Speaker
Description
Total-reflection high-energy positron diffraction: Principle and application
Yuki Fukaya$^{1}$
$^{1}$Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Naka, Ibaraki 319-1195, Japan
This study reports the principle of total-reflection high-energy positron diffraction (TRHEPD) method and its application to structure determination of two-dimensional (2D) materials [1,2].
The TRHEPD method is surface-sensitive due to the total reflection of positrons, antiparticles of electrons [1,2]. Unlike electrons, positrons experience a positive crystal potential, causing a positron beam incident at a grazing angle to be totally reflected at the crystal surface. The critical angle for total reflection can be estimated using Snell's law; for example, 2.0$^{\circ}$ for the Si(111) surface with a 10 keV positron beam. The positron beam penetrates less than approximately 1 $\mathrm{\mathring{A}}$ in the total reflection region, corresponding to the thickness of a single atomic layer. Therefore, the positron beam selectively probes the topmost surface layer, making TRHEPD highly useful for determining the structures of surface superstructures and 2D materials like graphene.
This presentation will discuss the origin of positron beam's surface sensitivity, along with recent results on intercalated graphene [3] and bismuthene (Bi counterpart of graphene) [4] obtained using the TRHEPD method.
References
[1] Y. Fukaya, A. Kawasuso, A. Ichimiya, and T. Hyodo, J. Phys. D: Appl. Phys. 52, 013002 (2019).
[2] “Chapter 4: Diffraction: Determination of Atomic Structure”, MONATOMIC TWO-DIMENSIONAL LAYERS: Modern Experimental Approaches for Structure, Properties, and Industrial Use, edited by I. Matsuda (Elsevier, 2018) p. 75-111.
[3] Y. Fukaya, S. Entani, and S. Sakai, Phys. Rev. B 108, 155422 (2023).
[4] Y. Fukaya et al., to be submitted.
