Formation of Holes in Alkanethiol Monolayers on Gold

Abstract

Self-assembled monolayers of alkanethiols (CnH2,,+lSH; n = 3, 8, 12, 18, and 22) adsorbed on gold(ll1) are investigated with (atomically resolved) scanning tunneling microscopy (STM) and wetting measurements. The characteristic depressions observed in these monolayers with STM are proven to be holes in the underlying top gold surface layer rather than defects in the thiol monolayer itself. The holes originate from an etching process of the gold during adsorption of the thiol molecules: a correlation is obtained between the number of holes observed with STM and the amount of gold measured with atomic absorption spectroscopy in the thiol solution after adsorption. The erosion process is found to vanish as soon as complete self-assembly is observed in STM and wetting. For a dodecanethiol monolayer on gold adsorbed from a diluted methanoic thiol solution, selfassembly is observed within 10-min adsorption time. The average amount of gold in the thiol solution after 10 min corresponds to dissolution of 2% of a monolayer Au( 11 1). The erosion strongly increases when the dodecanethiol adsorbs from undiluted thiol. The amount of holes also increases with decreasing thiol chain length as a result of a lower degree of self-assembly. The surface gold atoms underneath the thiol layer are highly mobile, which is manifest in STM tip-induced reorganization of the thiol layer and in penetration of evaporated gold through the thiol layer. This mobility is believed to be cruciai in the etching process. Due to the mobility of thiol molecules during the adsorption process prior to acquiring a complete self-assembled structure, gold dissolves, probably in the form of a gold thiolate complex.

Influence of ligand structure on the stability and oxidation of copper nanoparticles

“…As these observations were made under nitrogen atmosphere, and therefore no oxidation due to oxygen was possible, they could indicate etching of the copper nanoparticles in thiol-containing solutions. Similarly, etching of gold particles by thiols has been reported [39] and [40]. Additionally, similar trends were observed for the chain length and concentration of the thiol.…”

Quantifying thiol–gold interactions towards the efficient strength control

“…8). As discussed above, the reduced gold surface can weaken the Au-Au bond; (2) the formation of SAMs on gold surfaces may weaken the interactions between gold atoms in the top and lower layers because earlier scanning tunnelling microscopy studies have shown the mobility of Au thiolates within the SAMs of alkanethiols 62,63 .…”

Self‐Assembled Monolayers on Electrodes

“…19,50 Scanning tunneling microscopy (STM) studies (see section 3) suggest that the gold is slightly etched during self-assembly; gold has been detected in the deposition solution. 88,89 To remove kinetically trapped disordered states, the SAM is sometimes annealed by soaking it in hot deposition solution, 90 exposing it to warm temperatures in a gaseous ambient, 91 or subjecting the electrode to a cyclic voltammogram (CV) and repeated immersions in the deposition solution. 92 When two thiols are being co-deposited, the solvent, time and temperature all affect the mole fraction of each component in the SAM.…”