Adsorption structure of glycine on TiO2(110): a photoelectron diffraction determination

High-resolution core-level photoemission and scanned-energy mode photoelectron diffraction (PhD) of the O 1s and N 1s states have been used to investigate the interaction of glycine with the rutile TiO2(110) surface. Whilst there is clear evidence for the presence of the zwitterion NH3CH2COO with multilayer deposition, at low coverage only the deprotonated glycinate species, NH2CH2COO is present. Multiple-scattering simulations of the O 1s PhD data show the glycinate is bonded to the surface through the two carboxylate O atoms which occupy near-atop sites above the five-fold coordinated surface Ti atoms, with a Ti-O bondlength of 2.12±0.06 Å. Atomic hydrogen arising from the deprotonation is coadsorbed to form hydroxyl species at the bridging oxygen sites with an associated Ti-O bondlength of 2.01±0.03 Å. Absence of any significant PhD modulations of the N 1s emission is consistent with the amino N atom not being involved in the surface bonding, unlike the case of glycinate on Cu(110) and Cu(100). keywords: surface structure; chemisorption; photoelectron diffraction; titanium dioxide; glycine; amino acids ♦ corresponding author: email [email protected]