3D Precise Structure Determination of Single-Atom Cu Species on TiO₂ Using Polarization-Dependent Total Reflection Fluorescent X-ray Absorption Fine Structure Empowered by Chemically Constrained Micro Reverse Monte Carlo and Density Functi

We have developed a chemically constrained micro reverse Monte Carlo (CC-MRMC) method and have statistically determined the three-dimensional (3D) structure of single-atom Cu species dispersed on a 3-thiophene carboxylic acid (TCA)-premodified flat single-crystal oxide surface using a polarization-dependent total reflection fluorescent X-ray absorption fine structure (PTRF-XAFS) technique. The CC-MRMC analysis of the PTRF-XAFS data indicated that an S–Cu–O sandwich structure was adsorbed on the TiO2(110) surface at three equivalent sites of TiO2(110). We carried out density functional theory (DFT) calculations to select one structure among the three candidates. The Cu has a linear structure sandwiched with S in TCA and the bridging oxygen (OB) of TiO2. The TCA is adsorbed onto the TiO2(110) surface as a monodentate carboxylate species, CO(–Ti)O–, with a loss of H+. The advantages and disadvantages of the combination of the PTRF-XAFS + CC-MRMC and DFT methods are discussed.