/Angstrom(2) at room temperature without visible damage (at a resolution of 5 Angstrom). At elevated temperatures a higher dose can be tolerated before visible damage is observed. Removal of LiF coatings at room temperature occurs at 18 MV/cm. At 800 degrees C piecewise removal of the coating occurs at 9 MV/cm. Synergistic effects of the electron beam and the electrostatic field on the removal of the coating were not observed. The removal of LiF at any temperature is attributed to field-induced fatigue stress of the coating. Field desorption does not appear to play a significant role in the removal process. Implications for the production of ions from lithium fluoride thin films exposed to high electric fields (in laboratory experiments and in particle beam fusion accelerators such as PBFA II) are discussed.