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Spectroscopic signatures of edge states in hexagonal boron nitride

Nano Research 2019年第7期12卷 1663-1667页

作者： Chuang Gao Lei tao Yu-Yang Zhang Shixuan Du sokrates t. pantelides Juan Carlos Idrobo Wu Zhou Hong-Jun Gao School of Physical Sciences and CAS Key Laboratory of Vacuum Physics University of Chinese Academy of SciencesBeijing 100049China Institute of Physics Chinese Academy of SciencesBeijing 100190China Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science Vanderbilt UniversityNashvilleTN 37235USA CAS Centre for Excellence in topological Quantum Computation University of Chinese Academy of SciencesBeijing 100049China Center for Nanophase Materials Sciences Oak Ridge National LaboratoryOak RidgeTN 37831USA

We use Z-contrast imaging and atomically resolved electron energy-loss spectroscopy on an aberration-corrected scanning transmission electron microscope to investigate the local electronic states of boron atoms at different edge structures in monolayer and bilayer *** find that edges with bonding unsaturated sp2 boron atoms have a unique spectroscopic signature with a prominent pre-peak at - 190.2 eV in the B K-edge fine ***-principles calculations reveal that the observed pre-peak arises from excitations to the in-plane lowest-energy empty sp2 boron dangling bonds at the B-terminated *** spectroscopic signature can serve as a fingerprint to explore new edge structures in h-BN.

关键词： h-BN edge structure spectroscopic signatures electron energy-loss near edge structure

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Recovery of edge states of graphene nanoislands on an iridium substrate by silicon intercalation

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Nano Research 2018年第7期11卷 3722-3729页

作者： Hui Chen Yande Que Lei tao Yu-Yang Zhang Xiao Lin Wende Xiao Dongfei Wang Shixuan Du sokrates t. pantelides Hong-Jun Gao Institute of Physics & University of Chinese Academy of Sciences Chinese Academy of Sciences Beijing 100190 China Department of Physics and Astronomy Vanderbilt University Nashville Tennessee 37235 USA Department of Electrical Engineering and Computer Science Vanderbilt University Nashville Tennessee 3723S USA

Finite-sized graphene sheets, such as graphene nanoislands （GNIs）, are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate. We used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. this work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.

关键词： graphene nanoisland zigzag edge edge state scanning tunneling microscopy density functional theory

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Sulfur-doped graphene nanoribbons with a sequence of distinct band gaps

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Nano Research 2017年第10期10卷 3377-3384页

作者： Yan-Fang Zhang Yi Zhang Geng Li Jianchen Lu Yande Que Hui Chen Reinhard Berger Xinliang Feng Klaus Müllen Xiao Lin Yu-Yang Zhang Shixuan Du sokrates t. pantelides Hong-Jun Gao Institute of Physics & University of Chinese Academy of Sciences Chinese Academy of Sciences Beijing 100190 China Max Planck Institute for Polymer Research Ackermannweg 10 D-55128 Mainz Germany Center for Advancing Electronics Dresden (cfaed) & Department of Chemistry and Food Chemistry Technische Universitat Dresden D-01069 Dresden Germany School of Chemistry and Chemical Engineering Shanghai Jiao Tong University Shanghai 200240 China Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science Vanderbilt University Nashville Tennessee 37235 USA

Unlike graphene sheets, graphene nanoribbons （GNRs） can exhibit semiconducting band gap characteristics that can be tuned by controlling impurity doping and the GNR widths and edge structures. However, achieving such control is a major challenge in the fabrication of GNRs. Chevron-type GNRs were recently synthesized via surface-assisted polymerization of pristine or N-substituted oligophenylene monomers. In principle, GNR heterojunctions can be fabricated by mixing two different monomers. In this paper, we report the fabrication and characterization of chevron-type GNRs using sulfur-substituted oligophenylene monomers to produce GNRs and related heterostructures for the first time. First-principles calculations show that the GNR gaps can be tailored by applying different sulfur configurations from cyclodehydrogenated isomers via debromination and intramolecular cyclodehydrogenation. this feature should enable a new approach for the creation of multiple GNR heterojunctions by engineering their sulfur configurations. these predictions have been confirmed via scanning tunneling microscopy and scanning tunneling spectroscopy. For example, we have found that the S-containing GNRs contain segments with distinct band gaps, i.e., a sequence of multiple heterojunctions that results in a sequence of quantum dots. this unusual intraribbon heterojunction sequence may be useful in nanoscale optoelectronic applications that use quantum dots.

关键词： bottom-up fabrication chevron-type graphene nanoribbons nanoscale quantum dots scanning tunneling microscopy density functional theory

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