Adsorption structure of glycine on TiO_2(110): A photoelectron diffraction determination

摘要

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 TiO_2(110) surface. Whilst there is clear evidence for the presence of the zwitterion NH_3~+CH_2COO~- with multilayer deposition, at low coverage only the deprotonated glycinate species, NH_2CH_2COO 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-0 bondlength of 2.12 ± 0.06 A. Atomic hydrogen arising from the deprotonation is coad-sorbed to form hydroxyl species at the bridging oxygen sites with an associated Ti-0 bondlength of 2.01 ± 0.03 A. 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).