Paradoxically a very broad diffraction background, named the Bell-Shaped-Component (BSC), has been established as a feature of graphene growth. Recent diffraction studies as a function of electron energy on Gr/SiC have shown that the BSC is not related to scattering interference. The broad background is in-phase with the Bragg component of both the (00) and Gr(10) spots. Instead textbook diffraction states it should be out-of-phase since it should originate from destructive interference between adjacent terraces[1]. Additional experiments were carried out as a function of temperature over the range 1200° C-1300° C that single-layer-graphene (SLG) grows. Quantitative fitting of the profiles shows that the BSC follows the increase of the G(10) spot, proving directly that the BSC indicates high quality graphene[2]. The BSC has been also seen in graphene on metals including Gr/Ir(111) and on h-BN/Ir(111)[3,4]. Its presence in such a wide range of 2-materials suggests its origin must be general and fundamental, related to their unusual single layer uniformity. The BSC can be a diagnostic of high quality in the growth of other 2-d materials. One possible explanation of the BSC relates to electron confinement within a single uniform layer, according to the uncertainty principle, which generates spread in their wavevector as confirmed with ARPES[5]. The transfer of the large momentum spread to the diffracted electrons to generate the BSC requires better theoretical understanding of the graphene electron-beam electron interaction.

Work in collaboration with P. A. Thiel (deceased), S. Chen, E. Conrad, M. Horn von Hoegen, M. Petrovic, F.-J. Meyer zu Heringdorf

[1] S. Chen, et al. Phys. Rev. B. 100, 155307 (2019).

[2] S. Chen, et al. J. Phys. Chem. Lett. 11, 8937 (2020).

[3] K. Omambac et al , Appl. Phys. Lett. 118, 241902 (2021)

[4]M. Petrovic et al Nanotechnology 32 505706 (2021)

[5] T. Ohta et al. Phys. Rev. Lett. 98, 206802 (2007).