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IR Laser CVD OF Nanodisperse Ge-Si-Sn Alloys Obtained by Dielectric Breakdown of GeH4/SiH4/SnH4 Mixtures
Křenek, Tomáš ; Bezdička, Petr ; Murafa, Nataliya ; Šubrt, Jan ; Pola, Josef
Nowadays, great attention is devoted to Ge-Si-Sn ternary system, because Si1-x-yGexSny provides the potential of band gap engineering and tuning of the optical properties. IR laser irradiation of equimolar gaseous GeH4 + SiH4 + SnH4 + Ar mixture results in simultaneous decomposition of all three compounds and it allows deposition of nanostructured solid film. Analysis of the films by FTIR and Raman spectroscopy, X-ray diffraction analysis and electron microscopy revealed crystalline nanobodies of pure beta-Sn and crystalline nanoobjects of Ge1-x-ySixSny embedded in an amorphous metastable Ge-Si-Sn alloy. This process allows co-decomposition of all silicon, germanium and tin hydrides which is caused by combination of infrared multiple photon dissociation of absorbing silane and currently proceeding LIDB. This is followed by intermixing/clustering of extruded metal atoms in the gas phase.
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Microstructure and performance of titanium oxide coatings sprayed by oxygen-acetylene flame
Ctibor, Pavel ; Štengl, Václav ; Zahálka, F. ; Murafa, Nataliya
TiO2 nano-powders were agglomerated by a spray drying process for applying to thermal spraying. A conventional oxygen-acetylene flame torch was used to deposit porous partially nanostructured TiO2 coatings. Steel substrates were used as a support for tested samples. Scanning Electron Microscopy, X-ray microanalysis and X-ray diffraction were performed to study the morphology and the crystalline phases of the titania coatings. Optical bandgap and kinetics of the acetone decomposition was studied too. The best results were obtained for the powder which is available as a commercial spray feedstock. This powder seems to be most resistant against the reducing atmosphere in the jet of combustive gasses.
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Photocatalytic niobium and tantallum doped monodispersed nanoparticles of titania for visible-ligt applications
Štengl, Václav ; Houšková, Vendula ; Bakardjieva, Snejana ; Murafa, Nataliya
Niobium or tantalum doped anatase were prepared by thermal hydrolysis of peroxotitanium complex aqueous solutions dissolving niobium or tantalum peroxo-comples at 100 degrees C for 3 days The synthesized samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), surface area (BET) and porosity determination (BJH) The photocatalytic activity of doped titania samples was determined by decomposition of salicylic acid during irradiation at 365 nm and 400 nm Niobium-doping caused the increase of unit cell constants of anatase and the shape change of anatase crystallites from spindle-like to cubic-like structure. The niobium and tantalum doping increases the stability of anatase to above 1000 degrees C by inhibiting the growth of Mania crystallites.
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Synthesis of Ru-doped titania and its photocatalytic properties
Houšková, Vendula ; Štengl, Václav ; Murafa, Nataliya ; Bakardjieva, Snejana
rystalline Mania particles doped with ruthenium oxide have been prepared by homogenous hydrolysis of TiOSO4 in aqueous solutions in the presence of thioacetamide and RuCl3 at 80 degrees C After annealing at 600 degrees C in oxygen atmosphere for 2 hours the synthesis of the Ru-doped Mania powders was complete The effects of the Ru doping on the morphology and microstructure of TiO2 nanoparticles and their impacts on the photocatalytic activity were studied The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Nitrogen adsorption-desorption was used for surface area (BET) and porosity determination (BM) The photocatalytic activity of Ru-doped mania samples was determined by photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 nm and 400 nm wavelength The Ru-doped Mania samples demonstrated enhanced photocatalytic activity under UV and visible light.
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