Graphene-Based Junction Devices for Hydrogen Sensors

Graphene is quite a robust material for sensing hydrogen and other gases at room temperature as well as at elevated temperatures with high efficiency. This chapter deals with different junction devices based on graphene for hydrogen sensing. Graphene has excellent electronic attributes that make it suitable for gas sensor devices. However, till date, the research on graphene-based junction devices is not many. In this chapter, we present different types of graphene junction devices suitable for hydrogen sensing. Hydrogen sensor response of these junctions is analyzed, and the sensing mechanism is presented. The temperature- and atmosphere-dependent inversion of n-type to p-type conductivity in graphene is highlighted for hydrogen sensing. Moreover, the two dimensional nature of graphene makes it very convenient for device miniaturization. This chapter provides relevant information on the growth of graphene, the fabrication of different graphene junction devices, and hydrogen sensor applications. Also, the sensor-related concerns such as cross-sensitivity, signal drift, stability, and interference of humidity during hydrogen sensing are thoroughly discussed in this chapter

Versatile Graphene-Based Platform for Robust Nanobiohybrid Interfaces

Technologically useful and robust graphene-based interfaces for devices require the introduction of highly selective, stable, and covalently bonded functionalities on the graphene surface, whilst essentially retaining the electronic properties of the pristine layer. This work demonstrates that highly controlled, ultrahigh vacuum covalent chemical functionalization of graphene sheets with a thiol-terminated molecule provides a robust and tunable platform for the development of hybrid nanostructures in different environments. We employ this facile strategy to covalently couple two representative systems of broad interest: metal nanoparticles, via S-metal bonds, and thiol-modified DNA aptamers, via disulfide bridges. Both systems, which have been characterized by a multi-technique approach, remain firmly anchored to the graphene surface even after several washing cycles. Atomic force microscopy images demonstrate that the conjugated aptamer retains the functionality required to recognize a target protein. This methodology opens a new route to the integration of high-quality graphene layers into diverse technological platforms, including plasmonics, optoelectronics, or biosensing. With respect to the latter, the viability of a thiol-functionalized chemical vapor deposition graphene-based solution-gated field-effect transistor array was assessed

Synthesis and Gas Sensing Properties of Transition Metal Dichalcogenides materials (TMDs)

En el procés de monitorització industrial, el control d'emissions dels cotxes, la seguretat de la qualitat de l'aire interior i exterior i la protecció del medi ambient, la detecció contínua i fiable de diversos gasos és fonamental. Els òxids metàl·lics semiconductors, els materials més utilitzats en aplicacions de detecció de gasos, tenen limitacions substancials com ara un alt consum d'energia, una mala estabilitat a llarg termini, una selectivitat limitada i, sobretot, una alta sensibilitat creuada a la humitat. Els materials nous que permeten un funcionament a baixa temperatura poden resoldre problemes relacionats amb l'energia, donant lloc a xarxes de sensors millors i més fiables. Com a resultat, materials 2D com els dicalcogenurs de metalls de transició (TMD) han sorgit com a opcions viables per a la detecció de gasos. Aquests materials de nova generació tenen el potencial de millorar les propietats de detecció dels materials sensibles als gasos, com ara la sensibilitat, la selectivitat, l'estabilitat i la velocitat (temps de resposta-recuperació). Això es deu a les seves propietats úniques inherents, que inclouen el gruix a nanoescala, una gran superfície específica, abundants llocs de vora actiu i una alta sensibilitat a les molècules de gas a temperatures més baixes i fins i tot a temperatura ambient. La tesi actual intenta augmentar la fabricació d'aquests materials en capes 2D de nova generació i utilitzar-los per a aplicacions de detecció de gasos en aquest camp d'estudi. A més, els materials de detecció de gasos investigats en aquesta tesi tenen el potencial d'abordar l'esmentat anteriorment en la seva forma prístina o després d'alguna funcionalització. En aquest sentit, aquesta tesi proposa sensors de gas quimioresistius basats en diversos materials TMD.En el proceso de monitoreo industrial, el control de emisiones de automóviles, la seguridad de la calidad del aire interior y exterior y la protección del medio ambiente, la detección continua y confiable de varios gases es fundamental. Los óxidos de metales semiconductores, los materiales más utilizados en aplicaciones de detección de gases, tienen limitaciones sustanciales, como un alto consumo de energía, poca estabilidad a largo plazo, selectividad limitada y, sobre todo, alta sensibilidad cruzada a la humedad. Los nuevos materiales que permiten el funcionamiento a baja temperatura podrían resolver los problemas relacionados con la energía, lo que daría como resultado redes de sensores mejores y más fiables. Como resultado, los materiales 2D como los dicalcogenuros de metales de transición (TMD) han surgido como opciones viables para la detección de gases. Estos materiales de próxima generación tienen el potencial de mejorar las propiedades de detección de los materiales sensibles al gas, como la sensibilidad, la selectividad, la estabilidad y la velocidad (tiempo de respuesta-recuperación). Esto se debe a sus propiedades únicas inherentes, que incluyen espesor a nanoescala, gran área de superficie específica, abundantes sitios de borde activos y alta sensibilidad a las moléculas de gas a temperaturas más bajas e incluso a temperatura ambiente. La tesis actual intenta ampliar la fabricación de estos materiales en capas 2D de próxima generación y utilizarlos para aplicaciones de detección de gases en este campo de estudio. Además, los materiales de detección de gases investigados en esta tesis tienen el potencial de abordar lo mencionado anteriormente, ya sea en su forma original o después de alguna funcionalización. En este sentido, esta tesis propone sensores de gas quimiorresistivos basados en varios materiales TMDs.In the industrial monitoring process, car emission control, indoor and outdoor air quality safety, and environmental protection, continuous and reliable detection of various gases is critical. Semiconducting metal oxides, the most extensively used materials in gas sensing applications, have substantial limitations such as high power consumption, poor long-term stability, limited selectivity, and, most notably, high humidity cross-sensitivity. Novel materials that allow for low-temperature operation might solve power-related issues, resulting in better and more reliable sensor networks. As a result, 2D materials like transition-metal dichalcogenides (TMDs) have emerged as viable options for gas sensing. These next-generation materials have the potential to improve gas-sensitive materials' sensing properties such as sensitivity, selectivity, stability, and speed (response-recovery time).This is owing to their inherent unique properties, which include nanoscale thickness, large specific surface area, abundant active edge sites, and high sensitivity to gas molecules at lower temperatures and even at room temperature. The current thesis attempts to scale up the fabrication of these next-generation 2D layered materials and utilise them for gas sensing applications in this field of study. Furthermore, the gas sensing materials investigated in this thesis have the potential to address the aforementioned either in their pristine form or after some functionalization. In this regard, this thesis proposes chemoresistive gas sensors based on several TMDs materials

Two-Dimensional Electronics - Prospects and Challenges

During the past 10 years, two-dimensional materials have found incredible attention in the scientific community. The first two-dimensional material studied in detail was graphene, and many groups explored its potential for electronic applications. Meanwhile, researchers have extended their work to two-dimensional materials beyond graphene. At present, several hundred of these materials are known and part of them is considered to be useful for electronic applications. Rapid progress has been made in research concerning two-dimensional electronics, and a variety of transistors of different two-dimensional materials, including graphene, transition metal dichalcogenides, e.g., MoS2 and WS2, and phosphorene, have been reported. Other areas where two-dimensional materials are considered promising are sensors, transparent electrodes, or displays, to name just a few. This Special Issue of Electronics is devoted to all aspects of two-dimensional materials for electronic applications, including material preparation and analysis, device fabrication and characterization, device physics, modeling and simulation, and circuits. The devices of interest include, but are not limited to transistors (both field-effect transistors and alternative transistor concepts), sensors, optoelectronics devices, MEMS and NEMS, and displays

Nano Layers of 2D Graphene Versus Graphene Oxides for Sensing Hydrogen Gas

Hydrogen is one of the most useful but dangerous gases because of its broad combustion range and small ignition temperature. Currently, there is a great need for hydrogen detectors with selectivity, high sensitivity and reliable operations in view of its safe production, storage, transportation and other applications. In this regard, nano thin films of two dimensional materials like graphene, graphene oxide (GO) and reduced graphene oxide (rGO) have immense promise because their material attributes can be exceptionally tuned to achieve the desired characteristics. Also graphene oxide and reduced graphene oxide serve as potential sensing hosts due to the presence of functional groups on their surfaces. In this chapter, an attempt has been made to compare the work done in the field of hydrogen sensors using pure graphene and graphene derivatives such as graphene oxide and reduced graphene oxide. The response parameters like sensitivity, stability, selectivity, response time, recovery time, detection limit, linearity, dynamic range, and working temperatures for various graphene based sensors have been elaborately compared. Finally, a conclusion and future outlook on nano scale thin film of graphene and graphene oxides for gas sensing have been briefly discussed

Semiconductor Gas Sensors: Materials, Technology, Design, and Application

This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies. © 2020 by the authors. Licensee MDPI, Basel, Switzerland