Orientation of one-dimensional silicon polymer films studied by X-ray absorption spectroscopy

Mannan, M. A.*; Baba, Yuji  ; Sekiguchi, Tetsuhiro  ; Shimoyama, Iwao   ; Hirao, Norie; Nagano, Masamitsu*; Noguchi, Hideyuki*

Molecular orientations for thin films of one-dimensional silicon polymers grown by vacuum evaporation have been assigned by X-ray absorption fine structure (XAFS) using linearly polarized synchrotron radiation. For XAFS spectra of polydimethlysilane (PDMS) films on highly oriented pyrolytic graphite (HOPG), the intensities of two peaks were found to be strongly polarization dependent. Quantitative evaluation of the polarization dependence of the XAFS spectra revealed that the polymers are oriented nearly parallel to the surface. The observed orientation is opposite to the previously observed results for PDMS on oxide (indium tin oxide) and metal (polycrystalline copper). The flat-lying feature of PDMS observed only on HOPG surface is attributed to the interaction between CH bonds in PDMS and orbitals in HOPG surface.