ZnOナノロッドの水中結晶光合成と光・電子特性 [全文の要約]

この博士論文全文の閲覧方法については、以下のサイトをご参照ください。https://www.lib.hokudai.ac.jp/dissertations/copy-guides

Luminescence properties of ZnO-M heterostructures fabricated by galvanic-submerged photosynthesis of crystallites

By adapting hetero-nanostructures in optoelectronic device, a prominent luminescence characteristic can be obtained. The challenge is to engineer the band bending if a semiconducting surface gets contact with a metal. A galvanic replacement method is versatile for bimetallic hetero-nanostructures synthesis. However, the nanostructures morphologies can be varied depending on the metals pair or their supporting template. In this study, we demonstrate a facile 1-D ZnO nanorods (NRs) growth fabricated by galvanic replacement reactions. Without using bimetallic solution, the galvanic replacement reaction was implemented by joining Zn metal to Au, Pt, Ag, Cu, W, and Ni metals substrate. The luminescence properties of ZnO NRs were characterized by photoluminescence (PL) and cathodoluminescence in scanning transmission electron microscopy (STEM-CL). Based on PL analysis result, oxygen vacancy (V-O) was responsible for the visible light region emission in all ZnO-M samples. Then, STEM-CL analysis highlighted the presence of zinc interstitial (Zn-i) at the interface of ZnO-M. Due to band bending, interaction between V-O and Zn-i resulted the formation of zinc antisite (Zn-O) at the interface. There was no shift in visible light emission of the NRs due to Fermi-level pinning. The findings will be useful for future large-scale synthesis and engineering of hetero-nanostructures luminescent devices

Fabrication of Iron Oxide Nanoparticles via Submerged Photosynthesis and the Morphologies under Different Light Sources

Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO and CuO nanostructures have been successfully fabricated via this method. In this work, the SPSC process was applied for the fabrication of iron oxide and hydroxide nanoparticles. The experiments were conducted under visible light, ultraviolet light, and gamma-ray irradiation conditions and the morphologies of the obtained nanoparticles were observed and compared with that obtained without illumination. Then, the mechanism of the SPSC process for the fabrication of iron oxide nanoparticles was discussed. The results show that various kinds of morphologies of nanocrystallites were obtained on the Fe plate surface and the main morphologies are different under different conditions. For example, most FeOOH with the morphologies of nanorod and nanofiber exist by visible light irradiation; most faceted crystals of FeOOH and Fe2O3 with the morphologies of nanograular and nanorod exist by ultraviolet irradiation. In the SPSC process, light irradiation generates center dot OH at the crystal tips and promote the crystallization in apical growth of FeOOH

Galvanic-submerged photosynthesis of crystallites: Fabrication of ZnO nanorods@ Cu-surface

In this study, we report a facile fabrication method of 1-D ZnO nanorods (NRs) on a copper substrate surface by means of galvanic contact reactions. Instead of using bimetallic aqueous solution for the galvanic reactions, UV illumination on the Zn contacted with Cu surface in pure water environment was implemented, leading to galvanic combined submerged photo-synthesis of crystallites (G-SPSC) process. A pencil-like and flat-tip shape of NRs growth can be controlled as a function of UV irradiation time. In order to grow fine NRs, the galvanic process was essential for Zn2+ and OH-ions production. In particular, OH-accumulated at the vicinity surface of Cu to achieve a locally alkaline environment. Then, UV irradiation assisted the ZnO NRs initiated by water splitting process. Oxygen vacancy (V-O) was responsible for the growth of pencil-like shape NRs. A blue shift in visible light region of photoluminescence (PL) spectra was observed when the pencil-like NRs transformed into flat-tip shape. The successful heterojunction of ZnO-Cu also was observed in their PL spectra, which dictated by the formation of zinc antisite (ZnO). The G-SPSC method approach is versatile for other bimetallic system adaptation and is promising for large-scale environmentally friendly synthesis of optoelectronic devices

Synthesis of stainless steel nanoballs via submerged glow-discharge plasma and its photocatalytic performance in methylene blue decomposition

Stainless steel nanoparticles or 'nanoballs' have been synthesised using submerged glow-discharge plasma. Transmission electron microscopy showed that the nanoballs are uniformly spherical and size distribution estimation showed that their diameters are below 200nm. The decomposition of methylene blue solution under ultraviolet light with the wavelength of 354nm was observed in the presence of stainless steel nanoballs. A mixture of stainless steel nanoballs and 0.1% methylene blue dye was irradiated with ultraviolet light. The concentration of methylene blue was reduced to baseline level in 72hours. This shows that the stainless steel nanoballs have photocatalytic ability. In stainless steel nanoballs, methylene blue showed two different decomposition pathways; showing fast and slow reactions. Also, methylene blue was oxidised into sulphoxide before reducing into lighter by-products. X-ray diffraction analysis has shown that the nanoballs consist of Fe2O3 and Cr2O3, which are photocatalytically active species

The origin of opto-functional enhancement in ZnO/CuO nanoforest structure fabricated by submerged photosynthesis

Semiconductor hetero-nanostructures are of great interest for practical industry use. In this report, we demonstrated ZnO/CuO nanoforest (NFRs) fabricated by galvanic submerged photo-synthesis (G-SPSC) method, which utilizes light illumination in pure water without additives. For the first time, we elucidated the origin of its enhanced opto-functional properties. At the hetero-epitaxial interface, ZnO(001)/CuO(001) planes linkage were established, even though with 13.62 - 28.15% local lattice discrepancies along the c axis. Formed under Zn rich condition and photo-induced {110} ZnO surface, the NFRs exhibited photoluminescence emissions at 450 nm and 650 nm, due to zinc interstitial (I-Zn) and oxygen vacancies (V-O). Ternary oxide of ZnCuO2 was discovered. The interface exhibited significant emission at 650 - 700 nm and absorbance at 450 - 500 nm. On the basis of STEM-VEELS spectra and ab initio calculations, electrons occupancy at Cu 3p was responsible for 2.0 eV peak of the interface absorption coefficient. In particular, an interface dipole under interface-induced gap states (IFIGS) was clarified, caused by quasi defects zinc antisite (Zn-O). This led to an incommensurate charge density (ICCD) for a coherent ZnO(001)/CuO(001) interface. This is the origin for the opto-functional enhancement of the ZnO/CuO NFRs, where a maximum 12% IPCE at 550 nm, a 20% increase from similar NFRs morphology was demonstrated. Our results indicated a promising method and strategy for novel hetero-epitaxial nanostructures fabrication in the field of optoelectrical devices. (C) 2021 The Author(s). Published by Elsevier Ltd