74 results on '"Hong Jun Gao"'
Search Results
2. Collective Magnetic Behavior in Vanadium Telluride Induced by Self-Intercalation
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Roger Guzman, Shoucong Ning, Ruizi Zhang, Hongtao Liu, Yinhang Ma, Yu-Yang Zhang, Lihong Bao, Haitao Yang, Shixuan Du, Michel Bosman, Stephen J. Pennycook, Hong-Jun Gao, and Wu Zhou
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General Engineering ,General Physics and Astronomy ,General Materials Science - Published
- 2023
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3. Unveiling Electronic Behaviors in Heterochiral Charge-Density-Wave Twisted Stacking Materials with 1.25 nm Unit Dependence
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Liwei Liu, Xuan Song, Jiaqi Dai, Han Yang, Yaoyao Chen, Xinyu Huang, Zeping Huang, Hongyan Ji, Yu Zhang, Xu Wu, Jia-Tao Sun, Quanzhen Zhang, Jiadong Zhou, Yuan Huang, Jingsi Qiao, Wei Ji, Hong-Jun Gao, and Yeliang Wang
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General Engineering ,General Physics and Astronomy ,General Materials Science - Published
- 2023
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4. Ultralow-Loss Phonon Polaritons in the Isotope-Enriched α-MoO3
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Yongqian Zhao, Jiancui Chen, Mengfei Xue, Runkun Chen, Shangtong Jia, Jianjun Chen, Lihong Bao, Hong-Jun Gao, and Jianing Chen
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Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Published
- 2022
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5. Unveiling the Degradation Mechanism of High-Temperature Superconductor Bi2Sr2CaCu2O8+δ in Water-Bearing Environments
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Yuan Huang, Lei Zhang, Xiaocheng Zhou, Lei Liao, Feng Jin, Xu Han, Tao Dong, Shuxiang Xu, Lin Zhao, Yunyun Dai, Qiuzhen Cheng, Xinyu Huang, Qingming Zhang, Lifen Wang, Nan-Lin Wang, Ming Yue, Xuedong Bai, Yafei Li, Qiong Wu, Hong-Jun Gao, Genda Gu, Yeliang Wang, and Xing-Jiang Zhou
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General Materials Science - Published
- 2022
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6. Coexisting Ferromagnetic–Antiferromagnetic Phases and Manipulation in a Magnetic Topological Insulator MnBi4Te7
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Jianfeng Guo, Huan Wang, Xueyun Wang, Shangzhi Gu, Shuo Mi, Shiyu Zhu, Jiawei Hu, Fei Pang, Wei Ji, Hong-Jun Gao, Tianlong Xia, and Zhihai Cheng
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General Energy ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2022
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7. Size Dependence of Charge-Density-Wave Orders in Single-Layer NbSe2 Hetero/Homophase Junctions
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Zeping Huang, Xuan Song, Yaoyao Chen, Han Yang, Peiwen Yuan, Hang Ma, Jingsi Qiao, Yu Zhang, Jiatao Sun, Teng Zhang, Yuan Huang, Liwei Liu, Hong-Jun Gao, and Yeliang Wang
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General Materials Science ,Physical and Theoretical Chemistry - Published
- 2022
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8. Visualization of Charge-Density-Wave Reconstruction and Electronic Superstructure at the Edge of Correlated Insulator 1T-NbSe2
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Han Yang, Teng Zhang, Zeping Huang, Yaoyao Chen, Xuan Song, Xiaoyu Hao, Huixia Yang, Xu Wu, Yu Zhang, Liwei Liu, Hong-Jun Gao, and Yeliang Wang
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General Engineering ,General Physics and Astronomy ,General Materials Science - Published
- 2021
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9. Honeycomb AgSe Monolayer Nanosheets for Studying Two-dimensional Dirac Nodal Line Fermions
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Hong Ding, Tian Qian, Lei Gao, Hui Chen, Hong-Jun Gao, Shiru Song, Hang Li, Jianchen Lu, Shixuan Du, Gefei Niu, and Xiao Lin
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Materials science ,Condensed matter physics ,Dirac (software) ,Monolayer ,Honeycomb (geometry) ,General Materials Science ,Fermion ,NODAL ,Line (formation) - Published
- 2021
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10. Tuning Molecular Superlattice by Charge-Density-Wave Patterns in Two-Dimensional Monolayer Crystals
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Yanhui Hou, Xuan Song, Zeping Huang, Ziqiang Xu, Peiwen Yuan, Liwei Liu, Teng Zhang, Hong-Jun Gao, Han Yang, Huixia Yang, Yaoyao Chen, Yeliang Wang, and Quanzhen Zhang
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Materials science ,Condensed matter physics ,Superlattice ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Condensed Matter::Superconductivity ,Monolayer ,Phthalocyanine ,Molecule ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Physical and Theoretical Chemistry ,0210 nano-technology ,Charge density wave ,Commensurability (astronomy) - Abstract
Charge density wave (CDW) in two-dimensional (2D) crystals plays a vital role in tuning the interface structures and properties. However, how the CDW tunes the self-assembled molecular superlattice still remains unclear. In this study, we investigated the self-assembled manganese phthalocyanine (MnPc) molecular superlattice on single-layered 1T- and 2H-NbSe2 crystals under regulation by distinct CDW patterns. We observe that, in low coverage, MnPc molecules preferentially adsorb on 2H-NbSe2 compared to 1T-NbSe2. With increasing coverage, MnPc can form a highly ordered superlattice on 2H-NbSe2; however, it is randomly distributed on 1T-NbSe2. We reveal a perfect geometric commensurability between the molecular superlattice and intrinsic CDW pattern in 2H-NbSe2 and a poor commensurability for that of 1T-NbSe2. We believe that the subtly different geometric commensurability dominates the different adsorption and arrangement of the molecular superlattices on 2D CDW patterns. Our study provides a pioneering approach for tuning the molecular superlattices using the CDW patterns.
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- 2021
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11. Layer-by-Layer Epitaxy of Porphyrin−Ligand Fe(II)-Fe(III) Nanoarchitectures for Advanced Metal–Organic Framework Growth
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Carlos-Andres Palma, Xiaoxi Zhang, Peter S. Deimel, Vishal Gupta, Francesco Allegretti, Kai Qian, Juan Li, Murat Anil Öner, Hong-Jun Gao, Yan Wang, Johannes V. Barth, Shixuan Du, David A. Duncan, Shuai Zhang, Zishu Wang, and Xiao Lin
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Materials science ,Ligand ,Thermal desorption spectroscopy ,Layer by layer ,Heterojunction ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Epitaxy ,Porphyrin ,law.invention ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,General Materials Science ,Metal-organic framework ,Scanning tunneling microscope - Abstract
Precisely layered molecular heterostructures are promising but still largely unexplored materials, with the potential to complement and enhance the scope of two-dimensional heterostructures. The co...
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- 2020
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12. Insulating SiO2 under Centimeter-Scale, Single-Crystal Graphene Enables Electronic-Device Fabrication
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Qinghua Zhang, Xin Jin, Werner A. Hofer, Zhang Zhou, Hai Hu, Zhenzhong Yang, Yu-Yang Zhang, Shixuan Du, Qing Dai, Chengmin Shen, Hongliang Lu, Sokrates T. Pantelides, Hong-Jun Gao, Xiao Lin, Li Huang, Hui Guo, Lin Gu, Lihong Bao, and Xueyan Wang
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Fabrication ,Materials science ,Silicon ,Graphene ,business.industry ,Mechanical Engineering ,chemistry.chemical_element ,Bioengineering ,02 engineering and technology ,General Chemistry ,Quantum Hall effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,Grain size ,Amorphous solid ,law.invention ,chemistry ,law ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Single crystal - Abstract
Graphene on SiO2 enables fabrication of Si-technology-compatible devices, but a transfer of these devices from other substrates and direct growth have severe limitations due to a relatively small grain size or device-contamination. Here, we show an efficient, transfer-free way to integrate centimeter-scale, single-crystal graphene, of a quality suitable for electronic devices, on an insulating SiO2 film. Starting with single-crystal graphene grown epitaxially on Ru(0001), a SiO2 film is grown under the graphene by stepwise intercalation of silicon and oxygen. Thin (∼1 nm) crystalline or thicker (∼2 nm) amorphous SiO2 has been produced. The insulating nature of the thick amorphous SiO2 is verified by transport measurements. The device-quality of the corresponding graphene was confirmed by the observation of Shubnikov-de Haas oscillations, an integer quantum Hall effect, and a weak antilocalization effect within in situ fabricated Hall bar devices. This work provides a reliable platform for applications of large-scale, high-quality graphene in electronics.
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- 2020
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13. Force-Activated Isomerization of a Single Molecule
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Hong-Jun Gao, Junzhi Liu, Zhihai Cheng, Qi Zheng, Xinliang Feng, Huan Yang, Yixuan Gao, Reinhard Berger, Yun Cao, Jing Qi, Min Ouyang, Shixuan Du, Li Huang, Haihong Jia, Marcus Richter, Xiao Lin, and Hongliang Lu
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Steric effects ,Chemistry ,General Chemistry ,Molecular configuration ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,law.invention ,Molecular dynamics ,Colloid and Surface Chemistry ,law ,Chemical physics ,Electric field ,Molecule ,Scanning tunneling microscope ,Isomerization ,Quantum tunnelling - Abstract
Understanding and controlling isomerization at the single molecular level should provide new insight into the molecular dynamics and design guidelines of functional devices. Scanning tunneling microscopy (STM) has been demonstrated to be a powerful tool to study isomerization of single molecules on a substrate, by either electric field or inelastic electron tunneling mechanisms. A similar molecular isomerization process can in principle be induced by mechanical force; however, relevant study has remained elusive. Here, we demonstrate that isomerization of a N,N-dimethylamino-dianthryl-benzene molecule on Ag(100) can be mechanically driven by the STM tip. The existence of an out-of-plane dimethylamino group in the molecule is found to play a pivotal role in the isomerization process by providing a steric hindrance effect for asymmetric interaction between the STM tip and the molecule. This underlying mechanism is further confirmed by performing molecular dynamics simulations, which show agreement with experimental results. Our work opens the opportunity to manipulate the molecular configuration on the basis of mechanical force.
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- 2020
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14. Direct Visualization of Hydrogen-Transfer Intermediate States by Scanning Tunneling Microscopy
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Qing Huan, Sokrates T. Pantelides, Junhai Ren, Linghao Yan, Shixuan Du, Rongting Wu, Yu-Yang Zhang, Yan-Fang Zhang, Hong-Jun Gao, Yeliang Wang, and De-Liang Bao
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Materials science ,Hydrogen ,Hydrogen transfer ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Visualization ,chemistry ,Chemical physics ,law ,Physical phenomena ,General Materials Science ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Quantum tunnelling - Abstract
Hydrogen atoms bonded within molecular cavities often undergo tunneling or thermal-transfer processes that play major roles in diverse physical phenomena. Such transfers may or may not entail intermediate states. The existence of such fleeting states is typically determined by indirect means, while their direct visualization has not been achieved, largely because their concentrations under equilibrium conditions are negligible. Here we use density-functional-theory calculations and scanning-tunneling-microscopy (STM) image simulations to predict that, under specially designed nonequilibrium conditions of voltage-enhanced high transfer rates, the
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- 2020
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15. Observation of the Kondo Effect in Multilayer Single-Crystalline VTe2 Nanoplates
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Jiahao Yan, Liangmei Wu, Hong-Jun Gao, Hongtao Liu, Haitao Yang, Ce Bian, Chengmin Shen, Zhang Zhou, Wu Zhou, Yunzhou Xue, Yangu He, Roger Guzmán, Lihong Bao, Panpan Zhang, Jinan Shi, Ruisong Ma, and Jiancui Chen
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Materials science ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,Chemical vapor deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Characterization (materials science) ,Chemical physics ,Phase (matter) ,General Materials Science ,Kondo effect ,0210 nano-technology ,Transport studies - Abstract
We report the chemical vapor deposition (CVD) growth, characterization, and low-temperature magnetotransport of 1T phase multilayer single-crystalline VTe2 nanoplates. The transport studies reveal ...
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- 2019
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16. Quasi-2D Transport and Weak Antilocalization Effect in Few-layered VSe2
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Ruisong Ma, Ce Bian, Hongtao Liu, Liangmei Wu, Changzhi Gu, Shixuan Du, Junjie Li, Bingyu Che, Haifang Yang, Hong-Jun Gao, Lihong Bao, Zhang Zhou, Chengmin Shen, and R. R. Zhang
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Physics ,Coupling ,Condensed matter physics ,Mechanical Engineering ,Physics::Optics ,Bioengineering ,02 engineering and technology ,General Chemistry ,Spin–orbit interaction ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Condensed Matter::Disordered Systems and Neural Networks ,Condensed Matter::Materials Science ,Transition metal ,General Materials Science ,0210 nano-technology - Abstract
With strong spin–orbit coupling (SOC), ultrathin two-dimensional (2D) transitional metal chalcogenides (TMDs) are predicted to exhibit weak antilocalization (WAL) effect at low temperatures. The ob...
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- 2019
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17. Spontaneous Formation of 1D Pattern in Monolayer VSe2 with Dispersive Adsorption of Pt Atoms for HER Catalysis
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Lei Tao, Xu Wu, Li Huang, Bao Lei, Hong-Jun Gao, Sokrates T. Pantelides, Zhong-Liu Liu, Xiao Lin, De-Liang Bao, Jing Qi, Yeliang Wang, Yu-Yang Zhang, Zhi-Li Zhu, and Shixuan Du
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Adsorption ,Materials science ,Mechanical Engineering ,Monolayer ,General Materials Science ,Bioengineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,Condensed Matter Physics ,Photochemistry ,Catalysis - Abstract
Creation of functional patterns in two-dimensional (2D) materials provides opportunities to extend their potential for applications. Transition-metal dichalcogenides (TMDCs) are suitable 2D materia...
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- 2019
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18. Self-Assembly Evolution of Metal-Free Naphthalocyanine Molecules on Ag(111) at the Submonolayer Coverage
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Hong-Jun Gao, De-Liang Bao, Linghao Yan, Yeliang Wang, Junhai Ren, Rongting Wu, Shixuan Du, and Qing Huan
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Materials science ,Naphthalocyanine ,Intermolecular force ,Molecular electronics ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,General Energy ,chemistry ,law ,Chemical physics ,Lattice (order) ,Molecule ,Density functional theory ,Self-assembly ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology - Abstract
Structures of self-assembled films play essential roles in the performance of potential organic molecular electronics; therefore, detailed knowledge of molecular adsorption and structural evolution is fundamental for the implementation of molecular electronics. Here, we systematically investigated the initial adsorption and structure evolution of metal-free naphthalocyanine (H2Nc) on the Ag(111) surface from dimers to ordered self-assembled structures in the submonolayer range. H2Nc molecules deposited on Ag(111) at 100 K accumulate into clusters dominated by dimers. Subsequent sample annealing induces the emergence of two ordered self-assembled structures, denoted by Sl and Sll. Molecule-resolved scanning tunneling microscopy images confirm that structure Sl is more stable with six rotation domains lying in two chiralities. Deviations of the lattice parameters from a threefold symmetry indicate non-neglectable intermolecular interactions in self-assembled patterns. Combined with density functional theory...
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- 2019
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19. Controlled Surface Reconstruction on Ferromagnetic Oxides: Spin Pinning Effect to the Oxyhydroxide Layer and Its Enhanced Oxygen Evolution Activity
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Alexis Grimaud, Junling Wang, Haitao Yang, Joel W. Ager, Jose Gracia, Chengmin Sheng, Daniel Mandler, Tianze Wu, Guoyu Xian, Günther G. Scherer, Hong-Jun Gao, Xiao Ren, Shengnan Sun, Zhichuan J. Xu, Adrian C. Fisher, and Yuanmiao Sun
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chemistry.chemical_compound ,Magnetization ,Materials science ,Triplet oxygen ,chemistry ,Spin polarization ,Magnetic domain ,Magnetic moment ,Ferromagnetism ,Chemical physics ,Oxygen evolution ,Condensed Matter::Strongly Correlated Electrons ,Spin-½ - Abstract
The production of hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. As spin-dependent kinetics exist in OER, the spin alignment in active OER catalysts is critical for reducing the kinetic barriers in OER. It is effective to facilitate the spin polarization in ferromagnetic catalysts by applying external magnetic field, which increases the OER efficiency. However, more active OER catalysts tend to have dynamic open-shell orbital configurations with disordered magnetic moments, without showing an apparent long-range interatomic ferromagnetism; thus controlling the spin alignment of these active catalysts is challenging. In this work, we report a strategy with spin pinning effect to make the spins in active oxyhydroxides more aligned for higher intrinsic OER activity. Such strategy bases on a controllable reconstruction: ferromagnetic oxides with controlled sulfurization can evolve into stable oxideFM/oxyhydroxide configurations with a thin oxyhydroxide layer under operando condition. The spin pinning effect is found at the interface of oxideFM/oxyhydroxide. The spin pinning effect can promote spin selective electron transfer on OER intermediates to generate oxygens with parallel spin alignment, which facilitates the production of triplet oxygen and increases the intrinsic activity of oxyhydroxide by ~ 1 order of magnitude. Under spin pinning, the spins in oxyhydroxide can become more aligned after magnetization as long-range ferromagnetic ordering is established on the magnetic domains in oxideFM. The OER kinetics are facilitated accordingly after magnetization, implying that the spin pinning effect is involved in the rate-determining step and this step is spin dependent. The spin polarization process in OER under spin pinning is also believed to be sensitive to the existence of active oxygen ligand (O(-)) in oxyhydroxide. When the O(-) is created in 1st deprotonation step under high pH, the spin polarization of ligand oxygens will be facilitated, which reduces the barrier for subsequent O-O coupling and promotes the O2 turnover.
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- 2021
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20. Spin-Polarized Oxygen Evolution Reaction Under Magnetic Field
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Xiao Ren, Zhichuan J. Xu, Guoyu Xian, Tianze Wu, Haitao Yang, Chengmin Shen, Jose Gracia, Xianhu Liu, Yuanmiao Sun, Hong-Jun Gao, and Yan Li
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Materials science ,Science ,General Physics and Astronomy ,02 engineering and technology ,Electron ,010402 general chemistry ,01 natural sciences ,Quantitative Biology::Other ,Article ,General Biochemistry, Genetics and Molecular Biology ,Magnetization ,symbols.namesake ,Condensed Matter::Materials Science ,Pauli exclusion principle ,Singlet state ,Triplet state ,Physics::Chemical Physics ,Magnetic materials ,Spin (physics) ,Multidisciplinary ,Spin polarization ,Oxygen evolution ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,0104 chemical sciences ,Ferromagnetism ,Chemical physics ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Electrocatalysis ,0210 nano-technology ,Materials for energy and catalysis - Abstract
The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts., Here, authors demonstrate the ferromagnetic catalyst to facilitate spin polarization in water oxidation reaction. They find the ferromagnetic-exchange-like behaviour between the ferromagnetic catalyst and the adsorbed oxygen species.
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- 2021
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21. Reliable Spin Valves of Conjugated Polymer Based on Mechanically Transferrable Top Electrodes
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Wenbo Mi, Daoben Zhu, Shuaishuai Ding, Hong-Jun Gao, Ye Zou, Zhenjie Ni, Wenping Hu, Zhang Zhou, Hanlin Wang, Yuan Tian, and Huanli Dong
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Coupling ,chemistry.chemical_classification ,Fabrication ,Materials science ,Spintronics ,business.industry ,General Engineering ,Spin valve ,General Physics and Astronomy ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Ferromagnetism ,chemistry ,Electrode ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Spin-½ - Abstract
Organic spintronic devices present one of the most appealing technologies for future spintronic devices by taking advantage of the spin degree of freedom. Conjugated polymers are attractive for the exemplified device of organic spin valves (OSVs) due to their weak spin–orbit coupling, solution-processability, low production cost, and mechanical flexibility. However, the performance of polymer SVs is a matter of debate, as the evaporated top ferromagnetic (FM) electrode will penetrate into the organic layer during a typical fabrication process, especially in the device with an organic layer thickness of nanometers. It will cause a severe problem in controllable and reproducible spin manipulations, not to mention the clarification of the spin-dependent transport mechanism. Here, a universal, simple, and low-cost method based on a transferred electrode is developed for a polymer spin valve with stable and reliable state operation. It is demonstrated in an OSV device with a vertical structure of La2/3Sr1/3MnO...
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- 2018
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22. Controllable Density of Atomic Bromine in a Two-Dimensional Hydrogen Bond Network
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De-Liang Bao, Hong-Jun Gao, Zhenliang Hao, Jinming Cai, Yurou Guan, Zilin Ruan, Jianchen Lu, Cuixia Yan, Shixuan Du, Xiao Lin, Lingling Song, and Hui Zhang
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Bromine ,Materials science ,Hydrogen bond ,Network on ,Hydrogen bromide ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Pentacene ,Crystallography ,chemistry.chemical_compound ,General Energy ,chemistry ,law ,Molecule ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Molecular beam epitaxy - Abstract
Using atomic bromine (Br) and pentacene molecules, we successfully constructed and characterized a large-scale Br atom-mediated two-dimensional (2D) organic network on a Ag(111) surface by combining molecular beam epitaxy with scanning tunneling microscopy. The Br atoms form −C–H···Br hydrogen bonds with pentacene molecules in the network, and the number of Br atoms among pentacene molecules can be tuned from one to five by increasing the pressure or exposure time of hydrogen bromide (HBr) gas. In addition, all of the Br atoms of five 2D organic networks fill themselves in the position of maximum number of hydrogen bonds.
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- 2018
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23. Modification of the Potential Landscape of Molecular Rotors on Au(111) by the Presence of an STM Tip
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Cristian A. Strassert, Harald Fuchs, Hong-Jun Gao, Xiao Lin, Hongliang Lu, Anne Bakker, Karl-Heinz Ernst, Yun Cao, Shixuan Du, and Jing Qi
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Materials science ,Rotor (electric) ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Potential energy ,Molecular machine ,0104 chemical sciences ,law.invention ,symbols.namesake ,Dipole ,Chemical physics ,law ,Electric field ,symbols ,Molecule ,General Materials Science ,van der Waals force ,Scanning tunneling microscope ,0210 nano-technology - Abstract
Molecular rotors on solid surfaces are fundamental components of molecular machines. No matter whether the rotation is activated by heat, electric field or light, it is determined by the intrinsic rotational potential landscape. Therefore, tuning the potential landscape is of great importance for future applications of controlled molecular rotors. Here, using scanning tunneling microscopy (STM), we demonstrate that both tip-molecule distance and sample bias can modify the rotational potential of molecular rotors. We achieve the potential energy difference variations of ∼0.3 meV/pm and ∼18 meV/V between two configurations of a molecular rotor, a tetra- tert-butyl nickel phthalocyanine molecule on Au(111) substrate. Further analysis indicates that the mechanism of modifying the rotational potential is a combination of the van der Waals interaction and the interaction between the molecular dipole and an electric field. This work provides insight into the methods used to modify the effective rotational potential energy of molecular rotors.
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- 2018
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24. Barrierless On-Surface Metal Incorporation in Phthalocyanine-Based Molecules
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Hong-Jun Gao, De-Liang Bao, Sokrates T. Pantelides, Yu-Yang Zhang, and Shixuan Du
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Materials science ,Metalation ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Metal ,chemistry.chemical_compound ,Adsorption ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Drop (liquid) ,021001 nanoscience & nanotechnology ,Nitrogen ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,chemistry ,visual_art ,visual_art.visual_art_medium ,Phthalocyanine ,Density functional theory ,0210 nano-technology - Abstract
On-surface metalation of metal-free phthalocyanine derivatives is a simple and solvent-free way to fabricate MPc compounds. Using phthalocyanine (H2Pc) molecules on Ag(111) as an example, we investigated the atomic-scale mechanisms of on-surface metalation processes using first-principles calculations based on density functional theory. When the molecules are deposited on a substrate first, we find that transition-metal atoms, except for Zn, drop directly from the vacuum into the molecule’s cavity without an energy barrier and bond with the inner four nitrogen atoms, with the two pyrrolic H atoms still in place. Subsequently, the two H atoms transfer to the substrate by overcoming small energy barriers and diffuse away. The substrate participates in the reaction by hybridization. In the alternative process, when metal atoms are adsorbed first on the surface and the H2Pc molecules are then added, the metal atoms diffuse into the cavity of the molecule via the molecule–surface interface by overcoming finite...
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- 2018
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25. Epitaxial Growth of Flat Antimonene Monolayer: A New Honeycomb Analogue of Graphene
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Zhong-Liu Liu, Cai Cheng, Shiyu Zhu, Dongxia Shi, Hong-Jun Gao, Hang Liu, Yeliang Wang, Chen Liu, Jiaou Wang, Jia-Tao Sun, Kurash Ibrahim, Yan Shao, Yuqi Wang, and Xu Wu
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Materials science ,Condensed matter physics ,Graphene ,Mechanical Engineering ,chemistry.chemical_element ,Quantum anomalous Hall effect ,Bioengineering ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,01 natural sciences ,0104 chemical sciences ,law.invention ,Graphene monolayer ,Antimony ,chemistry ,law ,Monolayer ,Honeycomb ,General Materials Science ,0210 nano-technology - Abstract
Group-V elemental monolayers were recently predicted to exhibit exotic physical properties such as nontrivial topological properties, or a quantum anomalous Hall effect, which would make them very suitable for applications in next-generation electronic devices. The free-standing group-V monolayer materials usually have a buckled honeycomb form, in contrast with the flat graphene monolayer. Here, we report epitaxial growth of atomically thin flat honeycomb monolayer of group-V element antimony on a Ag(111) substrate. Combined study of experiments and theoretical calculations verify the formation of a uniform and single-crystalline antimonene monolayer without atomic wrinkles, as a new honeycomb analogue of graphene monolayer. Directional bonding between adjacent Sb atoms and weak antimonene-substrate interaction are confirmed. The realization and investigation of flat antimonene honeycombs extends the scope of two-dimensional atomically-thick structures and provides a promising way to tune topological properties for future technological applications.
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- 2018
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26. Lattice-Directed Construction of Metal–Organic Molecular Wires of Pentacene on the Au(110) Surface
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Linghao Yan, Hong-Jun Gao, De-Liang Bao, Aiwei Wang, Li Dong, Jia-Tao Sun, Junhai Ren, Lei Gao, Yeliang Wang, Shixuan Du, Jiahao Yan, Qing Huan, and Rongting Wu
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Materials science ,Annealing (metallurgy) ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Pentacene ,Molecular wire ,chemistry.chemical_compound ,General Energy ,Adsorption ,chemistry ,law ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Surface reconstruction - Abstract
The construction of metal–organic molecular wires is important for the design of specific functional devices but has been a great challenge for experimental technology. Here we report the formation of one-dimensional metal–organic structures by direct deposition of pentacene molecules on the Au(110) surface with subsequent thermal annealing. These metal–organic molecular wires were systematically explored by scanning tunneling microscopy (STM) and density functional theory calculations. At submonolayer coverage, during annealing at ∼470 K, the adsorbed molecules induce both Au(110)-(1 × 3) surface reconstruction, where two atomic rows are missing every three rows on the Au(110) surface, with the end-to-end pentacene configuration and Au(110)-(1 × 6) surface reconstruction, where five rows are missing every six rows on the surface, with the side-by-side configuration. Further annealing at ∼520 K results in Au-adatom-coordinated metal–organic molecular wires with a new side-by-side configuration of pentacen...
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- 2017
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27. Design of Two-Dimensional Graphene-like Dirac Materials β12-XBeB5 (X = H, F, Cl) from Non-graphene-like β12-Borophene
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Shixuan Du, Boris I. Yakobson, Shiru Song, Hong-Jun Gao, and Jihui Yang
- Subjects
Physics ,Work (thermodynamics) ,Global energy ,Condensed matter physics ,Graphene ,Dirac (software) ,chemistry.chemical_element ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Flexible electronics ,law.invention ,chemistry ,law ,0103 physical sciences ,Borophene ,General Materials Science ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Boron - Abstract
Two-dimensional (2D) Dirac materials and boron sheets have attracted intensive interest recently. However, 2D Dirac materials remain rare and difficult to be realized experimentally, and 2D boron sheets generally have high dynamical instability. Stimulated by the experimental observation of Dirac cones in nongraphene-like β12 boron sheets and based on the understanding of boron sheet electronic organization, we theoretically design new 2D Dirac materials β12-XBeB5 (X = H, F, Cl) with high stability. We confirm β12-HBeB5 as the global energy minimum among its 2D allotropes based on global structure search methods, a strong indication of its experimental feasibility. Our designed β12-HBeB5 has not only a high Fermi velocity, but also a Dirac state very robust against extraordinary large tensile strains, an advantage for flexible electronics applications. Our work opens a new avenue to designing feasible 2D Dirac materials and stabilizing borophene sheets.
- Published
- 2017
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28. Evidence for Ultralow-Energy Vibrations in Large Organic Molecules
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Lei Tao, Yu-Yang Zhang, De-Liang Bao, Wende Xiao, Jun-Long Zhang, Hong-Jun Gao, Hui Chen, Thomas Pope, Werner A. Hofer, Zhuo-Yan Wu, Shixuan Du, Sokrates T. Pantelides, Dongfei Wang, and Song Gao
- Subjects
Free electron model ,Range (particle radiation) ,Materials science ,Photon ,Inelastic electron tunneling spectroscopy ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Molecular physics ,Spectral line ,0104 chemical sciences ,Quantum mechanics ,Molecular vibration ,General Materials Science ,Quantum efficiency ,Physics::Chemical Physics ,0210 nano-technology - Abstract
The quantum efficiency or the rate of conversion of incident photon to free electron in photosynthesis is known to be extremely high. It has long been thought that the origin of this efficiency are molecular vibrations leading to a very fast separation of electrons and holes within the involved molecules. However, molecular vibrations are commonly in the range above 100 meV, which is too high for excitations in an ambient environment. Here, we analyze experimental spectra of single organic molecules on metal surfaces at ∼4 K, which often exhibit a pronounced dip. We show that measurements on iron(II) [tetra-(pentafluorophenyl)]porphyrin resolve this single dip at 4 K into a series of step-shaped inelastic excitations at 0.4 K. Via extensive spectral maps under applied magnetic fields and corresponding theoretical analysis we find that the dip is due to ultralow-energy vibrations of the molecular frame, typically in the range below 20 meV. The result indicates that ultralow energy vibrations in organic molecules are much more common than currently thought and may be all-pervasive for molecules above a certain size.
- Published
- 2017
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29. Controlled Synthesis of Nitrogen-Doped Graphene on Ruthenium from Azafullerene
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J. Neilson, Xiangmin Fei, Vanessa Lopez, Yanbang Li, Li Gao, Liangbing Gan, Hong-Jun Gao, and Simon J. Garrett
- Subjects
inorganic chemicals ,Materials science ,Inorganic chemistry ,chemistry.chemical_element ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Atomic units ,law.invention ,X-ray photoelectron spectroscopy ,law ,General Materials Science ,Graphene ,Mechanical Engineering ,Doping ,technology, industry, and agriculture ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Nitrogen ,0104 chemical sciences ,Ruthenium ,chemistry ,Chemical engineering ,Scanning tunneling microscope ,0210 nano-technology ,Layer (electronics) - Abstract
The controlled synthesis of high-quality nitrogen (N) doped single layer graphene on the Ru(0001) surface has been achieved using the N-containing sole precursor azafullerence (C59NH). The synthesis process and doping properties have been investigated on the atomic scale by combining scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements. We find for the first time that the concentration of N-related defects on the N-doped graphene/Ru(0001) surface is tunable by adjusting the dosage of sole precursor and the number of growth cycles. Two primary types of N-related defects have been observed. The predominant bonding configuration of N atoms in the obtained graphene layer is pyridinic N. Our findings indicate that the synthesis from heteroatom-containing sole precursors is a very promising approach for the preparation of doped graphene materials with controlled doping properties.
- Published
- 2017
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30. Identifying and Visualizing the Edge Terminations of Single-Layer MoSe2 Island Epitaxially Grown on Au(111)
- Author
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De-Liang Bao, Xiao Lin, Jianchen Lu, Shuai Zhang, Kai Qian, Shixuan Du, Hui Chen, and Hong-Jun Gao
- Subjects
Chemistry ,Scanning tunneling spectroscopy ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,Edge (geometry) ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Molecular physics ,law.invention ,Crystallography ,law ,0103 physical sciences ,Monolayer ,Coupling (piping) ,General Materials Science ,Density functional theory ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Molecular beam epitaxy - Abstract
Recently, single-layer transition-metal dichalcogenides have drawn significant attention due to their remarkable physical properties in the monolayer as well as at the edges. Here, we constructed high-quality, single-layer MoSe2 islands on the Au(111) surfaces in ultrahigh vacuum by molecular beam epitaxy. All of the islands have hexagonal or triangular shapes with two kinds of well-defined edges. Scanning tunneling spectroscopy (STS) curves show notable differences in positive sample bias for the two types of edges. Density functional theory calculations for several edge configurations of MoSe2 confirm that the STS differences are attributed to the coupling between the pz orbital of Se atoms and the dxz orbital of Mo atoms, and the two types of observed edge terminations are the bare Se edge and selenium-saturated Mo edge.
- Published
- 2017
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31. Sequence of Silicon Monolayer Structures Grown on a Ru Surface: from a Herringbone Structure to Silicene
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Jinbo Pan, En Li, Wenyan Xu, Yeliang Wang, Yan-Fang Zhang, Yunqi Liu, Shixuan Du, Hong-Jun Gao, Yande Que, Li Huang, Yu-Yang Zhang, and Sokrates T. Pantelides
- Subjects
Materials science ,Silicon ,Superlattice ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,02 engineering and technology ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Monolayer ,General Materials Science ,010306 general physics ,Silicene ,Graphene ,business.industry ,Mechanical Engineering ,Transistor ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,chemistry ,Structural stability ,Optoelectronics ,Scanning tunneling microscope ,0210 nano-technology ,business - Abstract
Silicon-based two-dimensional (2D) materials are uniquely suited for integration in Si-based electronics. Silicene, an analogue of graphene, was recently fabricated on several substrates and was used to make a field-effect transistor. Here, we report that when Ru(0001) is used as a substrate, a range of distinct monolayer silicon structures forms, evolving toward silicene with increasing Si coverage. Low Si coverage produces a herringbone structure, a hitherto undiscovered 2D phase of silicon. With increasing Si coverage, herringbone elbows evolve into silicene-like honeycomb stripes under tension, resulting in a herringbone-honeycomb 2D superlattice. At even higher coverage, the honeycomb stripes widen and merge coherently to form silicene in registry with the substrate. Scanning tunneling microscopy (STM) was used to image the structures. The structural stability and electronic properties of the Si 2D structures, the interaction between the Si 2D structures and the Ru substrate, and the evolution of the...
- Published
- 2017
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32. Intrinsic Two-Dimensional Organic Topological Insulators in Metal–Dicyanoanthracene Lattices
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Bing Huang, Zhiming Wang, Lizhi Zhang, Bin Cui, Hong-Jun Gao, Feng Liu, Shixuan Du, and Zhengfei Wang
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Bioengineering ,02 engineering and technology ,Electron ,01 natural sciences ,Metal ,symbols.namesake ,Lattice (order) ,0103 physical sciences ,Molecule ,General Materials Science ,Molecular orbital ,010306 general physics ,Quantitative Biology::Neurons and Cognition ,Condensed matter physics ,Chemistry ,Mechanical Engineering ,Fermi level ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,visual_art ,Topological insulator ,symbols ,visual_art.visual_art_medium ,Density functional theory ,0210 nano-technology - Abstract
We predict theoretical existence of intrinsic two-dimensional organic topological insulator (OTI) states in Cu-dicyanoanthracene (DCA) lattice, a system that has also been grown experimentally on Cu substrate, based on first-principle density functional theory calculations. The pz-orbital Kagome bands having a Dirac point lying exactly at the Fermi level are found in the freestanding Cu-DCA lattice. The tight-binding model analysis, the calculated Chern numbers, and the semi-infinite Dirac edge states within the spin-orbit coupling gaps all confirm its intrinsic topological properties. The intrinsic TI states are found to originate from a proper number of electrons filling of the hybridized bands from Cu atomic and DCA molecular orbitals based on which similar lattices containing noble metal atoms (Au and Cu) and those molecules with two CN groups (DCA and cyanogens) are all predicted to be intrinsic OTIs.
- Published
- 2016
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33. Strongly Interacting C60/Ir(111) Interface: Transformation of C60 into Graphene and Influence of Graphene Interlayer
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Xu Zhang, Li Gao, Vanessa Lopez, Xiangmin Fei, Gang Lu, and Hong-Jun Gao
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Materials science ,Graphene ,Nanotechnology ,Electronic structure ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,General Energy ,Adsorption ,law ,Chemical physics ,Quantum dot ,Density functional theory ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Bilayer graphene ,Graphene nanoribbons - Abstract
The adsorption, electronic structure, and thermodynamics of C60 molecules on Ir(111) and graphene/Ir(111) surfaces have been investigated by combining scanning tunneling microscopy and spectroscopy as well as density functional theory calculations. C60 is found to interact strongly with the Ir surface, leading to a spontaneous formation of graphene on the Ir surface at elevated temperatures. The introduction of a graphene interlayer at the C60/Ir(111) interface dramatically affects the interface properties, including the formation of larger molecular islands, improvement in ordering of molecular arrangements, suppression of charge transfer between C60 and Ir, and thermal desorption of C60 from the surface without decomposition or polymerization. We also find that C60 is an effective solid precursor for preparing small-sized graphene quantum dots as well as graphene layers on the Ir surface.
- Published
- 2015
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34. Reliable Exfoliation of Large-Area High-Quality Flakes of Graphene and Other Two-Dimensional Materials
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Jiabao Zheng, Hong-Jun Gao, Yuan Huang, Peter Sutter, Tianzhong Yang, Norman Nan Shi, Dirk Englund, and Eli Sutter
- Subjects
Yield (engineering) ,Materials science ,Graphene ,General Engineering ,General Physics and Astronomy ,Nanotechnology ,Substrate (electronics) ,Exfoliation joint ,law.invention ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,law ,Monolayer ,symbols ,General Materials Science ,Composite material ,Bismuth strontium calcium copper oxide ,Raman spectroscopy ,Contact area - Abstract
Mechanical exfoliation has been a key enabler of the exploration of the properties of two-dimensional materials, such as graphene, by providing routine access to high-quality material. The original exfoliation method, which remained largely unchanged during the past decade, provides relatively small flakes with moderate yield. Here, we report a modified approach for exfoliating thin monolayer and few-layer flakes from layered crystals. Our method introduces two process steps that enhance and homogenize the adhesion force between the outermost sheet in contact with a substrate: Prior to exfoliation, ambient adsorbates are effectively removed from the substrate by oxygen plasma cleaning, and an additional heat treatment maximizes the uniform contact area at the interface between the source crystal and the substrate. For graphene exfoliation, these simple process steps increased the yield and the area of the transferred flakes by more than 50 times compared to the established exfoliation methods. Raman and AFM characterization shows that the graphene flakes are of similar high quality as those obtained in previous reports. Graphene field-effect devices were fabricated and measured with back-gating and solution top-gating, yielding mobilities of ∼4000 and 12,000 cm(2)/(V s), respectively, and thus demonstrating excellent electrical properties. Experiments with other layered crystals, e.g., a bismuth strontium calcium copper oxide (BSCCO) superconductor, show enhancements in exfoliation yield and flake area similar to those for graphene, suggesting that our modified exfoliation method provides an effective way for producing large area, high-quality flakes of a wide range of 2D materials.
- Published
- 2015
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35. Highly Anisotropic Dirac Fermions in Square Graphynes
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Zhengfei Wang, Hong-Jun Gao, Zhiming Wang, Feng Liu, Lizhi Zhang, and Shixuan Du
- Subjects
Physics ,Condensed matter physics ,Fermi level ,Graphyne ,symbols.namesake ,Dirac fermion ,Quantum mechanics ,symbols ,General Materials Science ,Density functional theory ,Physical and Theoretical Chemistry ,Electronic band structure ,Anisotropy ,Hamiltonian (quantum mechanics) ,Fermi Gamma-ray Space Telescope - Abstract
We predict a family of 2D carbon (C) allotropes, square graphynes (S-graphynes) that exhibit highly anisotropic Dirac fermions, using first-principle calculations within density functional theory. They have a square unit-cell containing two sizes of square C rings. The equal-energy contour of their 3D band structure shows a crescent shape, and the Dirac crescent has varying Fermi velocities from 0.6 × 10(5) to 7.2 × 10(5) m/s along different k directions. Near the Fermi level, the Dirac crescent can be nicely expressed by an extended 2D Dirac model Hamiltonian. Furthermore, tight-binding band fitting reveals that the Dirac crescent originates from the next-nearest-neighbor interactions between C atoms. S-graphynes may be used to build new 2D electronic devices taking advantages of their highly directional charge transport.
- Published
- 2015
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36. Role of Cooperative Interactions in the Intercalation of Heteroatoms between Graphene and a Metal Substrate
- Author
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Geng Li, Yi Zhang, Min Ouyang, Haitao Zhou, Lida Pan, Andrea C. Ferrari, Hong-Jun Gao, Li Huang, Shixuan Du, and Wenyan Xu
- Subjects
Chemistry ,Graphene ,Heteroatom ,Intercalation (chemistry) ,Nanotechnology ,Heterojunction ,General Chemistry ,Substrate (electronics) ,Biochemistry ,Catalysis ,law.invention ,Colloid and Surface Chemistry ,law ,Chemical physics ,Monolayer ,Density functional theory ,Scanning tunneling microscope - Abstract
The intercalation of heteroatoms between graphene and a metal substrate has been studied intensively over the past few years, due to its effect on the graphene properties, and as a method to create vertical heterostructures. Various intercalation processes have been reported with different combinations of heteroatoms and substrates. Here we study Si intercalation between graphene and Ru(0001). We elucidate the role of cooperative interactions between hetero-atoms, graphene, and substrate. By combining scanning tunneling microscopy with density functional theory, the intercalation process is confirmed to consist of four key steps, involving creation of defects, migration of heteroatoms, self-repairing of graphene, and growth of an intercalated monolayer. Both theory and experiments indicate that this mechanism applies also to other combinations of hetero-atoms and substrates.
- Published
- 2015
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37. Spin-Dependent Conductance in Co/C60/Co/Ni Single-Molecule Junctions in the Contact Regime
- Author
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Vanessa Lopez, Li Gao, Hong-Jun Gao, Xiangmin Fei, Guangfen Wu, and Gang Lu
- Subjects
Condensed matter physics ,Chemistry ,Scanning tunneling spectroscopy ,Analytical chemistry ,Conductance ,Electrical contacts ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Tunnel magnetoresistance ,General Energy ,law ,Electrode ,Molecule ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Spin (physics) - Abstract
The spin-dependent conductance in Co/C60/Co/Ni single-molecule magnetic tunnel junctions has been measured by combining spin-polarized scanning tunneling spectroscopy and current-displacement measurements using an ultrahigh vacuum low temperature scanning tunneling microscope (STM) at 5 K. With an electrical contact between molecule and electrodes, the measured junction conductance is 0.02–0.13 G0 in the low-conductance state and 0.12–0.76 G0 in the high-conductance state, respectively. The investigated single-molecule junctions exhibit large tunnel magnetoresistance (TMR) ratios higher than −60%. A variation of TMR from −63% to −94% has been observed due to different Co/Ni electrodes.
- Published
- 2015
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38. Self-Assembled Patterns and Young’s Modulus of Single-Layer Naphthalocyanine Molecules on Ag(111)
- Author
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Hong-Jun Gao, Rongting Wu, Linghao Yan, Yeliang Wang, Junhai Ren, Haigang Zhang, Yan-Fang Zhang, De-Liang Bao, Qing Huan, and Shixuan Du
- Subjects
Materials science ,Naphthalocyanine ,Modulus ,Young's modulus ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,chemistry.chemical_compound ,Crystallography ,General Energy ,Adsorption ,chemistry ,law ,Lattice (order) ,symbols ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Scanning tunneling microscope - Abstract
Structural and mechanical properties of self- assembled metal-free naphthalocyanine (H2Nc) films on a Ag(111) surface are studied. Six self-assembled domains are observed by scanning tunneling microscopy (STM). Combin- ing the high-resolution STM images and density functional theory (DFT) based calculations, we found that molecules adsorbed flatly on the substrate by forming six different interlocked square-like unit cells with different lattice parameters. DFT calculations indicated comparable adsorption energies for all the configurations. Six domains with different lattice parameters present different strain states, giving us a possibility to evaluate the Young's modulus of the metal-free naphthalocyanine films on the Ag(111) surface. We found that the Young's modulus of H2Nc is comparable to those of typical conjugated organic-molecule-based crystals (e.g., naphthalene), providing useful information for future applications when the elastic properties should be concerned.
- Published
- 2015
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39. Structural and Electronic Properties of Pb- Intercalated Graphene on Ru(0001)
- Author
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Liwei Liu, Lizhi Zhang, Yande Que, Kai Yang, Xiangmin Fei, Hui Chen, Shixuan Du, Hong-Jun Gao, and Wende Xiao
- Subjects
Superstructure ,Materials science ,Graphene ,Intercalation (chemistry) ,Nanotechnology ,Substrate (electronics) ,Epitaxy ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,Crystallography ,General Energy ,law ,symbols ,Density functional theory ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Raman spectroscopy - Abstract
The Pb intercalation at the interface of monolayer graphene (MG) and Ru(0001) is studied by means of low temperature scanning tunneling microscopy (LT-STM) and Raman spectroscopy. Despite being covered by MG, the atomic structures of the Pb layer formed between MG and Ru(0001) have been directly imaged using LT-STM. The Pb layer intercalated underneath MG exhibits a √7 × √7-R19° superstructure with respect to the Ru(0001) surface. STM and Raman spectroscopy measurements and density functional theory calculations reveal that the epitaxial MG are effectively decoupled from the Ru(0001) substrate and recover its intrinsic electronic property after Pb intercalation.
- Published
- 2015
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40. Strain-Induced Anisotropic Transport Properties of LaBaCo2O5.5+δ Thin Films on NdGaO3 Substrates
- Author
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Chonglin Chen, Ming Liu, Chun Lin Jia, Hong-Jun Gao, Qiang Zou, Chunrui Ma, Haiming Guo, Shao Bo Mi, and Greg Collins
- Subjects
Diffraction ,Materials science ,law ,Transmission electron microscopy ,Analytical chemistry ,Oxygen transport ,General Materials Science ,Scanning tunneling microscope ,Thin film ,Epitaxy ,Anisotropy ,law.invention ,Pulsed laser deposition - Abstract
Thin films of double-perovskite structural LaBaCo2O5.5+δ were epitaxially grown on (110) NdGaO3 substrates by pulsed laser deposition. Microstructural studies by high-resolution X-ray diffraction and transmission electron microscopy revealed that the films have an excellent quality epitaxial structure. In addition, strong in-plane anisotropic strains were measured. Electrical transport properties of the films were characterized by an ultra-high-vacuum four-probe scanning tunneling microscopy system at different temperatures. It was found that the anisotropic in-plane strain can significantly tune the values of film resistance up to 590%.
- Published
- 2014
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41. Thermally Controlled Adenine Dimer Chain Rotation on Cu(110): The Critical Role of van der Waals Interactions
- Author
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Shengbai Zhang, Lei Meng, Yu-Yang Zhang, Yeliang Wang, and Hong-Jun Gao
- Subjects
Annealing (metallurgy) ,Dimer ,Nucleation ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,symbols.namesake ,General Energy ,chemistry ,Chemical physics ,Computational chemistry ,Metastability ,Physics::Atomic and Molecular Clusters ,symbols ,Surface modification ,Physical and Theoretical Chemistry ,van der Waals force - Abstract
The theory of adenine dimer chain assembly on Cu(110) surface is controversial, due in large to the lack of an adequate description of the van der Waals (vdW) interactions. Here, we show by a combined first-principles calculation and experiment that the role of the vdW interactions is to tilt the energy balance at different levels of chain hierarchy. We find that the stable chains are made of metastable dimers, whereas the metastable chains, close in energy to the stable ones, are made of stable dimers. As such, at room temperate deposition, adenine dimers exist primarily in their stable form. This leads to the formation of metastable chains. By annealing at elevated temperature, however, more dimers can exist in the metastable form. This leads to the nucleation of the stable chains at a different orientation. The thermally controlled chain rotation is expected to be of general importance to the understanding of amino acids assembly and functionalization at the most elemental level.
- Published
- 2014
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42. Growth and Structural Properties of Pb Islands on Epitaxial Graphene on Ru(0001)
- Author
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Liwei Liu, Kai Yang, Yuhang Jiang, Xiangmin Fei, Liangzhong Zhang, Wende Xiao, Hong-Jun Gao, and Shixuan Du
- Subjects
Crystallography ,General Energy ,Materials science ,Graphene ,law ,Hexagonal crystal system ,Annealing (metallurgy) ,Epitaxial graphene ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention - Abstract
Structural properties of Pb islands grown on graphene/Ru(0001) at various deposition temperatures (T-D) and annealing temperatures (T-A) are investigated by a low-temperature scanning tunneling microscope. Single-layer Pb islands with a 2 X 2 reconstruction are only formed at T-D of 80 K and disappear with post-annealing to room temperature (RT). It is revealed that a morphological transition of the Pb islands takes place, from irregular shapes to a hexagonal equilibrium shape, with increasing T-D or T-A to RT. Moreover, Pb islands grown at T-D of RT are larger than those grown at a T-D of 80 K and annealed to RT. All Pb islands with a T-A or T-D of RT are (111)-faceted with thicknesses of even-numbered atomic layers and exhibit a weak interaction between Pb and graphene.
- Published
- 2013
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43. Buckled Silicene Formation on Ir(111)
- Author
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Geng Li, Yi Zhang, Linfei Li, Werner A. Hofer, Rongting Wu, Yeliang Wang, Haitao Zhou, Shixuan Du, Lei Meng, Lizhi Zhang, and Hong-Jun Gao
- Subjects
Germanene ,Materials science ,Condensed matter physics ,Low-energy electron diffraction ,Silicene ,Graphene ,Mechanical Engineering ,Superlattice ,Bioengineering ,General Chemistry ,Condensed Matter Physics ,Electron localization function ,law.invention ,law ,Stanene ,General Materials Science ,Scanning tunneling microscope - Abstract
Silicene, a two-dimensional (2D) honeycomb structure similar to graphene, has been successfully fabricated on an Ir(111) substrate. It is characterized as a (√7×√7) superstructure with respect to the substrate lattice, as revealed by low energy electron diffraction and scanning tunneling microscopy. Such a superstructure coincides with the (√3×√3) superlattice of silicene. First-principles calculations confirm that this is a (√3×√3)silicene/(√7×√7)Ir(111) configuration and that it has a buckled conformation. Importantly, the calculated electron localization function shows that the silicon adlayer on the Ir(111) substrate has 2D continuity. This work provides a method to fabricate high-quality silicene and an explanation for the formation of the buckled silicene sheet.
- Published
- 2013
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44. Boron Sheet Adsorbed on Metal Surfaces: Structures and Electronic Properties
- Author
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Qing-Bo Yan, Gang Su, Hong-Jun Gao, Shixuan Du, and Lizhi Zhang
- Subjects
Materials science ,Graphene ,Analytical chemistry ,chemistry.chemical_element ,Nanotechnology ,Electronic structure ,Electron ,Electron deficiency ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Metal ,General Energy ,chemistry ,law ,visual_art ,Monolayer ,visual_art.visual_art_medium ,Density functional theory ,Physical and Theoretical Chemistry ,Boron - Abstract
Using first-principles calculations based on density functional theory, we studied the possible geometric configurations and electronic structures of three types of monolayer boron sheets (BSs) on different metal (Mg, Al, Ti, Au, and Ag) surfaces. We find that, when adsorbed on metal surfaces, hexagonal BS (h-BS) is more energy-favorable than triangular BS or mixed hexagonal-triangular BS, and the atop-site adsorption configuration is the most favored. For all h-BS/metal configurations, electrons are observed to transfer from metal to BS, due to the intrinsic electron deficiency of h-BS. Electronic structure analyses show that the substrates could be classified into two types according to the interactions between boron and metal: (1) h-BS on Mg(0001), Al(111), or Ti(0001) shows a relatively larger charge transfer and stronger BS–metal interactions, and the σ (in-plane) bands have the same profile as freestanding h-BS, except for a Fermi level shift caused by the charge transfer. (2) h-BS on Au(111) or Ag(...
- Published
- 2012
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45. Host–Guest Superstructures on Graphene-Based Kagome Lattice
- Author
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Yi Zhang, Liwei Liu, Jinhai Mao, Wende Xiao, Geng Li, Haitao Zhou, Hong-Jun Gao, Haigang Zhang, and Shixuan Du
- Subjects
Zinc phthalocyanine ,Materials science ,Graphene ,Supramolecular chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,Crystallography ,General Energy ,chemistry ,law ,Lattice (order) ,Phthalocyanine ,Molecule ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Nanoscopic scale - Abstract
The Kagome lattice of iron phthalocyanine (FePc) on the graphene moire pattern is employed as host template for two kinds of guest molecules, FePc and tert-butyl zinc phthalocyanine ((t-Bu)4–ZnPc), to fabricate stable host–guest molecular superstructures. Both FePc and (t-Bu)4–ZnPc molecules prefer to occupy the nanoscale pores of the Kagome lattice. Ordered superstructures with alternate rows of FePc and (t-Bu)4–ZnPc are formed after coadsorption of these two species with a ratio of 1:1 on the Kagome lattice. We elucidate that formation of ordered superstructures of guest FePc and (t-Bu)4–ZnPc are controlled by long-range interaction between the guest molecules mediated by the host Kagome lattice with additional contribution from the graphene/Ru(0001) substrate.
- Published
- 2012
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46. Self-Assembly of Metal Phthalocyanines on Pb(111) and Au(111) Surfaces at Submonolayer Coverage
- Author
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Lizhi Zhang, Yuhang Jiang, Liwei Liu, Jin Lian, Hong-Jun Gao, Shixuan Du, Kai Yang, and Wende Xiao
- Subjects
Materials science ,Inorganic chemistry ,chemistry.chemical_element ,Manganese ,Substrate (electronics) ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Metal ,Crystallography ,chemistry.chemical_compound ,General Energy ,chemistry ,law ,visual_art ,Phthalocyanine ,visual_art.visual_art_medium ,Molecule ,Density functional theory ,Self-assembly ,Physical and Theoretical Chemistry ,Scanning tunneling microscope - Abstract
Self-assembly of manganese phthalocyanine (MnPc) and iron phthalocyanine (FePc) molecules on Pb(111) and Au(111) surfaces is investigated by means of low-temperature scanning tunneling microscopy and density functional theory calculations. Both metal phthalocyanine (MPc) molecules form ordered close-packed islands on Pb(111) with different detail superstructures. In contrast, dispersive single molecules are observed for both MPc molecules on Au(111). The different self-assembling behaviors of MPc molecules on Pb(111) and Au(111) originate from a subtle balance between molecule–molecule and molecule–substrate interactions tuned by the substrate based on our theoretical calculation results.
- Published
- 2011
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47. Site- and Configuration-Selective Anchoring of Iron–Phthalocyanine on the Step Edges of Au(111) Surface
- Author
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Haiming Guo, Zhihai Cheng, Xiao Lin, Qing Huan, Lizhi Zhang, Hong-Jun Gao, Li Gao, Qi Liu, Xiaobo He, Zhitao Deng, Nan Jiang, and Shixuan Du
- Subjects
Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Crystallography ,Monatomic ion ,General Energy ,Adsorption ,Chemical physics ,Thin-film transistor ,law ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Selectivity ,Surface reconstruction - Abstract
Adsorption behavior of iron–phthalocyanine (FePc) at low submonolayer coverage on a reconstructed Au(111) single crystalline surface was investigated by a combination of low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. A site- and orientation-selective adsorption was found at different temperatures and molecular coverages by means of STM. Further DFT calculations demonstrate that the energy difference between different adsorption configurations leads to the selectivity, and thus the formation of one-dimensional molecular chains on the monatomic step edges in the fcc surface reconstruction domains. The exact adsorption site and configuration of the FePc molecule as well as the simulated STM images are obtained on the basis of DFT calculations, which is in good agreement with experimental observations.
- Published
- 2011
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48. Structural Transition and Thermal Stability of a Coronene Molecular Monolayer on Cu(110)
- Author
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Dongxia Shi, Lifeng Chi, Lei Zhang, Hong-Jun Gao, Shixuan Du, and Harald Fuchs
- Subjects
Chemistry ,Coronene ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Crystallography ,chemistry.chemical_compound ,General Energy ,Adsorption ,Electron diffraction ,Chemical physics ,Monolayer ,Molecule ,Density functional theory ,Thermal stability ,Physical and Theoretical Chemistry ,Molecular beam epitaxy - Abstract
A series of alternating structural transitions of coronene monolayers on Cu(110) surfaces are observed using in situ molecular beam epitaxy with low-energy electron diffraction when varying substrate temperature after deposition. The first transition is observed around 293 K, and the second one happens at 360 K. By employing molecular mechanics and density functional theory calculation, it is found that the first transition is due to the transition from physical adsorption to chemical adsorption, while the second transition can be explained by the adsorbed molecules diffusing from a metastable site to a thermodynamically more stable site. Moreover, the unchanged diffraction pattern in the subsequent cooling and reheating process indicates that the final monolayer structure has a high thermal stability. These transitions were compared with the reversible transitions of coronene on Ag(110).
- Published
- 2010
- Full Text
- View/download PDF
49. CO Adsorption on Thin MgO Films and Single Au Adatoms: A Scanning Tunneling Microscopy Study
- Author
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Hans-Joachim Freund, Hong-Jun Gao, Bing Yang, Niklas Nilius, and Xiao Lin
- Subjects
Oxide ,Analytical chemistry ,Infrared spectroscopy ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,General Energy ,Adsorption ,chemistry ,law ,Molecule ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Spectroscopy ,Deposition (law) - Abstract
The adsorption behavior of CO on a 2 ML thin MgO/Ag(001) film is investigated with scanning tunneling microscopy and spectroscopy at 5 K. Depending on the tip state, single CO molecules are imaged as Gaussian depressions or ring-like features on the oxide surface. The preferred CO adsorption sites are identified as the Mg2+ positions next to an oxide step edge. The deposition of single Au atoms followed by CO exposure gives rise to the formation of monocarbonyl species on the MgO surface. Their vibrational properties are explored by inelastic electron-tunneling spectroscopy. The acquired second-derivative spectra are dominated by a symmetric peak/dip structure at ±50 mV, which is assigned to the frustrated rotation of Au-bound CO molecules.
- Published
- 2010
- Full Text
- View/download PDF
50. N2O Adsorption on the Surface of MgO(001) Thin Films: An Infrared and TPD Study
- Author
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Jan Rocker, Esther Kieseritzky, Martin Sterrer, Anastasia Gonchar, Hong-Jun Gao, Ji Chun Lian, and Thomas Risse
- Subjects
Materials science ,Infrared ,Inorganic chemistry ,Analytical chemistry ,Thermal desorption ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Adsorption ,Desorption ,Molecule ,Physical and Theoretical Chemistry ,Thin film ,Spectroscopy - Abstract
The adsorption of N2O oil the surface of MgO(001) thin films has been studied at low temperature (60 K) Using infrared reflection-absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The observed infrared spectrum consists of several components indicating different adsorption sites for N2O. The different IR peaks can be related to particular thermal desorption features by combining the TPD spectra with temperature-dependent infrared measurement. By comparing spectra from films with different roughness and different supports, I band at 2236 cm(-1) call be assigned to N2O adsorbed oil the MgO terraces, while peaks at the higher frequency are assigned to molecules adsorbed oil low-coordinated sites.
- Published
- 2010
- Full Text
- View/download PDF
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