Barium adsorption on Si(100)-(2 x 1) at room temperature: a bi-polar scanning tunneling microscopy study

The initial stages of barium adsorption on Si(100)-(2 x 1) at room temperature has been studied by ultrahigh Vacuum scanning tunneling microscopy (STM) under both positive and negative sample-bias imaging conditions. Two distinct adsorption sites have been identified by the high-resolution STM images. It was found that, with the substrate held at room temperature, barium atoms can occupy both valley-bridge sites in the trough between silicon dimers and silicon-vacancy sites. It is possible to image the barium atoms at valley-bridge sites with both negative and positive sample bias, revealing filled and empty surface states, respectively. For barium atoms adsorbed at vacancy sites, however, it is only possible to obtain filled-state images, and imaging with positive sample bias will induce the removal of the atom, possibly transferred to the tip, revealing a missing silicon dimer below. (C) 2000 Elsevier Science B.V. All rights reserved.