Influence of Al Doping on the Morphological, Structural and Gas Sensing Properties of Electrochemically Deposited ZnO Films on Quartz Resonators

Gergana Alexieva,Nikolay Tyutyundzhiev,Miroslav Petrov,Rositsa Gergova,Konstantin Lovchinov

doi:10.3390/coatings12010081

Abstract

The detection of hazardous gases at different concentration levels at low and room temperature is still an actual and challenging task. In this paper, Al-doped ZnO thin films are synthesized by the electrochemical deposition method on the gold electrodes of AT-cut quartz resonators, vibrating at 10 MHz. The average roughness, surface morphology and gas sensing properties are investigated. The average roughness of Al-doped ZnO layers strongly depends on the amount of the doping agent Al2(SO4)3 added to the solution. The structural dependence of these films with varying Al concentrations is evident from the scanning electron microscopy images. The sensing properties to ethanol and ammonia analytes were tested in the range of 0–12,800 ppm. In the analysis of the sensitivity to ammonia, a dependence on the concentration of the added Al2(SO4)3 in the electrochemically deposited layers is also observed, as the most sensitive layer is at 3 × 10−5 M. The sensitivity and the detection limit in case of ammonia are, respectively, 0.03 Hz/ppm and 100 ppm for the optimal doping concentration. The sensitivity depends on the active surface area of the layers, with those with a more developed surface being more sensitive. Al-doped ZnO layers showed a good long-term stability and reproducibility towards ammonia and ethanol gases. In the case of ethanol, the sensitivity is an order lower than that for ammonia, as those deposited with Al2(SO4)3 do not practically react to ethanol.

Highlights

Air pollution in big cities and the attendant deterioration of the quality of life urge the development of accurate environment monitoring systems
Metal oxide nanomaterials have received a lot of attention in gas sensor fabrication due to their relatively easy controlled synthesis, diversity of surface morphology and grain size, and high sensing performance, especially good sensitivity, selectivity, and fast response and recovery time [6]
Vattappalam et al [22] reported the synthesis by successive ionic layer adsorption and reaction method of Al-doped ZnO thin films, which can be used as fast-response sensors for ethanol vapors

Summary

Introduction

Air pollution in big cities and the attendant deterioration of the quality of life urge the development of accurate environment monitoring systems. Different methods (sol–gel, chemical vapor deposition, electrospinning, etc.) have been applied for the synthesis of ZnO nanostructures with various sizes, morphologies and gas sensing properties [12].

Results

Conclusion