Adsorption structures of 2,3-butanediol on Si(001)

In the present study we used a combination of scanning tunneling microscopy and density functional theory calculations to examine the structures of 2,3-butanediol stereoisomers adsorbed on a Si(001)-2 × 1 surface at room temperature. We found that most molecules prefer to adsorb on the bridge between the ends of two adjacent dimers within the dimer row; this adsorption preference differs from that of alkene-type molecules, which undergo a cycloaddition reaction with a Si dimer on Si(001) surfaces. Determination of the absolute chirality of (R,R)- and (S,S)-2,3-butanediol adsorbates on Si(001) indicated that each molecule preserves its chirality during bonding to Si atoms. In addition, 2,3-butanediol preferred to adsorb in the CH₃-gauche conformation rather than the CH₃-anti conformation, which can be explained by steric considerations. These results suggest that alcohol-type organic molecules are useful agents for producing chirally modified Si surfaces.