A Chemical Gas Sensor from Large-Scale Thermal CVD Derived Graphene
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A Chemical Gas Sensor from Large-Scale Thermal CVD Derived Graphene Xiaojuan Song1*, Brent Wagner1 and Zhitao Kang1, 2 Electro-Optical System Lab, Georgia Tech Research Institute, Atlanta, Georgia 30332, U.S.A. 2 School of Material Science Engineering, Georgia Institute of Technology, Atlanta, GA 30332, U.S.A *Address correspondence to: [email protected] 1
ABSTRACT Large-scale graphene sheets were grown on thin nickel film coated Si substrates using a reliable and repeatable thermal Chemical Vapor Deposition (CVD) technique. The graphene films were then transferred onto a SiO2 coated Si wafer to fabricate a 5 mm x 5 mm resistive sensor structure. Raman spectroscopy analysis confirmed the existence of graphene. Preliminary sensing results were demonstrated by the detection of hazardous gases such as NO2 and MMH (mono-methyl hydrazine). Characterization of the device channel resistivity (switching response) was conducted as a function of the analyte type and concentration. The sensor response indicates a charge transfer mechanism between the analytes and graphene. INTRODUCTION Whether to detect a chemical leak that is hazardous to personnel or the environment, to detect trace vapors of explosive that pose a major threat in a world of terrorism and asymmetric warfare, or to detect bio-molecules, antigens and cancer cells for disease diagnostics, effective detection systems or sensors are in great demand. One of the best sensors would be the one that is able to detect a single molecule/atom of the chemical or bio-molecule of interest. The recent discovery of graphene has opened a completely new area that promises ultra-sensitive sensing due to graphene’s unique structure and electrical properties. [1, 2] As a two dimensional atomic layer of sp2-bonded carbon atoms, graphene is a semi-metal. However, due to the exposure of all of its atoms to the external environment, the electronic band structure of graphene is extremely sensitive to the atoms/molecules bonded to its surface, resulting in a significant change of properties, such as conductivity. For example, it has been reported that for oxygen atoms bonded to graphene (which functionalizes like an insulating graphite oxide layer), a resistivity increase of more than 5 orders of magnitude was observed.[3] It is expected that other molecules (C-N, C-S…) or chemisorptions will also affect the electric properties. Preliminary chemical sensor experiments with mechanically exfoliated graphene flakes have shown very high sensitivity, with single molecule detection claimed for NO2 in a high vacuum chamber. [2] The high sensitivity was explained as resulting from the extraordinary mobility of carriers in graphene, which enabled extremely low noise sensing at room temperature. The mechanism for sensing appears to be similar to that for carbon nanotubes, with both NO2 and MMH producing an increase in conductivity consistent with p-type and n-type doping, respectively.[4-8] In this paper, we report the development of a chemical sensor based on CVD grown graphene, as shown
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