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- Broitman, Esteban, 1958-, et al.
(författare)
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Comparative study on the properties of ZnO nanowires and nanocrystalline thin films
- 2012
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 213, s. 59-64
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural, morphological, optical and water-adsorption properties of nanocrystalline ZnO thin films and ZnO nanowires were studied and compared. The ZnO thin films were obtained by a sol–gel process, while the ZnO nanowires were electrochemically grown onto a ZnO sol–gel spin-coated seed layer. Thin films and nanowire samples were deposited onto crystalline quartz substrates covered by an Au electrode, able to be used in a quartz crystal microbalance. X-ray diffraction measurements reveal in both cases a typical diffraction pattern of ZnO wurtzite structure. Scanning electron microscopic images of nanowire samples show the presence of nanowires with hexagonal sections, with diameters ranging from 30 to 90 nm. Optical characterization reveals a bandgap energy of 3.29 eV for the nanowires and 3.35 eV for the thin films. A quartz crystal microbalance placed in a vacuum chamber was used to quantify the amount and kinetics of water adsorption onto the samples. Nanowire samples, which have higher surface areas than the thin films, adsorb significantly more water.
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- Marotti, R.E., et al.
(författare)
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Characterization of ZnO and ZnO : Al thin films deposited by the sol–gel dip-coating technique
- 2008
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 517:3, s. 1077-1080
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline zinc oxide films have been obtained by the sol–gel process. The films were deposited from precursor solutions by dip-coating on quartz substrates, and subsequently transformed into nanocrystalline pure or aluminium-doped ZnO films after a thermal treatment. The film microstructure and composition characterization was studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical properties were studied by transmittance spectroscopy. The water adsorption energy was measured by temperature programmed desorption (TPD) in the range 90–700 K. The optical transmittance in the UV region gives bandgap energy values of 3.27 eV for undoped samples, and higher than 3.30 eV for the Al-doped ones. The increase in bandgap energy in Al-doped samples may be explained by band-filling effects. The band edge absorption coefficient increases monotonically for the Al-doped samples but has a shoulder for the undoped ones, which may be assigned to room-temperature excitonic absorption.
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- Riveros, G, et al.
(författare)
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Single-step electrodeposition of polycrystalline CdSe microwire arrays : structural and optical properties
- 2008
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Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - : Springer Berlin/Heidelberg. - 0947-8396. ; 90:3, s. 423-430
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report on the single-step synthesis of CdSe microwires with good crystalline characteristics by template-assisted electrochemical deposition from an electrolytic solution containing CdSO4Ce+CeSeO2 and sulfuric acid. Deposition was conducted at three different temperatures (25 degrees C, 60 degrees C and 80 degrees C) under potentiostatic control using a commercial nanoporous alumina membrane as the working electrode. The best results were obtained when the electrodeposition was carried out at E=-0.610 V vs. Ag/AgCl and T=80 degrees C. Under these experimental conditions, the microwires are uniform, well aligned, have a high packing density, and present a good crystalline character according to XRD analysis. TEM observations revealed that they are dense and continuous, with a mean diameter ranging from 360-380 nm, greater than the channel diameters of the alumina template used. A detailed study of the reflectance in the region close to CdSe bandgap energy allows the determination of a weak direct absorption edge at 1.65 eV, close to the bulk bandgap energy. The Raman spectra consist of a strong mode centered at 208 cm(-1) arising from the LO phonon and a somewhat weak, but still strong, mode arising from the second order LO (2LO) appearing at 415 cm(-1)
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