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

Abstract

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 1.3 ± 0.1 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.

Formation of a Highly‐ordered Thiophene Monolayer on Au(111) via Vapor Phase Deposition

“…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 adsorption geometry of thiophene SAMs on Au(111) 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(111) in solution led to the formation of ordered SAMs with various adsorption structures depending on the preparation conditions.…”

“…In a previous study, the adsorption geometry of thiophene adsorbed on Au(111) from the vapor phase was proposed based on density functional theory calculations . STM imaging revealed that 3‐hexylthiophene SAMs on Au(111) grown via the vapor phase have a lying‐down striped phase . However, to date there are no molecular‐scale STM reports about the formation of thiophene SAMs on Au(111) via the vapor phase.…”

“…1,2 Numerous studies are devoted to the preparation of molecular thin films on metal surfaces and the characterization of their physical and structural properties. [3][4][5][6][7][8][9][10] 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. [3][4][5][6][7][8][9][10][11][12][13] The growth mechanism of SAM formation from thiophene or alkylthiophene in solution was monitored by surface plasmon resonance spectroscopy 4 and infrared reflection adsorption spectroscopy, 11 suggesting that their adsorption geometry changed from lying-down to an upright orientation with increasing surface coverage.…”

“…6 STM imaging revealed that 3-hexylthiophene SAMs on Au(111) grown via the vapor phase have a lying-down striped phase. 3 However, to date there are no molecularscale STM reports about the formation of thiophene SAMs on Au(111) via the vapor phase. To elucidate this issue, we investigated the formation and structure of thiophene SAMs on Au(111) prepared via vapor phase deposition using STM.…”