Au/SnO2 an excellent material for room temperature carbon monoxide sensing

Tin dioxide synthesized by the hydrothermal method, impregnated with Au has been used for the room temperature carbon monoxide sensing in air. Incorporation of poly ethylene glycol (PEG-6000) as a modifier during the synthesis procedure results in well dispersed nanosized particles of SnO₂ which influence the sensing capability dramatically. This tailored morphology leads to development of a material with improved sensor response. Incorporation of gold resulted in a composition that was capable of selectively sensing low concentrations (upto 10 ppm CO in air) at temperatures below 50 °C. The mechanism of improved sensing has been explained based on the gas sensing characteristics with support from TEM, UV-DRS, XPS and FTIR.     

Fabrication and liquefied petroleum gas (LPG) sensing performance of p-polyaniline/n-PbS heterojunction at room temperature

In the present work, we report the fabrication and liquefied petroleum gas (LPG) sensing performance of p-polyaniline/n-PbS heterojunction at room. The p-polyaniline/n-PbS heterojunction was fabricated by electrodepositing polyaniline on predeposited PbS thin film by chemical bath deposition. The PbS and polyaniline films were characterized for their structural as well as surface morphological analyses. The XRD analyses revealed that PbS thin film is polycrystalline whereas polyaniline exhibited amorphous nature. The scanning electron micrographs of PbS film showed the formation of compact and well covered nanograins whereas, polyaniline has interconnected fuzzy nanofibrous architecture. Room temperature LPG response of heterojunction in forward biased condition showed the maximum response up to 70% at 0.06 vol.% of LPG.     

Investigation on nanocrystalline copper-doped zirconia thin films for optical sensing of carbon monoxide at high temperature

Nanocrystalline copper-doped zirconia (CDZ; Cu:Zr = 16:84) thin films have been synthesized on long-period fiber gratings (CDZ-LPFG) by a polymeric precursor method. The CDZ-LPFG device was demonstrated to have high sensitivity and good reversibility for low-concentration CO sensing at high temperatures. The CDZ-LPFG responds with red shifts of its resonant wavelength (λ_R) to CO-containing gases and the λ_R shift reverses when it is exposed to air. The optical response of the CDZ-LPFG to CO is due primarily to the CDZ refractive index variations resulted from the reversible redox reactions (i.e. Cu²⁺ ⇔ Cu⁺) in reducing and oxidizing atmospheres. The magnitude of the λ_R shift exhibited a strong dependence on CO concentration in a range from 0 to 1000 ppm that is potentially useful for quantitative measurement.     

Ammonia sensing properties of polypyrrole thin films at room temperature

Polypyrrole thin films were synthesized in situ by chemical polymerization. Fourier transform infrared spectroscopy revealed formation of polypyrrole. The morphological studies by scanning electron microscopy showed formation of uniform granular structure with average grain size of 0.6 μm. The film composition was characterized by X-ray photoelectron spectroscopy for chemical composition in polypyrrole film. These films were investigated for their sensing behaviour towards NH₃ and NO at room temperature. It has been observed that these films are selective for NH₃ and the sensitivity exhibited a linear response in range of 4-80 ppm.     

Gas sensing properties at room temperature of a quartz crystal microbalance coated with ZnO nanorods

Gas sensors based on a quartz crystal microbalance (QCM) coated with ZnO nanorods were developed for detection of NH₃ at room temperature. Vertically well-aligned ZnO nanorods were synthesized by a novel wet chemical route at a low temperature of 90 °C, which was used to grow the ZnO nanorods directly on the QCM for the gas sensor application. The morphology of the ZnO nanorods was examined by field-emission scanning electron microscopy (FE-SEM). The diameter and length of the nanorods were 100 nm and 3 μm, respectively. The QCM coated with the ZnO nanorods gas sensor showed excellent performance to NH₃ gas. The frequency shift (Δf) to 50 ppm NH₃ at room temperature was about 9.1 Hz. It was found that the response and recovery times were varied with the ammonia concentration. The fabricated gas sensors showed good reproducibility and high stability. Moreover, the sensor showed a high selectivity to ammoniac gas over liquefied petroleum gas (LPG), nitrous oxide (N₂O), carbon monoxide (CO), nitrogen dioxide (NO₂), and carbon dioxide (CO₂).     

Examination of Au/SnO2 core-shell architecture nanoparticle for low temperature gas sensing applications

Au/SnO₂ core-shell structure nanoparticles (NPs) were synthesized using two methods, microwave and conventional precipitation. In both cases, the size of the Au core was 12-18 nm and the thickness of the SnO₂ shell was 8-12 nm. The particle size of SnO₂ synthesized using the microwave and precipitation method was 3-5 nm and 1-2 nm, respectively. Upon heating to 400-600 °C, both particles maintained their core-shell morphology but the smaller SnO₂ particles prepared using the precipitation method were more sintered. The resistance changes in films of these particles were measured as a function of CO concentration. The Au/SnO₂ particles prepared using the microwave method showed higher sensor response than those prepared using the precipitation method, even providing a significant signal at testing temperatures approaching ambient conditions, thereby affording a new class of material for gas sensing. Both sets of core-shell particles showed higher sensor response than the SnO₂ nanoparticles. The role of the Au core as a catalyst in improving the adsorption and oxidation of CO gas is important for improving the low temperature response. In addition, the maintenance of the size of SnO₂ in the microwave method during sintering contributed to the higher response towards CO sensing.     

Sensing of CO2 at room temperature using work function readout of (hetero-)polysiloxanes sensing layers

Organically modified silicates based on primary amino groups are known to be CO₂ sensitive, as they can undergo a reversible acid base reaction. In order to generate detectable CO₂ signals and to limit the cross-sensitivity to humidity, some sources suggest that these materials should be operated at higher temperatures (50-70 °C). In this paper, a new variant of CO₂ sensing is to be presented, namely a combination of work function readout and organically modified silicates, which yields CO₂ detection even at room temperature. Kelvin probe measurements are used for work function readout. The layers are intended to be used in a “Floating Gate Field Effect Transistors” (FGFETs) sensing platform (mySens) by Micronas. The reversible interaction of CO₂ with spin-coated heteropolysiloxane sensitive layers results in changes of the work function with typical signal heights of 15-20 mV (change from 400 to 4000 ppm CO₂) and response times of only a few minutes. Also, results will be presented regarding variations in the chemical nature of the films. The findings summarized in this paper point towards the possibility of a new room temperature CO₂ sensor, which comprises fast response times and sufficient sensitivity for ambient CO₂ variations.     

负温下炭黑/硅橡胶导电复合薄膜力敏特性研究

对炭黑/硅橡胶导电复合薄膜试样进行了负温条件下的力敏特性试验研究。测试结果表明,薄膜试样在负温下(最低温度达到-35℃)仍具有优良的拉伸敏感特性。试样电阻随拉伸变形的增大而增大,电阻与应变(最大应变达到20%)之间具有良好的线性关系。不同负温条件,复合薄膜试样表现出基本一致的力敏特性。炭黑含量越大,试样导电稳定性越好,但灵敏度相应有所降低。研究结果表明,薄膜元件可满足较低负温、较大应变下的拉伸变形测试,且线性度、稳定性都较好。     

Gas sensitivity of Zn doped α-Fe2O3(SO4, Sn, Zn) to carbon monoxide

It is shown that the doping of Zn and Sn can improve the gas sensitivity of α-Fe₂O₃-based sensing material to CO. X-ray photo-electron spectroscopy analysis suggests that this is mainly due to the fact that the simultaneous doping of Zn and Sn can increase the S and hence SO₄²⁻ contents in the α-Fe₂O₃(SO₄²⁻, Sn, Zn) sensing material. The results also suggest that under a given condition, the gas sensitivity of α-Fe₂O₃(SO₄²⁻, Sn, Zn) to CO can be optimised by properly adjusting the doped Zn content.     

In2O3 + xBaO (x = 0.5-5 at.%) - A novel material for trace level detection of NOx in the ambient

Indium oxide (In₂O₃) doped with 0.5-5 at.% of Ba was examined for their response towards trace levels of NO_x in the ambient. Crystallographic phase studies, electrical conductivity and sensor studies for NO_x with cross interference for hydrogen, petroleum gas (PG) and ammonia were carried out. Bulk compositions with x ≤ 1 at.% of Ba exhibited high response towards NO_x with extremely low cross interference for hydrogen, PG and ammonia, offering high selectivity. Thin films of 0.5 at.% Ba doped In₂O₃ were deposited using pulsed laser deposition technique using an excimer laser (KrF) operating at a wavelength of (λ) 248 nm with a fluence of ∼3 J/cm² and pulsed at 10 Hz. Thin film sensors exhibited better response towards 3 ppm NO_x quite reliably and reproducibly and offer the potential to develop NO_x sensors (Threshold limit value of NO₂ and NO is 3 and 25 ppm, respectively).