Unravelling local environments in mixed TiO2–SiO2 thin films by XPS and ab initio calculations

Abstract

Mixed Ti x Si 1−x O 2 oxide can exhibit a partial phase separation of the TiO 2 and SiO 2 phases at the atomic level. The quantification of TiO 2-SiO 2 mixing in the amorphous material is complicated and was so far done mostly by infrared spectroscopy. We developed a new approach to the fitting of X-ray photoelectron spectroscopy data for the quantification of partial phase separation in amorphous Ti x Si 1−x O 2 thin films deposited by plasma enhanced chemical vapour deposition. Several fitting constraints reducing the total number of degrees of freedom in the fits and thus the fit uncertainty were obtained by using core electron binding energies predicted by density functional theory calculations on Ti x Si 1−x O 2 amorphous supercells. Consequently, a decomposition of the O 1s peak into TiO 2 , SiO 2 and mixed components was possible. The component areas ratios were compared with the ratios predicted by older theoretical models based on the atomic environment statistics and we also developed several new models corresponding to more realistic atomic structure and partial mixing. Based on the comparison we conclude that the studied films are mostly disordered, with only a moderate phase separation.

TiO2-SiO2 mixed oxide deposited by low pressure PECVD: Insights on optical and nanoscale electrical properties

“…In-between these two peaks, another one can be identified in position 531.5 eV which is known from our previous studies to correspond to Ti-O-Si bond. The three components correspond to the local arrangement of TiO 2 , SiO 2 and main mixed environment of the O atoms as already reported [30]. Therefore, these specific mixed films can be notated as Ti x Si 1-x O y .…”

“…The fitting of recorded peaks in elemental components allows us to identify the different chemical environments for each element. The binding energy positions for Ti 2p 3/2 at 459 eV and Si 2p 3/2 at 102.4 eV highlight that the Ti and Si atoms have only the 4+ oxidation degree, as expected for such films deposited by PECVD [30]. The atomic concentration of O 1s, Ti 2p, C 1s and Si 2p were determined from the peak areas moderated by the sensitivity factor of each level.…”

“…eV and 1eV for Ti 2p and Si 2p respectively [30]. The fitting of recorded peaks in elemental components allows us to identify the different chemical environments for each element.…”

Efficient Method for the Concentration Determination of Fmoc Groups Incorporated in the Core-Shell Materials by Fmoc–Glycine

“…First, the successful formation of the TiO 2 @SiO 2 particles was confirmed through the appearance of strong Si2p peak doublet at approx. 102.1 eV, which is typical for SiO 2 monolayer surface coverage on TiO 2 [ 57 , 58 ] ( Figure 6 a). The TiO 2 @SiO 2 O1s reveals a complex nature, with multiple components characteristic for the SiO 2 (531.6 eV), TiO 2 (528.8 eV) and atomically mixed TiO 2 –SiO 2 thin film (530.2 eV) [ 16 , 58 ], which are further modified by the presence of small amounts of adventitious carbon, carbonate and adsorbed water contamination resultant from the air exposure [ 59 ].…”

TiO2–SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2/HMDSO low-pressure plasma

“…The contribution of oxygen bonded to silicon atoms, noted as O-Si appears at the binding energy of 532.6 eV whereas the one corresponding to the bond with titanium, noted as O-Ti, at 530.5 eV. [6] A noteworthy observation in this figure is that no peak corresponding to Ti-O-Si (at 531.5 eV [50]) can be found, as expected for a NC, confirming that only two different phases are detected in the film. [50] As reported by many authors [24,51], the signal of titanium element in XPS results from two separated peaks that can be attributed to Ti 2p3/2 and Ti 2p1/2.…”