TiO2-x/TiO2-Structure Based 'Self-Heated' Sensor for the Determination of Some Reducing Gases.

Arunas Jagminas,Alla Tereshchenko,Simonas Ramanavicius,Arunas Ramanavicius,Audrius Maneikis,Urte Bubniene,Vilma Ratautaite,Renata Karpicz

doi:10.3390/s20010074

Abstract

In this research we report the gas-sensing properties of TiO2-x/TiO2-based hetero-structure, which was ‘self-heated’ by current that at constant potential passed through the structure. Amperometric measurements were applied for the evaluation of sensor response towards ethanol, methanol, n-propanol and acetone gases/vapours. The sensitivity towards these gases was based on electrical resistance changes, which were determined by amperometric measurements of current at fixed voltage applied between Pt-based contacts/electrodes deposited on the TiO2-x/TiO2-based layer. X-ray diffraction (XRD) analysis revealed the formation of TiO2-x/TiO2-based hetero-structure, which is mainly based on Ti3O5/TiO2 formed during the hydro-thermal oxidation-based sensing-layer preparation process. Additionally, photoluminescence and time-resolved photoluminescence decay kinetics-based signals of this sensing structure revealed the presence of TiO2 mainly in the anatase phase in the TiO2-x/TiO2-based hetero-structure, which was formed at 400 °C annealing temperature. The evaluation of TiO2-x/TiO2-based gas-sensing layer was performed at several different temperatures (25 °C, 72 °C, 150 °C, 180 °C) and at these temperatures different sensitivity to the aforementioned gaseous materials was determined.

Highlights

Among many other inorganic semiconductor-based structures, TiO2 -based structures are often used for the development of gas-sensing devices due to their sensing properties [1]
Results obtained by Yoshimatsu et al [33] showed low-temperature superconductivity in both Ti 4O7 different, the composition and stoichiometry of both TiO2-x-based structures discussed here can be different at some extent
TiO2-x /TiO2 -based hetero-structure, which due to the formation of Ti3+ has Tin O2n-1 doped TiO2-x clusters (Figure 1B, 3rd layer) with significantly advanced electrical conductivity, can be synthesized by several different methods: plasma treatment [59], metallic zinc-based reduction [60], high-energy particle bombardment [61], laser irradiation [62] and some reactions at higher temperatures [63]. In addition to these methods, in recent research we have demonstrated that the hydro-thermal approach applied here is suitable for the formation of TiO2-x /TiO2 -based hetero-structures from initially deposited titanium-based layer

Summary

Introduction

Among many other inorganic semiconductor-based structures, TiO2 -based structures are often used for the development of gas-sensing devices due to their sensing properties [1]. Titanium dioxide (TiO2 ) is an n-type semiconductor, which exists in three main phases (i) anatase, (ii) rutile and (iii) brookite with bandgaps of 3.02, 3.23, and 2.96 eV, respectively [2]. The attractiveness of TiO2 has significantly increased since its water-splitting ability under ultraviolet (UV) light irradiation was discovered [3]. The discovery of the latter effect facilitated the exploitation of catalytic TiO2 properties in the design of sensors for gases and gaseous materials. Many different TiO2 -based structures have found applications in various technological areas including biosensors [4,5] and chemical sensors [6,7,8,9,10]

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