An X-ray diffraction study of the Si(111) (√3 × √3) R30°-indium reconstruction

The structure of the (√3 × √3)R30° reconstruction induced by the adsorption of 1 3 of a monolayer of In on the Si(111) surface has been determined using surface X-ray diffraction. The fractional order Patterson function obtained from structure factor intensities at zero perpendicular momentum transfer (l = 0), indicates lateral displacement in the silicon surface atoms. Intensity profiles of fractional order rods and one integer order rod gives information concerning displacements normal to the surface of the silicon substrate. The indium adatoms are shown to occupy the 4-fold coordinated T4 sites above the second layer silicon atoms. Keating elastic strain energy minimisation has been used to determine relaxations down to the sixth layer of the bulk.