Molecularly Adsorbed Oxygen Species on Si(111)-(7×7): STM-Induced Dissociative Attachment Studies

Science  19 Apr 1996:
Vol. 272, Issue 5260, pp. 385-388
DOI: 10.1126/science.272.5260.385


Scanning tunneling microscope (STM)-induced selective bond breaking in individual molecules and conventional STM imaging are combined to determine the nature of chemisorbed O2 species formed during the initial stages of silicon (111)-(7×7) oxidation. A selective atomic-scale modification mechanism that involves dissociative electron attachment of tip-emitted electrons to empty adsorbate orbitals is introduced. Two molecular species were found: one involves O2 bonded to an already oxidized silicon adatom, and the other involves an O2 molecule that is bonded to a second-layer rest atom and interacting with two silicon adatoms.