Low-dimensional benzotriazole-copper assemblies

For some time benzotriazole (BTAH, C₆H₅N₃) has been known to enhance the corrosion resistance of copper at the monolayer level, although the exact mechanism is still a matter of discussion and disagreement in the literature. In general, the corrosion inhibition action is related to BTAH strongly chemisorbing on copper. On less reactive surfaces such as Au(111), BTAH weakly physisorbs instead. To gain a better understanding of the chemistry of benzotriazole and its binding with copper, BTAH was dosed on copper-doped Au(111) surfaces and investigated through complementary surface sensitive techniques (NEXAFS, photoemission, HREELS, and STM) and supported by DFT modelling (StoBe).
In agreement with previous investigations, BTAH has been seen to physisorb as a hydrogen-bonded flat-lying species on unmodified Au(111), whereas on copper-rich areas dissociative chemisorption occurs. In fact, in the presence of co-adsorbed copper atoms, proton removal from the molecules leads to species better described as BTA-, interacting directly with the Cu atoms. In these situations the molecules adopt a more upright orientation and Cu(BTA)₂ and -[Cu(BTA)]_n- species are formed. The prevalent adsorbate is a Cu(BTA)₂

metal organic compound further coordinated with copper atoms on or in the gold surface top layers. Oligomers based on a Cu:BTA 1:2 stoichiometric ratio are also seen. On annealing such oligomers evolve into longer polymers, with a stoichiometric ratio moving in favour of 1:1. Heating treatments result also in diffusion of the unreacted copper into the bulk gold.

These findings contribute to a further understanding of the interaction between BTAH and copper and, in turn, are expected to help in rationalizing the mechanism at the basis of the protection of copper and copper alloys from corrosive phenomena.