An important task of studying the properties of modern materials is to study the surface, including determining the atomic and electronic structure of solid. A special place is occupied by 2D materials where the surface structure determines the properties of the material, such as topological insulators and other low-dimensional systems. Topological insulators, because of the special properties of the topologically protected surface, are promising materials for creating spintronic devices. In this regard, the knowledge of the atomic surface is an actual issue that requires the use of structural methods.
Among the methods that allow to obtain information about the structure of the local environment, we can distinguish the method of X-Ray photoelectron diffraction (XPD). Photoelectrons are generated by x-ray photons, creating an internal source of electrons inside the sample, and therefore the technique is sensitive to the type of atom. Core-level electrons have a high probability of being located in the inner part of the potential, and they can be considered as a source of localized monochromatic electron waves propagating from the center of the potential. Combined use with the method of photoelectron holography allows to obtain high-quality results of reconstruction of the atomic position.
Although it is possible to obtain diffraction patterns on laboratory electronic spectrometers, the use of synchrotron radiation has a number of advantages. First, synchrotron radiation can range from low energies (less than 100 eV) to several keV. This implements to perform photoelectron diffraction with scanning by energy (energy-scanned XPD), diffraction with scanning by angle (angle-scanned XPD), as well as angle-scanned XPD at different energies. Second, the photon flux must be high enough to accumulate a large number of points in the angular and energy spaces.
This paper presents the results of using synchrotron radiation to implement the method of X-Ray photoelectron diffraction on the surfaces of topological insulators - bismuth chalcogenides. The experiments were performed at the Bessy II synchrotron center on the U49-2 PGM1 line using p-polarization. The obtained experimental diffraction patterns are applied in the photoelectron holography method to reconstruct the surface atomic structure of solid.
The reported study was funded by RFBR, project number 19-29-12061 and was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Spin” No. АААА-А18-118020290104-2).