Особенности адсорбции и десорбции водяных паров на поверхности пленок нестехиометрического диоксида олова

Herein, the influence of water vapor adsorption and desorption processes on the surface of SnO2−δ nanocrystalline films with different concentrations of oxygen vacancies on their electrical conductivity at room temperature was studied. SnO2−δ films were synthesized by means of reactive magnetron sputtering of tin in an argon-oxygen plasma followed by 2-stage oxidative annealing. The concentration of oxygen vacancies in the films was varied by changing the 2nd stage annealing temperature within the range 350–400 °C. It was found that in the films with the highest concentration of oxygen vacancies (~1020 cm−3) in the region of low relative humidity (less than ~30 %), an increase in electrical conductivity was observed due to the dissociative adsorption of water molecules with the formation of hydroxyl groups. The adsorption of water vapor on the surface of SnO2−δ films at room temperature at relative humidity values higher than ~30 % was found to induce a decrease in the electrical conductivity of the samples. The generation of positive and negative EMF pulses between the open surface of SnO2−δ nanocrystalline films and the one covered by waterproof materials under the adsorption and desorption of water vapor, respectively, was detected. The change of resistance and the generated EMF value under the adsorption-desorption processes was found to increase with the concentration of free charge carriers in the films.Исследовано влияние процессов адсорбции и десорбции водяных паров на поверхности нанокристаллических пленок SnO2−δ с различной концентрацией кислородных вакансий на их электропроводность при комнатной температуре. Пленки SnO2−δ были синтезированы методом реактивного магнетронного напыления олова в аргон-кислородной плазме с последующим двухстадийным окислительным отжигом на воздухе. Концентрация кислородных вакансий в пленках варьировалась посредством изменения температуры отжига на второй стадии в диапазоне 350–400 °C. Установлено, что в пленках с наибольшей концентрацией кислородных вакансий (~1020 см−3) в области малых значений относительной влажности (менее ~30 %) наблюдается увеличение электропроводности в силу диссоциативной адсорбции молекул воды с образованием гидроксильных групп. Обнаружено, что адсорбция водяных паров на поверхности пленок SnO2−δ при комнатной температуре при значениях относительной влажности более ~30 % приводит к уменьшению электропроводности образцов. Обнаружена генерация положительного или отрицательного импульса ЭДС между открытой и закрытой водонепроницаемым материалом поверхностями нанокристаллических пленок SnO2–δ при адсорбции или десорбции на них паров воды соответственно. Установлено, что с увеличением концентрации кислородных вакансий в пленках изменение сопротивления и величина генерируемой ЭДС при адсорбции-десорбции паров воды возрастают

Review—Non-Invasive Monitoring of Human Health by Exhaled Breath Analysis: A Comprehensive Review

Exhaled human breath analysis is a very promisingfield of research work having great potential for diagnosis of diseases in non-invasive way. Breath analysis has attracted huge attention in thefield of medical diagnosis and disease monitoring in the last twodecades. VOCs/gases (Volatile Organic Compounds) in exhaled breath bear thefinger-prints of metabolic and biophysicalprocesses going on in human body. It’s a non-invasive, fast, non-hazardous, cost effective, and point of care process for diseasestate monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers ofdifferent diseases and their presence in excess amount is indicative of un-healthiness. Breath analysis has the potential for earlydetection of diseases. However, it is still underused and commercial device is yet not available owing to multiferrious challenges.This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of theiranalysis towards disease monitoring, analytical techniques involved, promising materials for breath analysis etc. Finally, relatedchallenges and limitations along with future scope will be touched upon.will be touched upon

Advancements in microfabricated gas sensors and microanalytical tools for the sensitive and selective detection of odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans’ olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoringPostprint (published version

Study of the optimization of a miniaturized gas sensor for odor monitoring

Climate change and the crisis of non-renewable natural resources have fostered a change in people's mentality, pushing them towards a future of shared mobility. This study aims to offer a solution to one of the main drawbacks of this type of mobility, the discomfort generated by malodors and poor air quality in shared-use vehicles. To that end, the use of an odor monitoring module is proposed which, through gas sensors, allows to improve the air quality inside vehicles after its use. In this thesis we find a study of the technology for odor tracking, the design and manufacture of a prototype for the module and its subsequent implementation in vehicles. The study concludes with pilot tests on different vehicles which contribute to the parameterization of the system, laying the foundations for projects with real application

Effect of Humid Aging on the Oxygen Adsorption in SnO2 Gas Sensors

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO2 particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO2 resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (K1; for O− adsorption, K2; for O2− adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K1 and K2 in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O− and O2−. These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO2 resistive-type gas sensors in dry and wet atmospheres

Micro- y nanoestructuras de NiO: síntesis, dopado con Sn y aplicaciones tecnológicas en energía y sensado

En la presente Tesis doctoral se exponen y discuten los principales resultados obtenidos de la investigación realizada en micro- y nanoestructuras de NiO tanto en estado puro como dopadas con Sn. El NiO es uno de los pocos óxidos semiconductores tipo p de forma intrínseca que existe, en contraste con una gran mayoría de óxidos semiconductores que presentan intrínsecamente carácter tipo n debido a vacantes de oxígeno. En las últimas décadas se está explotando este material debido a su amplia versatilidad en campos de investigación relacionados con dispositivos electrocrómicos, dispositivos magnéticos o dispositivos de almacenamiento de energía como las baterías de ion-litio o los supercapacitores. Además, este óxido destaca por su elevada estabilidad tanto química como térmica, su bajo coste de producción y su baja toxicidad. Mediante el control preciso de los parámetros experimentales se puede llegar a modular las dimensiones y morfologías de este material, reduciendo el tamaño del NiO y abriendo aún más el campo de aplicación. Otra manera de incrementar y/o mejorar sus aplicaciones, es mediante la incorporación de dopantes de forma controlada, modificando de esta manera sus propiedades ópticas, estructurales o magnéticas entre otras..