Surface irradiation effects by STM observation. Surface damage in Si under energetic ion irradiation

A link facility of a high vacuum STM and an ion accelerator is used to observe defect formation Si (111) plane with 7x7 structure by high energy heavy ion irradiation between 10 and 50 keV. Relatively low dose ion irradiation shows that single missing adatoms are most frequently observed and that missing of adatoms forms clusters especially at higher ion energy. Most of displacements at the surface are caused by low energy recoils, of which cross section decrease with ion energy. In the case of 10 keV Ar irradiation, density of vacant sites is much larger than those at 30 and 50 keV, and it is difficult to distinguish individual ion damage as agglomerations of vacant sites on the irradiated surface to 1.0x1012 ions cm-2. Site dependence of defect formation is clearly observed, and the center atoms on 7x7 structure tend to be ejected rather than corner atoms. The center-to-corner ratio is quantitatively estimated and its ion energy dependence is discussed. (author)