The optimum voltage in very high voltage electron microscopy

Abstract

A detailed study of specimen penetration using the many-beam dynamical theory of electron diffraction shows that the voltage which maximizes the penetration in electron microscopy is about 1 Mv for heavy materials, 2 Mv for medium weight materials and 3 Mv for light materials. However, the effects of contrast are not fully taken into account in the standard theory and it is tentatively suggested that significant penetration increases above 3 Mv could possibly occur if the crystal is oriented near to a first-order high-index reflecting position, and a large objective aperture is used. Accelerating voltages greater than about 10 Mv are unlikely to be useful owing to the effects of bremsstrahlung and radiation displacement damage.