Synthesis And Characterization Of Zno Nanowires For Nanosensor Applications

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H2 of a gas nanosensor based on an individual ZnO nanowire is also reported. © 2010 Elsevier Ltd. All rights reserved

Heat-Mediated Transformation of PMMA-SiO2 Core-Shell Particles into Hollow SiO2 Particles

Changes in the morphology and structure of the core-shell particles of polymethyl methacrylate-silicon dioxide and hollow SiO2 particles during their heat treatment were studied by electron microscopy, infrared spectroscopy, and X-ray diffraction. The polymeric core of the PMMA-SiO2 hybrid particle was found to undergo an unusual transformation when exposed to the electron microscope beam: its shrinkage occurs through the formation of a spherical cavity. It was shown that the process of silica-shell formation occurs in the temperature range of 200–600 °C and is accompanied by the loss of vinyl- and OH-groups. It was determined by the method of X-ray diffraction, that in the place of the interaction of PMMA and the shell, the degree of ordering of the polymer is higher than that in the volume of the polymer core. It was shown that the frequency of the TO3-vibrational mode (asymmetric stretching vibrations of the Si–O–Si bonds) increases with an increase in the annealing temperature, which is associated with the densification of the silicon dioxide shell

Heat-Mediated Transformation of PMMA-SiO₂ Core-Shell Particles into Hollow SiO₂ Particles

Changes in the morphology and structure of the core-shell particles of polymethyl methacrylate-silicon dioxide and hollow SiO2 particles during their heat treatment were studied by electron microscopy, infrared spectroscopy, and X-ray diffraction. The polymeric core of the PMMA-SiO2 hybrid particle was found to undergo an unusual transformation when exposed to the electron microscope beam: its shrinkage occurs through the formation of a spherical cavity. It was shown that the process of silica-shell formation occurs in the temperature range of 200–600 °C and is accompanied by the loss of vinyl- and OH-groups. It was determined by the method of X-ray diffraction, that in the place of the interaction of PMMA and the shell, the degree of ordering of the polymer is higher than that in the volume of the polymer core. It was shown that the frequency of the TO3-vibrational mode (asymmetric stretching vibrations of the Si–O–Si bonds) increases with an increase in the annealing temperature, which is associated with the densification of the silicon dioxide shell

Luminescence of high - temperature yttrium - based superconductors

Luminescense spectra of thin films and single crystals of YBa2Cu3O7−x high-temperature superconductors were measured under optical excitation by synchrotron radiation (E = 10.2 eV) and by electrons (cathodoluminescence) with an energy of 6 keV. It has been shown that in all the spectra the main contribution is made by a blue band with an energy of ≈2.9 eV, which is, apparently, the luminescence inherent to the crystal. The time characteristics of luminescence were measured. It turned out that 80% of all the luminescence requires a very long time (τ > 10−6 s) to reach its final level.A model of luminescence appearance is proposed, which is based on luminescence of oxygen quasi-molecules formed by the decay of electronic excitations (luminescence of self-localized and defect-localized excitons)