Multivariate Analysis of Light-Activated SMOX Gas Sensors.

Chemoresistive gas sensors made from SnO, ZnO, WO, and InO have been prepared by flame spray pyrolysis. The sensors' response to CO and NO in darkness and under illumination at different wavelengths, using commercially available LEDs, was investigated. Operation at room temperature turned out to be impractical due to the condensation of water inside the porous sensing layers and the irreversible changes it caused.

Modeling the Conduction Mechanism in Chemoresistive Gas Sensor Based on Single-Crystalline SnO Nanobelts: A Phenomenological In Operando Investigation.

Investigating the sensing mechanisms in semiconducting metal oxide (SMOx) gas sensors is essential for optimizing their performance across a wide range of potential applications. Despite significant progress in the field, there are still many gaps in comprehending the phenomenological processes occurring in one-dimensional (1D) nanostructures. This article presents the first insights into the conduction mechanism of chemoresistive gas sensors based on single-crystalline SnO nanobelts using the operando Kelvin Probe technique.

In Operando Investigation of the Concentration Dependent NO Sensing Mechanism of BiS Nanorods at Low Temperatures and the Interference of O.

The demand for gas sensors that can detect gases selectively at low temperatures has increased steadily over recent years. Most devices use semiconducting metal oxides as sensing materials which often require high operation temperatures and suffer from a lack of selectivity. Semiconducting metal sulfides were found to be a reasonable alternative for the application in sensing devices at low temperatures.

Proof of Concept for Operando Infrared Spectroscopy Investigation of Light-Excited Metal Oxide-Based Gas Sensors.

Light-excitation of semiconducting metal-oxide (SMOX)-based gas sensors is a promising means to lower their operation temperature, thereby reducing power consumption, which would allow for their broader application. Despite increased research interest in light-excited gas sensors, progress has been slow because of a lack of mechanistic understanding. Notably, significant differences between light-excitation and, the better understood, thermal-excitation mechanisms have been identified.

The Role of Different Lanthanoid and Transition Metals in Perovskite Gas Sensors.

Beginning with LaFeO, a prominent perovskite-structured material used in the field of gas sensing, various perovskite-structured materials were prepared using sol-gel technique. The composition was systematically modified by replacing La with Sm and Gd, or Fe with Cr, Mn, Co, and Ni. The materials synthesized are comparable in grain size and morphology.

Effects of Gas Adsorption Properties of an Au-Loaded Porous InO Sensor on NO-Sensing Properties.

Gas adsorption properties of semiconductor-type gas sensors using porous (pr-) InO powders loaded with and without 0.5 wt % Au (Au/pr-InO and pr-InO sensors, respectively) at 100 °C were examined by using diffuse reflectance infrared Fourier transform spectroscopy, and the effect of the Au loading onto pr-InO on the NO-sensing properties were discussed in this study. We found the following: the resistance of the Au/pr-InO sensor in dry air is lower than that of the pr-InO sensor; the DRIFT spectra of both the sensors show a broad positive band between 1600 and 1000 cm in dry air (reference: in dry N at 100 °C), which mainly originates from oxygen adsorbates and/or lattice oxygen, and that this band is much larger for the Au/pr-InO sensor than for the pr-InO sensor; the Au loading also increases the adsorption amount of HO and the reactivity of NO on the pr-InO surface; and the NO response of the Au/pr-InO sensor in dry air is marginally higher than that of the pr-InO sensor in the examined concentration range of NO (0.

Investigations on the Temperature-Dependent Interaction of Water Vapor with Tin Dioxide and Its Implications on Gas Sensing.

This work presents an operando infrared spectroscopic study of the temperature-dependent water adsorption on pristine SnO surfaces and discusses the possible implications on the oxygen ionosorption and gas-sensing mechanism. The impact of water on the sensor resistance, CO-sensing performance, and CO conversion was studied, and the obtained phenomenological results provide the basis for discussing the operando spectroscopic investigation findings. The provided information allows identification of three different water adsorption regimes ranging from physisorption and dominant associative adsorption to mainly dissociative water adsorption.

Chemoresistive CO Gas Sensors Based On LaOCO: Sensing Mechanism Insights Provided by Operando Characterization.

Our previous studies demonstrated that rare-earth oxycarbonates LnOCO (Ln = La, Nd, and Sm) and rare-earth oxides LnO (Ln = Nd, Sm, Gd, Dy, Er, and Yb) are sensitive to CO and that hexagonal LaOCO is the best among them in terms of sensitivity, stability, and selectivity. In this study, we have conducted a comprehensive operando characterization on a hexagonal LaOCO based sensor for the basic understanding of the sensing mechanism. This was done by performing under actual operating conditions simultaneous DC resistance and work function changes measurements, AC impedance spectroscopy measurements, and simultaneous DC resistance and DRIFT spectroscopy measurements.

Gas sensors based on mass-sensitive transducers. Part 2: Improving the sensors towards practical application.

Within the framework outlined in the first part of the review, the second part addresses attempts to increase receptor material performance through the use of sensor systems and chemometric methods, in conjunction with receptor preparation methods and sensor-specific tasks. Conclusions are then drawn, and development perspectives for gravimetric sensors are discussed.

Dominant Role of Heterojunctions in Gas Sensing with Composite Materials.

It is well known that composite materials, consisting of at least two metal oxides, show qualities and sensing behavior very different from the single components. Recently, the preparation of core-shell nanomaterials for gas sensors has become extremely popular. Specifically, these materials have been found to show desirable sensor responses.

WO-Based Gas Sensors: Identifying Inherent Qualities and Understanding the Sensing Mechanism.

Semiconducting metal oxide-based gas sensors are an attractive option for a wide array of applications. In particular, sensors based on WO are promising for applications varying from indoor air quality to breath analysis. There is a great breadth of literature which examines how the sensing characteristics of WO can be tuned via changes in, for example, morphology or surface additives.

Conductance Model for Single-Crystalline/Compact Metal Oxide Gas-Sensing Layers in the Nondegenerate Limit: Example of Epitaxial SnO(101).

Semiconducting metal oxide (SMOX)-based gas sensors are indispensable for safety and health applications, for example, explosive, toxic gas alarms, controls for intake into car cabins, and monitor for industrial processes. In the past, the sensor community has been studying polycrystalline materials as sensors where the porous and random microstructure of the SMOX does not allow a separation of the phenomena involved in the sensing process. This led to conduction models that can model and predict the behavior of the overall response, but they were not capable of giving fundamental information regarding the basic mechanisms taking place.

Current Understanding of the Fundamental Mechanisms of Doped and Loaded Semiconducting Metal-Oxide-Based Gas Sensing Materials.

Introducing additives in semiconducting metal oxides includes, besides the use of filters, dynamic operation procedures and chemometric approaches, the most common way of tuning the sensitivity, selectivity, and stability of chemoresitsive gas sensors. For the vast majority of commercially used gas sensing materials, the introduction of additives is essential and is one of the longest lasting topics in gas sensor research. This Review discusses the different chemical and electrical sensitization mechanisms of additives as well as the role of different structures.

Gas sensors based on mass-sensitive transducers part 1: transducers and receptors-basic understanding.

The scientific interest in gas sensors is continuously increasing because of their environmental, medical, industrial, and domestic applications. This has resulted in an increasing number of investigations being reported in the literature and communicated at conferences. The present review, organized in two parts, addresses the peculiarities of gas sensors based on mass-sensitive transducers, starting with their structure and functionality and progressing to implementation and specific use.

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.

Response of Gallium Nitride Chemiresistors to Carbon Monoxide is Due to Oxygen Contamination.

We report on the influence of oxygen impurities on the gas sensing properties of gallium nitride (GaN) chemiresistors. As shown by XRD, elemental analysis, and TEM characterization, surface oxidation of GaN-for example, upon contact to ambient air atmosphere-creates an oxidative amorphous layer which provides the sites for the sensing toward CO. Treating this powder under dry ammonia at 800 °C converts the oxide layer in nitride, and consequently the sensing performance toward CO is dramatically reduced for ammonia treated GaN gas sensors.

Understanding the Potential of WO₃ Based Sensors for Breath Analysis.

Tungsten trioxide is the second most commonly used semiconducting metal oxide in gas sensors. Semiconducting metal oxide (SMOX)-based sensors are small, robust, inexpensive and sensitive, making them highly attractive for handheld portable medical diagnostic detectors. WO₃ is reported to show high sensor responses to several biomarkers found in breath, e.

Quantitative Determination of Ceramide Molecular Species in Dendritic Cells.

Background/aims: The activation of acid sphingomyelinase by cellular stress or receptors or the de novo synthesis lead to the formation of ceramide (N-acylsphingosine), which in turn modifies the biophysical properties of cellular membrane and greatly amplifies the intensity of the initial signal. Ceramide, which acts by re-organizing a given signalosome rather than being a second messenger, has many functions in infection biology, cancer, cardiovascular syndromes, and immune regulation. Experimental studies on the infection of human cells with different bacterial agents demonstrated the activation of the acid sphingomyelinase/ceramide system.

Selectivity Enhancement by Using Double-Layer MOX-Based Gas Sensors Prepared by Flame Spray Pyrolysis (FSP).

Here we present a novel concept for the selective recognition of different target gases with a multilayer semiconducting metal oxide (SMOX)-based sensor device. Direct current (DC) electrical resistance measurements were performed during exposure to CO and ethanol as single gases and mixtures of highly porous metal oxide double- and single-layer sensors obtained by flame spray pyrolysis. The results show that the calculated resistance ratios of the single- and double-layer sensors are a good indicator for the presence of specific gases in the atmosphere, and can constitute some building blocks for the development of chemical logic devices.

Grain shape influence on semiconducting metal oxide based gas sensor performance: modeling versus experiment.

A model for sensing with semiconducting metal oxide (SMOX)-based gas sensors was developed which takes the effect of the shape of the grains in the sensing layers into account. Its validity is limited to materials in which the grains of the SMOX sensing layer are large enough to have an undepleted bulk region (large grains). This means that in all experimental conditions, the SMOX properties ensure that the influence of surface phenomena is not extended to the whole grain.

Impact of Pt additives on the surface reactions between SnO2, water vapour, CO and H2; an operando investigation.

The impact of Pt doping on the surface reactions between tin dioxide, water vapour, CO and H2 was investigated by a combination of simultaneously performed operando DRIFT (Diffuse Reflectance Infrared Fourier Transform) spectroscopy, DC resistance measurements and analysis of the reaction products by using a MS (Mass Spectrometer). Both undoped and Pt doped tin dioxide sensors were exposed to different test gases in synthetic air or in N2 backgrounds. The approach made it possible to identify the differences between the two materials with respect to their surface chemistry and their impact on the gas sensing performance.

An Au clusters related spill-over sensitization mechanism in SnO2-based gas sensors identified by operando HERFD-XAS, work function changes, DC resistance and catalytic conversion studies.

The role of Au additives in SnO(2)-based thick film gas sensors was investigated by a combination of operando investigation techniques, namely spectroscopic high energy resolved fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) and simultaneous DC resistance and work function change measurements. The results have shown that the Au is present in the form of small metallic particles at the surface of the host metal oxide without changing its bulk or surface electronic properties. The sensitization effect of Au can therefore be attributed to the "spill-over effect", meaning that the Au particles enrich the surface of the active metal oxide with oxygen species which consequently react with reducing gases such as CO and H(2).

Operando X-ray absorption spectroscopy studies on Pd-SnO2 based sensors.

SnO2 gas sensors with palladium as additive in the range of 0.2 wt% and 3 wt% were studied by in situ X-ray absorption spectroscopy under idealized and real operating conditions. Simultaneously to the structural studies, measurements of the sensing properties were undertaken allowing for the determination of structure-function relationships.