In situ STM imaging of polyethylene glycol adsorbed on an Au(111) electrode in pH 3

• Polyethylene glycol (PEG) adsorbed on Au(111) in pH 3 sulfate media is imaged by STM.
• PEG6000 admolecules appear as winding linear segments spanning ~ 40 nm.
• A smooth PEG film completely covers the Au(111) electrode before hydrogen evolves.
• PEG film dissolves and leaves a high density of clusters on Au(111) at positive potential.

In situ scanning tunneling microscopy (STM) is used to examine the electrified interface of Au(111) immersed in a pH 3 sulfate medium containing polyethylene glycol (PEG) with an average molecular weight of 6000. The cyclic voltammograms thus obtained show two sharp peaks at − 0.35 and − 0.38 V (vs. reversible hydrogen electrode), which correlates with the STM observation of a highly ordered (2 × 2 √ 3)rect structure and the adsorption of PEGs. X-ray photoelectron spectroscopy is used to examine the film formed at − 0.4 V, revealing prominent C–C and C–O–C structures, thereby supporting the view of adsorption and reduction PEGs on the Au(111) electrode. STM imaging at the initial stage of PEG's adsorption reveals winding linear segments 0.6 nm wide and 20–40 nm long, implying helical conformations of PEGs. The PEG film dissolves and yields a high density of nanoclusters, as the potential is switched stepwise from − 0.4 to 0.9 V.

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