Controlling Carboxyl Deprotonation on Cu(001) by Surface Sn Alloying

A. CARRERA; L. J. CRISTINA; S. BENGIÓ; A. COSSARO; A. VERDINI; L. FLOREANO; J. D. FUHR; J. E. GAYONE; H. ASCOLANI

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. 117 p. 17058 - 17065

1932-7447

We find that for adsorbed terephthalic acid (TPA) molecules surface Sn alloyingdeactivates the Cu(001) surface by decoupling the adsorbed molecules from the substrate. Thiseffect is investigated for the case of the 0.5 ML phase of the Sn/Cu(001) surface alloy byapplying fast X-ray photoemission spectroscopy, scanning tunneling microscopy, near-edge Xrayabsorption fine structure spectroscopy, and density functional theory calculations. Theexperimental results conclusively show that the deprotonation reaction of the carboxyl groupsoccurring in the clean Cu(001) is fully inhibited on this Sn/Cu(001) surface alloy, which allowsthe molecules to form two-dimensional arrays stabilized by [OH···O] hydrogen bonds. Theformed arrays exhibit a crystal structure that is practically indistinguishable from thattheoretically obtained for unsupported TPA sheets, suggesting an extremely weak molecule/substrate interaction. This is supported by DFT calculations of the adsorption energy landscapeof the TPA sheets formed on the Sn/Cu(001) template: the lateral variation of the adsorption energy (corrugation) is estimated to be less than 0.2 eV, with an adsorption energy per molecule in the range 1.6−1.8 eV and a contribution of each double [OH···O] bond of 1 eV. Finally, the performed thermal desorption experiments show that the TPA sheets remain stable on the surface alloy until their desorption. From these experiments, a value of 1.5 eV was determined for the desorption energy barrier, which is consistent with the important contribution of the [OH···O] bonds to the stability of the sheets as theoretically predicted. The results reported in this study suggest that a gradual activation of the interaction between the TPA molecules and the Cu(001) surface will also be obtained for decreasing Sn coverage.