ATOMIC-STRUCTURE OF SI(111)-(5X2)-AU FROM HIGH-RESOLUTION ELECTRON-MICROSCOPY AND HEAVY-ATOM HOLOGRAPHY

The main elements of the atomic structure of the Si(111)-(5 X 2)-Au surface have been found by combining off-zone high resolution electron microscopy with chi(2) electron diffraction minimization and direct phasing of the diffraction data using heavy-atom holography. The structure is different from recent models based upon interpreting scanning tunneling microscope and x-ray data in terms of disordered arrangements of gold atoms, and much simpler. It contains two lines of gold atoms decorating a surface dislocation plus an expanded surface arrangement of silicon atoms. This model appears to explain all the available experimental data and is consistent with an expansive surface stress for Si(111).