Influence of GLAD Sputtering Configuration on the Crystal Structure, Morphology, and Gas-Sensing Properties of the WO3 Films

Arkadiusz Zarzycki,Jie Xu,Maciej Sitarz,Katarzyna Dyndał,Artur Rydosz,Feng Gao,Konstanty Marszałek

doi:10.3390/coatings10111030

Abstract

In this paper, we describe a deposition method and investigation of the physical properties of WO3 films. We investigated tungsten oxide due to its potential application as a gas sensor. Thin films of the WO3 were deposited on glass, silicon, and alumina substrates by magnetron GLAD sputtering. The crystallinity of films was determined by X-ray diffraction (XRD) and the thickness by X-Ray Reflectivity (XRR) and spectroscopic ellipsometry (SE). Surface morphology, which is important for gas sensitivity, was measured by atomic force microscopy (AFM). We studied the gas-sensing characteristics under exposure to acetone in the 0.1–1.25 ppm range which covers the levels of exhaled breath acetone. We show that WO3 sensors have different sensitivity for different sputter angle. Furthermore, we demonstrate the influence of temperature during gas content measurement.

Highlights

Tungsten oxide is a well-known semiconductor with a rich phase diagram, including WO2, W18 O49, W24 O68, WO3, and a series of nonstoichiometric WO3−x [1]
The green points are data points and the red lines are the fits for a series of WO3 thin films with different glancing angle deposition (GLAD) angles
Our investigation of WO3 thin films indicates the influence of sputtering geometry on films physical properties, especially sensor properties

Summary

Introduction

Tungsten oxide is a well-known semiconductor with a rich phase diagram, including WO2 , W18 O49 , W24 O68 , WO3, and a series of nonstoichiometric WO3−x [1]. Tungsten trioxide forms many different polymorphic phases, i.e., monoclinic, triclinic, orthorhombic, tetragonal, cubic, as well as hexagonal [2,3]. The WO3 compound is built from a corner shared octahedrons of a W–O6 , in which tungsten atoms are surrounded by 6 oxygens. A decrease in the symmetry of tungsten trioxide leads to the systematic deformation of the WO6 octahedrons, first stretching and bending. Tungsten oxide has attracted a large interest due to its unique applications for example in the transmittance and reflection modulation devices [4,5], and as a photoanode for the use in photoelectrochemical cells [6]. Tungsten oxide exhibits properties critical for the fields of bioelectronics and biosensor development [9,10]

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Results

Conclusion