AN X-RAY-DIFFRACTION STUDY OF THE SI(111)(ROOT-3X-ROOT-3)R30-DEGREES INDIUM RECONSTRUCTION

The structure of the (square-root3 x square-root3)R30-degrees reconstr uction 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 in tensities at zero perpendicular momentum transfer (l = 0), indicates l ateral displacement in the silicon surface atoms. Intensity profiles o f fractional order rods and one integer order rod gives information co ncerning displacements normal to the surface of the silicon substrate. The indium adatoms are shown to occupy the 4-fold coordinated T4 site s 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.