Three-Dimensional Structure Analyses of Cu Species Dispersed on TiO₂(110) Surfaces Studied by Polarization-Dependent Total-Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS)

Abstract

Three-dimensional analysis of structures for dispersed Cu species on a TiO 2 (110) surface has been performed by a polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) technique. The dispersed Cu species were prepared by a chemical reaction between Cu(DPM) 2 and a TiO 2 (110) surface and reduced with H 2 . The Cu(DPM) 2 dissociatively adsorbed on the 2-fold site of bridging oxygen atoms of the TiO 2 (110) surface to form a Cu(DPM)(O-) 2 species. Subsequent reduction of the Cu species with H 2 at 363 K produced Cu 3 trimers that were bound to the bridging oxygen atoms with the trimer plane inclined at about 30°from the TiO 2 (110) normal. There were direct Cu-O bonds at the Cu 3 trimer/TiO 2 (110) interface in addition to Cu-Cu bonds. Further reduction at 473 K produced three-dimensional prismatic small Cu 6 clusters by vertical growth in the [110] direction of the Cu fcc lattice. Orientations of the Cu 3 triangle and Cu 6 prism clusters may be regulated by the interaction between the Cu atoms and the bridging oxygen atoms on the anisotropic TiO 2 (110) surface.

Angle resolved total reflection fluorescence XAFS and its application to Au clusters on TiO2(110) (1 * 1)

“…We have developed the polarization-dependent total reflection fluorescence XAFS (PTRF-XAFS) and demonstrated preciselycharacterized three-dimensional structures of Ni, Cu, Mo species dispersed on TiO 2 (110), ¡-Al 2 O 3 (0001), and MgO(100) single crystal surfaces. 1)6) We found Mo dimer 1) and Cu trimer 4) on TiO 2 (110) and (110)-like Ni cluster interacting strongly with oxygen of TiO 2 (110). 6) Recently, the Cu structure can be controlled by the surface chemical modifications.…”

Fine tuning and orientation control of surface Cu complexes on TiO2(110) premodified with mercapto compounds: the effect of different mercapto group positions

“…Polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) analysis can provide three-dimensional structural information about the region around highly dispersed metal species on single crystal surfaces .2 We have determined the three-dimensional structures of Cu, Co, 45 Pt and Mo complexes and their derivatives grafted onto SiO 2 (0001), Al 2 O 3 (0001) and TiO 2 (110) in order to elucidate the metal-support interactions at the atomic level. [3][4][5][6][7][8] Grafting methods typically require the preparation of organometallic compounds in advance, although these 50 compounds are often unstable in air or high temperature. However, if the oxide support surface is premodified with an organic ligand that strongly anchors to a metal atom through a covalent bond, then a well-defined atomic metal species can be obtained without the need for organometallic compounds.…”

“…Considering the anisotropic surface structure of TiO 2 (110), PTRF-XAFS measurements were conducted with three different orientations against the electric 50 vector (E) of the incident X-rays, i.e., two orientations parallel to the surface, E//[001], ̅ and an orientation perpendicular to the surface, E//[110], as reported elsewhere. 5,6,8,9,16,[18][19][20] The polarization dependence of an overall XAFS oscillation  obs (k) can be given by equation The Cu Kα fluorescence was detected using a 19-element Ge solid state detector (SSDGL0110S, Canberra, USA). PTRF-XAFS analysis was performed using REX 2000 (Rigaku Co., Japan) for curve fitting analysis and FEFF8.02 code for theoretical simulation of 65 the extended X-ray absorption fine structure (EXAFS) oscillation,  cal (k).…”

“…27 Previous results for Cu deposited directly on To determine the accurate structure of the Cu species, an iteration method was employed using a FEFF code and a real-10 space model structure. 5,6,8,9,16,[18][19][20] We determined the structure based on the following results and knowledge about o-MBA and TiO 2 (110) surface.…”

Structure of low coverage Ni atoms on the TiO2(110) surface – Polarization dependent total-reflection fluorescence EXAFS study

“…[11,-14]. PTRF-XAFS(polarization dependent total reflection fluorescence XAFS), a combination of total reflection fluorescence detection mode and polarization-dependent XAFS allows us to carry out the surface XAFS measurement of heavy elements with their coverage less than 0.1ML(ML=monolayer corresponding to 2 x 10 14 atoms / cm 2 ) [15]. In this work, we have studied Ni on TiO2(110) at the low surface density of 1×10 13 atoms / cm 2 to obtain atomically dispersed Ni species.…”