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Bayati M.R.,North Carolina State University | Joshi S.,Amity Institute of Nanotechnology | Narayan R.J.,North Carolina State University | Narayan J.,North Carolina State University
Journal of Materials Research | Year: 2013

We have investigate. The formation o. The rutile an. The anatase polymorphs of TiO2, with emphasis on epitaxial growth characteristics, and defect content as a function of laser and substrate variables. X-ray diffraction (XRD) studies revealed tha. The rutile phase is more stable at higher substrate temperatures and lower oxygen pressures; in contrast, decreasin. The temperature and increasin. The oxygen pressure gave rise to formation of anatase. Epitaxial rutile films with a <100] orientation were obtained at 450 °C usin. The pressure of 5 × 10-4 Torr, and laser energy of 3.5-4.0 J/cm2. The epitaxial relationship, determined by 2θ-θ and φ scan of XRD and confirmed by transmission electron microscopy (TEM) diffraction patterns, was shown to be rutile(100)||sapphire(0001), rutile[001]||sapphire[1010] and rutile[010]||sapphire[1210]. An atomically sharp interface betwee. The rutile epitaxial film an. The sapphire substrate was observed i. The scanning transmission electron microscopy (STEM) images. The films exhibited a transmittance of 75-90% ove. The visible region. The absorption edge was observed to shift toward longer wave lengths at higher deposition temperatures or lower pressures. X-ray photoelectron spectroscopy and photoluminescence results showed that concentration of lattice point defects, namely oxygen vacancies and titanium interstitials, increased at lower oxygen pressures. Formation of nanostructured films with a surface roughness of -1.5-13.1 nm was confirmed by atomic force microscopy investigations. © 2013 Materials Research Society.

Bayati M.R.,North Carolina State University | Joshi S.,Amity Institute of Nanotechnology | Molaei R.,North Carolina State University | Narayan R.J.,North Carolina State University | Narayan J.,North Carolina State University
Journal of Solid State Chemistry | Year: 2012

We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using φ-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 -1 0), and rutile(0 1 0)||sapphire(1 -2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UVVIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation. © 2012 Elsevier Inc. © 2012 Elsevier Inc. All rights reserved.

Kumar P.,CSIR - Central Electrochemical Research Institute | Bharadwaj L.M.,Amity Institute of Nanotechnology | Paul A.K.,CSIR - Central Electrochemical Research Institute | Deep A.,CSIR - Central Electrochemical Research Institute
Inorganic Chemistry Communications | Year: 2014

A nanocrystal metal organic framework (NMOF1) has been investigated for molecular recognition. NMOF1 {[Cd(atc)(H2O)2]n} has been synthesized by the reaction of Cd(II) ions with the sodium salt of 'atc' ('atc' = 2-aminoterephthalic acid) in aqueous medium at room temperature. Pendent COOH group of the organic linker was activated using EDC [(1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide] intermediated organic reaction, followed by the bioconjugation of NMOF1 with anti-BSA (anti-bovine serum albumin). NMOF1/anti-BSA complex has been used for the sensing of BSA (bovine serum albumin) based on the fluorescence quenching phenomena. Estimated limit of detection of the proposed molecular probe is 7 mg/mL. © 2014 Elsevier B.V.

Bayati M.R.,North Carolina State University | Joshi S.,Amity Institute of Nanotechnology | Molaei R.,North Carolina State University | Narayan R.J.,North Carolina State University | Narayan J.,North Carolina State University
Journal of Applied Physics | Year: 2013

We have demonstrated dark hydrophilicity of single crystalline rutile TiO2(100) thin films, in which rapid switching from a hydrophobic to a hydrophilic surface was achieved using nanosecond excimer laser irradiation. The TiO2/YSZ/Si(001) single crystalline heterostructures were grown by pulsed laser deposition and were subsequently irradiated by a single pulse of a KrF excimer laser at several energies. The wettability of water on the surfaces of the samples was evaluated. The samples were hydrophobic prior to laser annealing and turned hydrophilic after laser annealing. Superhydrophilic surfaces were obtained at higher laser energy densities (e.g., 0.32 J.cm -2). The stoichiometries of the surface regions of the samples before and after laser annealing were examined using XPS. The results revealed the formation of oxygen vacancies on the surface, which are surmised to be responsible for the observed superhydrophilic behavior. According to the AFM images, surface smoothening was greater in films that were annealed at higher laser energy densities. The samples exhibited hydrophobic behavior after being placed in ambient atmosphere. The origin of laser induced wetting behavior was qualitatively understood to stem from an increase of point defects near the surface, which lowered the film/water interfacial energy. This type of rapid hydrophobic/hydrophilic switching may be used to facilitate fabrication of electronic and photonic devices with novel properties. © 2013 American Institute of Physics.

Jain C.,Amity Institute of Nanotechnology | Mukund V.,Amity Institute of Nanotechnology | Kaur M.,Bhabha Atomic Research Center | Ganapathi K.,Bhabha Atomic Research Center | And 4 more authors.
AIP Conference Proceedings | Year: 2010

Hierarchical heterostructures consisting of W18O49 nanowires grown on CuO nanowires have been prepared and studied for their gas sensing properties. SEM images show that W18O49 initially grow as an shell over core CuO nanowire with protusion like branches whose thickness depends on oxygen partial pressure. These CuO:W18O 49 structures were dielectrophoretically isolated and studied for their gas sensing properties. The results show potential of use of tailored hierarchical heterostructures for the fabrication of gas sensors. © 2010 American Institute of Physics.

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