A theoretical analysis is presented of the current from a field-emission tip terminated by a single atom. The calculations yield a relatively focused, high-current beam with a narrow energy distribution, in agreement with recent experimental studies. The results are physically interpreted in terms of channel filtering by an adiabatic constriction.

• Received 24 May 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.1499