Surface structures and adsorption states of self-assembled monolayers formed by various COOH-terminated alkanethiols on Au(111)

Abstract

Surface structures and adsorption states of self-assembled monolayers (SAMs) formed by COOH-terminated alkanethiols (ATs) with different alkyl chain lengths were examined by scanning tunneling microscopy (STM), contact angle measurement, and X-ray photoelectron spectroscopy (XPS). STM imaging reveals that COOH-terminated ATs with longer alkyl chains [HS(CH2)(n)COOH, n >= 7] can easily form well-ordered SAMs, while COOH-tenninated ATs with shorter alkyl chains hardly form ordered SAMs [HS(CH2)(n)COOH, n <= 5]. From contact angle and XPS measurements, however, we found that the most surface characteristics, such as surface wettability as well as the adsorption state and the amount of adsorbed molecules, are independent of alkyl chain length. In this study, we elucidate that the intermolecular interaction between alkyl chains is a very important factor in obtaining two-dimensional well-ordered COOH-terininated SAMs.