Enhanced clustering tendency of Cu-impurities with a number of oxygen vacancies in heavy carbon-loaded TiO2 - the bulk and surface morphologies

TL;DR

This study investigates how high carbon loadings and copper sensitization affect the morphology and electronic structure of TiO2, revealing specific impurity states and phases through combined experimental and theoretical analysis.

Contribution

It provides new insights into the impurity-induced phase formation and electronic structure modifications in heavy carbon-loaded Cu-doped TiO2 using XPS and DFT calculations.

Findings

Dominance of neutral C-C bonds in heavy carbon-loaded TiO2

Identification of specific copper oxidation states in samples

Role of neutral carbon impurities as precursors for phase growth

Abstract

The over threshold carbon-loadings (~50 at.%) of initial TiO2-hosts and posterior Cu-sensitization (~7 at.%) was made using pulsed ion-implantation technique in sequential mode with 1 hour vacuum-idle cycle between sequential stages of embedding. The final Cx-TiO2:Cu samples were qualified using XPS wide-scan elemental analysis, core-levels and valence band mappings. The results obtained were discussed on the theoretic background employing DFT-calculations. The combined XPS and DFT analysis allows to establish and prove the final formula of the synthesized samples as Cx-TiO2:[Cu+][Cu2+] for the bulk and Cx-TiO2:[Cu+][Cu0] for thin-films. It was demonstrated the in the mode of heavy carbon-loadings the remaining majority of neutral C-C bonds (sp3-type) is dominating and only a lack of embedded carbon is fabricating the O-C=O clusters. No valence base-band width altering was established after sequential carbon-copper modification of the atomic structure of initial TiO2-hosts except the dominating majority of Cu 3s states after Cu-sensitization. The crucial role of neutral carbon low-dimensional impurities as the precursors for the new phases growth was shown for Cu-sensitized Cx-TiO2 intermediate-state hosts.