Senzory

Tato disertační práce se zabývá chemorezistivními senzory toxických plynů na bázi uhlíkových nanotrubic modifikovaných jinými organickými materiály. Modifikace je prováděna za účelem zlepšení některých senzorových vlastností. Práce je rozdělena na dva větší celky. V první části, zahrnující kapitoly 2, 3 a 4, je popsána obecná teorie týkající se senzorů, jejich vlastností a obecných principů. Dále zahrnuje popis uhlíkových nanoalotropických modifikací, přičemž největší pozornost je věnována právě uhlíkovým nanotrubicím, které jsou předmětem disertační práce. V poslední kapitole první části práce se zaměřuji na důležité vlastnosti a metody výroby CNT. Druhá část této práce, počínaje kapitolou č. 5 až do konce, popisuje celkový vývoj senzorového elementu. Obsahem 5. kapitoly je studium technologických procesů nezbytných k vytvoření tenkých homogenních vrstev, tedy příprava disperze a depozice uhlíkových nanotrubic. Následuje kapitola podrobně popisující modifikace CNT jinými organickými materiály vedoucí ke zlepšení některých parametrů. Součástí této kapitoly je série experimentů ukazující progres v odezvách modifikovaných CNT vůči nebezpečným plynům a následné možnosti desorpce těchto plynů z povrchu CNT. V této druhé části jsou řešeny níže popsané cíle disertační práce, které by měly být vědeckým přínosem v oblasti senzorové techniky.NeobhájenoThis thesis deals with a chemoresistive, toxique gas sensors based on carbon nanotubes modified by other organic materials. The modification is carried out in order to improve certain sensor properties. The thesis is divided into two major parts. In the first part, including chapters number 2, 3 and 4, is described the general theory of the gas sensors, especially their properties and general principles. In addition it this parts describes carbon nanostructures, with the attention is devoted to carbon nanotubes which are the main subject of this thesis. In the last chapter of this part, I focus on the important properties and producing methods of carbon nanotubes. The second part of my work deals with the overall development of the sensor element (beginning by chapter number5 until the end). Technological processes necessary to create thin homogeneous layers are the content of this part and include preparing a dispersion and deposition of carbon nanotubes. The next chapter describes CNT modifications by other organic materials lead to improving certain parameters of the sensors. This part is followed a series of experiments showing progress in the responses of the modified CNTs. The modified CNT was tested against ammonia and nitrogen dioxide. The consequent desorption of these gasses from the surface of the CNT was studied too. In this second part are solved objectives of the dissertation thesis described below which should be a scientific contribution in the field of sensor technology

Impedance spectroscopy for sensor elements optimalization

One of the possibilities of evaluating the response of sensor systems is the use of impedance spectroscopy, which identifies changes in impedance in the frequency domain in case of the analytes exposure. However, the high-frequency properties of the sensors are affected by parameters such as the topology and material composition of the sensor elements. This article deals with the influence of the different geometric form of electrodes and material composition of sensor elements on its high-frequency response. Based on the obtained results, the optimization of sensor elements topology and material composition for the detection of gases and vapours used sensitive layers from carbon nanostructures was performed. The presented results will find application especially in the design of sensor elements suitable for impedance spectroscopy.One of the possibilities of evaluating the response of sensor systems is the use of impedance spectroscopy, which identifies changes in impedance in the frequency domain in case of the analytes exposure. However, the high-frequency properties of the sensors are affected by parameters such as the topology and material composition of the sensor elements. This article deals with the influence of the different geometric form of electrodes and material composition of sensor elements on its high-frequency response. Based on the obtained results, the optimization of sensor elements topology and material composition for the detection of gases and vapours used sensitive layers from carbon nanostructures was performed. The presented results will find application especially in the design of sensor elements suitable for impedance spectroscopy

Influence of sweat on joint and sensor reliability of E-textiles

This article addresses reliability under the sweat of interconnection techniques for the mounting surface mounted device (SMD) components and fully printed humidity sensors onto conductive stretchable textile ribbons. Samples underwent testing for the effect of ageing by artificial sweat on their electrical resistance using both alkaline and acidic artificial sweat. The best results in terms of electrical resistance change were obtained for samples soldered to the conductive fibers interwoven in the ribbon. However, this method can damage the ribbon due to the high temperature during soldering and significantly reduce the mechanical properties and flexibility of the ribbon, which can lead to a limited service life of samples. On the other hand, adhesive bonding is a very interesting alternative, where the above‐mentioned properties are preserved, but there is a significant effect of sweat ageing on electrical resistance. The results of fully printed graphene‐based humidity sensors show that, for the intended use of these sensors (i.e., detection of changes in moisture on the human body), usage of the samples is possible, and the samples are sufficiently reliable in the case of sweat degradation. In addition, the response of the sensor to humidity is quite high: 98% at a relative humidity of 98%.This article addresses reliability under the sweat of interconnection techniques for the mounting surface mounted device (SMD) components and fully printed humidity sensors onto conductive stretchable textile ribbons. Samples underwent testing for the effect of ageing by artificial sweat on their electrical resistance using both alkaline and acidic artificial sweat. The best results in terms of electrical resistance change were obtained for samples soldered to the conductive fibers interwoven in the ribbon. However, this method can damage the ribbon due to the high temperature during soldering and significantly reduce the mechanical properties and flexibility of the ribbon, which can lead to a limited service life of samples. On the other hand, adhesive bonding is a very interesting alternative, where the above‐mentioned properties are preserved, but there is a significant effect of sweat ageing on electrical resistance. The results of fully printed graphene‐based humidity sensors show that, for the intended use of these sensors (i.e., detection of changes in moisture on the human body), usage of the samples is possible, and the samples are sufficiently reliable in the case of sweat degradation. In addition, the response of the sensor to humidity is quite high: 98% at a relative humidity of 98%

Simultaneous detection of NH3 and N02 by modified impedance spectroscopy in sensors based on carbon nanotubes

There are many gaseous substances that need to be monitored for possible damage to health or the environrnent. This requires many sensors. The solution to reducing the number of sensors is to use one sensor to detect several gaseous substances simultaneously. Efforts to simplify sensor systems thus lead to the use of a sensor with a suitable sensitive layer and to finding a suitable method of detecting individua! gaseous substances within one sensor. The aim is to find a suitable method to detect various gaseous substances acting on the sensor. For this purpose, modified impedance spectroscopy in the high-frequency range is applied, where the scattering parameters of the sensor based on carbon nanotubes are measured under the action of N02 and NH3 gases. For this method of detection of gaseous substances, a suitable sensor platform structure was designed to enable the measurement of the electrical properties of the sensor in the GHz range. Based on the obtained results, it is possible to use one sensor to detect different types of gaseous substances.There are many gaseous substances that need to be monitored for possible damage to health or the environrnent. This requires many sensors. The solution to reducing the number of sensors is to use one sensor to detect several gaseous substances simultaneously. Efforts to simplify sensor systems thus lead to the use of a sensor with a suitable sensitive layer and to finding a suitable method of detecting individua! gaseous substances within one sensor. The aim is to find a suitable method to detect various gaseous substances acting on the sensor. For this purpose, modified impedance spectroscopy in the high-frequency range is applied, where the scattering parameters of the sensor based on carbon nanotubes are measured under the action of N02 and NH3 gases. For this method of detection of gaseous substances, a suitable sensor platform structure was designed to enable the measurement of the electrical properties of the sensor in the GHz range. Based on the obtained results, it is possible to use one sensor to detect different types of gaseous substances

Graphene-based temperature sensors–comparison of the temperature and humidity dependences

Four different graphene-based temperature sensors were prepared, and their temperature and humidity dependences were tested. Sensor active layers prepared from reduced graphene oxide (rGO) and graphene nanoplatelets (Gnp) were deposited on the substrate from a dispersion by air brush spray coating. Another sensor layer was made by graphene growth from a plasma discharge (Gpl). The last graphene layer was prepared by chemical vapor deposition (Gcvd) and then transferred onto the substrate. The structures of rGO, Gnp, and Gpl were studied by scanning electron microscopy. The obtained results confirmed the different structures of these materials. Energy-dispersive X-ray diffraction was used to determine the elemental composition of the materials. Gcvd was characterized by X-ray photoelectron spectroscopy. Elemental analysis showed different oxygen contents in the structures of the materials. Sensors with a small flake structure, i.e., rGO and Gnp, showed the highest change in resistance as a function of temperature. The temperature coefficient of resistance was 5.16−3·K−1 for Gnp and 4.86−3·K−1 for rGO. These values exceed that for a standard platinum thermistor. The Gpl and Gcvd sensors showed the least dependence on relative humidity, which is attributable to the number of oxygen groups in their structures

Highly Sensitive Room-Temperature Ammonia Sensors Based on Single-Wall Carbon Nanotubes Modified by PEDOT

An ammonia gas sensor material based on sulfonic functionalized single-wall carbon nanotubesmodified by poly(3,4-ethylenedioxythiophene), namely, PEDOT/SWCNTSO3H, was prepared via in situ polymerization. A thin active layer of PEDOT/SWCNT-SO3H was deposited on a polyimide substrate with interdigital electrodes by air-brush spray coating. The morphology of the prepared material was studied by scanning electron microscopy, and the presence of PEDOT in the structure of SWCNT-SO3H was examined with Raman spectroscopy. The obtained results showed that PEDOT was successfully bound to SWCNT-SO3H and that this modification significantly improved the NH3 sensing performance of the sensor. The sensor exhibited a strong response to ammonia (102% at 50 ppm),minimal drift in the electrical resistance during cyclic exposure, and good spontaneous desorption, all at room temperature. In the range from 20 ppm to 100 ppm ammonia, the calibration curve is considered linear, with a sensitivity of a 0.7% resistance change per 1 ppm ammonia. Furthermore, the sensor shows the ability to detect ammonia at sub-ppm concentration, and the response is 4.4% at 300 ppb. With regard to the material structure, the sensing mechanisms of both materials, i.e., PEDOT/SWCNT-SO3H and SWCNT-SO3H, are discussed in the article

Investigation of π stacking functionalization of carbon allotropes for RH sensing

This paper is focused on the noncovalent functionalization of CNT by π stacking of molecules for relative humidity (RH) sensing. This type of functionalization is not used frequently, but it potentially offers a simple way how to control the level of functionalization of the carbon allotropes. The base idea is to stack the molecules with base hexagonal carbon structure on the carbon allotropes like carbon nanotubes or graphene. This paper deals with experiments with different materials with carbon hexagonal structure, which can be able to do π stacking interaction and also can be able to react on air relative humidity.This paper is focused on the noncovalent functionalization of CNT by π stacking of molecules for relative humidity (RH) sensing. This type of functionalization is not used frequently, but it potentially offers a simple way how to control the level of functionalization of the carbon allotropes. The base idea is to stack the molecules with base hexagonal carbon structure on the carbon allotropes like carbon nanotubes or graphene. This paper deals with experiments with different materials with carbon hexagonal structure, which can be able to do π stacking interaction and also can be able to react on air relative humidity

Selective methane chemiresistive detection using MWCNTs array decorated by metal organic framework layer

Methane as a main component of natural gas, but simultaneously an explosive compound with pronounced negative environmental impact. Therefore, methane should be detected with high precision and reliability. However, the inertness and non-polar nature of methane is limiting its simple detection (e.g., by a chemiresistive approach) living a gap in sensing solution. In this paper, we propose a selective chemiresistive methane sensor consisting of abundant carbon materials (multi-walled carbon nanotubes - MWCNTs) with a metal-organic framework (PCN-14). The sensor is based on decorating a non-ordered array of MWCNTs with PCN-14, which is known to have high selectivity towards methane. The methane molecules are selectively entrapped by PCN-14 pores, which significantly affect the resistance of created hybrid materials. As a result, we could detect methane under air pressure and at room temperature, with a negligible false response from other interfering gases or moisture (except hydrogen or ethane). Despite its extreme simplicity, our chemiresistive sensor does not require chemical reaction or material-destructive binding/oxidation of methane. Therefore, long operation time and sensor stability were expected and experimentally confirmed. Finally, the initial resistance of MWCNTs-PСN-14 hybrid materials was adjusted to be measurable by a portative multimeter range, which makes our approach very simple and technically undemanding