2023 Fiscal Year Research-status Report
Next generation XUV source for time-resolved nano-ARPES and PEEM
| Project/Area Number |
22K18270
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
Dani Keshav 沖縄科学技術大学院大学, フェムト秒分光法ユニット, 教授 (80630946)
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| Project Period (FY) |
2022-06-30 – 2025-03-31
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| Keywords | Extreme UV light source / High order / harmonic generation / XUV-PEEM / Nano-ARPES / Twisted 2D material / Moire pattern |
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| Outline of Annual Research Achievements |
The goal of this Kakenhi proposal is to develop a table-top XUV photon source with sufficient photon flux to enable time-, angle-, spectral-, and momentum-resolved photoemission spectroscopies with nanoscale spatial resolution. This fiscal year, we have continued to explore various methods to enhance photon flux. We discovered that meticulous gas management in and after the gas plasma interaction region is crucial for this improvement. Utilizing our XUV photon sources, we conducted several experiments using the photoemission microscope. Specifically, we examined and analyzed defects and electronic structures in hBN ferroelectric samples. Furthermore, we applied our XUV-PEEM technique to investigate the origin of mid-gap states in polycrystalline perovskite thin films. Additionally, we have started testing the beamline on a momentum microscope, which will be capable of performing TR-XUV-nano-ARPES.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The objectives of this research are: (A) to develop an XUV light source with photon flux density orders of magnitude higher than currently available; (B) to utilize this new light source for time-resolved PEEM and nano-ARPES measurements; and (C) to explore moire; structures and their excitons in 2D heterostructures. Up to now, we have made significant progress in all areas. Below is a summary of our achievements:
(A) Our XUV light source has achieved a spot size of 32 x 7 um and a flux density of up to 4 x 10^18 photons/sec/ cm^2, which is two orders of magnitude better than our previous light source (1 x 10^16 photons/sec/cm^2). In addition to optimizing phase matching and laser parameters, we found that effective gas management at and immediately following the gas plasma interaction region is crucial for improving photon flux.
(B) We have successfully performed XUV-PEEM with a spatial resolution better than 100 nm. We are now working on coupling the light source with a momentum microscope to conduct micro/nano-ARPES experiments.
(C) We have investigated defects and ferroelectric domain structures in twisted 2D materials and are currently writing up this manuscript. Additionally, we conducted experiments to study mid-gap defects in perovskite thin films using this XUV light source.
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| Strategy for Future Research Activity |
This year, we will continue to make progress on our three objectives:
(A) To further optimize the flux density of our XUV light source, we plan to investigate phase matching conditions under varying gas jet diameters, gas pressures, and laser fluences. Additionally, we intend to invest in an improved motorization setup and a new ellipsoidal mirror, which should help us achieve higher flux density.
(B) We will optimize and couple the XUV light source with a momentum microscope, which offers better energy resolution than the PEEM system we used previously. This enhancement will enable high-resolution TR-XUV-nano-ARPES experiments.
(C) With the new TR-XUV-nano-ARPES setup in place, we will focus on studying moire-localized excitons in various 2D heterostructures.
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| Causes of Carryover |
The motorization stage and the XUV focusing mirror are essential for obtaining tighter focus of the XUV beam, which will help us reach or excess the flux density we have planned in objective A. We planned to buy the motorization stage and the XUV focusing mirror in FY23, but had to postpone the purchase to FY24 due to the delivery deadline longer than expected and could not meet our procurement rules.
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