Atomic-scale insights into electronic structure of lattice-work structures on rutile TiO2(001) surface

Abstract

The lattice-work structure (LWS), a {114}-faceted surface reconstruction on rutile TiO₂(001), has been recognized for its potential in visible-light-driven photocatalysis. Although various spectroscopic techniques have provided insights into its electronic properties, their resolution was insufficient to directly correlate electronic states with the atomic structure, a key factor for understanding LWS-based photocatalysis. In this study, we investigated the atomic and electronic structures of LWS on rutile TiO₂(001) using ambient atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and ultrahigh-vacuum scanning tunneling microscopy (STM). AFM imaging revealed that annealing induces the formation of short, bright rows along the $\left[110\right]$ and $\left[1\bar{1}0\right]$ directions, which subsequently elongate and eventually cover the surface. Adjusting the annealing parameter thus allows us to control the LWS coverage. KPFM surface potential mapping indicated that these rows are negatively charged relative to the surrounding terraces, suggesting localized charge accumulation. Atomic-resolution STM and scanning tunneling spectroscopy confirmed a site-dependent electronic structure, with the atomic sub-row atop the LWS exhibiting a reduced band gap (∼1.75 eV) compared to that in valley parts of the LWS (>3.0 eV). These findings directly linked the atomic structure of LWS to its local electronic states, clarifying the role of LWS in photocatalysis. Moreover, controlling LWS coverage via annealing enables tuning of the electronic states and local band gap variations, which can significantly influence photocatalytic performance under specific wavelengths of light.