Surface-based manipulation of point defects in rutile TiO2

Abstract

Role of point defects and HfO2/TiN interface stoichiometry on effective work function modulation in ultra-scaled complementary metal-oxide-semiconductor devices Structure, stability, and mobility of small Pd clusters on the stoichiometric and defective TiO2 (110) surfaces

Reversible oxygen scavenging at room temperature using electrochemically reduced titanium oxide nanotubes

“…Hollister and colleagues found that the spatial profiles of isotope-labelled oxygen absorbed by TiO 2 are decaying exponentials (Supplementary Fig. 6), consistent with the interstitial oxo-species diffusion model 8,9 . We found a remarkably good fit between the temporal profiles predicted by the inward diffusing oxo-species model for all profiles measured (for example, Figs 2, 4 and 5), while the square-root uptake profile predicted by the standard vacancy diffusion model is not capable of a good fit (for example, Fig.…”

“…Materials that depend on this mechanism are useful only at high temperatures, or have a low oxygen uptake capacity that is limited by the sites available for surface absorption or adsorption. However, recent evidence presented by Seebauer and co-workers 8,9 supports a hypothesis that there may also be an interstitial oxygen defect in TiO 2 that can be exceptionally mobile. If it does indeed exist, this new entity could necessitate a revision of more than 50 years of literature on defects in oxides.…”

“…Such a fast oxygen uptake at a remarkably low temperature suggests a non-typical mechanistic pathway for the re-oxidation of TiO 2−x . Modelling the diffusion of oxygen, we show that a likely pathway involves 'exceptionally mobile' interstitial oxygen [8][9][10] produced by the oxygen adsorption and decomposition dynamics, recently observed on the surface of anatase 6 .…”

“…If this particular hopping process were the underlying mechanism for the fast oxygen uptake observed in this study, the data presented would be macroscopic evidence of its existence. The alternative possibility is that low-temperature oxospecies transport to the bulk does not proceed by vacancy diffusion but rather by the proposed 'exceptionally mobile' interstitial oxygen defect 8,9 . A common strategy used to determine diffusion rates and mechanisms is to measure the spatial profiles of isotope-labelled tracers 8,9,19,26 . The high uptake rates achieved here render oxygen uptake rates macroscopically measurable in real time, and thus afford a new means to observe and infer transport rates.…”

Relevance of non-equilibrium defect generation processes to resistive switching in TiO2

“…Typical activation energies associated with oxygen vacancy diffusion in TiO 2 are of the order 2.6 eV. [51][52][53][54] Even considering the effect of hole trapping which can reduce the activation energy to oxygen vacancy generation, these results suggest that diffusion of pre-existing oxygen vacancies is always much more facile than defect generation in bulk TiO 2 . However, activation energies near the electrode interface [70][71][72] or at grain boundaries 12,73,74 may be considerably lower.…”