XPS and NEXAFS study of fluorine modified TiO2 nano-ovoids reveals dependence of Ti3+ surface population on the modifying agent

Abstract

Crystalline titanium dioxide was synthesised under mild conditions by the thermal degradation of peroxotitanic acid in the presence of a number of fluoride-containing surface modifying agents (NH 4 F, NH 4 BF 4 , NH 4 PF 6 , NBu 4 F, NBu 4 BF 4 , NBu 4 PF 6). The resulting materials were characterised by PXRD, SEM, HRTEM, XPS and NEXAFS. Particle phase, size, and surface area were noticeably affected by the choice of surface modifying agent. Both the cation and anion comprising the modifying agent affect the surface Ti 3+ population of the materials, with two apparent trends observed: F À > BF 4 À > PF 6 À and NBu 4 + > NH 4 +. All materials displayed evidence of fluorine doping on their surfaces, although no evidence of bulk doping was observed.

X-ray scattering characterisation of nanoparticles

“…Alternatively, two crystallite sizes and a high degree of crystallographic texture can be incorporated as independent parameters in full-pattern analysis fitting. [87] More complex models describing the crystallite shape can also be derived. [88] Stacking faults.…”

“…For larger nanoparticles, the crystallite sizes along different directions can be obtained by single peak fitting [88,164] or by incorporating two different crystal sizes with preferential orientation in a Rietveld refinement. [87] Zhang et al used XRD to follow the grain growth of ZnO nanoparticles formed by a sol-gel method. [165] As-prepared ZnO particles 20-30 nm in size were heated at temperatures from 500°C to 1100°C.…”

Electrospun Black Titania Nanofibers: Influence of Hydrogen Plasma-Induced Disorder on the Electronic Structure and Photoelectrochemical Performance

“…The spin orbit splitting between the two p peaks is 5.7 eV and the intensity ratio is 2:1, as expected. The 2p 3/2 component can be well fitted with a single peak, centered at a binding energy (BE) of 459.5 eV, having a full width at half maximum (FWHM) of 1.24 eV.These values are characteristic for octahedral Ti 4+ in TiO 2 [29][30]. In contrast, hydrogen plasma treated fibres at 500°C(Figure 3b)show a change in the spectrum shape, with the appearance of low-BE shoulders that suggest the co-presence of Ti oxidation states lower than 4.…”

Surface Fluorination of ALD TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells

“…After the CF 4 plasma, the Ti2p3/2 signal consists of two contributions: one at BE of 458.3 eV, typical of Ti2p3/2 peak, and associated to Ti–O bond, and one at 459.4 eV, assigned to the combination of Ti–F bonds and fluorinated TiO 2 environments . A small additional peak centered at 456.5 eV is also observed and assigned to titanium at lower oxidation states, i.e., related due to oxygen vacancies . In case of the reference ALD TiO 2 , the main contribution arises from the Ti–O bonds (Figure d), with the additional small shoulder at lower BE (456.5 eV).…”

“…We therefore investigate the effect of the CF 4 treatment on the ALD layer by X‐ray photoelectron spectroscopy (XPS). The measurement of the TiO 2 surface after the CF 4 plasma reveals a high intensity of the F 1s signal at binding energy (BE) 684.7 eV (see Figure a), which is assigned to the Ti–F bond, without any contribution at higher BE (688–689 eV), therefore excluding the presence of fluorine–carbon bonds. No fluorine is detected in case of the reference ALD TiO 2 layer (without CF 4 treatment) as reported in Figure a.…”