Bo Tian
Ph.D. Candidate supervised by Prof. Xixiang Zhang

Event Location: Ibn Sina Building (Bldg. 3), Room 5220
Zoom link: https://kaust.zoom.us/j/97174478278

ABSTRACT: Owning to the fundamental interests in moiré physics and their potential applications, van der Waals (vdWs) heterostructures of differently stacked graphene and hexagonal boron nitride (hBN) have attracted considerable interest. Although the conventional exfoliation and layer-by-layer transfer techniques were used to fabricate most of the heterostructures, they have serious limitations in acquiring large-size, contamination-free samples. Chemical vapor deposition (CVD) should be one of the best alternative techniques and has been demonstrated to be very successful in the synthesis of high-quality, large-scale, two-dimensional (2D) materials. We have successfully fabricated AAB-stacked single-crystal graphene/hBN/graphene trilayer vdWs heterostructures. We have also developed a technique to fabricate the wafer-scale graphene-mesh films with zigzag edges for advanced nano-electronics with the single-crystal monolayer graphene synthesized using CVD.

We proposed an in situ CVD growth strategy for synthesizing wafer-scale AAB-stacked single-crystal graphene/hBN/graphene trilayer vdWs heterostructures. Single-crystal monolayer hBN was first synthesized on the surface of Single-crystal CuNi(111) films prepared on sapphire substrates. Then, single-crystal monolayer graphene was epitaxially grown onto the hBN surface to form graphene/hBN bilayer heterostructures. A controlled decrease in the growth temperature allows the carbon atoms to precipitate out of the CuNi(111) alloy to form single-crystal graphene at the interface between hBN and CuNi(111), thereby producing graphene/hBN/graphene trilayer vdWs heterostructures. The stacking modes between as-grown 2D layers were investigated using Raman spectroscopy and transmission electron microscopy. This study provides an in situ CVD approach to directly synthesize large-scale single-crystal low-dimensional vdWs heterostructures and facilitates their application in future 2D-material-based integrated

We also developed a technique to produce wafer-scale high-quality single-crystal nucleus-free graphene-mesh metamaterial films with zigzag edges. We utilize the 13C-isotopic labeling graphene-growth approach, large-area Raman mapping techniques, and a uniquely designed high-voltage localized-space air-ionization etching method to remove the graphene nuclei directly. Subsequently, a hydrogen-assisted anisotropic etching process is employed for transforming irregular edges into zigzag edges within the hexagonal-shaped holes, producing a large-scale single-crystal high-quality graphene-mesh metamaterial film on a Cu(111) substrate. The findings of this study enable the large-scale contamination-free production of high-quality low-dimensional graphene-mesh metamaterials for applications in integrated circuits based on graphene and other 2D metamaterials.