Adsorption site determination of light elements on heavy substrates by low-energy ion channeling

Ion channeling in the low-keV energy range is demonstrated by means of the technique of time-of-flight scattering and recoiling spectrometry. The pred ictions of the Lindhard string model of ion channeling are compared with th e experimental findings. Qualitative agreement was obtained between the exp erimentally measured critical angles and the predictions of the model. The technique of low-energy ion channeling is shown to be capable of quantitati vely probing the positions of light elements on heavy substrates with analy sis by simple geometrical constructs. Classical ion trajectory simulations using the scattering and recoiling imaging code were used to observe the de tails of the ion trajectories. Quantitative analysis of the Pt(111)-(1x1)-H surface using 5 keV Ne+ shows that the hydrogen atoms preferentially popul ate the threefold fcc sites with a height of 0.9 +/- 0.1 Angstrom above the first-layer Pt atoms and a corresponding Pt-H bond length of 1.9 +/- 0.1 A ngstrom. (C) 1999 American Institute of Physics. [S0021-8979(99)03321-6].