Paper published (self-assembled monolayers)

Striped Phase of 3-Hexylthiophene Self-Assembled Monolayers on Au(111) Formed by
Vapor Phase Deposition

Youngwoo Kim1, Hungu Kang1, Azuho Tsunoi2, Tomohiro Hayashi2, Masahiko Hara2, and Jaegeun Noh1 3 ∗

1Department of Chemistry, Hanyang University, Seongdong-Gu, Seoul 133-791, Korea 2Department of Electronic Chemistry, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8502, Japan
3Institute of Nano Science and Technology, Hanyang University, Seoul 133-791, Korea

The formation and surface structure of 3-hexylthiophene (HTP) self-assembled monolayers (SAMs) on Au(111) prepared by solution and ambient-pressure vapor deposition at room temperature (RT) for 24 h were examined by means of scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging revealed that HTP SAMs formed by solution deposition have a disordered phase, whereas those formed by vapor deposition exhibit a striped phase with a unidirectional orientation. The distance between the rows in the striped phase was measured to be 13±01 nm, and the hexyl molecular backbones of HTP in the SAMs on Au(111) are oriented parallel to the Au(111) surface with the head-to-head orientation. From this STM observation, we suggest that the formation of this striped phase in HTP SAMs prepared by vapor deposition were mainly driven by the optimization of van der Waals interactions between the hexyl chains on the surface. CV measurements also demonstrated that HTP SAMs show a high blocking efficiency for electron transfer reactions between electrolytes and the gold electrode, suggesting the formation of SAMs on Au(111) from the vapor phase. Our results obtained here will be very useful for understanding the formation and structure of HTP SAMs on Au(111) surfaces and how they are influenced by deposition method.