Field Emission from Mercury Whiskers

Abstract

A method for growing metal whiskers in a modified field emission tube has been developed and applied to Hg. Emission patterns from whiskers show these to be 110 oriented single crystals when grown on a tungsten substrate. Their strength, estimated from the electric field necessary for emission is ∼10¹⁰ d/cm². An electrical method of following length based on the relation between this quantity and the surface field, has been used to elucidate whisker growth kinetics. It is found that growth is positively exponential, indicating that it occurs by diffusion of impinging atoms to the growing end, where incorporation occurs. From the length where exponential growth ceases it is possible to find a limit for the diffusion coefficient of Hg on Hg and to estimate the activation energy of the surface diffusion as ∼1.1 kcal. Elastic twisting under tensile stress is sometimes found and ascribed to the presence of screw dislocations. Possible applications of the technique are pointed out.