STM image of Ag adatoms. (a) High resolution STM image of Ag adatoms on HOPG (1.5 mV, 1.7 nA). (b) An image of a cluster of Ag adatoms showing the adsoption sites on HOPG. The superimposed hexagon illustrates the location of B-type (black circles) and A-type (open circle) carbon atom arrangement on HOPG. (c) 3-D view of the image in (b). A line scan (d) along the line in (b) shows the variation in height of the C atoms and Ag adatoms.