Atomically Sharp Field Emitters and Oxygen Caused Thermal Faceting of W[111] Tip

This paper demonstrates and summarises both temperature and oxygen exposure limitations of faceting in the system O/W[111], including facets evolution with-oxygen exposure leading to globally or steplike faceted tip, for intermediate O2 exposures 0.3 L-3 L (31 L at elevated annealing temperature 1700 K). The results presented here were obtained using FIM technique. Results show that after annealing at temperatures lower than 800 K, higher than 1850 K or for Oa exposures lower than 0.5 L the oxygen caused faceting of W[111] tip was not observed. For exposures 0.5-1.9 L and annealing temperatures 800-1600 K well developed {112} facets with sharp edges formed, and the globally faceted tip topography formed mainly after exposing the emitter to 1-1.9 L of oxygen and annealing it at temperatures 1400-1600 K. For exposures higher than 2.0 L edges of the {112} facets were broadening and disappearing, what has been attributed to the formation of 3-dimensional tungsten oxides. The oxides could be easily removed by annealing the tip at 1700 K, what lead to the formation of sharp facet edges. On the basis of these results a method of atomically sharp field emitter preparation is proposed