Static low-energy ion scattering

A new type of energy analyzer (EARISS) has been developed that makes a very efficient use of the back-scattered ions. This enables the use of extremely low ion doses ("static" conditions). For instance, a spectrum of an Au20Pd80 alloy could be obtained with a dose as low as 100 pC. Together with measurements on HOPG(0001) it demonstrates the new possibilities for LEIS using EARISS

On a peculiarity of low-energy ion scattering from a well-ordered bcc W(2 1 1) surface

A peculiarity in the backscattering of keV He+ ions by a well-ordered high-purity W(2 1 1) surface is reported. Besides the normal elastic binary collision peak and the low-energy tail due to backscattering in deeper layers, an extra peak is observed for an inelastic loss of about 95 eV. This unusually large loss has a constant value over a wide range of primary energies (1.5-4.5 keV). An extra peculiarity is that the peak is only observed for the scattering in normal incidence towards the (2 1 1) plane. It is also not seen for polycrystalline W. The energy loss may be due to a quasi-double or -triple collisions of He particles with the row-trough structure of W(2 1 1) involving electronic excitation of both He and W atoms. Alternatively it may be due to a special channeling/dechanneling process for the incident ions

Developments in low-energy ion scattering from surfaces

Low-energy (0.1-10 keV) ion scattering (LEIS) can be used to analyze the atomic composition of the outermost layer of a surface. Possibilities for quantification and in-depth information are discussed. Using a new type of energy analyzer (EARISS) which enables the simultaneous detection of a large part of the energy spectrum, a greatly improved sensitivity is obtained. Even for a catalyst consisting of a highly dispersed carbon support (1000 m2/g) and a low loading of Pd/Pt clusters, the surface composition can be determined using a 2 keV Ne+ ion beam current of only 30 pA

Composition and structure of the Cu85Pd15(110) (2 × 1) surface: a low energy ion scattering investigation

We have investigated the composition and structure of the outermost two layers of the Cu85Pd15(110) (2 × 1) surface using low-energy ion scattering. Time-of-flight forward scattering and recoiling measurements show that the surface is unreconstructed. From the energy and azimuthal distributions of backscattered 2 keV Ne+ ions as obtained with the EARISS (energy and angular resolved ion scattering spectrometer) it is concluded that the first layer is possibly depleted in Pd whereas the second layer is strongly enriched. These results are in agreement with a previously proposed model for the surface based on LEED, angle resolved XPS and TPD measurements