| 講演要旨： |
Neutral atoms and molecules with energies from 300 eV up to some 10 keV are scattered under a grazing angle of incidence from a clean and flat LiF(001) surface. For scattering along low index directions in the surface plane ("axial surface channeling") we observe defined patterns in the intensity distributions for scattered atoms [1,2]. The data can be understood by diffraction of fast atoms at the surface where the symmetry of the crystal lattice and of the interaction potential between atom and surface determine the diffraction pattern. The peaks in the angular distributions of scattered atoms result from a "fast" motion parallel to the surface plane and a "slow" one normal to axial strings of atoms along low index directions in the surface plane. Based on a separation of these two different regimes, the fast parallel motion results in diffraction patterns with large initial and final momentum vectors (equivalent to de Broglie wavelengths as low as some 10-3 Å), whereas scattering in a plane normal to axial strings of surface atoms proceeds in the eV-regime and results in diffraction affected by the corrugation of the overall interaction potential showing minima between adjacent strings. The corrugation of the potential and diffraction effects give rise to an intensity pattern which is fairly similar to "supernumerary rainbows" in the atmospheric phenomenon or thermal He atom scattering. We will demonstrate that the resulting diffraction pattern is extremely sensitive to the interaction potential and, in particular, to its corrugation. This allows one to derive the atomic interaction potentials in the eV regime with high accuracy. An important prerequisite for the observation of diffraction for fast atoms is the suppression of excitations of the target surface which give rise to decoherence phenomena in the scattering process. For grazing scattering of neutral atoms from surfaces of broad band-gap insulators it was observed that such excitations play a minor role even in the keV domain. On the other hand, for ions charge transfer and excitation of optical phonons takes place accompanied by a non negligible projectile energy loss. In the present experiments, we have not observed so far diffraction patterns for scattering of ions.
- [1] A. Schüller, S. Wethekam, and H. Winter, Phys. Rev. Lett. 98, 016103 (2007).
- [2] P. Rousseau, H. Khemliche, A.G. Borisov, and P. Roncin, Phys. Rev Lett. 98, 016104 (2007).
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