Structures of Aniline and Polyaniline Molecules Adsorbed on Au(111) Electrode: as Probed by in Situ STM, ex Situ XPS, and NEXAFS

Abstract

In situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) were used to examine the electrified interface of Au(111) in 0.1 M H2SO4 containing 0.030 M aniline. In agreement with cyclic voltammogram (CV), which revealed two pairs of peaks at 0.48 and 0.62 V, in situ STM imaging yielded two highly ordered aniline adlattices, (√19 × 5) at 0.55 V and (3 × 2√3)rect at 0.85 V [vs reversible hydrogen electrode, RHE]. According to XPS results obtained with Au(111) emersed at 0.85 V from 0.1 M H2SO4 + 0.030 M aniline, bisulfate anions were coadsorbed in an amount equal to that of aniline. The (3 × 2√3)rect−aniline structure was examined carefully by STM using different imaging conditions. Results revealed that imaging with a tunneling current of 10 nA at a −300 mV bias voltage allowed molecular resolution of both aniline admolecules and bisulfate anions. These species could form acid−base pairs and mingled uniformly on the Au(111) ele...