Surface and interstitial Ti diffusion at the rutile TiO2(110) surface

Diffusion of Ti through the TiO2 (110) rutile surface plays a key role in the growth and reactivity of TiO2. To understand the fundamental aspects of this important process, we present an analysis of the diffusion of Ti adspecies at the stoichiometric TiO2(110) surface using complementary computational methodologies of density functional theory corrected for on-site Coulomb interactions (DFT+U) and a charge equilibration (QEq) atomistic potential to identify minimum energy pathways. We find that diffusion of Ti from the surface to subsurface (and vice versa) follows an intersticialcy exchange mechanism, involving exchange of surface Ti with the 6-fold coordinated Ti below the bridging oxygen rows. Diffusion in the subsurface between layers also follows an interstitialcy mechanism. The diffusion of Ti is discussed in light of continued attempts to understand the re-oxidation of non-stoichiometric TiO2(110) surfaces

Tight-binding variable-charge model for insulating oxides: Application to TiO

We have developed a new variable-charge model aimed at performing large-scale realistic simulations of oxide surfaces and interfaces. This model is based on the charge equilibration (QEq) method and explicitly takes into account the mixed iono-covalent character of the metal-oxygen bond by means of a tight-binding analytical approach. We present the first results obtained for TiO2 and ZrO2 polymorphs, which are in very good agreement with the experimental data and recent ab initio results

SU‐GG‐T‐279: Evaluation of a Novel 4D In‐Vivo Dosimeter

Purpose: To present the latest quality assurance and characterization tests of the RADPOS 4‐D in vivo dosimetry system. Method and Materials: The dosimetric evaluation of this system included the measurement of in‐air dose profiles in [formula omitted], 6 MV, and 18 MV beams, and the investigation of the dependence of detector response on beam angle and field size. The stability and accuracy of the positioning component of the RADPOS detector was studied as well as the effect of metals and other commonly used materials on the RADPOS signal. Results: The dose profiles measured with the RADPOS detector and the diode agreed in within 0.41%, 0.53%, and 2.69% for the [formula omitted], 6 MV, and 18 MV beams, respectively. The angular response of the RADPOS probe over 360° was isotropic within 1.6% (1SD). Over a period of seventy minutes, the position of the RADPOS was read every 30 s and found stable within 0.37 mm. The system can also measure the displacement of a RADPOS detector with an accuracy of (0.45 ± 0.07) mm and (0.75 ± 0.07) mm for step sizes up to 50 mm and 200 mm respectively. The only materials that caused significant interference with the RADPOS signal were aluminum, brass, steel and lead. However, once the separation between the detector and the sample was >100 mm, the interference was minimal (the average deviation was less than 1.00 mm for all samples and sizes). Conclusion: Results of the preliminary tests indicate that the device can be used for in‐vivo dosimetry in [formula omitted] and high‐energy beams from linear accelerators. Future work will involve technical improvements to the device, experiments in a 4D phantom and finally patient in‐vivo dosimetry. Acknowledgement: This project has been supported by a grant from HTX‐OCE‐IRAP and Best Medical

Use of a variable-charge interatomic potential for atomistic simulations of bulk, oxygen vacancies, and surfaces of rutile TiO 2

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