| 研究実績の概要 |
In the previous fiscal year, the synthesis process of high-quality dumbbell-shaped graphene nanoribbons (DS-GNR) of width less than 30-nm, the transfer process, and the fabrication of suspended DS-GNR structures on electrodes composed of two different metals (Pd and Ti) for the photovoltaic sensor architecture has been well-established. The device with a ribbon width of 30-nm DS-GNR showed a very superior photonic responsivity of about 5.5x10^3 (A/W) under irradiation of a focused beam of 532-nm. This value was comparatively larger than several others reported in various literature. In addition to this, the proposed method for controlling the effective bandgap of GNR after the fabrication process has also been established and validated in the previous fiscal year. Two devices of width 80-nm and 150-nm fabricated on a silicon substrate showed a clear change in the electronic properties under 3 different strain conditions with an observed gauge factor of about 1500. Under the irradiation of a focused laser beam of wavelength 635-nm, the device showed an improvement of about 4.5 times under applied strain as compared to an unstrained sample. These results confirmed the proposed method for controlling the effective bandgap of GNR structures, which is very novel and unique to this research.
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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
The research has made progress with expected pace. Even it can be said that it paced out relatively quicker than expected. The experiments has resulted in few breakthrough discoveries which require implementation of accurate interpretation of the current data, hence, the results haven't been reported in high-ranked academic journals at this stage. After careful evaluation and interpretation of the data, in this fiscal year, the data will be published in academic journals. I will be carrying out more experiments to confirm repeatability and reliability of the fabrication process and electronic performance of the device. So far, the fabrication process proves to be highly reliable, however, the electronic response is not repeatable due to several limitations such as edge effects of graphene, orientation of the ribbons, impurities that causes to change the doping level of graphene, surface charge effects on graphene, etc. The controllability of these effects is under research. In addition, the effects of tensile strain on the change in electronic band properties of graphene nanoribbon has been studied and validated as was proposed. As predicted by theoretical calculations, graphene nanoribbons showed very high responsivity to the change in effective applied strain. Due to the band opening in narrow width graphene nanoribbons, the photonic properties was drastically enhanced after applied mechanical strain.
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| 今後の研究の推進方策 |
In the future works, the current data will be published in high ranked academic journals. In addition, experiments will be carried out to further optimize and improve the efficiency of the device by applying hybrid heterostructures to the current structure to effectively separate electron hole pairs. The photonic response of the current device was observed to be very high, however, the photovoltaic efficiency was not exceptionally high. The potential is vast, which will be explored in this year. In addition, strain controlled effect has been studied on the graphene nanoribbon structures, however, in the current experiments, only tensile effect was studied. In future works, effect of compressive strain on the change in electronic properties of graphene nanoribbons will be carried out. The photovoltaic performance of the dumbbell-shaped graphene nanoribbon structures will be studied under the application of both tensile and compressive strain. This will give direction in plotting a calibration curve which will be an important tool in controlling and tuning the effective bandgap of graphene nanoribbon devices after the fabrication process. This year, high resolution TEM analysis, XPS analysis to measure the effective band gap, and AFM will be utilized in this research to create an in-depth evaluation and study on the fabricated nanoscale graphene nanoribbons. Finally, the results is expected to be reported in higher ranked academic journals.
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