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Structure and Bonding of Ordered Organic Monolayers of 1,3,5,7-Cyclooctatetraene on the Si(001) Surface: Surface Cycloaddition Chemistry of an Antiaromatic Molecule

1998; American Chemical Society; Volume: 102; Issue: 4 Linguagem: Inglês

10.1021/jp9727308

1520-6106

Jennifer S. Hovis, Robert J. Hamers,

Semiconductor materials and interfaces

Cycloaddition reactions have been utilized widely in organic chemistry and are now emerging as a method for attachment of organic molecules to silicon(001) surfaces in a controlled way. Scanning tunneling microscopy (STM), Fourier transform infrared spectroscopy (FTIR), and ab initio molecular orbital calculations have been used to investigate the structure and bonding of 1,3,5,7-cyclooctatetraene (COT), an antiaromatic molecule, on the Si(001)-2 × 1 surface. STM images show that the COT molecules spontaneously order on Si(001) at room temperature. The individual molecules are separated by 7.7 Å, equal to twice the separation between SiSi dimers on the underlying reconstructed Si(001)-2 × 1 surface. FTIR measurements in conjunction with STM experiments show that the COT molecules bond to Si(001) via the direct interaction of two CC units with two adjacent SiSi dimers within a single dimer row. Ab initio molecular orbital calculations show that the lowest-energy geometry bonding of two CC groups with two SiSi dimers is a di-σ configuration via a double [2 + 2] cycloaddition reaction. The result of this bonding is a monolayer organic film that terminates in an ordered array of alkene groups exposed to the vacuum.