Shashwati Sen

Structural, Morphological, Optical, and Electrical Properties of PANi-ZnO Nanocomposites

Thin films of polyaniline (PANi) and PANi–Zinc oxide (ZnO) nanocomposites have been synthesized by a spin-coating technique. The ZnO powder of particle size 50–60 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The nanocomposite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), UV–Vis spectroscopy, and four probe technique, and the results were compared with polyaniline films.

Room Temperature Ammonia Gas Sensor Based on Polyaniline-TiO

In the present work, we report on the performance of room temperature ammonia gas sensor based on polyaniline-titanium dioxide (PANi-TiO2) nanocomposite. The nanocomposite was fabricated using the spin coating method on glass substrates. PANi-TiO2 (0%-50%) nanocomposite films were characterized for their structural as well as surface morphologies, UV-Vis and various gas responses were studied. The XRD analysis showed formation of nanocrystalline TiO2, while polyaniline exhibited amorphous nature. Morphological analysis using scanning electron microscopy of PANi-TiO2 nanocomposite film revealed uniform distribution of TiO2 nanoparticles in PANi matrix. The absorption peaks in FTIR and UV-Vis spectra of PANi-TiO2 composite film were found to shift to a higher wave number as compared to those observed in pure PANi. The observed shifts were attributed to the interaction between the TiO2 particle and PANi molecular chains. The gas sensing properties showed the sensor exhibit selectivity to ammonia (NH3) at room temperature.

_{2}

The polyaniline-titanium dioxide (PANi-TiO₂) nanocomposite was prepared from PANi, and TiO₂, which were synthesized by oxidative chemical polymerization and sol gel methods, respectively. Nanocomposites of PANi- TiO₂ were doped with Camphor Sulfonic Acid (CSA) with concentrations as high as 50 wt%. The composites obtained (PT CSA) were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). The CSA doped PANi-TiO₂ thin-film sensors were prepared by the sol gel spin coating technique. The sensitivity measurements were carried out for ammonia (NH₃), ethanol (C₂H₅-OH), methanol (CH₃-OH), nitrogen dioxide (NO₂) and hydrogen sulfide (H₂S) gases, and it was found that the sensor exhibited selectivity to NH₃. The effect of varying doping percentage on response to varying NH₃ concentration was also studied. The result showed increasing response of sensor when NH₃ concentration was changed from 20 to 100 ppm. It was also found that, the sensor exhibited smaller response time and larger response magnitude but at the cost of longer recovery time.

Nanocomposite

The field-emission properties of SnO(2):WO(2.72) hierarchical nanowire heterostructure have been investigated. Nanoheterostructure consisting of SnO(2) nanowires as stem and WO(2.72) nanothorns as branches are synthesized in two steps by physical vapor deposition technique. Their field emission properties were recorded. A low turn-on field of ~0.82 V/μm (to draw an emission current density ~10 μA/cm(2)) is achieved along with stable emission for 4 h duration. The emission characteristic shows the SnO(2):WO(2.72) nanoheterostructures are extremely suitable for field-emission applications.

New Method for Fabrication of CSA Doped PANi-

A nanocomposite of polyaniline-titanium dioxide (PANi-TiO2, 50 wt%) was doped with camphor sulfonic acid (CSA) by solid state reaction with increasing CSA content up to 50 wt% in a smooth agate mortar. CSA doped PANi-TiO2 was dissolved in m-cresol and films were cast using a spin-coating technique. The doping effect of CSA on PANi-TiO2 nanocomposite was characterized and evaluated by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and electrical conductivity measurement. The XRD spectra showed that the addition of CSA has no effect on crystallinity of PANi-TiO2. SEM studies revealed that CSA has a strong effect on morphology of PANi-TiO2. The FTIR spectra revealed the interaction between CSA and PANi-TiO2 nanocomposite. Electrical conductivity measurements indicated that with the increasing content of CSA, the conductivity shows an orderly increase.

{\rm TiO}_{2}

Tellurium nanotubes have been grown by physical vapor deposition under inert environment at atmospheric pressure as well as under vacuum conditions. Different techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical absorption have been utilized for characterization of grown structures. Films prepared using both types of tellurium nanotubes were characterized for sensitivity to oxidizing and reducing gases and it was found that the relative response to gases depends on the microstructure. Nanotubes prepared at atmospheric pressure (of argon) showed high sensitivity and better selectivity to chlorine gas. Impedance spectroscopy studies showed that the response to chlorine is mainly contributed by grain boundaries and is therefore enhanced for nanotubes prepared under argon atmosphere.

Thin-Film Ammonia Sensor

Abstract Starting with Mg in two different forms, namely, powder and flakes, and B as powder, MgB 2 superconductor has been synthesized using solid-state sintering method under atmospheric pressure of argon. The grain growth of MgB 2 was greatly enhanced when magnesium flakes were employed. MgB 2 grains having a size of up to 3×2×1 mm 3 could be retrieved from the samples synthesized using magnesium flakes. The synthesized samples have been characterized by optical microscopy, X-ray diffraction and temperature dependence of resistivity and magnetization measurements. The critical current density of the MgB 2 sample synthesized using magnesium flakes was determined to be 3.9×10 5 A/cm 2 (5 K, 1 T), which is comparable to that reported for samples synthesized under high pressures.

Enhanced Field-Emission from SnO2:WO2.72 Nanowire Heterostructures

Polycrystalline MgB2, synthesized using a conventional solid-state reaction route, has been investigated for its magnetic field dependent microwave absorption using a standard X-band EPR spectrometer. The changes in microwave absorption as a function of temperature and/or magnetic field were recorded by following the microwave reflectivity of a sample-loaded cavity. The modulated low-field microwave absorption signal was found to be similar to that observed in high-temperature superconducting materials. The field dependent direct microwave absorption in the 0-10 kG range was used to determine Hc1 values at different temperatures, and the value of Hc1(0) was found to be 250 G. The absorbed microwave power has been found to obey a (H)1/2 dependence with a change of slope indicating a transition from a strongly pinned flux lattice to the flux flow regime.

Camphor Sulfonic Acid Doped Polyaniline-Titanium Dioxide Nanocomposite: Synthesis, Structural, Morphological, and Electrical Properties

One-dimensional (1D) nanostructures of semiconductor oxides are of interest for various applications including gas sensors. For gas sensors, nanostructures have advantages of improved gas-sensing characteristics and have potential in fabrication of miniature sensor. In this paper, we review some of the work done in our laboratory towards growth of nanostructures of SnO2, ZnO and CuO and hierarchical nano-heterostructures of CuO:W18O49, SnO2: W18O49 and ZnO:18O49 as well as investigation of their gas-sensing properties. All nanostructures except CuO have been prepared by thermal evaporation technique. CuO nanowires have been grown by thermal oxidation of copper foils under oxygen atmosphere. Gas sensing has been investigated in: isolated 1D structures placed between two electrodes; films prepared from their suspension in organic solvents or direct growth of nanostructured films on substrates. The results show that isolated 1D nanostructures of pure SnO2 and ZnO are highly sensitive for room temperature detection of H2S and NO gases respectively while SnO2:W18O49 heterostructures may be used for the detection of chlorine.

Chlorine gas sensors using one-dimensional tellurium nanostructures

Surface engineering of SiO2 dielectric using different self-assembled monolayer (SAM) has been carried out, and its effect on the molecular packing and growth behavior of copper phthalocyanine (CuPc) has been studied. A correlation between the growth behavior and performance of organic field effect transistors is examined. Depth profiling using positron annihilation and X-ray reflectivity techniques has been employed to characterize the interface between CuPc and the modified and/or unmodified dielectric. We observe the presence of structural defects or disorder due to disorientation of CuPc molecules on the unmodified dielectric and ordered arrangement on the modified dielectrics, consistent with the high charge carrier mobility in organic field effect transistors in the latter. The study also highlights the sensitivity of these techniques to the packing of CuPc molecules on SiO2 modified using different SAMs. Our study also signifies the sensitivity and utility of these two techniques in the characterization of buried interfaces in organic devices.