A two-stage data-analysis method for total-reflection high-energy positron diffraction (TRHEPD)

sim-trhepd-rheed -- Open-source simulator of total-reflection high-energy positron diffraction (TRHEPD) and reflection high-energy electron diffraction (RHEED)

The present paper reports sim-trhepd-rheed (STR), an open-source simulator of total-reflection high-energy positron diffraction (TRHEPD) and reflection high-energy electron diffraction (RHEED) experiments which are used for atom-scale surface structure determination of a material. The STR simulator is used for the analysis of experimental diffraction data by simulating the rocking curve from a given trial surface structure by solving the partial differential equation of the dynamical quantum diffraction theory for positron or electron wavefunctions. Using the obtained surface structure, electr…

Development of data-analysis software for total-reflection high-energy positron diffraction (TRHEPD)

The present paper reports on the recent activity of the data analysis software development for total-reflection high-energy positron diffraction (TRHEPD), a novel experimental technique for surface structure determination. Experiments using TRHEPD are being conducted intensively at the Slow Positron Facility, Institute of Materials Structure Science, High Energy Accelerator Research Organization, revealing surface structure of interest. The data analysis software provides a solution to the inverse problem in which the atomic positions of a surface structure are determined from the experimental…

Data-driven sensitivity analysis in a total-reflection high-energy positron diffraction (TRHEPD) experiment of the Si$_4$O$_5$N$_3$ / 6H-SiC (0001)-($\sqrt{3} \times \sqrt{3}$) R30$^\circ$

The present article proposes a data analysis method for experimentally-derived measurements, which consists of an auto-optimization procedure and a sensitivity analysis. The method was applied to the results of a total-reflection high-energy positron diffraction (TRHEPD) experiment, a novel technique of determining surface structures or the position of the atoms near the material surface. This method solves numerically the partial differential equation in the fully-dynamical quantum diffraction theory with many trial surface structures. In the sensitivity analysis, we focused on the experiment…

Data-analysis software framework 2DMAT and its application to experimental measurements for two-dimensional material structures

An open-source data-analysis framework 2DMAT has been developed for experimental measurements of two-dimensional material structures. 2DMAT offers five analysis methods: (i) Nelder-Mead optimization, (ii) grid search, (iii) Bayesian optimization, (iv) replica exchange Monte Carlo method, and (v) population-annealing Monte Carlo method. Methods (ii) through (v) are implemented by parallel computation,which is efficient not only for personal computers but also for supercomputers.The current version of 2DMAT is applicable to total-reflection high-energy positron diffraction (TRHEPD), surface X-ra…

利用全反射高能正电子衍射测定氢插层准自由站立单层石墨烯与6H-SiC(0001)之间的间距

Determination of the Spacing Between Hydrogen-Intercalated Quasi-Free-Standing Monolayer Graphene and 6H-SiC(0001) Using Total-Reflection High-Energy Positron Diffraction

本文利用全反射高能正电子衍射结合动力学衍射理论摇摆曲线分析，精确测定了氢插层准自由站立单层石墨烯与6H-SiC(0001)衬底的间距为4.18(6)Å，结果与已有DFT计算高度吻合。

Structure of Superconducting Ca-intercalated Bilayer Graphene/SiC studied using Total-Reflection High-Energy Positron Diffraction

We have investigated the atomic structure of superconducting Ca-intercalated bilayer graphene on a SiC(0001) substrate using total-reflection high-energy positron diffraction. By comparing the experimental rocking-curves with ones calculated for various structural models using a full-dynamical theory, we have found that Ca atoms are intercalated in the graphene-buffer interlayer, rather than between the two graphene layers. From transport measurements, the superconducting transition was observed to be at Tc_onset = 4K for this structure. This study is the first to clearly identify the relation…