Growth of twisted bilayer graphene: Interactions between grains

Che-Men Chu^1*, Wei-Yen Woon¹

¹Physics, National Central University, Taoyuan, Taiwan

* Presenter:Che-Men Chu, email:a1234gy@gmail.com

Magic-angle twisted bilayer graphene (MA-TBLG) becomes promising material, once it displays the superconductivity and insulator phenomenon. Related to the appearance of narrow, flat, and isolated electronic bands, MA-TBLG exhibits various many-body phenomena. MA-TBLG presents a variety of complex experimental phenomenology, electron-electron (phonon) interactions and nontrivial Bloch wavefunctions associated with the narrow bands included.
The investigation of the growth of twisted bilayer graphene through chemical vapor deposition (CVD) is conducted and there are some ambiguous models, related to the nucleation, the abundance of carbon, adlayer grains interaction. In our previous work, we established a methodology to identify twist angles and the growth model.
Sub-millimeter-sized single crystalline graphene grains with multi-layered adlayer grains formed underneath are identified through optical microscopy. The distribution of the twist angles is investigated through micro-Raman mapping. the twist angles were unambiguously identified and categorized into five types through the careful inspection of the acquired characteristic of 2D and G bands, inclusive of the height width and symmetry. With a number of spatial mapping of Raman spectrum, the statistics show that no TBLG is formed for isolated BLG. Furthermore, the probability of TBLG formation is largely proportional to the gas H2/CH4 ratio.
This research focus on the grain interaction of adlayer underlay the first layer with direct and powerful evidence. The growth mechanism of the TBLG is discussed in light of the interactions between the second layer grains. Further, we examine the growth multilayer graphene to prove the relation of twist angle and merging with the isotope methane introduced to label the growth front through a distinguished Raman shift of G and 2D bands. With the inspection of the geometry of the growth, the interaction among adlayer grains is eventually figured out.

Keywords: graphene , twisted bilayer graphene , Raman spectroscopy, CVD, isotope