A study of gas sensing properties of ZnO nanostructures activated by UV light

Abstract

Abstract-In this paper the response of resistance gas sensors is investigated, based on zinc oxide nanostructures to NO2. The research is focused on the influence of ultraviolet light on the operation of such sensors at room temperature. Comparative experiment results are presented and discussed for thermal (200˚C) and UV (LED: λ=390 nm) activation in different carrier gases (air and nitrogen).Zinc oxide (ZnO) is widely used as a gas sensing material. It can be applied in resistance and optical gas sensors to detect gases such as: NO 2 , H 2 , NH 3 , as well as humidity and other changes [1][2][3][4]. To stabilize the operation, ZnO based sensors require activation by high temperature (≥200˚C) or by UV radiation [5]. Room temperature sensing structures of small concentrations of NO 2 are very desirable due to their low consumption of energy and potential application, such as explosives vapor detection [6,7]. Currently, the attention of researchers in the field of gas sensors is mainly focused on materials with a developed surface area, including: nanostructures of metal oxides [7,8], graphene and its compounds [9,10] carbon nanotubes [11] and other nanostructures [12].This paper deals with a resistance gas sensor based on ZnO nanostructures. The construction of a sensor, measurement chamber and a measurement stand is presented in this work. Characterization of investigated nanostructures is also presented. The sensor response to low concentrations of NO 2 in different conditions is presented and studied. Structure responses to NO 2 are compared and discussed in two different carrier gases (air and pure nitrogen) activated by means of high temperature or UV light.ZnO nanostructures were obtained by the chemical method which was described in our earlier paper [3]. Obtained material was deposited on an interdigital transducer (50 nm gold layer, 5μm distance and width of electrodes, substrate: 10mm×10mm Si plate with 1μm SiO 2 layer). To deposit nanostructures on the transducer, the drop coating method was used. The resulting structures were dispersed in hexane in ultrasonic bath, and then the suspension was dropped on the transducer. After the hexane had dried, a non-adhering material was removed with compressed air.The morphology and distribution of nanostructures on the transducer was investigated using scanning electron microscopy (Inspect S50, FEI). The SEM image of ZnO structures deposited on the transducer is shown in Fig. 1. It can be noted that, in terms of morphology, the obtained nanostructures are a mixture of nanotubes, tenths of micrometers long and nanopowder rice-shaped. The chemical composition was examined by means of Raman spectroscopy. In the Raman spectrum shown in Fig. 2 (NTEGRA Spectra, NT-MDT, excitation λ=532nm) peaks characteristic of ZnO nanostructures can be observed [13,14]. That proves that the examined structures are pure ZnO nanostructures.The prepared sensor structure deposited on the transducer was immobilized on the heater on an alumina (Al 2 O 3 ) substrate. The heater with the st...

Impact of Temperature and UV Irradiation on Dynamics of NO2 Sensors Based on ZnO Nanostructures

“…In recent years, attempts have been made to solve this problem using UV radiation [ 30 , 31 , 32 ]. The application of UV allows for the gas detection at room temperature (RT), but response times under these conditions are often unsatisfactorily long [ 30 , 32 , 33 ]. There have only been a few studies discussing the combination of the UV illumination of the sensor at higher temperature and the mechanisms responsible for operation under such conditions [ 34 , 35 ].…”

Influence of External Gaseous Environments on the Electrical Properties of ZnO Nanostructures Obtained by a Hydrothermal Method

“…Also the humidity effect on the gas sensing structures has to be taken into account due to its different values under real operating conditions [28]. Many publications emphasized the potential of ZnO nanostructures in gas sensors [8,25,27,29,30]. …”

STUDY THE RESPONSE OF GAS SENSOR USING ZnO NANORODS SYNTHESIZED BY HYDROTHERMAL METHOD

“…This is primarily due to the high mobility of conduction electrons in the material and good chemical and thermal stability under operating conditions [4]. It is a direct band gap wurtzite type semiconductor with band gap energy of 3.37 eV at room temperature, and a very large exciton binding energy of about 60 meV.…”