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The feasibility of angle resolved APECS (Auger Photo-Electron Coincidence Spectroscopy)on solids is demonstrated with an experiment performed at the ALOISA (ELETTRA, Trieste) beamline on the L3M45M45Auger transition of the Cu(111) surface. This beamline,with its multicoincidence detection system based on several individual electron analysers, was designed in order to perform such experiment with good efficiency. The correlation effects displayed by the measured angular distribution are not explained by the two step model, that conversely is commonly accepted for non coincidence experiments performed at the same energy and on the same orbital.

The order-disorder phase transition of the Rh(111)-(√3 × √3)R30°-CO phase was investigated by He scattering. The critical temperature turned out to be 330 ± 5K, while the critical exponents are consistent with a phase transition belonging to the 3-state Potts universality class. The temperature dependence below the critical temperature of both CO phases was studied using elastic He scattering and LEED. These measurements demonstrate that a simple Debye-Waller evaluation of the diffraction data is not appropriate to provide information on the vibrational properties of the CO molecules. From LEED measurements at low temperatures (< 70K) and various CO partial pressures there is evidence of the formation of a disordered second CO layer in equilibrium with the gas phase. The isosteric heat of CO adsorption in the second layer is about 6 kJ mol−1.

Using He atom scattering, layer-by-layer erosion of InSb(110) by low energy ion bombardment has been observed to proceed via nucleation of vacancy islands, island growth and coalescence. The mechanism is in full agreement with theoretical models developed for crystal growth, with diffusing adatoms substituted by diffusing vacancies. In particular it has been observed that coalescence of the vacancy islands sets in after the removal of small fractions of a monolayer and that the average terrace width increases with increasing number of sputtered monolayers.