On the Role of Oxygen Vacancies in the Determination of the Gas-Sensing Properties of Tin-Oxide Nanowires
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0915-R04-06
On the Role of Oxygen Vacancies in the Determination of the Gas-Sensing Properties of Tin-Oxide Nanowires Roberto Mosca1, Mingzheng Zha1, Davide Calestani1, Laura Lazzarini1, Giancarlo Salviati1, Andrea Zappettini1, Lucio Zanotti1, Elisabetta Comini2, and Giorgio Sberveglieri2 1 CNR-IMEM, Parma, 43100, Italy 2 Sensor Lab., INFM-Università di Brescia, Brescia, 25133, Italy ABSTRACT SnO2 nanowires have been recently employed in the “gas-sensors” field and excellent results of conductometric and optical tests on SnO2 nanowires-based gas sensors have been reported. However, the mechanism that controls the gas-sensing effect in metal oxides nanowires is not fully understood yet. Here the authors present the first results of an in-depth study about the influence of post growth treatments on the physical and gas sensing properties of SnO2 nanowires. In particular, SnO2 nanowires grown by a vapour transport technique were annealed in a oxygen-rich atmosphere and then characterized by different techniques to assess the influence of the treatment on the nanowires properties. The annealing in oxygen atmosphere is shown to strongly affect the PL and CL spectra, the electrical resistivity as well as the gas sensing properties of the nanowires. The obtained results are consistent with a reduction of the oxygen vacancies concentration induced by the O2 treatment and seem to confirm the role of these defects in affecting the gas response of SnO2 nanowires-based sensors. INTRODUCTION Tin oxide (SnO2) is, up to now, the most employed and promising semiconductor metal oxide in the gas sensor field. Even if it is mainly available in the film form, recently the excellent properties of SnO2 nanowires for gas-sensors applications have been demonstrated [1,2]. The measured high sensitivity of nanowires has been mainly ascribed to the huge surface to volume ratio and to the small wire diameter. At the same time, high stability is expected for nanowires-based gas sensors, due to the single-crystal structure of the nanowires [1]. Moreover, for the first time, it has been recently demonstrated [3, 4] that the SnO2 nanowires grown by this group may be also employed as an “optical gas-sensor”. In fact, it was observed that the intensity of the visible luminescence band of SnO2 nanowires is reduced by the presence of few ppm of NO2. Because of the promising results coming from this kind of nanostructure, a better knowledge about the basic phenomena for the evidenced physical properties of SnO2 nanowires is needed. Such results, in fact, may lead towards the right route for a further enhancement of these properties and of the gas sensitivity of tin oxide nanowires. In this article the authors present the first experimental results about the possible correlation between the properties of SnO2 nanowires and the density of oxygen vacancies (VO) in their structure.
EXPERIMENT SnO2 nanowires have been grown by a vapor phase growth furnace (described in [5]), starting from a SnO source and operating at about 900°C in an argon flow. The ob
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