Selective chemical reaction of HBO molecules on the 2 Si 111/-7=7 surface studied by scanning tunneling microscopy

In the chemical reaction of HBO2 molecules with Si 111.-7=7 surface, change in the charge density on the adatoms of the 7=7 units during the process was found to play an exceedingly important role. The molecules preferentially reacted with the center adatoms in the unfaulted half units first. In the filled state STM images, the center adatoms surrounding the reacted center adatoms became dark compared to those in the normal 7=7 units, which indicates existence of some charge transfer caused by the reacted center adatoms. Since HBO2 molecules tend to react with the adatoms in less charge density, such charge redistribution is supposed to increase the chemical reactivity of the modified center adatoms. In fact, center adatoms in the faulted half units, which were adjacent to the firstly reacted center adatoms, reacted subsequently with the HBO2 molecules. According to this process, chain structures were formed by the reacted center adatoms, which may be related to the B network structure previously observed. q1998 Elsevier Science B.V. All rights reserved