AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS+EL+OF-ThM

Paper SS+EL+OF-ThM6
Superexchange Interactions in STM-Organic-Semiconductor Systems

Thursday, November 7, 2002, 10:00 am, Room C-112C

Session: Reactions and Patterning of Organics on Silicon
Presenter: L.C. Teague, University of North Carolina at Chapel Hill
Authors: L.C. Teague, University of North Carolina at Chapel Hill
J.J. Boland, University of North Carolina at Chapel Hill
Correspondent: Click to Email
The incorporation of organic layers and individual molecules into existing semiconductor technologies requires a thorough understanding of surface/molecule reactions. Although numerous studies have focused on the reaction of individual molecules with the Si(100) surface, the specific reaction mechanisms remain poorly understood. The similarity of the Si(100)-2 x 1 surface chemistry with that of C=C systems opens up the possibility of a wide range of organic chemistry reactions. Here, a combination of Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study and interpret the reaction of 1,3-cyclohexadiene (1,3-CHD) with the bare Si(100)-2 x 1 surface. Because STM probes the local density of states (LDOS), the local bonding geometry of 1,3-CHD can be inferred from the location of the @pi@ bond in the adsorbed molecule. Other groups have reported similar observations.@footnote 1,2@ However, DFT calculations indicate the @pi@* orbital is located several eV above the Fermi Energy and should be energetically inaccessible under typical bias conditions. Here, we show that these images can be understood by considering the interaction between the STM tip and the molecule-surface system. The superexchange mixing of the tip dangling bond state with the filled @pi@ state on the molecule produces a new state within the tunneling window. This state is responsible for the observed image contrast and suggests superexchange effects of this type may be important in understanding the charge transfer that occurs through these molecular systems. @FootnoteText@ @footnote 1@ Hamaguchi, K.; Machida, S.; Nagao, M.; Yasui, F.; Mukai, K.; Yamashita, Y.; Yoshinobu, J.; Kato, H. S.; Okuyama, H.; Kawai, M.; Sato, T.; Iwatsuki, M. J. Phys. Chem. B 2001, 105, 3718. @footnote 2@ Hovis, J. S.; Liu, H.; Hamers, R. J. J. Phys. Chem. B, 1998, 102, 6873.