From Disorder to Order Process in Self-Assembled Monolayer: Alkanethiols on Si (111)
Lo Yueh Chang1, Yen-Chien Kuo1, Hong Wei Shiu1, Shangjr Gwo1,2, Chia-Hao Chen1*
1Nano Science, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Department of Physics, National Tsing Hwa University, Hsinchu, Taiwan
* presenting author:Lo Yueh Chang,
The hybridization between organic molecules and metals/semiconductors have attracted a lot of attention because of their biocompatibility and tunable electronic characteristics. In such hybrid systems, the intermolecular Van der Waals’ force and molecule-substrate interaction usually dominate the molecular structures and geometries, which are correlated with energy alignments, reactivity, and charge transportations. Among these systems, the simplest form is the self-assembled monolayer which has well-ordered molecular structure that formed two-dimensional monolayer, controllable tail groups, and varied substrates to understand the role of self-assembly process. However, most of the studies were focused on thiol molecules with relatively weak interaction with noble metals, in the case of stronger molecule-substrate interaction and the weaker Van der Waals’ force, the growth mechanism is seldom discussed.

In this work, we studied the disorder-order transition of self-assembling process of alkanethiols (ATs, SH(CH2)nCH3, n = 4 ~ 16) on Si (111) surface. The ATs on Si (111) surface was characterized by means of water contact angle measurement and synchrotron radiation based and high-resolution X-ray photoelectron spectroscopy (HR-XPS) to verify the chemical states. The molecular structures of AT/Si (111) were monitored by near-edge X-ray absorption fine structure spectroscopy (NEXAFS) to analyze molecular orientations. By integrating those surface analysis measurements, this self-assembling growth behavior is understood in the relationship of molecule-substrate interaction.

Keywords: Self-Assembled Monolayer, Van der Waals' Force