AVS 49th International Symposium
    Nanometer Structures Monday Sessions
       Session NS+BI-MoA

Paper NS+BI-MoA7
Resolving Scanning Tunneling Microscopy Features of Oligomers Adsorbed on Si(100)

Monday, November 4, 2002, 4:00 pm, Room C-207

Session: Nanobiology
Presenter: B. Grandidier, IEMN, France
Authors: B. Grandidier, IEMN, France
Mathieu Dubois, IEMN, France
C. Delerue, IEMN, France
J.P. Nys, IEMN, France
D. Stievenard, IEMN, France
J. Roncali, IMMO, France
Correspondent: Click to Email
Scanning tunneling microscopy (STM) gives the possibility to observe complex organic molecules on silicon surfaces in ultra-high vacuum. Although the reactivity of the silicon surfaces often leads to the modification of the molecular electronic states, a clever synthesis of the molecules can keep their structures intact after adsorption. As a result, the molecules are imaged in their integrity and the contrast variation observed along the molecules is usually associated with the highest occupied and lowest unoccupied electronic states of the molecules. Here, we have investigated the STM imaging of conjugated oligomers on Si(100) by tight binding simulations. The molecules are physisorbed on the surface and extend over a few dimers rows. Due to coupling of the molecular states with the electronic states of the silicon surfaces, we show that the off-resonance tunneling process is the major contribution to the tunneling current in usual tunneling conditions. As a result, the potential barrier is lowered when the tip scans above a molecule and the contrast variation gives an enhancement of the Si dimer rows. Experimental STM images of conjugated oligomers confirm this theoretical prediction.