Successful isolation of single layer of graphene from graphite by mechanical exfoliation method, attracted a great
attention due to its unique structural, optical, mechanical and electronic properties. This makes the graphene as a
promising material in many possible applications such as energy-storage, sensing, electronic, optical devices and
polymer composite materials. High quality of reduced graphene oxide (rGO) material was prepared by chemical
reduction method at 100°C. The structural and optical properties of the rGO sheets were characterized by FT-IR,
micro Raman, powder XRD and UV-vis-NIR techniques. FT-IR reveals the absence of oxygen functional groups on
rGO due to the reduction process. Powder XRD shows the broad peak at 2θ=24.3° corresponding to interlayer
spacing 3.66Å which is smaller than the graphene oxide (GO). UV-vis-NIR of rGO displays the absorption peak at
271 nm indicates the reduction of GO and the restoration of C=C bonds in the rGO sheets. The cladding removed
and rGO coated poly-methyl methacrylate (PMMA) optical fiber is used for methanol and ethanol vapors detection
in the concentration ranging from 0 to 500 ppm at room temperature. The spectral characteristics along with output
intensity modulation of cladding removed and rGO coated fiber optic sensor reveal the potential of methanol and
ethanol vapor sensing properties.
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.
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.
The semicarbazone of p-dimethylamino benzaldehyde (SCPDB) is a potential organic nonlinear optical material. SCPDB has been synthesized and the solubility studies were carried out in the temperature range 30-60°C. Following the slow evaporation technique, single crystals of SCPDB have been grown and the unit cell parameters have been evaluated by single crystal x-ray diffraction technique. The UV-Vis-NIR transmittance spectrum was recorded in the range 200-1100nm. Fourier transform IR and Fourier transform Raman spectra were recorded in the range 400-4000 cm-1 and the characteristic vibrational frequencies of the functional groups present in the system have been assigned. Second Harmonic Generation efficiency measurements were carried out using Nd:YAG laser.
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