The effect of high electric fields on oxidation of molybdenum single crystals

Abstract

The effect of high negative and positive electric fields on oxidation of molybdenum single crystals in 8 × 10 −5 Torr of oxygen at 1000–1200 K was investigated by means of a field emission and a transmission electron microscope. Exposure of a field emitter of molybdenum to oxygen in the absence of an electric field caused the build-up of the emitter tip. The application of a negative field so high as to induce field elctron emission, on the other hand, resulted in the formation of a thin oxide layer at the tip apex. The oxide layer exhibited a range of roof-like structures at its surface and was confirmed by electron diffraction to be monocrystalline molybdenum tri-oxide. The behavior in positive fields was basically identical with zero field oxidation, but evidence was obtained that oxide crystallites grow selectively on the Mo {100} planes when a high positive field is present.