  In this work we show using atomistic simulations that the biased diffusion in
high electric field gradients creates a mechanism whereby nanotips may start
growing from small surface asperities. It has long been known that atoms on a
metallic surface have biased diffusion if electric fields are applied and that
microscopic tips may be sharpened using fields, but the exact mechanisms have
not been well understood. Our Kinetic Monte Carlo simulation model uses a
recently developed theory for how the migration barriers are affected by the
presence of an electric field. All parameters of the model are physically
motivated and no fitting parameters are used. The model has been validated by
reproducing characteristic faceting patterns of tungsten surfaces that have in
previous experiments been observed to only appear in the presence of strong
electric fields. The growth effect is found to be enhanced by increasing fields
and temperatures.
