The Si (100) surface: Symmetric or asymmetric dimers?

We present new results obtained with medium energy ion beam crystallography on the clean Si (100)?(2 × 1) surface. This study, meant to discriminate between symmetric and asymmetric dimer models for the reconstruction, shows that symmetric dimers are not consistent with our results. We conclude that the Si (100)?(2 × 1) surface is reconstructed in asymmetric dimers, accompanied by extensive subsurface distortions.     

Two-atom model for the calculation of surface blocking in medium and high energy ion scattering

A two-atom blocking model has been developed to analyze surface blocking patterns recently obtained in medium energy ion scattering experiments. In the model the mean square thermal vibration amplitude of a surface atom can be used as a fitting parameter in comparison with experimental results. Anisotropic surface vibrations have been taken into account by assuming a non-spherical Gaussian probability distribution for the thermal displacement of the surface atom. In addition, some analytical expressions have been derived for the effective nuber of target atoms contributing to the yield of ions backscattered into a blocking direction.     

Non-respiring rat liver mitochondria do not have a Ca2+/2H+ antiporter

Liver mitochondria take up Ca2+ by the Ca2+ uniporter, whereas at steady state efflux is believed to occur mainly by means of a ruthenium red-insensitive Ca2+/2H+ antiporter. The latter activity was studied in respiration-inhibited mitochondria in the presence of ruthenium red and was measured as Ca2+ uptake following acidification of the matrix by addition of nigericin, which catalyzes K+/H+ exchange. Ca2+ uptake was stimulated by protonophorous uncoupling agents and inhibited by increasing the concentration of ruthenium red. However, the rates were always smaller than those obtained by addition of valinomycin instead of nigericin. This indicates that under these conditions, Ca2+ fluxes are not mediated by a Ca2+/2H+ antiporter but by residual uniporter activity.     

On the structure of the laser irradiated Si(111)-(1 × 1) surface

We have studied the geometric structure of the Si(111)-(1 × 1) surface, prepared from a Si(111)-(7 × 7) surface with a pulsed ruby laser. With the technique of medium energy ion scattering, in combination with channeling and blocking, we find that this surface has a structure very similar to the (7 × 7) surface. Our results are inconsistent with a simple relaxation model.     

Ion-beam crystallography of clean and sulfur covered Ni(110)

Medium energy ion scattering has been used to determine the atomic structure of a Ni(110) surface covered with 0.5 monolayer of sulfur. After having confirmed that the sulfur atom resides in a fourfold-coordinated hollow site, it was found that its distance above the plane of the first Ni layer is 0.87 ± 0.03 Å. We measured a 6 ± 3% outward relaxation effect for the sulfur covered Ni(110) surface layer and an inward relaxation of 4 ± 1% when this surface is clean.