Immobilization of alkyl chain molecules on oxide surface using phosphonic acid as an anchor

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

To apply organic thin films as new devices, it is important to immobilize organic molecules on oxide surfaces. In this study, we investigated the formation of organic self-assembled monolayer on the oxide surface. Decyl phosphonic acid (DPA) molecules were used as the adsorbed molecule on the surface. The DPA film was prepared by immersing the sapphire substrate in DPA ethanol solution. The sample was measured by XPS using synchrotron soft X-ray. For the P 1s XPS spectra of the DPA powder and the DPA film on the sapphire surface, a single peak was observed and the binding energies of the two samples were almost the same. And we measured the sample by the total reflection (TR) XPS, which is highly surface sensitive method. Compared with the normal XPS, the intensity of the C 1s peak in TR-XPS was enhanced. As a result, it was elucidated that the phosphonic acid of the DPA molecule was located at the lower side, while the alkyl chain was located at the upper side on the surface.