Smart control of chemical gas sensors for the reduction of their time response

Sensors and Actuators B: Chemical, Volume 229, 28 June 2016, Pages 1-6

M. Dominguez-Pumar, L. Kowalski, R. Calavia, E. Llobet

Abstract:The objective of this paper is to show the first results obtained with a gas sensor made of Au-functionalized WO3 nanoneedles working under a closed-loop control designed to reduce its time response. The average temperature applied to the sensor is modulated to keep constant the average surface potential of the sensing nanostructures. This is done by periodically monitoring the resistivity of the sensing layer and generating temperature waveforms that enforce the condition: constant resistivity of the sensing layer at a reference temperature. Changes induced by the target gases must be compensated by changes in the average temperature being applied to the sensing layer. This signal, the average temperature applied to the sensor, is the new sensor output.

Enhancement of methane gas sensing characteristics ofgrapheme(石墨烯) oxide sensor by heat treatment and laser irradiation

Journal of Colloid and Interface Science, Volume 483, 1 December 2016, Pages 275-280

Mohammadreza Assar, Rouhollah Karimzadeh

Abstract:The present study uses a rapid, easy and practical method for cost-effective fabrication of a methane gas sensor. The sensor was made by drop-casting a graphene oxide suspension onto an interdigital circuit surface. The electrical conductivity and gas-sensing characteristics of the sensor were determined and then heat treatment and in situ laser irradiation were applied to improve the device conductivity and gas sensitivity. Real-time monitoring of the evolution of the device current as a function of heat treatment time revealed significant changes in the conductance of the graphene oxide sensor. The use of low power laser irradiation enhanced both the electrical conductivity and sensing response of the graphene oxide sensor.

Tin oxide-based thin films prepared by pulsed laser deposition for gas sensing

Sensors and Actuators B: Chemical, Volume 236, 29 November 2016, Pages 865-873

Elisabeth M. Preiß, Tobias Rogge, Andreas Krauß, Helmut Seidel

Abstract:Thin tin dioxide films were prepared by large-area pulsed laser deposition, a ceramic target in oxygen atmosphere was used. The layers were structured on interdigitated electrode substrates using a two-side trenched silicon shadow mask. The influence of the oxygen background pressure during deposition on the electrical and morphological properties was investigated using four-point probe measurements, scanning electron microscopy, X-ray diffraction, and X-ray photo spectroscopy investigations. Pd was introduced into the films by DC magnetron sputtering. It was found that the resistive response to CO is increased for the Pd-doped samples. Cross-sensitivity to the oxidizing gas NO2 was investigated and the sensor showed high signals for this gas at lower temperatures.

Highly selective NH3 gas sensor based on Au loaded ZnO nanostructures prepared using microwave-assisted method

Journal of Colloid and Interface Science, Volume 479, 1 October 2016, Pages 127-138

K. Shingange, Z.P. Tshabalala, O.M. Ntwaeaborwa, D.E. Motaung, G.H. Mhlongo

Abstract:ZnO nanorods synthesized using microwave-assisted approach were functionalized with gold (Au) nanoparticles. The Au coverage on the surface of the functionalized ZnO was controlled by adjusting the concentration of the Au precursor. According to X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results, it was confirmed that Au form nanoparticles loaded on the surface of ZnO. The small Au loading level of 0.5 wt% showed the highest response of 1600–100 ppm of NH3 gas at room temperature (RT) whereas further increase of Au loading level resulted in poor detection of NH3. All Au loaded ZnO (Au/ZnO) based sensors exhibited very short recovery and response times compared to unloaded ZnO sensing materials. The responses of ZnO and Au/ZnO based sensors (0.5–2.5 wt%) to other flammable gases, including H2, CO and CH4, were considerably less, demonstrating that Au/ZnO based sensors were highly selective to NH3 gas at room temperature. Spill over mechanism which is the main reason for the observed enhanced NH3 response with 0.5 Au loading level is explained in detail.

A miniaturized optical gas-composition sensor with integrated sample chamber

Sensors and Actuators B: Chemical, Volume 236, 29 November 2016, Pages 917-925

N. Pelin Ayerden, Mohammadamir Ghaderi, Peter Enoksson, Ger de Graaf, Reinoud F. Wolffenbuttel

Abstract:A robust and highly miniaturized optical gas sensor based on optical absorption spectroscopy is presented. By using the resonator cavity of a linear variable optical filter (LVOF) also as a gas chamber, a compact and robust optical sensor is achieved. The device operates at the 15th order in 3.2–3.4 μm wavelength range for distinguishing hydrocarbons. The physical cavity length at the μm-level is translated into an effective optical absorption path length at the mm-level by the use of highly reflective (R > 98%) Bragg mirrors. The optical design using the Fizeau interferometer approach is described. Moreover, the CMOS-compatible fabrication method is explained. In addition to the wideband and single wavelength filter characterization, absorption of methane in the LVOF cavity is demonstrated at 3392 nm and 3416.60 nm wavelengths.

High performance CuS p-type thin film as a hydrogen gas sensor

Sensors and Actuators A: Physical, Volume 249, 1 October 2016, Pages 68-76

Fayroz A. Sabah, Naser M. Ahmed, Z. Hassan, Hiba S. Rasheed

Abstract:In this study, CuS thin films with p-type behaviour were prepared using two solvent types: deionized water (S1) and deionized water mixed with ethanol (S2). The thin films were deposited onto substrates comprising glass slide, multilayer of ZnO/Cu/ZnO, ZnO nanorods and Poly(methyl methacrylate) (PMMA). XRD analysis revealed the presence of covellite-CuS phase and chalcocite-Cu2S phase with average crystallite sizes of 14.1 nm and 15.4 nm, respectively in S1 sample while only covellite-CuS phase with an average crystallite size of 11.6 nm was identified for S2. Morphological observations (SEM) showed smaller sized nanoplates in S1 compared to S2. The results from implementation of the two devices as hydrogen gas sensors revealed S1 exhibits better sensitivity (98.9% at 1000 ppm) and shorter response and recovery times (16 s and 34 s at 800 ppm, respectively) compared to S2 (sensitivity of 78.4% at 1000 ppm; response and recovery times of 35 s and 24.4 s at 1000 ppm, respectively). The sensitivity was found to increase with increasing gas concentration for both samples. It was inferred from the results that CuS thin film prepared with only deionized water (S1) has a higher H2 gas detection potential.

Pulsed laser deposition of metal oxide nanostructures for highly sensitive gas sensor applications

Sensors and Actuators B: Chemical, Volume 236, 29 November 2016, Pages 978-987

Joni Huotari, Ville Kekkonen, Tomi Haapalainen, Martin Leidinger, Tilman Sauerwald, Jarkko Puustinen, Jari Liimatainen, Jyrki Lappalainen

Abstract:Nanosecond and picosecond(皮秒；微微秒) pulsed laser deposition (PLD) was used to prepare metal oxide nanostructures with different morphologies as gas sensing materials on top of oxidized silicon substrates and commercial SGX Sensortech SA MEMS microheater platforms. The layers were formed of different types of nanostructures including nanoparticles, agglomerates, and nanotrees with fractal-like growth. Clear dependencies between the deposition parameters, structural morphology, and gas sensing performance were found. Also, some differences in the morphologies of the layers were seen when picosecond PLD was used instead of nanosecond PLD. Many of the sensing materials were found to be highly sensitive to different types of gaseous species. We investigated inorganic gases in the ppm range (2–400 ppm) including NO, CO, and NH3, and the selectivity and sensitivity were shown to be dependent, not only on layer morphology, but also on the measurement temperature. Moreover, an investigation with volatile organic compound gases in the ppb range demonstrated that WO3 layers are highly sensitive and selective towards naphthalene at least down to 2.5 ppb.