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Edge-Controlled Growth and Etching of Two-Dimensional GaSe Monolayers
Li, Xufan,Dong, Jichen,Idrobo, Juan C.,Puretzky, Alexander A.,Rouleau, Christopher M.,Geohegan, David B.,Ding, Feng,Xiao, Kai American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.1
<P>Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of wafer-sized, single-crystalline, high-quality 2D crystals and heterostructures. Etching, in many cases regarded as the reverse process of material growth, has been used to study the growth kinetics of graphene. In this work, we explore a growth-etching-regrowth process of monolayer GaSe crystals, including single-crystalline triangles and irregularly shaped domains formed by merged triangles. We show that the etching begins at a slow rate, creating triangular, truncated triangular, or hexagonally shaped holes that eventually evolve to exclusively triangles that are rotated 60 degrees with respect to the crystalline orientation of the monolayer triangular crystals. The regrowth occurs much faster than etching, reversibly filling the etched holes and then enlarging the size of the monolayer crystals. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed morphology evolution of the monolayer GaSe crystals and etched holes during the growth and etching processes, showing that they are governed by the probability of atom attachment/detachment to/from different types of edges with different formation energies of nucleus/dents mediated by chemical potential difference Ait between Ga and Se. Our growth-etching-regrowth study provides not only guidance to understand the growth mechanisms of 2D binary crystals but also a potential method for the synthesis of large, shape-controllable, high-quality single-crystalline 2D crystals and their lateral heterostructures.</P>
Synthesis of Patched or Stacked Graphene and hBN Flakes: A Route to Hybrid Structure Discovery
Kim, Soo Min,Hsu, Allen,Araujo, P. T.,Lee, Yi-Hsien,Palacios, Tomá,s,Dresselhaus, Mildred,Idrobo, Juan-Carlos,Kim, Ki Kang,Kong, Jing American Chemical Society 2013 Nano letters Vol.13 No.3
<P>Two-dimensional (2D) materials such as graphene and hexagonal boron nitride (hBN) have attracted significant attention due to their remarkable properties. Numerous interesting graphene/hBN hybrid structures have been proposed but their implementation has been very limited. In this work, the synthesis of patched structures through consecutive chemical vapor deposition (CVD) on the same substrate was investigated. Both in-plane junctions and stacked layers were obtained. For stacked layers, depending on the synthesis sequence, in one case turbostratic stacking with random rotations were obtained. In another, “AA-like”, slightly twisted stacking between graphene and hBN was observed with lattice orientation misalignment consistently to be <1°. Raman characterizations not only confirmed that hBN is a superior substrate but also revealed for the first time that a graphene edge with hBN passivation displays reduced D band intensity compared to an open edge. These studies pave the way for the proposed well-ordered graphene/hBN structures and outline exciting future directions for hybrid 2D materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-3/nl303760m/production/images/medium/nl-2012-03760m_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl303760m'>ACS Electronic Supporting Info</A></P>