Mr. Shobin L. R. Profile

Shobin L. R.

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Proceedings Article | 24 October 2014 Paper

Room temperature ammonia vapor sensing properties of transparent single walled carbon nanotube thin film

L. Shobin, S. Manivannan

Proceedings Volume 9270, 92701M (2014) https://doi.org/10.1117/12.2071830

KEYWORDS: Sensors, Resistance, Coating, Electrodes, Single walled carbon nanotubes, Thin films, Transmittance, Molecules, Glasses, Scanning electron microscopy

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Carbon nanotube (CNT) networks are identified as potential substitute and surpass the conventional indium doped tin oxide (ITO) in transparent conducting electrodes, thin-film transistors, solar cells, and chemical sensors. Among them, CNT based gas sensors gained more interest because of its need in environmental monitoring, industrial control, and detection of gases in warfare or for averting security threats. The unique properties of CNT networks such as high surface area, low density, high thermal conductivity and chemical sensitivity making them as a potential candidate for gas sensing applications. Commercial unsorted single walled carbon nanotubes (SWCNT) were purified by thermal oxidation and acid treatment processes and dispersed in organic solvent N-methyl pyrolidone using sonication process in the absence of polymer or surfactant. Optically transparent SWCNT networks are realized on glass substrate by coating the dispersed SWCNT with the help of dynamic spray coating process at 200ºC. The SWCNT random network was characterized by scanning electron microscopy and UV-vis-NIR spectroscopy. Gas sensing property of transparent film towards ammonia vapor is studied at room temperature by measuring the resistance change with respect to the concentration in the range 0-1000 ppm. The sensor response is increased logarithmically in the concentration range 0 to 1000 ppm with the detection limit 0.007 ppm. The random networks are able to detect ammonia vapor selectively because of the high electron donating nature of ammonia molecule to the SWCNT. The sensor is reversible and selective to ammonia vapor with response time 70 seconds and recovery time 423 seconds for 62.5 ppm with 90% optical transparency at 550 nm.

Proceedings Article | 17 January 2011 Paper

Carbon nanotubes coated fiber optic ammonia gas sensor

S. Manivannan, L. Shobin, A. Saranya, B. Renganathan, D. Sastikumar, Kyu Chang Park

Proceedings Volume 7941, 79410M (2011) https://doi.org/10.1117/12.874375

KEYWORDS: Sensors, Carbon nanotubes, Cladding, Fiber coatings, Optical fibers, Gas sensors, Fiber optics, Polymethylmethacrylate, Coating, Molecules

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We report, intrinsic fiber optic carbon nanotubes coated sensor for the detection of ammonia gas at room temperature. Multimode step index polymethyl methacrylate (PMMA) optical fiber passive cladding is partly replaced by an active coating of single and multi-walled carbon nanotubes following the dip coating technique and the reaction with ammonia is studied by measuring the change in output intensity from the optical fiber under various ammonia gas concentrations in the range 0-500 ppm in step of 50 ppm. The sensitivity is calculated for different wavelengths in the range 200-1100 nm both for single and multi-walled carbon nanotubes coated fiber. Higher sensitivities are obtained as 0.26 counts/ppm and 0.31 counts/ppm for single-walled (average diameter 1.3 nm, 30 wt.% purity) and multi-walled (average diameter 10-15 nm, 95 wt.% purity) carbon nanotubes respectively. The role of diameter and purity of carbon nanotubes towards the ammonia sensing is studied and the results are discussed.

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