Rare earth oxycarbonates as a material class for chemoresistive CO2 gas sensors

AbstractIn this work we compare the CO2 gas sensing properties of two new materials synthesized from rare earth hydroxide (La(OH)3,Pr(OH)3) precursors, with the already reported ones for neodymium oxycarbonate, which was synthesized from the corresponding Nd(OH)3 precursor. In-situ XRD measurements show that by following similar thermal treatment, praseodymium hydroxide is transforming to the metal oxide while lanthanum hydroxide forms an oxycarbonate, like in the case of neodymium. The chemoresistive effects we found for the lanthanum oxycarbonate were even higher than the ones recorded for the neodymium oxycarbonate; for the praseodymium metal oxide we could not find any CO2 sensitivity. Accordingly, we think that the condition for CO2 sensing is the formation of the rare earth oxycarbonate

CO2 sensing with chemoresistive Nd2O2CO3 sensors - Operando insights

AbstractIn this work the sensing of Nd2O2CO3-based chemoresistive CO2 sensor was investigated combining DRIFT and DC-resistance measurements. Besides the already reported effect of CO2 exposure, we found that exposure to CO determines comparable effects and that the presence of oxygen in the background is not important. The humidity significantly influences the response for both gases. The spectroscopic results reveal that the exposure to both CO and CO2 consumes the water-related surface species – the rooted-hydroxyls being the electrically active one – and increases the concentration of carbonates; the decrease of the rooted-hydroxyls is probably the cause of the resistance increase

Sensing low concentrations of CO using flame-spray-made Pt/SnO2 nanoparticles

Tin dioxide nanoparticles of different sizes and platinum doping contents were synthesized in one step using the flame spray pyrolysis (FSP) technique. The particles were used to fabricate semiconducting gas sensors for low level CO detection, i.e. with a CO gas concentration as low as 5ppm in the absence and presence of water. Post treatment of the SnO2 nanoparticles was not needed enabling the investigation of the metal oxide particle size effect. Gas sensors based on tin dioxide with a primary particle size of 10nm showed signals one order of magnitude higher than the ones corresponding to the primary particle size of 330nm. In situ platinum functionalization of the SnO2 during FSP synthesis resulted in higher sensor responses for the 0.2wt% Pt-content than for the 2.0wt% Pt. The effect is mainly attributed to catalytic consumption of CO and to the associated reduced sensor response. Pure and functionalized tin dioxide nanoparticles have been characterized by Brunauer, Emmett and Teller (BET) surface area determination, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) while the platinum oxidation state and dispersion have been investigated by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). The sensors showed high stability (up to 20days) and are suitable for low level CO detection: <10ppm according to European and 50ppm according to US legislation, respectivel

The potential of operando XAFS for determining the role and structure of noble metal additives in metal oxide based gas sensors

Noble metal additives significantly improve the performance of SnO2 based sensors. Recently, it has been found that X-ray absorption spectroscopy is an excellent tool to identify their structure under sensing conditions, despite of the low concentrations and the rather thin (50 μm) and highly porous layers. For this purpose a new in situ approach has been established and here we highlight the potential with an overview on the results of Pd-, Pt-, and Au-additives in SnO2-based sensors at work. Emphasis was laid on recording the structure (by XANES and EXAFS) and performance at the same time. In contrast to earlier studies, Pd- and Pt-additives were observed to be in oxidized and finely dispersed state under sensing conditions excluding a spillover from metallic noble metal particles. However, Au was mainly present as metallic particles in the sensing SnO2-layer. For the Pt- and Au-doped SnO2-layers high energy-resolved fluorescence detected X-ray absorption spectra (HERFD-XAS) were recorded not only to minimize the lifetime-broadening but also to eliminate the Au- and Pt-fluorescence effectively and to record range-extended EXAFS

Platelet‐Oriented Inhibition in New TIA and Minor Ischemic Stroke ( POINT ) Trial: Rationale and design

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99014/1/ijs12129.pd

Microsystem Technology for Ambient Assisted Living (AAL)

AbstractAAL is certainly an application area with sensor as well as actuator needs. Some of the requirements can be fulfilled by state of the art technology; some areas however still need a lot of R&D efforts for potential applications in homes. The contribution describes two areas of interest and actual development: One is the topic of robust fire detection; the other domain is fall detection. For both application areas one has to understand both the state of the art and the drawbacks of the current solutions. One can state clearly that there is a huge potential for the development of new microsystems. Still one has to keep in mind that usage in elderly homes also requires consent and cooperation of the users which is the focus of the user centered design principle

Self-activated ultrahigh chemosensitivity of oxide thin film nanostructures for transparent sensors

One of the top design priorities for semiconductor chemical sensors is developing simple, low-cost, sensitive and reliable sensors to be built in handheld devices. However, the need to implement heating elements in sensor devices, and the resulting high power consumption, remains a major obstacle for the realization of miniaturized and integrated chemoresistive thin film sensors based on metal oxides. Here we demonstrate structurally simple but extremely efficient all oxide chemoresistive sensors with similar to 90% transmittance at visible wavelengths. Highly effective self-activation in anisotropically self-assembled nanocolumnar tungsten oxide thin films on glass substrate with indium-tin oxide electrodes enables ultrahigh response to nitrogen dioxide and volatile organic compounds with detection limits down to parts per trillion levels and power consumption less than 0.2 microwatts. Beyond the sensing performance, high transparency at visible wavelengths creates opportunities for their use in transparent electronic circuitry and optoelectronic devices with avenues for further functional convergence.open181

Rhodium oxide surface-loaded gas sensors

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO₃, SnO₂, and In₂O₃—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified