AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM10
Adsorption of Cata-condensed Aromatic Compounds on Si(100)

Monday, November 15, 2004, 11:20 am, Room 210C

Session: Functionalization of Semiconductor Surfaces
Presenter: M. Niwano, Tohoku University, Japan
Authors: K. Okamura, Tohoku University, Japan
Y. Hosoi, Tohoku University, Japan
Y. Kimura, Tohoku University, Japan
H. Ishii, Tohoku University, Japan
M. Niwano, Tohoku University, Japan
Correspondent: Click to Email
We have investigated the adsorption of cata-condensed aromatic compounds on a Si(100)-2x1 surface using infrared absorption spectroscopy (IRAS) in the multiple internal reflection geometry (MIR). Si samples (prisms) used for MIR-IRAS measurements were prepared from n-type Si wafers and pre-cleaned by the conventional RCA treatment. The 2x1 reconstructed surface was obtained by flashing the sample surface at about 1300 @super o@C following thermal annealing at 900 @super o@C in an UHV chamber. To dose the 2x1 surface with small aromatic compounds (benzene, naphthalene and anthracene), we introduced them into the chamber in gas phase, while larger aromatic compounds were adsorbed on the surface by vacuum evaporation. We have collected IRAS spectra of those aromatic compounds adsorbed on the 2x1 surface, and analyzed the spectra in the region of C-H stretching vibration modes. It is well known that carbon in the sp2 coordinate exhibits absorption peaks in the region of 3000-3100 cm@super -1@, and carbon in the sp3 coordinate shows peaks in the region of 2900-3000 cm@super -1@. All of the measured spectra exhibited C-H stretching vibration peaks at both regions, indicating that some of the carbon atoms of the molecule are transformed from the sp@super 2@ to sp@super 3@ coordinate to form Si-C bonds when the aromatic compounds adsorb on the surface. We observed that these aromatics adsorb on the surface in different manners depending on the surface coverage. Compared with cluster calculation based on the density functional theory method, we determined that small aromatic compounds adsorb in a relatively simple conformation at low coverage, while high-coverage produces some complicated adsorption configurations. Larger aromatic compounds exhibited two different kinds of peaks; one is due to the molecule adsorbed directly on the Si surface (chemisrption), and the other is due to that adsorbed on the monolayer-covered surface (physisorption).