Influence of Mg Doping Levels on the Sensing Properties of SnO2 Films.

Bouteina Bendahmane,Farida Mansour,Stella Vallejos,Isabel Gràcia,Milena Tomić,Nour El Houda Touidjen

doi:10.3390/s20072158

Abstract

This work presents the effect of magnesium (Mg) doping on the sensing properties of tin dioxide (SnO2) thin films. Mg-doped SnO2 films were prepared via a spray pyrolysis method using three doping concentrations (0.8 at.%, 1.2 at.%, and 1.6 at.%) and the sensing responses were obtained at a comparatively low operating temperature (160 °C) compared to other gas sensitive materials in the literature. The morphological, structural and chemical composition analysis of the doped films show local lattice disorders and a proportional decrease in the average crystallite size as the Mg-doping level increases. These results also indicate an excess of Mg (in the samples prepared with 1.6 at.% of magnesium) which causes the formation of a secondary magnesium oxide phase. The films are tested towards three volatile organic compounds (VOCs), including ethanol, acetone, and toluene. The gas sensing tests show an enhancement of the sensing properties to these vapors as the Mg-doping level rises. This improvement is particularly observed for ethanol and, thus, the gas sensing analysis is focused on this analyte. Results to 80 ppm of ethanol, for instance, show that the response of the 1.6 at.% Mg-doped SnO2 film is four times higher and 90 s faster than that of the 0.8 at.% Mg-doped SnO2 film. This enhancement is attributed to the Mg-incorporation into the SnO2 cell and to the formation of MgO within the film. These two factors maximize the electrical resistance change in the gas adsorption stage, and thus, raise ethanol sensitivity.

Highlights

The monitoring of volatile organic compounds (VOCs), including ethanol (C2 H6 O), acetone (C3 H6 O), and toluene (C7 H8 ), is routinely needed for evaluating environmental quality and industrial safety [1]
The as-prepared Mg-doped SnO2 thin films were subsequently annealed at 450 ◦ C in dry air for 60 min in order to ensure the stability of the materials during the gas sensing test
Mg-doped SnO2 thin films synthesized via a spray pyrolysis method were investigated for ethanol, acetone, and toluene sensing

Summary

Introduction

The monitoring of volatile organic compounds (VOCs), including ethanol (C2 H6 O), acetone (C3 H6 O), and toluene (C7 H8 ), is routinely needed for evaluating environmental quality and industrial safety [1]. The monitoring of VOCs has gained importance in clinical applications as a promising tool to identify pathological conditions at early stages (via breath analysis of anomalous concentrations of certain VOCs) [2]. In this context, metal oxides (MOXs)-based gas sensors (chemoresistive sensors) are attractive devices that can be miniaturized and integrated as array systems into compact VOC monitoring equipment at reduced fabrication costs as compared to other technologies (e.g., spectrometers) [1,2]. Various efforts have been focused on this line, pointing out the importance of enhancing both chemical and electronic sensitization by incorporating intentional impurities (e.g., doping) or modifying the surface of traditional gas-sensitive MOXs [6,8]

Methods

Results

Conclusion