Band alignment of rutile and anatase TiO2

Abstract

The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO₂. The discovery of the photolysis of water on the surface of TiO₂ in 1972 launched four decades of intensive research into the underlying chemical and physical processes involved. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO₂ (ref. ). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

CO2 Reduction: From the Electrochemical to Photochemical Approach

“…d) Proposed VB and CB alignment for the anatase/rutile interface. Reproduced with permission 197. Copyright 2013, Nature Publishing Group.…”

“…A good example is the anatase and rutile polymorphs of TiO 2 . When brought together, they form a type II, staggered band alignment with ≈0.4 eV difference in band position 197. Such a difference is significant enough to promote the migration of electrons from rutile to anatase, and holes from anatase to rutile, rendering the mixed‐phase photocatalyst generally superior to individual polymorphs.…”

Electric-dipole effect of defects on the energy band alignment of rutile and anatase TiO2

“…A lot of previous experimental works were devoted to probe the migration direction of carriers at the interface. However, two opposite results have been obtained: 1) electrons transfer from anatase to rutile [11][12][13] and 2) electrons transfer from rutile to anatase [14][15][16][17] .…”

Trilayer Tunnel Selectors for Memristor Memory Cells

“…A high nonlinearity was observed experimentally in a TaO x /TiO 2 /TaO x trilayer structure and attributed to the crested barrier effect 12. However, the electron affinity of the middle layer (TiO 2 , ≈4.1 eV)12, 23, 24 should be larger than that of the outer layers (Ta 2 O 5 , ≈3.2 eV)12, 25 in this case, which was opposite to the proposed design of a crested barrier 21, 22. Defects created by the diffusion of Ta into TiO 2 were assumed to somehow lead to the formation of a crested barrier, but this proposal requires further clarification 12.…”