Latha Kumari

X-ray diffraction and Raman scattering studies on large-area array and nanobranched structure of 1D MoO2 nanorods

One-dimensional (1D) MoO2 nanorods in the form of a large-area array and nanobranched structure were prepared by hot-filament metal?oxide vapour deposition at low and high pressures in atmospheric argon flows respectively. The x-ray diffraction (XRD) patterns of both as-synthesized samples show that the 1D MoO2 nanorods are monoclinic crystals in space group P 21/c. The Raman spectrum of the large-area array of 1D MoO2 nanorods appears to be the same as that of a two-dimensional (2D) MoO2 thin film. The Raman spectrum of the nanobranched structure of 1D MoO2 nanorods showed a downshift and asymmetric broadening of the Raman first-order TO peak when compared with the bulk (q = 0) mode. The Raman shift and broadening were attributed to phonon confinement effect in the 1D nanorods. The in?situ Raman spectra of laser-induced oxidation of the nanobranched structure of 1D MoO2 nanorods demonstrate that they can be oxidized easily and more strongly than the 3D bulk MoO2 powder.

Synthesis and Thermoelectric Properties of Bi2Se3 Nanostructures

Bismuth selenide (Bi2Se3) nanostructures were synthesized via solvothermal method. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of rhombohedral Bi2Se3. Electron microscopy examination indicates that the Bi2Se3 nanoparticles have hexagonal flake-like shape. The effect of the synthesis temperature on the morphology of the Bi2Se3 nanostructures has also been investigated. It is found that the particle size increases with the synthesis temperature. Thermoelectric properties of the Bi2Se3 nanostructures were also measured, and the maximum value of dimensionless figure of merit (ZT) of 0.096 was obtained at 523 K.

Integration of Carbon Nanotubes to C-MEMS for On-chip Supercapacitors

Carbon nanotubes (CNTs)/carbon microelectromechanical systems (C-MEMS) composites were fabricated as electrode materials for on-chip supercapacitors. By using photolithography and pyrolysis process, 3-D C-MEMS architectures were prepared. The iron catalyst particles were conformally coated on the C-MEMS by electrostatic spray deposition (ESD) and CNTs were synthesized on the surfaces of C-MEMS by catalytic CVD method. The CNT/C-MEMS composites exhibited higher specific capacitance than C-MEMS. Furthermore, the composites with more homogeneous CNTs showed better capacitance. After treatment of oxygen plasma, the specific capacitance of the composite increased due to the contribution of oxygen functional groups.

Monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).

Laser oxidation and wide-band photoluminescence of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of various microstructures were synthesized by thermal evaporation at varying substrate temperatures. The substrate temperature strongly affects the surface morphology and crystalline orientation of the Bi thin films. Peak shift and broadening of the Raman bands (Eg and A1g modes) observed with an increase in substrate temperature can be attributed to the phonon confinement and compressive stress effects. The Bi thin film depicts a laser-induced oxidation and phase transition as a function of varying laser power. Photoluminescence spectra show visible–near infrared broadband emission for polycrystalline Bi thin film prepared at high substrate temperature. This result indicates that polycrystalline Bi thin film can be a promising candidate for broadband optical fibre amplifiers and tunable lasers.

Effect of iodine incorporation on the electrical properties of amorphous conducting carbon films

In this work, the influence of iodine incorporation on the electrical properties of amorphous conducting carbon films, prepared by the vapor phase pyrolysis of maleic anhydride, is reported and discussed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies reveal structural changes in the system. The anomalous behavior in the electrical properties of the intercalated system at low temperatures is investigated. The system shows a positive temperature coefficient of resistance (TCR) at low temperatures, which suggests reasons for the induced ordering of the system at low temperatures with the iodine incorporation. Also, a systematic increase in the conductivity of the sample is observed. The crossover temperature depends on the disorder in the system. The results indicate the possibility of metal-insulator (M-I) transition as a function of preparation temperature, iodine concentration and magnetic field.

Effect of Surfactants on the Structure and Morphology of Magnesium Borate Hydroxide Nanowhiskers Synthesized by Hydrothermal Route

Magnesium borate hydroxide (MBH) nanowhiskers were synthesized using a one step hydrothermal process with different surfactants. The effect surfactants have on the structure and morphology of the MBH nanowhiskers has been investigated. The X-ray diffraction profile confirms that the as-synthesized material is of single phase, monoclinic MgBO2(OH). The variations in the size and shape of the different MBH nanowhiskers have been discussed based on the surface morphology analysis. The annealing of MBH nanowhiskers at 500 °C for 4 h has significant effect on the crystal structure and surface morphology. The UV–vis absorption spectra of the MBH nanowhiskers synthesized with and without surfactants show enhanced absorption in the low-wavelength region, and their optical band gaps were estimated from the optical band edge plots. The photoluminescence spectra of the MBH nanowhiskers produced with and without surfactants show broad emission band with the peak maximum at around 400 nm, which confirms the dominant contribution from the surface defect states.

Structural and electrical properties of amorphous carbon-sulfur composite films

In this paper, we discuss the synthesis of carbon-sulfur composite (a-C:S) films by vapour phase pyrolysis of maleic anhydride and sulfur. Structural changes in the system are analysed by scanning electron microscopy and powder X-ray diffraction. Microhardness test depicts an increase in the value of hardness with an increase in sulfur concentration. Electrical conductivity of composite samples varies with sulfur concentration. Magnetoresistance (MR) measurements show a drastic increase in the value of MR for the samples prepared at < 900°C. Thermal stability of these samples is analysed by thermogravimetric analysis, which depends on the host structure and the amount of intercalated species.

Synthesis and structure of undoped and indium-doped thermoelectric lead telluride nanoparticles

Undoped and indium (In)-doped lead telluride (PbTe) nanostructures were synthesized via solvothermal/hydrothermal route. The crystalline structure of the as-prepared undoped and In-doped PbTe samples was examined by X-ray diffraction (XRD) which indicated the formation of face-centered single-phase cubic crystal. A first principle calculation on indium doping shows that the indium atoms are more likely to replace lead (Pb) rather than to take the interstitial sites. Laser-induced breakdown spectroscopy (LIBS) analysis confirms that indium is incorporated into the PbTe matrix of the indium-doped PbTe samples. The effects of surfactant and synthesis temperature on the structure and morphology of the undoped PbTe were also investigated; it was found that PbTe nanostructures synthesized with the addition of surfactants exhibited uniform shapes and their size increased with the synthesis temperature.

Tuning of the metal-insulator transition in iodine incorporated amorphous carbon

We present the synthesis and properties of iodine incorporated amorphous carbon films. Optical studies depict a decrease in band gap with variation in iodine content and pyrolysis temperature. Tuning of the metal-insulator transition is achieved by varying the pyrolysis temperature and iodine concentration. Appreciable decrease in magnetoresistance is observed with iodine incorporation, but negative magnetoresistance typical behavior of metallic samples is not witnessed.