A study of the effect of morphology on the optical and electrical properties of TiO₂ nanotubes for gas sensing applications

Abstract

<jats:p>In this paper, we report the results of the optical and electrical properties of TiO<jats:sub>2</jats:sub> nanotubes with different morphologies for gas sensing applications. Four nanomaterials of TiO<jats:sub>2</jats:sub> were prepared by electrochemical anodization using four different electrolyte solutions: 0.255 wt% NH<jats:sub>4</jats:sub>F with 1 wt%, 3 wt%, 6 wt% and 9 wt% of deionized water in ethylene glycol. Micrographs by scanning electron microscopy (SEM) showed different morphologies caused by the variation in the water content of the solutions. Consequently, as an effect of morphology, the photoluminescence intensity in the visible spectrum was modified. By a change of the crystalline phase of TiO<jats:sub>2</jats:sub> nanotubes, the oxygen vacancies increased and affected to the optical and electrical properties of TiO<jats:sub>2</jats:sub> films. These films were used for detecting gas at room temperature. Hence, we studied and analyzed the relationship of the morphology, elemental composition, phase composition, band gap energy and defect states as a function of the electrical resistance change of TiO<jats:sub>2</jats:sub> nanotubes to understand and improve the sensor response.</jats:p>

Design of p–p heterojunctions based on CuO decorated WS2 nanosheets for sensitive NH3 gas sensing at room temperature

“…Table S2 records the ratios of the different areas. The blue region gradually increases with the CuO content, which means that the oxygen vacancies content increase [62]. Oxygen vacancies enhance the adsorption process between sensitive materials and gas molecules, and provide more active sites for the gas molecules' adsorption [63].…”

Fabrication and characterization of TiOx based single-cell memristive devices

“…These results have been supported by Photoluminescence (PL) measurements as seen in figure 4. The main defect states of nanostructured TiO 2 are self-trapped excitons (STE), single ionized oxygen vacancies (Vo * ), doubly ionized oxygen vacancies (Vo ** ), and excited states of Ti 3+ at 416 nm, 443 nm, 531 nm and 802 nm, respectively [65][66][67][68][69][70]. As can be seen form the figure 4 we observed excitation at 416 nm, 443 nm, 531 nm referring to the oxygen vacancies after thermal treatment under vacuum conditions.…”

Branching TiO2 nanowire arrays for enhanced ethanol sensing

“…502 nm, which originates from the oxygen vacancies [43]. The relative quantity of single-ionized (V o *) and doublyionized (V o **) oxygen vacancies can be evaluated through the ratio of deconvoluted peak area (peak 2 and peak 3, respectively) [44][45][46], as demonstrated in figures 4(b) and (c), and the results are listed in table 1. The total area of peak 2 and peak 3 increases for the TiO 2 nanotree array according to table 1, indicating the enhanced oxygen vacancies, which is consistent with the XPS results.…”

“…The UV-vis diffuse reflection spectra and the evaluated band gap suggest that the band gap decreases from 2.34 eV to 2.27 eV after branching (figure S10). The enhanced amount of oxygen vacancies for the nanotrees provided more electrons and can be considered as a bulk donor to narrow the band gap [42,44,46]. The BET specific surface area and total pore volume for the pristine TiO 2 nanowire powder are 48.5 m 2 g −1 and 0.403 cm 3 g −1 , respectively.…”