Development of a low-energy positron diffraction (LEPD) station and its application to surface structure determination of spintronic heavy-element 2D materials

Research Project

Project/Area Number	23K17150
Research Category	Grant-in-Aid for Early-Career Scientists
Allocation Type	Multi-year Fund
Review Section	Basic Section 80040:Quantum beam science-related
Research Institution	High Energy Accelerator Research Organization
Principal Investigator	Ahmed Rezwan 大学共同利用機関法人高エネルギー加速器研究機構, 物質構造科学研究所, 博士研究員 (90900291)
Project Period (FY)	2023-04-01 – 2026-03-31
Project Status	Granted (Fiscal Year 2023)
Budget Amount *help	¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000) Fiscal Year 2025: ¥390,000 (Direct Cost: ¥300,000、Indirect Cost: ¥90,000) Fiscal Year 2024: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000) Fiscal Year 2023: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
Keywords	positron diffraction / surface / lepd / 2D materials / ultra-high vacuum
Outline of Research at the Start	We will upgrade the new Low-energy positron diffraction (LEPD) experimental station at the slow positron facility in KEK. The purpose is to enable accurate surface structure determination and create an environment to easily transfer the sample to other beamlines for other surface characterization.
Outline of Annual Research Achievements	Research purpose is to build and establish a low-energy positron diffraction (LEPD) ultra-high vacuum (UHV) experimental station at KEK for the accurate determination of surface atomic structures. Although theoretically LEPD has shown interesting phenomenon for accurate surface structure determination but experimentally not verified. Last fiscal year we prepared the experimental station which has enabled to conduct actual LEPD experiments for surface structure determination. We conducted the 1st experiment on Cu(001) surface and showed that the LEPD diffraction pattern is much more simple and portraying sharper Bragg peaks which gave much improved agreement with the theoretical data. Now we have the plan to accurately determine complex 2D atomic structures using the new LEPD station.
Current Status of Research Progress	Current Status of Research Progress 2: Research has progressed on the whole more than it was originally planned. Reason We have built the LEPD experimental station and conducted our first experiment on Cu(001) surface. We have obtained a very simple LEPD diffraction pattern which signifies less multiple scattering with sharper and simple Bragg peaks compared to the conventional low-energy electron diffraction (LEPD). We have also checked the multi-probe experimental facility in our system where we successfully transferred the clean Cu(001) sample from LEPD station to beamline-13B for ARPES measurement. Now we can do multi-beam experimental analysis for determining the surface and its band structure. The intensity of positrons obtained from linac in KEK showed some fluctuations during the experiment due to some connection fault of the magnetic coils. Later it was identified and the operation is now smooth.
Strategy for Future Research Activity	In this research my plan is to determine the 2D structure of Pb atoms (plumbene) on Pd(111) surface. Plumbene shows very interesting physical characteristics so accurate structure determination is necessary. Pb is a heavy atom (higher atomic number) which shows complex scattering factor and difficult to be determined by conventional LEED analysis. We already successfully prepared Cu(001) sample and determined the structure very accurately and showed that LEPD has simple diffraction curve with less multiple scattering. Therefore we want to prepare the plumbene on Pd(111) surface at the preparation chamber and determine the surface structure using LEPD. Later we want to transfer the prepared sample using portable UHV chamber to the beamline 13B in PF for ARPES measurement.