Host: The Japan Society of Vacuum and Surface Science
Name : Annual Meeting of the Japan Society of Vacuum and Surface Science 2023
Location : [in Japanese]
Date : October 31, 2023 - November 02, 2023
This talk reports the structure determination of two-dimensional (2D) materials fabricated on substrate surfaces using a positron beam.
Total-reflection high-energy positron diffraction (TRHEPD) is a surface structure analysis tool by utilizing the positive charge of the positron (Fig. 1) [1-4]. The positron, the antiparticle of the electron, has the same mass, elementary charge, and spin as the electron, but the positive charge, opposite to the electron. The crystal potential of every materials acts as a potential barrier to the positron beam. Especially at low grazing incidence, the total reflection occurs. The critical angle for total reflection can be estimated via Snell's law. For example, when a positron beam with an energy of 10 keV is incident on a Si surface, the critical angle corresponds to 2.0°. Under total reflection conditions, the penetration depth of the positron beam is less than approximately 0.5 Å, which is comparable to the thickness of one atomic layer. Thus, the spot intensities in the diffraction pattern under total reflection conditions contain information about the atomic configurations of the topmost layer only. Beyond the critical angle, the penetration depth of the positron beam gradually increases with increasing glancing angle. Hence, information about the underlying layers are involved in the spot intensities at higher glancing angles. Through rocking curve (spot intensity versus glancing angle) analysis including these glancing angle regions, TRHEPD enables to determine the atomic coordinates of 2D materials and the interface layer with the substrate.
In this talk, we will show the recent results of the structure determination of quasicrystal graphene [5] and intercalated graphene, together with the origin of the surface sensitivity of TRHEPD method.
References
[1] A. Ichimiya, Solid State Phenom. 28&29, 143 (1992).
[2] A. Kawasuso and S. Okada, Phys. Rev. Lett. 81, 2695 (1998).
[3] Y. Fukaya, A. Kawasuso, A. Ichimiya, and T. Hyodo, J. Phys. D: Appl. Phys. 52, 013002 (2019).
[4] Monatomic Two-Dimensional Layers: Modern Experimental Approaches for Structure, Properties, and Industrial Use, edited by I. Matsuda (Elsevier, Amsterdam, 2019).
[5] Y. Fukaya, Y. Zhao, H.-W. Kim, J. R. Ahn, H. Fukidome, and I. Matsuda, Phys. Rev. B 104, L180202 (2021).
