Silicon adatom switching and manipulation on Si(111)- 7 x 7

We report on a multiple-state switching behavior in the tip height or tunneling current of scanning tunneling microscopy on the Si(111)- 7 x 7 surface. This switching is caused by displacement of silicon adatoms under the influence of energetic tunneling electrons. When the tip is fixed over a center adatom, five well-defined levels appear in the measured tip height and tunneling current. These levels are attributed to different electronic structures, depending on the configuration of the center adatoms in the unit cell. We also demonstrate manipulations of the center adatoms by controlling the sample bias.