  Ion beams are used routinely for processing of semiconductors, particularly
sputtering, ion implantation and direct-write fabrication of nanostructures.
However, the utility of ion beam techniques is limited by crystal damage and
surface roughening. Damage can be reduced or eliminated by performing
irradiation at elevated temperatures. However, at these conditions, surface
roughening is highly problematic due to thermal mobility of adatoms and surface
vacancies. Here we solve this problem using hydrogen gas, which we use to
stabilize surface mass flow and suppress roughening during ion bombardment of
elemental and compound semiconductors. We achieve smooth surfaces during
ion-beam processing, and show that the method can be enhanced by radicalizing
H2 gas using a remote plasma source. Our approach is broadly applicable, and
expands the utility of ion beam techniques for the processing and fabrication
of functional materials and nanostructures.
