Electronic and geometric structure of Si(111)-5X2-Au

Si(111)-5x2-Au is investigated in detail using scanning tunneling microscopy and spectroscopy at 78 K. It is shown that topographic features in STM images are strongly dependent on bias voltages, including a new atomic feature, V unit. Detailed investigations of local distributions of electronic states by scanning tunneling microscopy, point spectroscopy, and current imaging tunneling spectroscopy suggest extensive charge transfers between intra- and interlocal unit cells. Comparisons of experimental and theoretical structural models proposed up to date are made and it is found that none of models truly reproduces all the features observed so far. Our findings suggest that further investigation is required.