Development of Pd/TiO2 Porous Layers by Pulsed Laser Deposition for Surface Acoustic Wave H2 Gas Sensor.

Izabela Constantinoiu,Cristian Viespe

doi:10.3390/nano10040760

Abstract

The influence of sensitive porous films obtained by pulsed laser deposition (PLD) on the response of surface acoustic wave (SAW) sensors on hydrogen at room temperature (RT) was studied. Monolayer films of TiO2 and bilayer films of Pd/TiO2 were deposited on the quartz substrates of SAW sensors. By varying the oxygen and argon pressure in the PLD deposition chamber, different morphologies of the sensitive films were obtained, which were analyzed based on scanning electron microscopy (SEM) images. SAW sensors were realized with different porosity degrees, and these were tested at different hydrogen concentrations. It has been confirmed that the high porosity of the film and the bilayer structure leads to a higher frequency shift and allow the possibility to make tests at lower concentrations. Thus, the best sensor, Pd-1500/TiO2-600, with the deposition pressure of 600 mTorr for TiO2 and 1500 mTorr for Pd, had a frequency shift of 1.8 kHz at 2% hydrogen concentration, a sensitivity of 0.10 Hz/ppm and a limit of detection (LOD) of 1210 ppm. SAW sensors based on such porous films allow the detection of hydrogen but also of other gases at RT, and by PLD method such sensitive porous and nanostructured films can be easily developed.

Highlights

The final properties of the materials are strongly influenced by their morphology
The influence of sensitive porous films obtained by pulsed laser deposition (PLD) on the response of surface acoustic wave (SAW) sensors on hydrogen at room temperature (RT) was studied
Film Morphology The different pressures under which the TiO2 films were deposited led to the obtaining of obviously different film morphologies, as it can be seen in Figures 2 and 3

Summary

Introduction

The final properties of the materials are strongly influenced by their morphology. it is very important for each type of application to study an optimum morphology, so as to obtain its best results. PLD has the advantages of high deposition rate, maintaining the stoichiometry of the target, wide choice of materials and a relatively high reproducibility [7,8] This technique has some unique features: the control of stoichiometry, the possibility to use thermally stable substrates, the capability to grow nanostructures in the presence of a gas [8]. These advantages come from the ability to control the parameters as laser power, pulse frequency, substrate temperature, rate deposition, pressure deposition, the distance between target and substrate, etc. As the depositing pressure increases, the porosity of the material increases [12]

Methods

Results

Conclusion