Abstract
A room-temperature ammonia (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) sensor based on amorphous-carbon/silicon(a-C/Si) heterojunction derived capacitive device is proposed in this article. Herein, controlled pyrolysis of lithographically patterned negative photoresist (SU8) thin films has been performed to realize highly stable a-C/Si junctions. Use of pyrolysis is an economic way of realizing the carbon films, as opposed to the conventional means of sputtering. Additionally, use of the photoresist allows us to preferably pattern the carbon film to develop heterojunction devices of varying shape and surface area. In this study, we have explored the NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> sensing properties of an unpatterned a-C film based heterojunction, where change in the capacitance-frequency (C-f) response of the heterojunction upon adsorption of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> molecules on to the a-C surface is used as the transduction principle. The sensor accounts for a limit of detection (LoD) of 0.26 ppm, a response time of 5-10 s, a postexposure recovery time of 3-5 min, and excellent selectivity, in addition to facilitating room-temperature gas sensing.
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