LOW-ENERGY ION-SCATTERING AND RECOILING

Ion scattering spectrometry was developed as a surface elemental analysis technique in the late 1960's. Further developments during the 1970's and 80's revealed the ability to obtain surface structural information. The recent use of time-of-flight (TOF) methods has led to a surface crystallography that is sensitive to all elements, including hydrogen, and the ability to directly detect hydrogen adsorption sites. TOF detection of both neutrals and ions provides the high sensitivity necessary for non-destructive analysis. Detection of atoms scattered and recoiled from surfaces in simple collision sequences, together with calculations of shadowing and blocking cones, can now be used to make direct measurements of interatomic spacings and adsorption sites within an accuracy of less than or equal to 0.1 Angstrom. Structures are determined by monitoring the angular anisotropies in the scattered primary and recoiled target atom flux. Applications of such surface structure and adsorption site determinations are in the fields of catalysis, thin film growth, and interfaces. This article provides a short historical account of these developments along with some examples of the most recent capabilities of the technique.