Papers by Author: D. Mangalaraj

Abstract: Silica nanotubes with controlled diameter and length were synthesised by using a novel and modified template-sol-gel method. The consistency and order of silica nanotubes mainly depend on the anodic alumina membrane (AAO) template that was used during the preparation process. The AAO membrane was chemical etched using different concentrations (5, 7 and 10 wt %) of phosphoric acid. The obtained silica nanotubes had diameters in the range of 220-280 nm and thicknesses around 70-90 nm as observed by field emission scanning electron microscopy (FE-SEM). Scanning transmission electron microscopy (STEM) images enable us to view the arrangement of the hollow cylindrical silica nanotubes. Porosity of the silica nanotubes was investigated by nitrogen adsorption-desorption. The mesoporous silica nanotubes show characteristic type IV isotherm behaviour, with double capillary condensation step in the relative pressure range of 0.2-1.0 (p/p₀). Thermogravimetric (TGA) and differential thermal (DTA) analyses confirm the thermal stability of the silica nanotubes and their weight changes and endo and exothermic reactions. The structural and functional group analyses of the silica nanotubes were carried out by using X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FT-IR).

Abstract: Vanadium pentoxide thinfilms have been deposited by vacuum evaporation method and the effect of deposition temperatures on the surface morphology of the prepared sample has been analyzed. Structural and morphological were carried out on the prepared samples, using X-Ray Diffractometer (XRD) and Scanning Electron Microscopy (SEM). The samples deposited at elevated temperature showed nanopetal like structures on their surface which were found to be around 100-200 nm. The formation of the V2O5 phase has been confirmed through TG/DTA analysis which shows a sharp peak around 690°C corresponding to the melting point of vanadium pentoxide. The best sample was subjected to gas sensing analysis and the change in the resistance of the sensing element with respect to the test gas concentration was measured by noting down the resistance at each concentration for various time intervals. Sensitivity of the material linearly increased with different concentration of the test gas.

Abstract: Nanostructured vanadium pentoxide films have been synthesized by using a sol–gel technology from V2O5 powder and hydrogen peroxide. The V2O5 powder was dissolved in hydrogen peroxide solution, agitated and heated up to 65oC to form gel by the dissociation of the peroxide complexes. The obtained gel was deposited by dip coating technique and dried in air at room temperature. Structural, morphological and compositional analyses were carried out on the prepared samples using X-Ray Diffractometer (XRD), Raman spectrometer and scanning electron microscopy (SEM). The as-prepared films show an amorphous nature, while those annealed at 400oC exhibit orthorhombic structures. The films seem to have grain like structures on annealing which are expected to help the gas sensing properties of the V2O5 films. The annealed films were connected with copper electrodes and used as sensing element. The change in the resistance of the sensing element with respect to the test gas concentration was measured by noting down the resistance at each concentration. Sensitivity of the material linearly increased with different concentrations of ethanol and ammonia. It is clearly seen that the material has more sensing response for ethanol when compared to that of ammonia.

Abstract: The relationship between metal-induced chemical bonding and the mechanical properties of Me/a:C-H (Me- Ti and Ni) films are discussed. Nanocomposite films were deposited onto the Si substrates via biased target ion beam sputtering of metal combined with reactive ion beam deposition of a:C-H using CH4/Ar gas mixture. The chemical composition, microstructure and mechanical properties were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and nanoindentation. XPS analysis revealed that both Ti and Ni atoms were preferentially bonded to carbon to form its metal carbide phase. Irrespective of its kind, both the metal carbide clusters induces more graphite like bondings in a:C-H matrix. From the nanoindentation analysis it was found that there is no crack propagation and damage around the indent region even at very high indentation loads. Additionally, it was found that a:C-H film shows higher hardness compared to that of Ti/a:C-H and Ni/a:C-H films.

Abstract: TaN-Cu nanocomposite thin films used as materials for thin-film resistors (TFR) were prepared by magnetron pulsed dc reactive sputtering. Structural and morphological properties of films deposited on (100) Si as a function of nitrogen flow rate and substrate temperature is investigated. With the introduction of N2 gas flow indicated with different phases of nanocrystalline h-Ta, Ta2N, TaN, Ta4N5 and Cu. XRD analysis of the films deposited with increasing substrate temperature at constant flow rate of nitrogen 10 sccm indicated that the nanocrystalline with bi-phasic (fcc-TaN and fcc-Cu). The microstructure of the films was investigated by scanning electron microscopy and high-resolution transmission electron microscopy.

Abstract: Multiform morphologies of hydroxyapatite nanostructures were synthesized by different methods. Some novel methods were adopted for preparing different morphologies. The morphological analysis confirms that the preparation method greatly influences the morphological characterization. The morphological analysis further confirmed by the TEM analysis. The nanostructure clearly depicts the growth stages of the HAp. The interplanar distances measured in segments (fringes) of the HRTEM micrograph were ~0.35 nm, corresponding to the interplanar spacing of the [002] plane of the hexagonal hydroxyapatite. X-ray Diffraction (XRD) measurements indicate the formation of crystalline hexagonal hydroxyapatite. The morphological dependent properties were analyzed in detail.

Abstract: Cerium-iron oxide composite nanorods were synthesized by a surfactant free precipitation method. The synthesized products were characterized by XRD, FESEM, BET and TEM. Increase in the mole concentration causes the morphology of the cerium oxide to change from nanorods into nanocubes. X-ray diffraction pattern shows a diffraction peak at 28.5° corresponding to (111) reflection plane normal to c axis of a cubic fluorite structure of CeO2 and also hexagonal phase of Fe2O3 and orthorhombic phase of FeO (OH). EDAX analysis on individual nanorod conform the presences of Iron, which supports the XRD spectra. From transmission electron microscopy (TEM), the length and width of the nanorods were estimated in the range of ~100-350 nm and ~20-40 nm respectively. The Brunauer Emmett Teller (BET) analysis showed the increase in surface area for the obtained nanorods with respect to the increase in Fe concentration which in turn enhanced the formation and growth of nanorods.

Abstract: In the present work, vertical ZnO nanorods (NRs) were grown onto ITO substrates by a simple two step chemical process at relatively low temperature by using successive ionic layer absorption and reaction method (SILAR) and chemical bath deposition (CBD) method. The investigated on n- ZnO/ p-Polythiophene heterojunction device have been fabricated with ZnO nanorods. Structural analysis reveals that the grown ZnO NRs exhibit (002) reflection with higher intensity, indicating that the ZnO NRs grown in c-axis orientation. FESEM image shows the surface morphology of grown ZnO nanorods was of hexagonal wurtzite structure whose diameter varies from 200 nm to 1μm. Room temperature Photoluminescence exhibited strong UV emission at ∼386 nm and a negligible green band confirms the presence of very low concentration of oxygen vacancies in the well-aligned ZnO nanorods. The current–voltage (I –V) characteristics of the heterojunctions show good rectifying diode characteristics. These results indicate that hybrid device fabricated from solution process is a promising approach for future light-emitting diodes (LEDs) devices.

Abstract: ZnO nanorods (NRs) have been synthesized by a chemical bath deposition (CBD) method on simple glass substrate that had been precoated by successive ionic layer absorption and reaction (SILAR) with a thin ZnO film. ZnO NR array was obtained by using zinc acetate and hexamethylenetetramine as aqueous solutions at optimized pH concentration and deposition time. X-ray diffraction (XRD) and SEM analysis were used to confirm the growth of ZnO nanorods. The pH and deposition time of the solution was found to influence the growth behavior of ZnO NRs. PL analysis also reflected the growth behavior of ZnO NRs.

Abstract: Titanium dioxide films were deposited using DC magnetron sputtering technique onto silicon substrates at ambient temperature and at an oxygen partial pressure of 7×10 –5 mbar and sputtering pressure (Ar + O2) of 1×10–3 mbar. The composition of the films, analyzed by Auger Electron Spectroscopy (AES), revealed the stoichiometry with an O and Ti ratio of 2.08. The optical constants of the as-deposited TiO2 thin film were determined by Spectroscopic Ellipsometry in the photon energy range 1.2 to 5.5 eV at room temperature. The measured dielectric-function spectra reveal distinct structures at energies of the E1, E1+D1 and E2 critical points due to interband transitions. The Dielectric constant values were found to be substantially lower than those for the bulk TiO2. The dielectric related optical constants, such as the refractive index, extinction coefficient, absorption coefficient and normal incidence of reflectivity are presented and analyzed. The deposited films were calcinated at 673 and 773 K. The influence of post-deposition calcination on the Raman scattering of the films was studied. The existence of Raman active modes A1g, B1g and Eg corresponding to the Raman shifts are reported in this paper. The improvement of crystallinity of the TiO2 films as shown by the Raman scattering studies has also been reported.