The self-consistent field Hartree-Fock cluster procedure applied to B and Al adsorbed on Si(111) surface shows a greater binding energy for the B atom when it is located in the five-fold coordinated B 5 site as compared to the four-fold T 4 site. This is in contrast to Al which prefers the T 4 site. The result demonstrates strong theoretical support for recent conclusions from measurements of the B/Si(111) surface by a number of different experimental techniques including the results of our ion channeling measurements presented.

Si(100)(2×1) reconstructed surface was studied by a combination of conventional (backscattering) and transmission channeling. In a conventional channeling study, the angular dependence of the conventional surface peak intensity along the normal axis 〈100〉 and off-normal axis 〈111〉 were measured and compared to several models by use of Monte Carlo simulation including the domain effect. The buckled dimer model (YC) gives better fit to the experimental results, but still underestimates the distortion in the atomic arrangement beneath the first monolayer, especially the larger displacement along the 〈100〉 axis should be considered. The measured transmission surface peak intensity is compared to the model prediction based on the flux peaking effect, indicating that, at least one of the two atoms consisting of the dimer needs to be displaced from the 〈100〉 axis larger than 0.96 Å; the displacement perpendicular to the (110) plane (Δy) should be involved. The YJM model involving the displacement Δy gives the best agreement to the measured result.

Monte Carlo calculations have been performed to evaluate the surface peak from 1 MeV He ions incident on Si(001) and Si(111) crystal surfaces. Detailed angular dependences of the surface peaks were obtained for tilt angles of ⩽2° and azimuthal angles of ⩽45° in the vicinity of axial channeling directions. The validity of the triangular background subtraction is discussed for cases of tilted incidence from axial channeling directions. The multiple scattering effect in thin adlayers on the crystal, which is important in application of MeV ion scattering to interfaces studies, is simulated and correlated with evaluation of the interface peak value of the substrate atoms.

The displacement-sensitive MeV ion-scattering measurement has been performed on Si(111) surfaces covered with Au and/or Ag evaporated at room temperature. For single metal depositions, the reactivity of Ag atoms with Si atoms was very low compared to Au. For sequential depositions of both Ag and Au, the reactivity of the system was dominated by the more reactive material Au while the onset of the Si displacement depends on the amount of both metals for 0.5–2.0 ML coverage of predeposited materials (1 ML=7.83×1014 atoms/cm2). No significant differences were observed between Au/Si(111) 7×7 and Au-stabilized 3×1 surfaces for subsequent Ag depositions. The mechanism of the reaction between the noble metal and Si atoms is discussed in terms of current models.

The shapes of crystal-blocking angular distributions have been used to study the fission decay of excited compound nuclei produced by bombardment of tungsten with $^{16}\mathrm{O}$ ions. The results show that while most of the fission decays (\ensuremath{\sim}80%) occur with lifetimes too short to be measured by the blocking technique ($\ensuremath{\tau}\ensuremath{\lesssim}{10}^{\ensuremath{-}18}$ sec), a large fraction (\ensuremath{\sim}20%) corresponds to lifetimes $\ensuremath{\tau}\ensuremath{\gtrsim}{10}^{\ensuremath{-}16}$ sec. This indicates a significant contribution from fission after evaporation of several neutrons.