SULFUR CHEMISORPTION ON NI(111) - THE CLOCK STRUCTURE OF THE (5-ROOT-3X2)S PHASE

From an interplay between x-ray diffraction and scanning tunneling microscopy the atomic structure of the (5 root 3x2)S reconstruction on Ni(111) has been revealed. It consists of four squarelike tetramers of Ni atoms, rotated in pairs similar to 14 degrees clockwise and counterclockwise, onto which eight fourfold-coordinated S atoms are chemisorbed. The results have a significant bearing on the understanding of the detailed structure of postulated pseudo-(100) reconstructions of fcc(111) surfaces and support a general principle of increased adsorbate coordination as being decisive for the reconstruction.