Department of Electrical and Electronics Engineering

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    Highly selective formaldehyde sensing using ZnO nano-rods
    (AIP, 2023-03) Choudhary, Sumita; Hazra, Arnab; Gangopadhyay, Subhashis
    Early detection of formaldehyde emission from any household materials is technologically very demanding as it can be a serious human health hazard. Even indirect inhaling of formaldehyde may cause significant harm to our eyes, skin, mouth or any other organs. Hence, fabrication of a simple and sensitive formaldehyde sensor would be of high practical importance. Within this work, formation of ZnO nano-rods by controlled thermal oxidation of vacuum deposited thin Zn films in air ambient, followed by fabrication of formaldehyde sensor operating at relatively lower operating temperature are reported. The crystal structure, surface morphology and optical properties of the as grown ZnO nano-rods have been investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Raman spectroscopy, respectively. The XRD patterns of ZnO suggested the formation of highly crystalline oxide films whereas FESEM images have revealed its nano-rods surface morphology with significantly high (length to diameter) aspect ratio. Raman spectroscopy confirms the thermal oxidation of the Zn thin films. As-grown ZnO nano-rods were then subsequently used to fabricate the chemi-resistive formaldehyde sensors. These sensors showed an extremely high formaldehyde sensing performance at a relatively lower operating temperature of 200°C. In a static measurement mode, the sensor exhibited a gas response of about 53% toward 100 ppm of formaldehyde, with a reasonable fast response and recovery time. Moreover, these ZnO nano-rod based sensors have also been tested with similar type of VOCs such as benzene, xylene, alcohols and acetone and appeared with an excellent selectivity towards formaldehyde over the other VOCs.
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    Application of Mono Layered Graphene Field Effect Transistors for Gamma Radiation Detection
    (IEEE, 2018-10) Rao, V. Ramgopal
    In this work, we report the application of graphene field effect transistors (GFETs) as a gamma radiation sensor. The GFETs were irradiated at room temperature by 60 Co gamma radiation source for 10 kGy and 20 kGy gamma dose. The Electrical measurements and Raman spectroscopy showed that gamma radiation induced p-doping in graphene. Large positive shifts in Dirac point and significant degradation in electron mobility were observed post-gamma irradiation. Thus modulation in transport properties of GFETs was utilized here to measure the absorbed gamma radiations. We propose, a GFET based radiation detector with high sensitivity of + 113 V for 20 kGy gamma dose operating in ambient condition.
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    A Passive Gamma Radiation Dosimeter Using Graphene Field Effect Transistor
    (IEEE, 2020-03) Rao, V. Ramgopal
    In this work, Graphene-based field-effect transistors (GFETs) are demonstrated as a highly sensitive dosimeter for gamma radiation. Graphene-based field-effect transistors exhibit p-type doping with the Dirac point shifting in the positive direction upon exposure to gamma radiation. Concurrently, an asymmetric degradation in the electron and hole mobility was observed with the former degrading more rapidly. It is shown that change in the Dirac voltage and carrier mobility is strongly dependent on the dose of gamma radiation. A sensitivity of ~1 V/kGy is reported. Gamma radiation causes partial aerial oxidation of graphene-channel which leads to p-doping as confirmed by the emergence of a higher binding energy peak (286.8 eV) in X-ray photoelectron spectra (XPS). The decrease in contact potential difference estimated through Kelvin probe force microscopy (KPFM) confirms this finding. The radiated devices showed a stable response for ~70 days. Our work demonstrates that gamma irradiation can also be used to induce large and stable hole concentrations in graphene. Such highly sensitive GFET can serve as real-time dosimeter operating in ambient conditions.