Analysis of bonding structure of ultrathin films of oligothiophene molecules grown on passivated silicon surfaces

Toyoshima, Hiroaki*; Hiraga, Kenta*; Ono, Shinya*; Tanaka, Masatoshi*; Ozawa, Kenichi*; Mase, Kazuhiko*; Hirao, Norie; Sekiguchi, Tetsuhiro  ; Shimoyama, Iwao   ; Baba, Yuji  

The knowledge of the interaction between organic molecules and semiconductor surfaces plays an important role in adapting organic semiconductors into the semiconductor technology. In the present study, the process of -sexithiophene (-6T) thin layer formation on passivated silicon (Si) surfaces has been investigated in-situ by means of PES, angle-depended NEXAFS (near-edge X-ray absorption fine-structure), SDRS, and RDS. For water-adsorbed Si(001), it was found that the majority of -6T molecules are standing on the substrate. Above 3 nm, most of molecules are standing and constitute well ordered islands or films. For ethylene adsorbed Si(001) on the contrary, some of -6T molecules are flat-lying, resulting in less prominent orientation. Thus, the orientation of molecules depends on the method of passivation, which opens the possibility of controlling the molecular orientation by the surface modification.