{"id":4092,"date":"2019-07-30T01:18:42","date_gmt":"2019-07-29T19:48:42","guid":{"rendered":"http:\/\/www.physics.iisc.ac.in\/~aveek_bid\/?p=4092"},"modified":"2019-07-30T01:20:09","modified_gmt":"2019-07-29T19:50:09","slug":"sensors-based-on-graphene-and-metal-nanowires","status":"publish","type":"post","link":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/sensors-based-on-graphene-and-metal-nanowires\/","title":{"rendered":"Sensors based on graphene and metal nanowires"},"content":{"rendered":"

Graphene based chemical sensors:<\/h3>\n

We have been exploring ultra-sensitive material sensors based on graphene. We have demonstrated that graphene sensors, based on our digital signal processing platform, have extremely high-sensitivity and specificity towards\u00a0chemicals. Being a pure two-dimensional system, graphene represents the ultimate NEMS system with all its atoms exposed to the surface. This makes the conductance of graphene extremely sensitive to the ambient and the presence of a single adsorbed molecule on its surface can significantly modify its electrical characteristics. Several unique properties of graphene make it exceptionally suitable for making sensors.\u00a0 Firstly, it is highly conductive even in very low carrier density regimes\u00a0and hence has extremely low levels of Johnson-Nyquist thermal noise as compared to semiconductor based sensors. It also has fewer kinds of defects and hence has intrinsically low levels of 1\/f noise arising out of thermal switching of defects. It is relatively easy to make four terminal measurements on graphene strips making contact resistances much easier to deal with than for example in carbon nanotubes which share almost all other advantages of graphene. All these factors combine to give a very large signal-to-noise ratio in graphene sensors even at room temperatures giving it the ability to detect changes in local charge concentration of less than the charge of a single electron. Properties like atomically thin layers, very high absorption coefficient, high mobility of charge carriers and high mechanical strength make it an ideal candidate for use as radiation sensors. Making an effective sensor requires interface accessibility, good transduction, mechanical\/electrical robustness, ease of preparation and integration into existing technologies. Graphene seems to satisfy this entire list of criterion and hence has the potential to emerge as the sensor material of choice in future.<\/p>\n

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Reduced graphene-oxide based pressure sensors:<\/h3>\n

Sensing of mechanical stimuli forms an important communication pathway between humans\/environment\u00a0and machines. The progress in such sensing technology has possible impacts on the functioning of\u00a0automated systems, human machine interfacing, health-care monitoring, prosthetics and safety systems.\u00a0The challenges in this field range from attaining high sensitivity to extreme robustness. We have demonstrated the sensing of complex mechanical stimuli with a patch of taped crumpled reduced graphene oxide (rGO). The sensor can can typically be assembled under household conditions. The ability of this\u00a0sensor to detect a wide variety of pressures and strains in conventional day-to-day applications has been\u00a0demonstrated. An extremely high gauge factor (\u223c103) at ultra-low strains (\u223c10\u22124<\/sup>) with fast response times\u00a0(~ 20.4 ms) could be achieved with such sensors. Pressure resulting from a gentle touch to over human\u00a0body weight could be sensed successfully. The capability of the sensor to respond in a variety of environments\u00a0could be exploited in the detection of water and air pressures both below and above atmospheric,\u00a0with a single device.<\/p>\n

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Ultra-thin nanowires (Au and Te) based chemical sensors:<\/h3>\n

Te-nanowire:<\/strong> Band structure engineering is a powerful technique both for\u00a0the design of new semiconductor materials and for imparting new\u00a0functionalities to existing ones. In this article, we present a novel and\u00a0versatile technique to achieve this by surface adsorption on low\u00a0dimensional systems. As a specific example, we demonstrate, through\u00a0detailed experiments and ab initio simulations, the controlled modification\u00a0of band structure in ultra-thin Te nanowires due to 2<\/sub> adsorption.\u00a0Measurements of the temperature dependence of resistivity of single\u00a0ultra-thin Te nanowire field-effect transistor (FET) devices exposed to\u00a0increasing amounts of NO2<\/sub> reveal a gradual transition from a semiconducting\u00a0to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO2<\/sub>\u00a0supports the appearance of a metallic state in 2<\/sub> adsorbed Te. Ab initio simulations attribute these observations to the\u00a0appearance of mid-gap states in NO2<\/sub> adsorbed Te nanowires. Our results provide fundamental insights into the effects of ambient\u00a0on the electronic structures of low-dimensional materials and can be exploited for designing novel chemical sensors.<\/p>\n

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Au-nanowire:<\/strong> We have demonstrated that, contrary to\u00a0expectations, the adsorption of common chemicals like methanol and acetone has a profound\u00a0impact on the electrical transport properties of the ultra-thin gold nanowires of diameter ~ 4nm. Our measurements and subsequent calculations\u00a0establish conclusively that in gold nanowires, semiconductor-like sensitivity to the ambient arises\u00a0because of changes induced in its local density of states by the surface adsorbed molecules. The\u00a0extreme sensitivity of the resistance fluctuations of the gold nanowires to ambient suggests their possible\u00a0use as solid-state sensors.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Graphene based chemical sensors: We have been exploring ultra-sensitive material sensors based on graphene. We have demonstrated that graphene sensors, based on our digital signal processing platform, have extremely high-sensitivity and specificity towards\u00a0chemicals. Being a pure two-dimensional system, graphene represents the ultimate NEMS system with all its atoms exposed to the surface. This makes the […]<\/p>\n","protected":false},"author":4,"featured_media":4094,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[41],"tags":[],"class_list":["post-4092","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/posts\/4092","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/comments?post=4092"}],"version-history":[{"count":1,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/posts\/4092\/revisions"}],"predecessor-version":[{"id":4096,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/posts\/4092\/revisions\/4096"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/media\/4094"}],"wp:attachment":[{"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/media?parent=4092"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/categories?post=4092"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~aveek_bid\/wp-json\/wp\/v2\/tags?post=4092"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}