Annealing behaviour of ion-bombarded WSe2. A combined LEED and STM study

The effect of ion bombardment and subsequent annealing of surfaces of the layered semiconductor tungsten diselenide (WSe2) is investigated with LEED and STM. The STM investigations are performed both in air and under UHV, yielding comparable results. After bombardment with argon ions at energies between 5 and 10 keV, individual impact craters with diameters of about 6 nm or surfaces covered with time-stable mounds of typically 1 to 4 nm in diameter and about 0.1 to 0.5 nm in height are found, depending on the ion doses. While the atomically resolved STM images of the ion-bombarded samples show a preserved atomic order of the surface on a local scale, LEED studies indicate that even the long-range atomic order of the ion-bombarded samples is largely preserved. By thermal annealing at about 900 K, the surfaces regain a smooth appearance, while LEED still gives indications of remaining disorder.