Chemical state analysis of interface between oxides and organic molecules studied by XAFS

Narita, Ayumi; Baba, Yuji  ; Sekiguchi, Tetsuhiro  ; Shimoyama, Iwao   ; Hirao, Norie; Yaita, Tsuyoshi

It is difficult to immobilize organic molecules on an inorganic material, because the lattice constants of organic crystals are larger than those of inorganic ones. Especially, there are few reports about the immobilization of organic molecules on oxide. In this study, we have investigated that the immobilization of alkane molecules on oxide surfaces. Octadecyl-triethoxy-silane (ODTS) molecules were adsorbed on a sapphire single crystal, and the chemical states of the interfaces were measured by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) using synchrotron radiation. The Si 1s XPS spectrum of ODTS monolayer on sapphire suggested that silicon alokoxides of ODTS formed chemical bond with the surface. For Si-K edge XAFS spectra of ODTS monolayer, the polarization dependence was observed. On the basis of the angle dependence, it was elucidated that one of the Si-O bonds in the ODTS molecule is perpendicular to the surface.