Abstract

The technique of helium atom scattering is intrinsically very sensitive to all types of surface defects. With dynamic sensitivites of order 10⁵, or more, one is able to observe and characterise very low densities of either point^[1] or linear type defects^[2]. The diffuse elastic scattering from isolated step edge defects, for example, is able to give detailed information about the characteristic shape of a step edge, as observed by the thermal energy He probe^[3]. The linear nature of a step edge ensures that the intensity is scattered predominately along certain crystallographic azimuths. The large angle diffraction, from the non-periodic defect, is dominated by the strongly repulsive part of the interaction potential. Hard wall calculations may be used to deduce the shape of single step edges. Experimentally, only a very small incident-energy dependence is found. However, it has been shown that a soft potential calculation may improve the optimum fits, or comparison between calculation and experiment^[4]

© 1989 Optical Society of America