The growth and atomic structure of the silicon(111)-indium interface determined by surface x-ray diffraction.

The growth and atomic structure of indium on the 7x7 reconstructed (111) surface of silicon has been studied using X-ray scattering and synchrotron radiation. A correlation is seen between features in the X-ray reflectivity curves and breaks in the Auger signal versus time plot as indium is grown. The oscillation of the X-ray signal indicates that below 400C two consecutive pseudomorphic indium layers are formed before three dimensional islanding occurs. Kinematic analysis predicts the shape of the X-ray signal versus time curve and yields the perpendicular displacement of the indium layers from the substrate. It is proposed that the first layer of indium atoms are bonded vertically above the top most layer of silicon atoms in T1 sites. The structure of the ?3 x ?3 R30 reconstruction induced by the adsorption of ? of a monolayer of In has been determined. The Patterson function obtained from structure factor intensities at zero perpendicular momentum transfer, indicates lateral displacement in the silicon surface atoms. The indium adatoms are shown to occupy the 4-fold coordinated T4 sites above the second layer silicon atoms. Elastic strain energy minimisation has been used to show that relaxations extend down to the first six layers of the bulk. The Patterson function for the 4x1 adsorbate phase indicates that the saturation coverage is 1 monolayer with each surface unit cell having four indium atoms rather than two as indicated by Scanning Tunnelling microscopy images. The results show that the indium atoms sit in a complicated arrangement on the Si substrate near T1, T4 and H3 sites. Intensity profiles of one fractional order rod and the (00L) reflectivity give information concerning displacement of the indium adatoms normal to the surface.