Observations of Needle Crystals of Tungsten Oxide by Field Emission and Electron Microscopy

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Abstract
The needle crystals of tungsten oxide grown on the tungsten substrate from vapor phase were studied by field emission and electron microscopy. The observed FEM patterns of the needles were quite similar to the pattern of the oxidized W emitter and mostly had twofold symmetry. Less frequently, the FEM patterns having nearly threefold and fourfold symmetries could be observed. From the comparison of the electron micrographs as well as the FEM patterns of a needle and an oxidized W emitter, evidence was obtained that the surface of the oxidized emitter tip had been covered with thin layer of a crystallized tungsten oxide.