Ultra-High-Resolution Transmission Electron Microscopy of Atomically Thin Hexagonal Boron Nitride (h-BN) N. Alem 1,2,3 , R. Erni 3,4 , C. Kisielowski 3,4 , M. D. Rossell 3,4 , W. Gannett 1,3 , A. Zettl 1,2,3 1 Department of Physics, University of California at Berkeley 2 Center of Integrated Nanomechanical Systems, University of California at Berkeley 3 Materials Sciences Division, Lawrence Berkeley National Laboratory 4 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory Berkeley, California 94720 Atomically thin 2D ordered crystals, such as graphene and hexagonal boron nitride (h-BN), are considered new emerging materials with potential applications in sensing and in the electronic industry [1-5]. The electrical, thermal, chemical and mechanical properties of such crystals are strongly influenced by their atomic structure. Therefore, understanding the atomic scale stability and dynamics of defects and vacancies with the add-atoms and molecules in such membrane systems is crucial to predict their resulting properties and potential applications. While graphene is a zero band gap material with high carrier mobility, h-BN is a wide band gap insulating material with potential applications in hydrogen storage and DUV light emitters [1, 3]. Graphene and h-BN both consist of single sheets of sp 2 -bonded atoms forming a honeycomb cell structure [6-7]. They, however, have different atomic stackings. In h-BN the boron atoms are stacked on top of nitrogen on the adjacent planes resulting in AAA atomic layer stacking, while graphite forms a Bernal Stacking sequence. In a recent study, we have successfully isolated one monolayer (1 ML) of h-BN and have unambiguously identified the boron atom from nitrogen in a unit cell of an atomically thin h-BN using an ultra-high-resolution transmission electron microscope [8]. Figure 1a shows a high resolution TEM image of h-BN taken by the TEAM 0.5 microscope located at the National Center for Electron Microscopy (NCEM). This image shows a one- to four-layer region of h-BN with vacancies and holes. Using high resolution TEM imaging, we use the projected potential of the atoms to unambiguously identify their chemical nature (boron or nitrogen) throughout the sample. To enhance the signal to noise ratio in this identification, we consider the projected potential of the summation of twenty unit cells in h-BN for each layer thickness. According to the intensity line profile of the h-BN unit cell, a clear asymmetry is observed in the projected potential of the atoms in the adjacent h-BN columns in the odd layer-number regions (n=1 and 3). No discernible asymmetry, however, is observed for adjacent columns in even-layer-number regions (n=2 and 4). Figure 1b shows the nitrogen atom yielding the stronger intensity in the unit cell images with 1 and 3 ML. This atom identification technique has further enabled us to study the nature of defects and edges in h-BN. We observe that defects in h-BN are formed mainly as a result of the ejection of boron atoms from the lattice, while the edges are in the form of nitrogen-terminating zigzag edges. Single layer 2D crystal membranes offer a unique model system to study the stability and dynamics of defects, edges and vacancies, and their interactions with adatoms or molecules. In this investigation, we address the stability and dynamics of vacancy formation in h-BN and the interaction dynamics between the adatoms/molecules and the defects/edges in this membrane. 120 doi:10.1017/S1431927610058897 Microsc. Microanal. 16 (Suppl 2), 2010 © Microscopy Society of America 2010 https://doi.org/10.1017/S1431927610058897 Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 12 Jun 2020 at 05:48:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.