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 Functional Theory

Abstract

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 (O_B) 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.