Discovery of deep and shallow trap states from step structures of rutile TiO2 vicinal surfaces by second harmonic and sum frequency generation spectroscopy

Abstract

In this report, local electronic structures of steps and terraces on rutile TiO(2) single crystal faces were studied by second harmonic and sum frequency generation (SHG∕SFG) spectroscopy. We attained selective measurement of the local electronic states of the step bunches formed on the vicinal (17 18 1) and (15 13 0) surfaces using a recently developed step-selective probing technique. The electronic structures of the flat (110)-(1×1) (the terrace face of the vicinal surfaces) and (011)-(2×1) surfaces were also discussed. The SHG∕SFG spectra showed that step structures are mainly responsible for the formation of trap states, since significant resonances from the trap states were observed only from the vicinal surfaces. We detected deep hole trap (DHT) states and shallow electron trap (SET) states selectively from the step bunches on the vicinal surfaces. Detailed analysis of the SHG∕SFG spectra showed that the DHT and SET states are more likely to be induced at the top edges of the step bunches than on their hillsides. Unlike the SET states, the DHT states were observed only at the step bunches parallel to [1 1 1] [equivalent to the step bunches formed on the (17 18 1) surface]. Photocatalytic activity for each TiO(2) sample was also measured through methylene blue photodegradation reactions and was found to follow the sequence: (110) < (17 18 1) < (15 13 0) < (011), indicating that steps along [0 0 1] are more reactive than steps along [1 1 1]. This result implies that the presence of the DHT states observed from the step bunches parallel to [1 1 1] did not effectively contribute to the methylene blue photodegradation reactions.

Probing electrons in TiO2 polaronic trap states by IR-absorption: Evidence for the existence of hydrogenic states

“…1(a) we show IR-spectra recorded in transmission geometry for r-TiO 2 powder particles exposed to UV-light. In agreement with previous works7910111213142122 on such powders, we find that photoexcited electrons trapped in shallow states below the conduction band give rise to pronounced absorption features located at 900–940 cm −1 . The corresponding results for the r-TiO 2 (110) single crystal surface are also shown in Fig.…”

“…In this work we focus on shallow trap states located below the conduction band minimum of rutile, r-TiO 2 101112151819202122. Since these states play a crucial role in photo- and charge-induced photocatalytic reactions, they have been studied in a number of previous works35.…”

Structural Dependence of Competitive Adsorption of Water and Methanol on TiO2 Surfaces

“…Recently, many experimental results have been reported on the anisotropic photocatalytic activity of TiO 2 nanoparticles enclosed with specific facets. [2][3][4][5] These results demonstrate the dramatic effect of TiO 2 surface structures on the photocatalytic activity.…”

TiO2 nanocluster modified-rutile TiO2 photocatalyst: a first principles investigation

“…It is important to point out that the cluster with the least negative adsorption energy has no change in the number of terminal oxygen atoms while in other clusters, with more favourable 105 adsorption energies, there is always a reduction in the number of terminal oxygen atoms, so that increasing the coordination of terminal oxygen atoms may play an important role in the stability of adsorbed clusters at the TiO 2 surface. [62][63][64][65] (which are also found in this work) and proposed in the rutile (011) (2x1) reconstructed surface [70][71][72][73] . Given that the free nanoclusters are stable with titanyl groups, it is not so surprising that the majority of the adsorbed cluster structures are also stable with titanyl groups and these 15 are found in both the QEq and DFT+U relaxations.…”