Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces. From comparison of measured and calculated diffraction patterns we deduce the rumpling of the topmost surface layer of LiF(001) (i.e., an inward shift of Li + ions with respect to F − ions). The effect of thermal vibrations on the measurement of rumpling is accounted for by ab initio calculations of the mean-square vibrational amplitudes of surface ions. At room temperature this leads to a reduction of the apparent rumpling by 0.008Å. We then obtain a rumpling of (0.05 ± 0.04)Å, which improves its accuracy achieved in previous work.

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Observation of the enhanced electron screening in metallic environments is of fundamental importance for the understanding of strongly coupled astrophysical plasmas. Experimental screening energies determined by different groups for many metals are much larger than the theoretical predictions. However, a comparison between experimental and theoretical data is rather ambiguous because of the contributions of systematic errors in the experiments. One of the most important problems is the uncertainty resulting from the oxidation of the target surface during the measurements. Here, we present results of the first ultra-high vacuum (UHV) experiments studying d+d nuclear reactions in a deuterized Zr target for which the experimental discrepancies are especially large. The total cross sections and angular distributions of the 2 H(d,p) 3 H and 2 H(d,n) 3 He reactions have been measured using a deuteron beam of energies between 8 and 30 keV provided by an electron cyclotron resonance ion source with excellent long-term stability. The cleanness of the target surface has been assured by combining Ar sputtering of the target and Auger spectroscopy. In an on-line analysis method, the homogeneity of the implanted deuteron densities could be monitored also. The resulting screening energy for Zr confirms the large value obtained in a previous experiment under poorer vacuum conditions.

The coherence for diffraction effects during grazing scattering of fast hydrogen and helium atoms from a LiF(001) surface with energies up to some keV is investigated via the coincident detection of two-dimensional angular distributions for scattered projectiles with their energy loss. For keV H atoms, we identify electronic excitations of the target surface as the dominant mechanism for decoherence, whereas for He atoms this contribution is small. The suppression of electronic excitations owing to the band gap of insulators plays an essential role for preserving quantum coherence and thus for the application of fast atom diffraction as a surface analytical tool.

The structure of a monolayer silica film on a Mo(112) surface is investigated by grazing scattering of 25 keV H0 atoms. By detection of the number of projectile induced emitted electrons as function of azimuthal angle of rotation of the target surface, the geometrical structure of atoms forming the topmost layer of the silica film is determined via ion beam triangulation. From our data we find evidence for the arrangement of surface atoms in terms of a two-dimensional Si-O-Si network model.