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[2014 01 14] 특별세미나 (BK21PLUS)

Stitching and Stacking Atomic Membranes for New 2D Structures

MSE Graduate Students and Researchers

관리자 | 2014.01.13 09:28 | 조회 3055


Reception: MSE Graduate Students and Researchers

Reference: MSE Professors

Subject: MSE Special Seminar_ Dr. Cheol-Joo Kim

 

Date: 2014. 1. 14(TUE), 16:00 ~ 17:30

Place: Science Building, Room. 202 Multimedia Room

Title: Stitching and Stacking Atomic Membranes for New 2D Structures

Speaker: Dr. Cheol-Joo Kim

Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States

Host of a Seminar: Prof. Byeong-Joo Lee


Abstract
Recently, various atomic membranes, such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides have been reported with their novel properties.[1] Interestingly, these atomic membranes can be freestanding without any substrate, implying that they can be used as building blocks for designing new complex materials.[2] The properties of these hybrid systems can be customized over a large energy range, providing additional structural and compositional degrees of freedom that conventional semiconductor material systems do not have. However, their crystalline structures and resultant properties are still largely unknown. Here, as a starting point, we study new 2D structures based on the two simplest layered crystalline materials?graphene and mono layer h-BN. By lateral stitching and vertical stacking of the atomic membranes, we fabricate two kinds of structures-1) spatially controlled graphene/h-BN lateral heterostructures and 2) h-BN bilayers with different stacking orders.[3] For synthesizing the materials, we employ catalyst assisted chemical vapor depositions.[4] Then, we investigate how their properties are correlated with changes to their local physical structures by using various structural and functional imaging techniques such as dark field transmission electron microscopy (DF-TEM), 2D Raman and hyperspectral optical imaging. [5]
In the first part, we present a versatile and scalable process, which we call
patterned regrowth, that allows for the spatially controlled synthesis of lateral junctions between electrically conductive graphene and insulating h-BN, as well as between intrinsic and substitutionally doped graphene. We demonstrate that the resulting films form mechanically continuous sheets across these heterojunctions. Conductance measurements confirm laterally insulating behaviour for h-BN regions, while the electrical behavior of both doped and undoped graphene sheets maintain excellent properties, with low sheet resistances and high carrier mobilities.
In the second part, optical and topological properties of h-BN bilayer correlated with their local stacking orders are introduced. Our data show that there exist two distinct h-BN bilayer structures with different interlayer symmetries that give rise to a distinct difference in their second harmonic generation (SHG) intensities. In particular, the SHG signal in h-BN bilayers is observed only for structures with broken inversion symmetry, with intensity much larger than that of single layer h-BN. In addition, our DF-TEM data identify the formation of interlayer topological defects in h-BN bilayers, likely induced by local strain, whose properties are determined by the interlayer symmetry and the different interlayer potential landscapes.

 

Department of Materials Science and Engineering

MSE BK21+ / Center for Advanced Soft Electronics



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