Electrochemically Grown ZnO Vertical Nanowire Scintillator with Light‐Guiding Effect

Abstract

The <0001>-oriented ZnO vertical nanowires (vnws) have been prepared by electrochemical growth for the electric charge of 0.3, 0.7, and 1.5 Ccm À2 on a <0001>-Ga:ZnO/soda-lime glass substrate in an simple aqueous 0.8 mmol L À1 zinc nitrate hydrate solution. All the ZnO-vnws emitted strong ultraviolet light that originated from the recombination of a bound exciton and weak visible light due to native defects. The best performance regarding the intensity ratio and ultraviolet light intensity was obtained for the ZnO-vnws prepared for 0.7 Ccm À2 , and the performance changed depending on the electric charge. The ZnO-vnws also showed the best scintillator performance with the luminous efficiency of 8.3% and spatial resolution of 4 mm, and the scintillator performance was closely related to the light-guiding effects originating from the nanowire dimension in addition to the photoluminescence characteristic. ExperimentalZnO vertical nanowires were prepared by electrodeposition in an aqueous 0.8 mmol L À1 zinc nitrate hydrate solution at 333 K. The solution was prepared by using reagent grade chemical and distilled water purified by the Millipore Ellix-UV-Advantage system. The electrodeposition was carried out at a potential of À0.8 V referenced to the Ag/AgCl electrode for an electric charge from 0.3 to 1.5 Ccm À2 using the potentiostat (Hokuto Denko, M. Izaki, M. Kobayashi, T. Koyama

Preferred orientation of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene molecules on inorganic single-crystal substrates with various orientations

“…It was reported for inorganic semiconductors such as oxides that the lattice relationship including the lattice mismatch strongly affected the growth of the oxide layer, as demonstrated for the 〈0001〉-ZnO layer growth on 〈111〉-Au 28,29) and 〈0001〉-Ga:ZnO layers. 30,31) However, the atomic arrangement and lattice mismatch did not affect the growth of the C8-BTBT layer, and a similar preferred orientation was obtained regardless of the material and orientation. The C8-BTBT layer formed a continuous layer with the growth of the C8-BTBT island in the direction parallel to the substrate surface and then transferred to layerby-layer growth in the direction normal to the substrate surface in the case of the C-sapphire substrate.…”

Electrochemically Fabricated SrGa2S4:Eu/ZnO-Vertical Nanowire Bilayer Scintillator for X-ray Imaging

“…The best spatial resolution for the SrGa 2 S 4 :Eu (60 V-10 s)/ZnO-vnws bilayer scintillator was slightly larger than 5.4 μm estimated for the ready-made LuAG scintillator in the same manner. This is thought to be due to the light-guiding effect caused by the ZnO-vnws morphology functioning as an optical waveguide 12 which guided the radial light emitted by SrGa 2 S 4 :Eu into unidirectional light. However, the spatial resolution of the SrGa 2 S 4 :Eu/ZnO-vnws bilayer scintillator became larger as the thickness of the SrGa 2 S 4 :Eu layer increased which then remained almost constant at a corresponding thickness ratio of 1.9 to the ZnO-vnws layer with the SrGa 2 S 4 :Eu layer thickness over 10.3 μm.…”

“…On the other hand, SrGa 2 S 4 :Eu phosphor particles 8,9 can be stacked and adhered to a substrate by electrophoresis deposition without any binder, and the layer has been demonstrated to act as a scintillator for X-ray radiation. 10 Zinc oxide (ZnO) is an n-type semiconductor with a bandgap energy of 3.3 eV and an exciton binding energy of 59 meV, which vertical nanowires (ZnO-vnws) have also been attracting attention as a next-generation scintillator material, 11 due to the possession of waveguiding effect based on the morphology of ZnO-vnws, 12 although its luminescence intensity was lower than single-crystal scintillators such as LuAG and GAGG. The <001>-oriented ZnOvnws can be prepared by electrochemical reactions, [13][14][15] and the morphology of the length and width can be controlled by the solution formulation, and concentration of Cl impurity, which act as a donor in a ZnO semiconductor.…”

Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications

“…When compared to the planar crystal design, the scintillation light could be better guided through the nanorods in a nano array design, which leads to less scattering but high spatial resolution. For X-ray imaging applications requiring high spatial resolution, it has been shown by simulation and experiments that vertically aligned ZnO nanoarrays could help obtain high image quality and spatial resolution 9 – 13 . A nanoarray scintillator, which has additional light guiding reducing the scattering of X-ray generated optical photons as described above, could play a visible-light-converting role in the visible-light-converted type 2D-detector, which will be one of the main important components to affect image resolution 14 – 17 .…”