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Decoding the structure of interfaces and impurities in 2D materials by photoelectron holography
摘要： The properties of atomically thin materials essentially depend on their structures, including impurities, defects and interfaces with underlying substrates. Thus, the detailed structural information is relevant for creation of 2D materials with desired properties. Here, we explore the capabilities of photoelectron diffraction and holography for structural analysis of atomically thin layers using as examples such systems as h-BN, graphene, and modified graphene with boron impurities. We show that for planar 2D crystals with commensurate interface to the substrate, it is possible to visualize the interface and impurities with high spatial resolution, and to distinguish possible non-equivalent structural units. Our approach applied to B-doped graphene on Ni(1 1 1) and Co(0 0 0 1) surfaces has allowed to reveal asymmetry of boron concentrations in the two carbon sublattices and established its dependence on the applied synthesis procedure and chosen substrate. The obtained results suggest that such approach can be widely applied for studies of various 2D systems, where the structures of interfaces and defects are of remarkable importance.
关键词： doping,structure,photoelectron diffraction,graphene,hexagonal boron nitride,photoelectron holography
更新于2025-09-19 17:13:59
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Data processing for atomic resolution holography
摘要： In photoelectron holography, the intensity of the angular distribution of photoelectrons is measured to obtain a hologram. Thus, a hologram can be defined as a function on a sphere. X-ray fluorescence holography is similar to photoelectron holography. In this study, we describe methods for representing spherical functions that are suitable for atomic resolution holography, and the theory of conversion from the coordinate system of measurement to the various projections. We describe methods for rotational transformations and symmetry operations for atomic resolution hologram and the image composition from measured hologram fragments. In addition, several ways to remove the background from the raw hologram data are discussed.
关键词： atomic resolution holography,photoelectron holography,X-ray fluorescence holography,background removal,spherical functions,symmetry operations,rotational transformations,image composition
更新于2025-09-16 10:30:52
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[IEEE 2019 19th International Workshop on Junction Technology (IWJT) - Kyoto, Japan (2019.6.6-2019.6.7)] 2019 19th International Workshop on Junction Technology (IWJT) - Three-dimensional dopant imaging in semiconductor crystals using photoelectron holography with chemical state identification
摘要： Doping is an important technology for modern science. For example, to create a semiconductor device, a circuit is formed by controlling carriers by doping. It is important to search for appropriate conditions since the carrier emission from dopant differs depending on the doping conditions. The atomic arrangement around the dopant differs depending on the conditions. Therefore, it has been desired to observe the atomic arrangement around the dopant, but it has been difficult with conventional measurement methods. The resolution holography such as photoelectron atomic holography, x-ray fluorescence holography, neutron holography, which are methods that can measure the three-dimensional (3D) atomic arrangement of the dopant. Among them, photoelectron holography can measure the atomic structure of each dopant depending on the chemical state. We have built photoelectron holography apparatuses at BL25SU in SPring-8. We also developed a software platform 3D-AIR-IMAGE for data processing, simulation of photoelectron holograms, and 3D atomic image reconstruction.
关键词： photoelectron holography,doping,semiconductor,chemical state identification,3D atomic arrangement
更新于2025-09-16 10:30:52
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Photoelectron holography from multiple-return backscattering electron orbits
摘要： We theoretically investigate the photoelectron momentum distributions of a diatomic molecule in a linearly polarized two-color laser ?eld by solving the time-dependent Schr?dinger equation. An upward curvature interference pattern is found in the two-dimensional photoelectron momentum spectra. Resorting to a simple semiclassical analysis and the strong-?eld approximation theory, we show that the interference pattern corresponds to a holographic pattern from the second-return backscattering electron orbits and, furthermore, the underlying physics of the distinct observation of such interference pattern is revealed. The holographic patterns from the backscattering electron orbits with the different return times may encode the information of the target structure at different times after ionization.
关键词： strong-?eld approximation theory,backscattering electron orbits,time-dependent Schr?dinger equation,photoelectron holography
更新于2025-09-16 10:30:52
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Improved molecular structure retrieval method for photoelectron holography
摘要： Photoelectron holography is a method that retrieves molecular structure information from photoelectron diffraction patterns generated by x-ray free-electron lasers, which have the promise of following dynamic molecular structure evolutions with angstrom spatial and femtosecond temporal resolutions (the so-called molecular movie). However, an additional phase is introduced when the photoelectron is scattered by an atom, and this scattering phase turns into a spatial error when the position of the atom is retrieved using a Fourier-type transform. We propose a method to remove, or greatly suppress, this error, with demonstrations using numerical examples.
关键词： x-ray free-electron lasers,Fourier-type transform,molecular structure retrieval,scattering phase,photoelectron holography
更新于2025-09-12 10:27:22
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Enhances surface sensitivity of X-ray photoelectron holography through the example of Bi2Te3(111) surface
摘要： X-ray photoelectron holography (XPH) is new tool in surface science capable to visualize in real space coordination of the atom of interest (emitter). To study surface phenomena the ultimate and variable (in the range of 1-5 ML) surface sensitivity is needed. Here we discuss possibilities to improve surface sensitivity of XPH by the example of Bi2Se3 (111) surface where different coordinations of the same kind of atoms are present in different layers. To reach ultimate surface sensitivity we used both lower electron kinetic energy and partial analysis of hologram related to grazing angle photoemission. Using calculations of diffraction patterns based on EDAC code and reverse reconstruction of the real space within SPEA-MEM formalism we evaluate the contribution of each atomic layer into diffraction pattern and found that the surface relaxation could be directly visualised at the kinetic energy less than 100 eV, whereas the contribution of the second quintuple layer can be vanished at 200 eV or below. The same effect can be achieved by partial analysis of hologram at grazing detection angles more than 55° to the surface normal. This approach enables broader practical applications of the XPH to various materials in applied surface science.
关键词： surface structure,photoelectron holography
更新于2025-09-11 14:15:04