| 研究概要 |
This study aims to investigate the effect of high pressure on the properties and morphologies of nanoparticles (NPs) prepared via the laser ablation in liquid (LAL) technique. So far, no effect of environment pressure on product NPs was reported in detail, though LAL is gaining in popularity as a convenient preparative method.
The last year, we mainly investigated the effect of medium pressure on the ablation of Sn in CO2. In-situ shadowgraphy was used to study the temporal behavior of the ablated zone as it first emerged, then developed as a bubble-like structure (BLS), and finally collapsed. The produced NPs were also analyzed. The BLS was found to follow 4 independent phases: formation, expansion, shrinkage and final collapse. The BLS lifetime is shown to be pressure-dependent, being the longest near the density fluctuation ridge of the medium, i.e., at 8.8 MPa at 40 degrees Celsius (in case of CO2). The NP size was also the smallest in this pressure range. The results present, for the first time, experimental proof of the slower dynamics of the ablated zone near the medium density fluctuation maximum, which can be used in NP synthesis and processing. We demonstrate that via adjusting the medium conditions, the BLS lifetime can be used as another processing parameter. It exhibits a maximum around the pressure with density fluctuation maximum and has an impact on the product NPs, as their size distribution changes. This effect can be more profound in the systems where chemical reactions are also involved during NP formation, and therefore needs to be studied more.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Though some of the initial plans were slightly adjusted, the research is believed to proceed rather smoothly.
1) Two systems were already studied, both demonstrating the effect of pressure on the product properties (nanoparticle size and size distribution, optical properties, etc.).
2) Abnormalities or discontinuities in the properties of the products were observed at pressures close to the supercritical values of media, which may be used for future syntheses (especially upon more detailed investigations).
3) Two reports in peer-reviewed journals were already published (on results immediately relevant to this project), with several reports at scientific meetings (both domestic and international).
4) More interesting results are already being observed when the optical properties of ZnO nanomaterials prepared in different liquid media (and at different pressures) are being examined (the research being underway).
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| 今後の研究の推進方策 |
During the current year, we plan to continue the research related to the present project as follows (a part of the plans being already underway):
(1) Preparation of ZnO nanoparticles via laser ablation in different liquids (water, ethanol, water/ethanol, etc.). The materials will be prepared at different pressures, thus the effect of pressure will be studied in several systems. (2) Characterization of the prepared nanomaterials. A set of analytical techniques to be used: X-ray diffraction, transmission and scanning electron microscopy, photoluminescence and Raman spectroscopy, etc. The nanomaterials’ phase and chemical composition, morphology, size distribution and surface and bulk defects responsible for their optical properties will be studied. (3) Detailed and comprehensive study of the aging effect on the photoluminescent properties of ZnO nanomaterials. This is expected to provide valuable information on the stability and dynamics of defects in ZnO nanomaterials. So far, information on the stability of photoluminescence in nanostructured ZnO has been seldom reported. In this context, comparison of ZnO prepared via laser ablation in different liquids and at different pressures looks very promising. (4) Nanomaterials produced by ablating Sn in different liquids and at different pressures will also be attempted. Both ZnO and SnO2 nanomaterials are also planned to be doped (to modify their optical properties) or surface-modified in situ. The preparation of doped semiconducting nanomaterials via laser ablation in pressurized media has never been reported so far.
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