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Fabrication and manipulation of nanosized graphene homojunction with atomically-controlled boundaries

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Nano Research 2020年第12期13卷 3286-3291页

作者： Hui Chen De-Liang Bao Dongfei Wang yande que Wende Xiao Yu-Yang Zhang Jiatao Sun Shixuan Du Hong-Jun Gao Institute of Physics and University of Chinese Academy of Sciences Beijing100190China CAS Key Laboratory of Vacuum Physics University of Chinese Academy of SciencesBeijing100049China

Controlling the atomic configurations of structural defects in graphene nanostructures is crucial for achieving desired ***,we report the controlled fabrication of high-quality single-crystal and bicrystal graphene nanoislands(GNI)through a unique top-down etching and post-annealing procedure on a graphite ***-temperature scanning tunneling microscopy(STM)combined with density functional theory calculations reveal that most of grain boundaries(GBs)formed on the bicrystal GNIs are 5-7-5-7 *** nanodomains separated by a 5-7-5-7 GB are AB stacking and twisted stacking with respect to the underlying graphite substrate and exhibit distinct electronic properties,forming a graphene *** addition,we construct homojunctions with alternative AB/twisted stacking nanodomains separated by parallel 5-7-5-7 ***,the stacking orders of homojunctions are manipulated from AB/twist into twist/twist type through a STM *** controllable fabrication and manipulation of graphene homojunctions with 5-7-5-7 GBs and distinct stacking orders open an avenue for the construction of GBs-based devices in valleytronics and twistronics.

关键词： homojunction graphene nanoislands manipulations grain boundaries twisted stacking

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

Impurity-induced formation of bilayered graphene on copper by chemical vapor deposition

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Nano Research 2016年第9期9卷 2803-2810页

作者： Jun Li Jianing Zhuang Chengmin Shen Yuan Tian yande que Ruisong Ma Jinbo Pan Yanfang Zhang Yeliang Wang Shixuan Du Feng Ding Hong-Jun Gao Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China Institute of Textiles and Clothing Hong Kong Polytechnic UniversityKowloonHong KongChina Beijing Key Laboratory for Nanomaterials and Nanodevices Beijing 100190China

High-quality single-layered and bilayered graphene (SLG and BLG) was synthesized on copper foil surfaces by controllable chemical vapor deposition (CVD). Impurity nanoparticles formed on the copper foil surface by hightemperature annealing were found to play a crucial role in the growth of BLG. Analysis of energy-dispersive spectrometry (EDS) data indicated that these nanoparticles consisted of silicon and aluminum. According to the inverted wedding cake model, these nanoparticles served as nucleation centers for BLG growth and the free space between a nanoparticle and graphene served as the center of C injection for the continuous growth of the adlayer beneath the top layer. By combining phase-field theory simulations, we confirmed the mechanism of BLG growth and revealed more details about it in comparison with SLG growth. For the first time, this study led to a complete understanding of the BLG growth mechanism from nucleation to continuous growth in the CVD process, and it has opened a door to the thickness-controllable synthesis of graphene. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

关键词： graphene chemical vapor deposition (CVD) bilayer growth mechanism

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

Low-temperature growth of large-scale,single-crystalline graphene on Ir(111)

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Chinese Physics B 2019年第5期28卷 11-15页

作者： Hui Guo Hui Chen yande que Qi Zheng Yu-Yang Zhang Li-Hong Bao Li Huang Ye-Liang Wang Shi-Xuan Du Hong-Jun Gao Institute of Physics and University of Chinese Academy of Sciences CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences

Iridium is a promising substrate for self-limiting growth of graphene. However, single-crystalline graphene can only be fabricated over 1120 K. The weak interaction between graphene and Ir makes it challenging to grow graphene with a single orientation at a relatively low temperature. Here, we report the growth of large-scale, single-crystalline graphene on Ir(111) substrate at a temperature as low as 800 K using an oxygen-etching assisted epitaxial growth method. We firstly grow polycrystalline graphene on Ir. The subsequent exposure of oxygen leads to etching of the misaligned *** growth cycle, in which the leftover aligned domain serves as a nucleation center, results in a large-scale and single-crystalline graphene layer on Ir(111). Low-energy electron diffraction, scanning tunneling microscopy, and Raman spectroscopy experiments confirm the successful growth of large-scale and single-crystalline graphene. In addition, the fabricated single-crystalline graphene is transferred onto a SiO_2/Si substrate. Transport measurements on the transferred graphene show a carrier mobility of about 3300 cm^2·V^(-1)·s^(-1). This work provides a way for the synthesis of large-scale,high-quality graphene on weak-coupled metal substrates.

关键词： graphene low-temperature growth single-crystalline Ir(111)

Intercalation of metals and silicon at the interface of epitaxial graphene and its substrates

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Intercalation of metals and silicon at the interface of epit...

Analysis of wire antennas mounted on large perfectly conducting platforms using MLFMA

中国真空学会2014学术年会

作者： Li Huang Wenyan Xu yande que Jinhai Mao Lei Meng Lida Pan Geng Li Yeliang Wang Shixuan Du YunQi Liu Hong-Jun Gao Institute of Chemistry Chinese Academy of Sciences Institute of Physics Chinese Academy of Sciences

Intercalations of metals and silicon between epitaxial graphene and its substrates are *** metal intercalation,seven different metals have been successfully intercalated at the interface of graphene/Ru(0001)and form different intercalated ***,graphene maintains its original high quality after the intercalation and shows features of weakened interaction with the *** silicon intercalation,two systems,graphene on Ru(0001)and on Ir(111),have been *** both cases,graphene preserves its high quality and regains its original superlative properties after the silicon *** importantly,we demonstrate that thicker silicon layers can be intercalated at the interface,which allows the atomic control of the distance between graphene and the metal *** results show the great potential of the intercalation method as a non-damaging approach to decouple epitaxial graphene from its substrates and even form a dielectric layer for future electronic applications.

关键词： graphene metal intercalation silicon intercalation scanning tunneling microscopy

来源： cnki会议评论

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Journal of Systems Engineering and Electronics 2007年第4期18卷 679-684页

作者： que Xiaofeng Nie Zaiping School of Electronic Engineering University of Electronic Science and Technology of China Chengdu 610054 P. R. China

The electric field integral equation (EFIE) combined with the multilevel fast multipole algorithm (MLFMA) is applied to analyze the radiation and impedance properties of wire antennas mounted on complex conducting platforms to realize fast, accurate solutions. Wire, surface and junction basis functions are used to model the current distribution on the object. Application of MLFMA reduces memory requirement and computing time compared to conventional methods, such as method of moment (MOM), especially for the antenna on a large-sized platform. Generalized minimal residual (GMRES) solver with incomplete LU factorization preconditioner using a dual dropping strategy (ILUT) is applied to reduce the iterative number. Several typical numerical examples are presented to validate this algorithm and show the accuracy and computational efficiency.

关键词： wire antennas platform MOM MLFMA GMRES ILUT.

Tunable low frequency band gaps and sound transmission loss of a lever-type metamaterial plate

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Applied Mathematics and Mechanics(English Edition) 2022年第8期43卷 1145-1158页

作者： Wenzheng que Xiaodong YANG Wei ZHANG Beijing Key Laboratory of Nonlinear Vibrations and Strength of Mechanical Structures Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing100124China

A novel metamaterial plate with subwavelength lever-type resonators is proposed to obtain low frequency broadband band gaps and good sound insulation *** band structure is theoretically derived,and the validity of the theoretical method is verified by the finite element *** formation mechanisms of the band gaps are illustrated by the analysis of the effective dynamic mass density and group *** effect of the lever ratio on the band gaps is *** results indicate that as the lever ratio increases,the first band gap shifts to lower frequencies,while the bandwidth is ***,the sound insulation performance of the proposed metamaterial plate is evaluated via examining the sound transmission loss(STL).Compared with the metamaterial plates without lever accessories,the proposed metamaterial plates with a suitable lever ratio have better sound insulation performance at low frequencies.

关键词： tunable band gap metamaterial plate lever-type resonator low frequency broadband sound transmission loss(STL)

Microstructure and thermal properties of dissimilar M300–CuCr1Zr alloys by multi-material laser-based powder bed fusion

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International Journal of Minerals,Metallurgy and Materials 2024年第1期31卷 118-128页

作者： Xiaoshuang Li Dmitry Sukhomlinov Zaiqing que Aerosint SA B-4040 HerstalBelgium Aalto University Department of Chemical and Metallurgical EngineeringEspoo 02150Finland VTT Technical Research Centre of Finland Espoo 02044Finland

Multi-material laser-based powder bed fusion (PBF-LB) allows manufacturing of parts with 3-dimensional gradient and additional functionality in a single step. This research focuses on the combination of thermally-conductive CuCr1Zr with hard M300 tool *** interface configurations of M300 on CuCr1Zr and CuCr1Zr on M300 were investigated. Ultra-fine grains form at the interface due to the low mutual solubility of Cu and steel. The material mixing zone size is dependent on the configurations and tunable in the range of0.1–0.3 mm by introducing a separate set of parameters for the interface layers. Microcracks and pores mainly occur in the transition *** of these defects, the thermal diffusivity of bimetallic parts with 50vol% of CuCr1Zr significantly increases by 70%–150%compared to pure M300. The thermal diffusivity of CuCr1Zr and the hardness of M300 steel can be enhanced simultaneously by applying the aging heat treatment.

关键词： multi-material additive manufacturing laser-based powder bed fusion thermal diffusivity dissimilar metals copper alloy