Formation and Surface Structures of Highly Ordered Self-Assembled Monolayers of Alkyl Selenocyanates on Au(111) via Ambient-Pressure Vapor Deposition

Abstract

The formation and surface structures of self-assembled monolayers (SAMs) of octyl selenocyanate (OSC, CH3(CH2)(7)-SeCN) on Au(111) prepared by solution and ambient-pressure vapor deposition were investigated by X-ray photoelectron spectroscopy and scanning tunneling microscopy (STM). STM observations revealed that OSC SAMs on Au(111) formed in a 1 mM ethanol solution at room temperature (RT) for 6 h were mainly composed of a disordered phase, whereas vapor-deposited OSC SAMs at RT for 6 h contained an ordered phase with many bright molecular rows, bright aggregates, and dark molecular defects. Therefore, we concluded that vapor deposition is a more effective method for fabricating SAMs of alkyl selenocyanates on Au(111) to achieve a a high degree of structural order compared with solution deposition. When vapor deposition temperatures increased to 348 K, OSC SAMs on Au(111) after deposition for 6 h were much more uniform, containing a small number of loosely packed domains. The ordered phase can be described as a (2\/5 X 6)R49 degrees structure. Moreover, the structural quality of OSC SAMs on Au(111) formed at a higher deposition temperature of 363 K for 1 or 6 h was markedly enhanced, showing long-range ordered domains with a few structural defects. This ordered phase can be assigned to a (\/3 x 2-V11)R30 degrees structure. In this study, we report the first molecular-scale features of SAMs on Au(111) formed by adsorption of alkyl selenocyanates. We also clearly demonstrated that organic selenocyanates could be used as an excellent new precursor for the fabrication of high-quality selenolate SAMs on Au(111) using a vapor deposition method at an elevated temperature.