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Now showing items 1 - 16 of 152

  • Review of borophene and its potential applications

    Wang, Zhi-Qiang   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances. First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic, optical and superconducting properties are summarized. We also discuss in detail the utilization of the borophene for wide ranges of potential application among the alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, sensor and catalytic in hydrogen evolution, oxygen reduction, oxygen evolution, and CO2 electroreduction reaction. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.
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  • Magnetic Transition in Monolayer VSe2 via Interface Hybridization

    Zhang, Wen   Zhang, Lei   Wong, Ping Kwan Johnny   Yuan, Jiaren   Vinai, Giovanni   Torelli, Piero   van der Laan, Gerrit   Feng, Yuan Ping   Wee, Andrew T. S.  

    Magnetism in monolayer (ML) VSe2 has attracted broad interest in spintronics, while existing reports have not reached consensus. Using element-specific X-ray magnetic circular dichroism, a magnetic transition in ML VSe2 has been demonstrated at the contamination-free interface between Co and VSe2. Through interfacial hybridization with a Co atomic overlayer, a magnetic moment of about 0.4 NB per V atom in ML VSe2 is revealed, approaching values predicted by previous theoretical calculations. Promotion of the ferromagnetism in ML VSe2 is accompanied by its antiferromagnetic coupling to Co and a reduction in the spin moment of Co. In comparison to the absence of this interface-induced ferromagnetism at the Fe/ML MoSe2 interface, these findings at the Co/ML VSe2 interface provide clear proof that the ML VSe2, initially with magnetic disorder, is on the verge of magnetic transition.
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  • Diverse Transport Behaviors in Cyclo[18]carbon-Based Molecular Devices

    Zhang, Lishu   Li, Hui   Feng, Yuan Ping   Shen, Lei  

    Scientists have been trying to synthesize ring-shaped pure carbon molecules for a half century. A breakthrough was made recently, and cyclo[18]carbon (C-18) was produced successfully by bonding an 18-atom ring of carbon. Because of its potential application in molecular devices, it is natural and timely to study the transport behaviors of C-18. Here we report the electron transport properties of the C-18-ring connected to various electrodes, including 1D carbon chain, 2D graphene, and 3D silver electrodes, using density-functional theory combined with the nonequilibrium Green's function technique. Diverse transport behaviors are found for the C-18 molecular devices, including an Ohmic characteristic, a quasi Schottky feature, and a current-limiting function. The origin and mechanism of unique nonlinear I-V characteristics are investigated by the transmission pathway, transmission spectra, density of states, and molecular frontier orbital theory. This study provides a theoretical guide for exploring the next-generation molecular devices based on this newcomer to the family of carbon allotropes.
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  • Hollow Mo-doped CoP nanoarrays for efficient overall water splitting

    Guan, Cao   Xiao, Wen   Wu, Haijun   Liu, Ximeng   Zang, Wenjie   Zhang, Hong   Ding, Jun   Feng, Yuan Ping   Pennycook, Stephen J.   Wang, John  

    Earth-abundant, efficient and durable electrocatalysts for water splitting are vitally important for a sustainable energy system. Here we report the rational design of hollow Mo-doped CoP (Mo-CoP) nanoarrays, which simultaneously combine electronic structure modification through doping with a high density of reaction sites through nanostructuring. With this strategy the Mo-CoP arrays give significantly improved hydrogen evolution reaction (HER) performance, and also, when in situ transformed into Mo-doped CoOOH (Mo-CoOOH) arrays, excellent activity towards the oxygen evolution reaction (OER) is obtained. The origin of the improvement is determined by atomic-resolution imaging combined with density functional theory (DFT). An electrolyzer using Mo-CoP and Mo-CoOOH can be powered by a single AA battery (similar to 1.5 V), and maintains a stable water-splitting current for 20 h, superior to most reported electrocatalysts in alkaline media, offering great promise for practical applications.
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  • Review of borophene and its potential applications

    Wang, Zhi-Qiang   Lü, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

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  • Abnormal behavior of potassium adsorbed phosphorene

    Zhang, Chao   Yang, Ming   Yang, Bao   Loh, Kian Ping   Wu, Jianlan   Feng, Yuan Ping  

    First-principles calculation is carried out to study adsorption of potassium (K) on phosphorene, a single layer of black phosphorus (BP). Interesting adsorption distance dependent electronic properties were found for the K adsorption on phosphorene surface, which is different from that for the K adsorption on a few-layer black phosphorus. While the bandgap of few-layer BP decreases monotonically as K approaches its surface and a Dirac point emerges, that of phosphorene decreases first and then increases, remaining open at any separation between K and phosphorene. This abnormal behavior is a result of weaker Stark effect and charge localization in phosphorene.
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  • A super-stretchable boron nanoribbon network

    Wang, Zhi-Qiang   Cheng, Hao   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    We have studied the mechanical properties of a two-dimensional (2D) boron nanoribbon network (BNRN) subjected to a uniaxial or a biaxial tensile strain using first principles calculations. The results show that the 2D BNRN is super-stretchable. The critical tensile strains of the BNRN in the chi-h1 phase along the a- and b-directions are 0.51 and 0.41, respectively, and that for the biaxial strain reaches an ultrahigh value of 0.84. By analyzing the B-B interatomic distance, coordination number and charge distribution, it is found that with increasing biaxial tensile strain, the chi-h1 BNRN undergoes two structural phase transitions, which are characterized by breaking of the B-B bonds and the partial transformation of the nanoribbon-like structures into chain-like structures. The strain-induced phase transitions significantly reduce the strain energy. We also discuss the elastic constants, Young's modulus, shear modulus, and Poisson's ratios. The super-stretchable and flexible mechanical properties of the BNRNs, together with their superior transport properties, make BNRNs useful in a wide range of applications in nanoscale electronic devices.
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  • Prospects of spintronics based on 2D materials

    Feng, Yuan Ping   Shen, Lei   Yang, Ming   Wang, Aizhu   Zeng, Minggang   Wu, Qingyun   Chintalapati, Sandhya   Chang, Ching-Ray  

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  • Ultra-low magnetic damping of perovskite La0.7Sr0.3MnO3 thin films

    Qin, Qing   He, Shikun   Song, Wendong   Yang, Ping   Wu, Qingyun   Feng, Yuan Ping   Chen, Jingsheng  

    The perovskite La0.7Sr0.3MnO3 (LSMO) films grown on different substrates were investigated by an angle resolved broadband ferromagnetic resonance technique. All films exhibited a four-fold magneto-crystalline anisotropy, which is in accord with the crystal structure. Moreover, a perpendicular uniaxial anisotropy changed from the (001)(pc) easy plane to the [001](pc) easy direction when the strain of LSMO films varies from tensile to compressive. The ultra-low magnetic damping constant of 5.2 x 10(-4) was obtained for a 44.6nm LSMO film on an NdGaO3 (110) substrate. The breathing Fermi surface model in which the damping constant is proportional to the density of states at Fermi energy is the dominant mechanism for the intrinsic magnetic relaxation. Published by AIP Publishing.
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  • Pressure induced topological phase transition in layered Bi2S3.

    Yang, Ming   Luo, Yong Zheng   Zeng, Ming Gang   Shen, Lei   Lu, Yun Hao   Zhou, Jun   Wang, Shi Jie   Sou, Iam Keong   Feng, Yuan Ping  

    A large bulk band gap and tunable Dirac carriers are desired for practical device applications of topological insulators. However, most known topological insulators are narrow gap materials and the manipulation of their Dirac surface states is limited by residual bulk charge carriers originating from intrinsic defects. In this study, via density functional theory based first-principles calculations, we predict that a layered hexagonal structure of Bi2S3 is stable, and it becomes a topological insulator under a moderate compressive pressure of about 5.3 GPa. Interestingly, we find that the strength of the spin-orbit interaction in Bi2S3 can be effectively enhanced by the applied pressure. This leads to an increased inverted band gap with pressure, which can reach 0.4 eV with a pressure of 13.7 GPa. Compared to Bi2Se3, intrinsic defects are suppressed in Bi2S3 under both cation- and anion-poor growth conditions. Our calculations predict a new Bi-based topological insulator, and also shed light on control over spin-orbit interactions in Bi2S3 and tuning of its topological properties.=20
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  • Si-24: An Efficient Solar Cell Material

    Linghu, Jiajun   Shen, Lei   Yang, Ming   Xu, Shuyan   Feng, Yuan Ping  

    Si-24, a recently syntheized allotrope of silicon, has received much attention due to its quasi-direct band gap around 1.3 eV. To explore its potential application as a solar cell device, we investigated the doping effect on the electronic properties of Si24 using first-principles calculations. It is found that Si24 can be easily doped as both p- and n-type, and the dopants are readily ionized. Furthermore, the incorporation of these dopants only reduces the band gap of Si24 slightly, which remains in the ideal region for solar cells. Boron and phosphorus are identified as the most promising elements for the p- type and n-type doping in Si24, respectively, due to their low formation energies, small ionization energies, and small reductions in the band gap. These properties suggest great potential in constructing a novel Si-24-based p-n junction which is highly desired for future industrial application of photovoltaic devices.
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  • Tunable and low-loss correlated plasmons in Mott-like insulating oxides

    Asmara, Teguh Citra   Wan, Dongyang   Zhao, Yongliang   Majidi, Muhammad Aziz   Nelson, Christopher T.   Scott, Mary C.   Cai, Yao   Yan, Bixing   Schmidt, Daniel   Yang, Ming   Zhu, Tao   Trevisanutto, Paolo E.   Motapothula, Mallikarjuna R.   Feng, Yuan Ping   Breese, Mark B. H.   Sherburne, Matthew   Asta, Mark   Minor, Andrew   Venkatesan, T.   Rusydi, Andrivo  

    Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible-ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1-xNb1-yO3+delta family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible-ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials.
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  • Band structure engineering of borophane by first principles calculations

    Wang, Zhi-Qiang   Lu, Tie-Yu   Wang, Hui-Qiong   Feng, Yuan Ping   Zheng, Jin-Cheng  

    We exploited the band structure engineering in W-borophane, the most stable conformer of the fully hydrogenated borophene in the literature, by first principles calculations. Uniaxial strains along the a and b direction, biaxial strains, shear strains, H vacancy and B-H dimer vacancy defects have been considered. Our results show that uniaxial strains along the a, b directions and biaxial strain can not open the band gap for W-borophane. However, band gap opening can be achieved by applying shear strain. The shear strain induced band gap is 53 meV when the applied shear strain is only 0.01. The band gap increases with the increasing shear strain. When the shear strain reaches 0.12, the band gap can reach up to 538 meV. Two different exchange-correlation potentials have been used to confirm the band gap opening. The excellent dynamical stability of W-borophane under shear strain has been proved by the phonon dispersion, indicating that applying shear strain is an effective and feasible approach to open the band gap for W-borophane. In addition, the Dirac cone of W-borophane is maintained well under the uniaxial and biaxial strains. In free-state, the Dirac fermions of W-borophane possess an ultrahigh Fermi velocity (2.13 x 106 m s(-1)) which is higher than that of graphene. It is very interesting that the Fermi velocities of W-borophane can be tuned in a wide range of values by applying uniaxial and biaxial strain.
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  • Adsorption-enhanced spin-orbit coupling of buckled honeycomb silicon

    Sun, Jia-Tao   Chen, Wei   Sakamoto, Kazuyuki   Feng, Yuan Ping   Wee, Andrew T. S.  

    We have studied the electronic structures of quasi-two-dimensional buckled honeycomb silicon (BHS) saturated by atomic hydrogen and fluorine by means of first-principles calculations. The graphene-like hexagonal silicon with chair configurations can be stabilized by atomic hydrogen and fluorine adsorption. Together with a magnetic ground state, large spin orbit coupling (SOC) of BHS saturated by hydrogen on either side (Semi-H-BHS) indicated by the band splitting of sigma bond at Gamma point in the Brillouin zone is attributed to the intermixing between the density of states of hydrogen atoms and pi bonds of unpassivated Si-2 around the Fermi level. The Zeeman spin splitting is most likely caused by the internal electric field induced by asymmetric charge transfer. (C) 2016 Elsevier B.V. All rights reserved.
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  • The RKKY Mechanism for Magnetic Ordering of Sparse Fe Adatoms on Graphene

    Zhu, Yan   Pan, Yanfei   Yang, Zhongqin   Wei, Xinyuan   Hu, Jun   Feng, Yuan Ping   Zhang, Hongbin   Wu, Ruqian  

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  • Robust two-dimensional bipolar magnetic semiconductors by defect engineering

    Cheng, Haixia   Zhou, Jun   Yang, Ming   Shen, Lei   Linghu, Jiajun   Wu, Qingyun   Qian, Ping   Feng, Yuan Ping  

    Bipolar magnetic semiconductors (BMS) are promising for applications in spintronic devices and quantum computers as 100% spin polarized currents with reversible spin direction can be easily controlled by a gate voltage in such materials. Herein, we perform first-principles calculations to investigate the structural and electronic properties of intrinsic defects in monolayer half-semiconductor CrSiTe3. Our calculations show that Cr-Si or Si-Cr antisite defects which are thermodynamically dominating in CrSiTe3 can trigger the bipolar magnetic property in CrSiTe3. These BMS characters are robust and survive under a large applied external biaxial tensile strain and electric field. Our results demonstrate a new path to design BMS materials by defect engineering, promoting the applications of two-dimensional magnetic materials in spintronics.
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