Characterization of Alkanethiol Molecules Self-Assembled on Oxide-Free Silicon (111) Surface
Yu-Xun Chen (陳宥勳)1,2*, Lo-Yueh Chang (張羅嶽)2, Jhih-Wei Chen(陳至瑋)3, Yen-Chien Kuo(郭言謙)2, Jenh-Yih Juang (莊振益)1, Chia-Hao Chen (陳家浩)2
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3Department of Physics, National Cheng Kung University, Tainan, Taiwan
* Presenter:Yu-Xun Chen (陳宥勳)
Since the first report of Si-C bound organic monolayers on oxide-free Si almost two decades ago[1], a substantial amount of research has focused on studying the fundamental mechanical and electronic properties of these self-assembled monolayers (SAMs)/Si surfaces and interfaces. However, alkanethiol (AT) grown on semiconductor surfaces was less systematically studied, especially on bare silicon surface, despite their prospective applications. Hence, the AT derived SAMs on silicon are of great interest to bridge inorganic and organic materials.

A commercially available 1-dodecandthiol (DDT) solution was employed, which reacted with hydrogen-terminated Si (111) surface through ultraviolet assisted chemical reaction in ambient condition[2]. The structures of SAMs have been characterized in detail by water contact angle measurement, synchrotron radiation based X-ray photoemission spectroscopy, polarization dependent near-edge X-ray absorption fine structure, X-ray reflectivity (XRR), and atomic force microscopy (AFM). The spectroscopy results indicate the DDT were directly attached on Si surface through Si-S bond formation and the molecules formed ordered organic monolayer. The AFM observations revealed that the surface topographic integrity and roughness changed by DDT. Further, utilizing XRR to provide information on the thickness and packing density of molecules within the SAMs. Electron transfer behavior of the modified Si surface was investigated by electrochemical techniques, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Preliminary data to probe the electronic and chemical structures of the hybrid system and the molecular orientation of the SAMs will be presented in the meeting.

[1] Allongue, P., et al. (1998). Electrochimica Acta 43(19): 2791-2798.
[2] Lou, J. L., et al. (2011). Langmuir 27(7): 3436-3441.

Keywords: self-assembled monolayers (SAMs), X-ray photoemission spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), X-ray reflectivity (XRR), electrochemical impedance spectroscopy (EIS)