Chapter 15 - Nanostructured tungsten oxide using pulsed laser deposition for biosensing and environmental sensing applications

Abstract

The continuous development of human society led to exceptional scientific and technological accomplishments, passing from micro- to nanoscale. Due to the necessity to miniaturization and to decrease the production costs, nanotechnology gained a considerable importance at international level. The versatility and functional properties of metallic oxides made them suitable for a large area of applications. For example, tungsten oxide is a good candidate for applications in gas sensors, and photocatalysis provided that it is synthesized as a strongly nanostructured material, having high-surface-specific area. Conversely, when used as window for solar cells or in electronic information displays and color memory devices, tungsten oxide must be grown in the form of smooth, compact thin films. In this work, tungsten oxide thin films are obtained by pulsed laser deposition (PLD) and radio-frequency-assisted pulsed laser deposition (RF-PLD). In the case of tungsten oxide thin films grown by RF-PLD process, it is observed that the decrease of the laser fluence results in increasing film crystallinity with a similar effect while increasing the substrate temperature. These smooth layers (roughness around 1nm), without droplets or cracks, can be successfully used for window for solar cells or in electronic information displays. Still, increasing the oxygen pressure, at high temperature, isolated WO3 nanoparticles appear. The high value of the specific surface area for these tungsten oxide nanostructures leads to application in gas sensing. In order to determine the properties of nanostructured thin films and their suitable applications, different investigation techniques were carried out. As techniques, X-ray diffraction, secondary ion mass spectroscopy, scanning electron microscopy, and Raman spectroscopy have been used to characterize the deposited layers.