BRIGHT-FIELD ANALYSIS OF FIELD-EMISSION CONES USING HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY AND THE EFFECT OF STRUCTURAL-PROPERTIES ON CURRENT STABILITY

High-resolution transmission electron microscopy has been used to anal yze 150 nm diameter by 150 nm high polycrystalline molybdenum field-em ission cones. The analysis shows that the cones comprise 5 to 10 nm th ick grains with tips having gross radii of curvature of about 5 nm and protrusions having radii of curvature of about 1 nm. Such small protr usions may explain why analysis of experimental emission data indicate s that the effective emission area of such tips is only 0.1 to 0.5 nm2 . Furthermore, the fact that the structure is composed of small grains indicates that there is a substantial number of molybdenum atoms at g rain boundaries and that many configurations of grains and boundaries are possible with minimal free energy. A qualitative model is proposed which links the structural properties to -current stabilization and h ydrogen passivation effects.