Epitaxy in Two Dimensions: Novel Structures and New Physics

非技术描述：纳米科学和纳米技术通常涉及降维材料，如一维(1D)纳米管和纳米线以及2D片状材料。降维通常会导致3D模型中没有观察到的新现象。该研究项目旨在合成两种不同的2D材料，将它们连接在一起形成一个单原子层厚度的平面。在这种面内异质结构中，组成的2D材料是结晶的，原子的有序不会穿过不同材料的尖锐界面而受到干扰。由于这些特性与3D外延异质结相似，平面内异质结的合成称为“2D外延”。这种结构的成功合成使得相关的新物理学的研究成为可能，这有望导致新的电子、光子和磁性器件的出现。研究过程中产生的新知识通过将研究融入教学直接传递给学生，不仅是为了传达对新发现的兴奋，也是为了激发好奇心。该项目还通过外展活动影响K-12 STEM教育。此外，该团队还参与了国家公共广播电台(NPR)的一项计划，对公众进行科学技术教育。技术描述：该研究项目专注于二维(2D)异质结构的合成和表征。这项研究的长期目标是：1)建立2D异质结构的生长科学；2)揭示这些结构非常丰富且经常是奇异的物理；3)基于新的物理开发新的电子、光子和磁器件概念。具体地说，本项目的范围包括：1)完善石墨烯-六方氮化硼(石墨烯-hBN)平面内异质结构的锯齿形边界。这涉及到通过在受控良好的环境中将非极性石墨烯生长到极性hBN的边缘来消除反相无序，以克服阻止这一生长序列的化学因素。界面的特征是原子分辨率、元素对比度成像，以调查真正原子锐化边界的可获得性。2)合成包含多个石墨烯-hBN结的复杂的平面内异质结构。除了自下而上的增长，必要时还会纳入自上而下的控制。3)对这些异质结构的新物理，如局域边界态之间的隧道效应和边界的自旋极化进行了初步的研究。电子能量损失谱中的二向色性是对边界态原子尺度的自旋极化进行初步实验探测的首选方法。

Non-technical Description: Nanoscience and nanotechnology often involve materials of reduced dimensionality, such as one-dimensional (1D) nanotubes and nanowires as well as 2D sheet materials. Reduced dimensionality frequently leads to new phenomena not observed in their 3D counterparts. This research project aims to synthesize two different 2D materials joined together to form a plane of single atomic-layer thickness. The constituent 2D materials in such an in-plane heterostructure are crystalline, and the atomic order is not disturbed crossing the sharp interfaces of the different materials. Due to these traits similar to those of epitaxial heterostructures in 3D, the synthesis of the in-plane heterostructures is called "epitaxy in 2D." Successful synthesis of such structures enables the investigation of the associated new physics, which is expected to lead to novel electronic, photonic, and magnetic devices. The new knowledge generated during the course of the research is passed directly to students by integrating research into teaching, not only to convey excitement of new discoveries but also to stimulate curiosity. This project also impacts K-12 STEM education through outreach activities. In addition, the team participates in a National Public Radio (NPR) program to educate the public on science and technology.Technical Description: This research project focuses on the synthesis and characterization of two-dimensional (2D) heterostructures. The long-term goals of the research are: 1) To establish the growth science of 2D heterostructures; 2) To reveal the very rich and often exotic physics of these structures; and 3) To develop novel electronic, photonic, and magnetic device concepts based on the novel physics. Specifically, the scope of this project includes: 1) Perfection of the zigzag boundary of the graphene-hexagonal boron nitride (graphene-hBN) in-plane heterostructure. This involves the elimination of antiphase disorders by growing the nonpolar graphene onto the edges of polar hBN in a well-controlled environment to overcome the chemical factors preventing this growth sequence. The interface is characterized by atomic resolution, element-contrast imaging to investigate the obtainability of a truly atomically sharp boundary. 2) Synthesis of complex in-plane heterostructures comprising multiple graphene-hBN junctions. Besides bottom-up growth, top-down control is incorporated when necessary. 3) Initial investigation of the novel physics, such as tunneling between localized boundary states and spin polarization of the boundaries, of these heterostructures. Dichroism in electron energy loss spectroscopy is the method of choice for the initial experimental probing of the spin polarization of the atomic-scale of the boundary states.