Active surface geometrical control of noise in nanowire-SAW sensors

2018

Sensors

Self Cite

The effect of nanostructure of PLD (Pulsed Laser Deposition)-deposited Pd/WO3 sensing films on room temperature (RT) hydrogen sensing properties of SAW (Surface Acoustic Wave) sensors was studied. WO3 thin films with different morphologies and crystalline structures were obtained for different substrate temperatures and oxygen deposition pressures. Nanoporous films are obtained at high deposition pressures regardless of the substrate temperature. At lower pressures, high temperatures lead to WO3 c-axis nanocolumnar growth, which promotes the diffusion of hydrogen but only once H2 has been dissociated in the nanoporous Pd layer. XRD (X-ray Diffraction) analysis indicates texturing of the WO3 layer not only in the case of columnar growth but for other deposition conditions as well. However, it is only the predominantly c-axis growth that influences film sensing properties. Bilayers consisting of nanoporous Pd layers deposited on top of such WO3 layers lead to good sensing results at RT. RT sensitivities of 0.12–0.13 Hz/ppm to hydrogen are attained for nanoporous bilayer Pd/WO3 films and of 0.1 Hz/ppm for bilayer films with a nanocolumnar WO3 structure. SAW sensors based on such layers compare favorably with WO3-based hydrogen detectors, which use other sensing methods, and with SAW sensors with dense Pd/WO3 bilayers.

Section: Discussionmentioning

confidence: 63%

Surface Acoustic Wave Hydrogen Sensors Based on Nanostructured Pd/WO3 Bilayers

Miu

Bı̂rjega

2018

Sensors

Self Cite

“…The center-to-center distance between IDTs was 10 mm. The IDTs were obtained using standard photolithographic techniques, and consist in a 150-nm thick gold layer on top of a 10 nm chromium layer, the latter ensuring good adhesion to the quartz substrate [ 27 , 28 , 29 , 30 ]. The 10 × 38 mm 2 quartz substrate was cut at a 45° angle, in order to reduce the effect of spurious SAW reflection from the edge of the piezoelectric substrate [ 31 ].…”

Section: Methodsmentioning

confidence: 99%

Surface Acoustic Wave Sensor with Pd/ZnO Bilayer Structure for Room Temperature Hydrogen Detection

Miu

2017

Sensors

Self Cite

A Surface Acoustic Wave (SAW) hydrogen sensor with a Pd/ZnO bilayer structure for room temperature sensing operation has been obtained by Pulsed Laser Deposition (PLD). The sensor structure combines a Pd layer with optimized porosity for maximizing mass effects, with the large acoustoelectric effect at the Pd/ZnO interface. The large acoustoelectric effect is due to the fact that ZnO has a surface conductivity which is highly sensitive to chemisorbed gases. The sensitivity of the sensor was determined for hydrogen concentrations between 0.2% and 2%. The limit of detection (LOD) of the bilayer sensor was about 4.5 times better than the single ZnO films and almost twice better than single Pd films.

“…Over time, several types of hydrogen sensing sensors have been developed, including chemiresistive gas sensors [24], SAW sensors [12], metal-oxide semiconductor gas sensors [23]. Different types of sensing materials have been used for hydrogen detection: metal oxide thin films (ZnO, TiO 2 , WO 3 , SnO 2 , In 2 O 3 ) [25,26], metal thin films (Pd, Pt) [27], multilayer of metal oxides and metals (Pd/WO 3 , Pd/V 2 O 5 , Pd/SnO 2 , Pd/ZnO) [12,23,28,29], composite materials [30], nanowires [31]. Some of these types of sensors have the ability to detect hydrogen at temperatures above 200 • C, which is inappropriate for hydrogen detection because the risk of the explosion becomes higher especially at high hydrogen concentrations [30].…”

Section: Introductionmentioning

confidence: 99%

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

Constantinoiu

2020

Nanomaterials

Self Cite

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 TiO 2 and bilayer films of Pd/TiO 2 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/TiO 2 -600, with the deposition pressure of 600 mTorr for TiO 2 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.