2021 Fiscal Year Research-status Report
Fabrication and characterization of a single-VO2-nanoparticle electronic nano-switch device
| Project/Area Number |
20K15145
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| Research Institution | Hokkaido University |
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Principal Investigator |
Pin Christophe 北海道大学, 電子科学研究所, 助教 (50793767)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Mott transition / vanadium dioxide / nonlinear optical force / spin-orbit coupling / angular momentum / optical tweezers |
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| Outline of Annual Research Achievements |
Gold plasmonic nanostructures have been designed using COMSOL Multiphysics for the optical trapping and thermal control of non-fluorescent nanoparticles. Gold nanostructures with nanogap about 10 nm large have been fabricated by ebeam lithogrphy. However, VO2 nanoparticles were found to be repelled instead of being attracted by the localized, enhanced electric field in nanogap of plasmonic antenna. This unexpected behavior is probably due to the reversal of the optical force when the insulator-to-metal phase transition occurs.
Optical trapping of VO2 nanoparticles and microparticles was achieved using optical tweezers at 1064 nm wavelength. Due to the temperature-dependent nonlinear change of the VO2 properties induced by the insulator-to-metal phase transition, the particles are optically trapped away from the laser focus, describing a ring-shaped trajectory around the laser beam center. This result demonstrate a new optical trapping regime enabled by the VO2 phase transition.
VO2 particles trapped away from the electric field intensity maxima were used as probe particles to study the spin-to-orbital angular momentum conversion between the incident laser beam and the trapped particle. We demonstrated that a circularly polarized laser beam induces the orbital rotation of the trapped particles, and the rotation direction is controlled by the spin angular momentum of the incident light.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
Due to the global pandemic of covid19 and lab management duties, experimental work has been slightly delayed, but both numerical and experimental results have been obtained. The nonlinear optical trapping phenomena caused by the phase transition of VO2 were unexpected and also explain the delay of the initial research project. However, those unexpected results are significant and original. The study of the optical trapping of VO2 particles and the spin-orbit angular momentum coupling between the light and the trapped particles has become the new research goal. Significant progress has been made towards this goal, preliminary results have been reported in oral presentations at international conferences, and experiments using structured laser beams are ongoing to prepare a research article.
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| Strategy for Future Research Activity |
Due to the difficulty of trapping VO2 nanoparticles using gold plasmonic nanostructures, different techniques will be investigated, such as photothermal printing of nanoparticles induced by the Marangoni flow near a laser-induced bubble, thermophoresis, or dielectrophoresis. Another option under investigation is the laser-induced hydrothermal synthesis of VO2. After formation of a VO2 nanojunction between two gold nanostructures (electrodes), the electrical properties of the device will be measured.
Based on our results, the nonlinear optical forces acting on VO2 particles will be further studied. The phase of the trapped particles, the influence of the phase transition hysteresis on the trapping potential, and the interaction between simultaneously trapped particles will be investigated.
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| Causes of Carryover |
Due to the global pandemic of covid19 and lab management duties, the experimental work has been slightly delayed. In addition, some unexpected results were obtained that added difficulty to achieve the initial goal of the research project. Based on those unexpected results, a new research goal was introduced and the research work was performed accordingly. The remaining research budget will be used during the new fiscal year to pursue the ongoing research work and investigate new techniques in order to achieve the initial goal of this research project.
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