Formation of a Highly-ordered Thiophene Monolayer on Au(lll) via Vapor Phase Deposition

摘要

Thiophene and its derivatives with interesting electronic characteristics have drawn enormous interest from a wide array of technological applications in molecular electronics. Numerous studies are devoted to the preparation of molecular thin films on metal surfaces and the characterization of their physical and structural properties. The adsorption of sulfur-containing organic molecules on gold is often applied in the formation of self-assembled monolayers (SAMs) with controllable orientation and thickness. The growth mechanism of SAM formation from thiophene or alkylthiophene in solution was monitored by surface plasmon resonance spectroscopy and infrared reflection adsorption spectroscopy, suggesting that their adsorption geometry changed from lying-down to an upright orientation with increasing surface coverage. A full understanding of the adsorption geometries and structural orders of thiophene and thiophene derivative SAMs on metal is quite important for practical applications since such characteristics directly affect device performance. The adsorption geometry of thiophene SAMs on Au(lll) was examined considering their near-edge X-ray adsorption fine structures. Scanning tunneling microscopy (STM) observations with molecular-scale resolution revealed that the adsorption of thiophene or alkylthiophene on Au(lll) in solution led to the formation of ordered SAMs with various adsorption structures depending on the preparation conditions.