Exchange of Methyl‐ and Azobenzene‐Terminated Alkanethiols on Polycrystalline Gold Studied by Tip‐Enhanced Raman Mapping

Abstract

Mixed thiol self-assembled monolayers (SAMs) presenting methyl and azobenzene head groups were prepared by chemical substitution from the original single-component n-decanethiol or [4-(phenylazo)phenoxy]hexane-1-thiol SAMs on polycrystalline gold substrates. Static contact-angle measurements were carried out to confirm a change in the hydrophobicity of the functionalized surfaces following the exchange reaction. The mixed SAMs presented contact-angle values between those of the more hydrophobic n-decanethiol and the more hydrophilic [4-(phenylazo)phenoxy]hexane-1-thiol single-component SAMs. By means of tip-enhanced Raman spectroscopy (TERS) mapping experiments, it was possible to highlight that molecular replacement takes place easily and first at grain boundaries: for two different mixed SAM compositions, TERS point-by-point maps with <50 nm step sizes showed different spectral signatures in correspondence to the grain boundaries. An example of the substitution extending beyond grain boundaries and affecting flat areas of the gold surface is also shown.

Photoswitchable Macroscopic Solid Surfaces Based On Azobenzene‐Functionalized Polydopamine/Gold Nanoparticle Composite Materials: Formation, Isomerization and Ligand Exchange

“…Along with studies of molecular self‐assembly on metallic surfaces, the molecular scale restructuring of such assemblies became a focus of interest . Restructuring processes may yield a completely new molecular layer with a different function or a mixed layer with two or more components.…”

Vibrational modes of aminothiophenol: a TERS and DFT study

“…The 633 nm excitation is far from the absorption bands of ATP 16 and resonant mechanism are excluded in our measurements. [17][18][19] The SPM is operated in scanning tunnelling microscopy (STM) mode; the tips used were prepared from Au wire pieces of a 250 mm diameter and 99.99% purity (from Goodfellow) by electrochemical etching in a concentrated HCl/ethanol 1 : 1 solution. 1).…”

Subnanometer-resolved chemical imaging via multivariate analysis of tip-enhanced Raman maps

“…However, despite this progress, it is still highly challenging to obtain a relatively high pixel density TERS image for an area of closely packed species with subnanometer resolution 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , even if the acquired image only has a very limited signal-to-noise ratio (SNR). This result is due to the acquisition time for each pixel being limited by the stability of the system (for example, the stability of molecules and the tip status, as well as the thermal drift), resulting in relatively weak Raman signals at each pixel.…”