Abstract
As the most common type of defects in WO3, surface oxygen deficiencies have been widely investigated in terms of their structure as well as physicochemical properties. In general, oxygen vacancy on the surface may lead to the reconstruction of the surface structure due to the need for surface energy minimization, especially for the area with high oxygen vacancy concentration. However, such a phenomenon has not been directly demonstrated or observed from the experiment. In the paper, we observed such surface reconstruction in the step area or high-index facets in WO3 using the spherical aberration-corrected scanning transmission electron microscope (Cs-STEM) with atomic-scale resolution. This surface reconstruction results in a structure of 5-fold symmetry pentagonal columns, which is first reported. According to the DFT calculation, the formation energy of oxygen vacancy in the step edge is much lower than the smooth surface. Furthermore, the formation energy of oxygen vacancy in the higher index (110) facet is lower than the low index (100) and (010) facets. Our experimental results support these findings, i.e., that the reconstruction is pronounced in the step or high-index facets with a high concentration of oxygen vacancy. Therefore, the high concentration of oxygen vacancy in the step or high-index facet area contributes to the formation of pentagonal column structures. This work could provide a novel insight into the correlation between intrinsic defect and surface structure formation in these materials.
Highlights
ATpupnligcsatteinonosxidinecslu(dWinOg3)sehnasvoeras,t1tra(cptheodtgor)ecaattainlytsetrse,2s−t 4in various electrochromic/optochromic devices, etc.[3,5,6] Oxygen vacancies are the most observed structural defects in WO3.7 In general, oxygen vacancies serve as shallow donors in WO3 that can provide electron carrier concentration and promote n-type conductivity.[8]
The emerging Cscorrected transmission electron microscopy (Cs-STEM) with ultimate sub-Ångström resolution enables the monitoring of such surface reconstruction at atomic scale.[21]
The oxygen vacancy at the sites closer to the step edges exhibits lower formation energies with −0.96, −0.52, and 0.19 eV, respectively. Such calculation indicates the oxygen vacancies are easier to generate at the step area, which could be expected as the driving force of the above-mentioned surface reconstruction observed at the same place
Summary
ATpupnligcsatteinonosxidinecslu(dWinOg3)sehnasvoeras,t1tra(cptheodtgor)ecaattainlytsetrse,2s−t 4in various electrochromic/optochromic devices, etc.[3,5,6] Oxygen vacancies are the most observed structural defects in WO3.7 In general, oxygen vacancies serve as shallow donors in WO3 that can provide electron carrier concentration and promote n-type conductivity.[8]. The emerging Cscorrected transmission electron microscopy (Cs-STEM) with ultimate sub-Ångström resolution enables the monitoring of such surface reconstruction at atomic scale.[21]. We characterized the surface structure of WO3 with a special focus on the step area or high-index facets using the spherical aberration-corrected scanning transmission electron microscope (Cs-STEM) with atomic-scale resolution. We observe the formation of characteristic pentagonal column structures in those areas for the first time. Density Functional Theory (DFT) calculations indicate the low formation energy of oxygen vacancy in all those step structures or high-index facets. We concluded the critical role of oxygen vacancy in displacing the neighboring W atoms column position and inducing the surface reconstruction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
