Transition metal oxides hold great promise for lithium-ion batteries(LIBs)and electrocatalytic water splitting because of their high abundance and high energy density.However,designing and fabrication of efficient,sta...Transition metal oxides hold great promise for lithium-ion batteries(LIBs)and electrocatalytic water splitting because of their high abundance and high energy density.However,designing and fabrication of efficient,stable,high power density electrode materials are challenging.Herein,we report rambutan-like hollow carbon spheres formed by carbon nanosheet decorated with nickel oxide(NiO)rich inmetal vacancies(denoted as h-NiO/C)as a bifunctional electrode material for LIBs and electrocatalytic oxygen evolution reaction(OER).When being used as the anode of LIBs,the h-NiO/C electrode shows a large initial capacity of 885mAh g−1,a robust stability with a high capacity of 817mAh g−1 after 400 cycles,and great rate capability with a high reversible capacity of 523mAh g−1 at 10Ag−1 after 600 cycles.Moreover,working as an OER electrocatalyst,the h-NiO/C electrode shows a small overpotential of 260mV at 10mAcm−2,a Tafel slope of 37.6mVdec−1 along with good stability.Our work offers a cost-effective method for the fabrication of efficient electrode for LIBs and OER.展开更多
This article describes a theory unifying the unusual performance of the undercoordinated adatoms,point defects,terrace edges,surfaces,and nanostructures of various shapes.The ideas of bond order-length-strength correl...This article describes a theory unifying the unusual performance of the undercoordinated adatoms,point defects,terrace edges,surfaces,and nanostructures of various shapes.The ideas of bond order-length-strength correlation and the associated nonbonding electron polarization(BOLS-NEP)feature that bonds between undercoordinated atoms contract spontaneously.Bond contraction raises the local density of charge and energy.Bond strength gain deepens the interatomic potential well to trap the core and bonding electrons deeply.In turn,the locally and densely entrapped electrons polarize those partially occupying the valence band and above pertaining to the lower-coordinated atoms.The BOLS-NEP theory reconciles the unusual behaviors of undercoordinated systems and the size dependency of nanostructures in their lattice oscillating dynamics,mechanical strength,thermal stability,photon emissivity,chemical reactivity,dielectric permeability,associated with generation of polarized Dirac fermions,serving as carriers for extraordinary catalysis,hydrophobicity,fluidity,lubricity,as well as monolayer high-TC superconductivity and topological insulator conductivity.展开更多
We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismu...We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between ＂layers＂, while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials （MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus）, including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories： phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.展开更多
Two-dimensional(2D)materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures.The study of the mechanical properties o...Two-dimensional(2D)materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures.The study of the mechanical properties of 2D materials plays an important role in next-generation flexible mechanical electronic device applications.Unfortunately,traditional experiment models and measurement methods are not suitable for 2D materials due to their atomically ultrathin thickness,which limits both the theoretical research and practical value of the 2D materials.In this review,we briefly summarize the characterization of mechanical properties of 2D materials by in situ probe nanoindentation experiments,and discuss the effect of thickness,grain boundary,and interlayer interactions.We introduce the strain-induced effect on electrical properties and optical properties of 2D materials.Then,we generalize the mechanical sensors based on various 2D materials and their future potential applications in flexible and wearable electronic devices.Finally,we discuss the state of the art for the mechanical properties of 2D materials and their opportunities and challenges in both basic research and practical applications.展开更多
Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties.Here,we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grati...Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties.Here,we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grating array to an MoS_(2) monolayer in the strong coupling regime between localized surface plasmons(LSPs)and surface plasmon polaritons(SPPs).By means of femtosecond pump-probe spectroscopy,the measured hot electron transfer time is approximately 40 fs with a maximum external quantum yield of 1.65%.Our results suggest that strong coupling between LSPs and SPPs has synergetic effects on the generation of plasmonic hot carriers,where SPPs with a unique nonradiative feature can act as an‘energy recycle bin’to reuse the radiative energy of LSPs and contribute to hot carrier generation.Coherent energy exchange between plasmonic modes in the strong coupling regime can further enhance the vertical electric field and promote the transfer of hot electrons between the Au grating and the MoS_(2) monolayer.Our proposed plasmonic strong coupling configuration overcomes the challenge associated with utilizing hot carriers and is instructive in terms of improving the performance of plasmonic opto-electronic devices.展开更多
Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,...Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,the mechanism behind the superlubricity remains uncertain.This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice,self-lubrication of dry solids,and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation.The presence of nonbonding electron polarization,atomic or molecular undercoordination,and solute ionic electrification of the hydrogen bond as an addition,ensures the superlubricity.Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation.Molecular undercoordination shortens the covalent bond with local charge densification,which in turn polarizes the nonbonding electrons making them localized dipoles.The locally pinned dipoles provide force opposing contact,mimicking magnetic levitation and hovercraft.O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant.Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact.Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice,wet and dry frictions,which also reconciles the superhydrophobicity,superlubricity,and supersolidity at contacts.展开更多
Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact d...Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact differently with circularly polarized light exhibiting opposite handedness(left-handed and right-handed). However, the interaction between chiral molecules and chiral light is very weak. In contrast, artificial chiral plasmonic structures can generate "super-chiral" plasmonic near-field, leading to enhanced chiral light-matter(or chiroptical) interactions. The "super-chiral" near-field presents different amplitude and phase under opposite handedness incidence, which can be utilized to engineer linear and nonlinear chiroptical interactions. Specifically,in the interaction between quantum emitters and chiral plasmonic structures, the chiral hot spots can favour the emission with a specific handedness. This article reviews the state-of-the-art research on the design, fabrication and chiroptical response of different chiral plasmonic nanostructures or metasurfaces. This review also discusses enhanced chiral light-matter interactions that are essential for applications like chirality sensing, chiral selective light emitting and harvesting. In the final part, the review ends with a perspective on future directions of chiral plasmonics.展开更多
Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, fo...Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, forming stable MoS2-xOx ternary compounds, or adsorb on top of the sulfur atoms. The substituting oxygen provides a decrease of the band gap from 1.86 to 1.64 eV and transforms the material from a direct-gap to an indirect-gap semiconductor. The surface adsorbed oxygen atoms decrease the band gap up to 0.98 eV depending on their location tending to the metallic character of the electron energy bands at a high concentration of the adsorbed atoms. Oxygen plasma processing is proposed as an effective technology for such band-gap modifications.展开更多
We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has be...We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.展开更多
The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study,...The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.展开更多
In the conventional optical coating, the minimum thickness required to achieve anti-reflection should be quarter wavelength(λ/4n, where n is the refractive index). However, it was demonstrated that a lossy thin film ...In the conventional optical coating, the minimum thickness required to achieve anti-reflection should be quarter wavelength(λ/4n, where n is the refractive index). However, it was demonstrated that a lossy thin film with the thickness below quarter wavelength can also sustain the interference effect leading to a high absorption close to unity. In this paper we show that by depositing a phase change material Ge2Sb2Te5(GST) thin film(amorphous) on a metal reflector, unity absorption is attainable. We attribute the high absorption to the interference effect within the GST thin film even though its thickness is less than a quarter wavelength. The wavelength of the absorption peak can be tuned by adjusting the GST film thickness. In addition, the performance of this perfect absorber is insensitive to the incidence angle variation. Relying on the fact that GST is a phase change material, the absorption band can be tuned by inducing the phase transition of GST. The huge difference of the reflectivity between amorphous and crystalline phase leads to a high optical contrast ratio as high as 400 at the specific wavelength, suggesting the potential in the application of optical switch and rewritable data storage.展开更多
Manipulation of valley pseudospins is crucial for future valleytronics. lhe emerging transition metal dichalcogenides （TMDs） provide new possibilities for exploring the interplay among the quantum degrees of freedom...Manipulation of valley pseudospins is crucial for future valleytronics. lhe emerging transition metal dichalcogenides （TMDs） provide new possibilities for exploring the interplay among the quantum degrees of freedom, including real spin, valley pseudospin, and layer pseudospin. For example, spin-valley coupling results in valley-dependent circular dichroism in which electrons with particular spin （up or down） can be selectively excited by chiral optical pumping in monolayer TMDs, whereas in few-layer TMDs, the interlayer hopping further affects the spin-valley coupling. In addition to valley and layer pseudospins, here we propose a new degree of freedom--stacking pseudospin--and demonstrate new phenomena correlated to this new stacking freedom that otherwise require the application of external electrical or magnetic field. We investigated all possible stacking configurations of chemical-vapor-deposition-grown trilayer MoS2 （AAA, ABB, AAB, ABA, and 3R）. Although the AAA, ABA, 3R stackings possess a sole peak with lower degree of valley polarization than that in monolayer samples, the AAB （ABB） stackings exhibit two distinct peaks, one similar to that observed in monolayer MoS2 and findings provide a more future valleytronics. an additional unpolarized complete understanding of peak at lower energy. Our valley quantum control for展开更多
MoS_(2) nanomaterial with the micro-pompon structure was synthesized by a surfactant-assisted hydrothermal method.The morphologies and structures of as-prepared MoS_(2) micro-pompon were investigated by adding differe...MoS_(2) nanomaterial with the micro-pompon structure was synthesized by a surfactant-assisted hydrothermal method.The morphologies and structures of as-prepared MoS_(2) micro-pompon were investigated by adding different types of surfactants such as cetyltrimethyl ammonium bromide(CTAB),sodium dodecylbenzene sulphonate(SDBS),and polyvinyl pyrrolidone(PVP).The results indicated that the morphology of MoS_(2) could be controlled and changed effectively by the cationic sur-factant of CTAB.A reasonable growth mechanism for hollow structured MoS_(2) micro-pompon by hydrothermal processes was proposed.Further,photocatalytic degradation properties of MoS_(2) micro-pompon under visible light were evaluated by degradation of common organic dyes,which include rhodamine B(RhB),congo red,methyl orange,and methylene blue.The results indicated that MoS_(2) micro-pompon owned the highly selective catalytic ability to RhB with degradation efficiency of 95%in 60 min and 68%in 30 min.With the additive of the surfactant,the MoS_(2)-CTAB sample exhibited an enhanced ability of photocatalytic activity where degradation efficiency was improved to 92%in 30 min.The method employed in this work could be expanded to fabricate other sulfides with the controllable morphology and structure to further regulate the photocatalytic performance.展开更多
Thin-film electronics played an important role in flexible healthcare sensor applications.The common status of their constituent blocks are solid film and network structures.However,the solid film could only sustain b...Thin-film electronics played an important role in flexible healthcare sensor applications.The common status of their constituent blocks are solid film and network structures.However,the solid film could only sustain bend in a narrow range due to cracks,and the network structure decreased the sensitivity of flexion sensors due to the strong interactions between nanowires.New materials and technologies are urgently required for flexible sensing electronics,to produce the reliable data for assessment of the human body.Here,we report on a novel three-dimensional(3D)carbon nanorods array(CNA)that is characterized as vertically aligned nanorods and self-cross-linked junctions.We also demonstrate the CNA-based flexible healthcare sensors in monitoring the Parkinsonian tremors.Comparing with two-dimensional(2D)carbon nanotube networks and solid thin films,such self-cross-linked geometries are highly resistant to crack and fragmentation under strain.In the meantime,it shows high sensitivity and good stability(~10,000 times)to detect the flexions.These CNA-based flexible devices are capable of recording low-frequency vibrations(<6 Hz)and make it excellent to monitor the rest tremor of the human body,which is an initial symptom of Parkinson’s disease.The 3D self-cross-linked CNA film shows great potential in the fabrication of cost-effective and durable flexible sensors for early diagnosis of disease by monitoring the health-related rest tremors.展开更多
基金We acknowledge Dr Hangjun Ying from Ningbo Institute of Materials Technology and Engineering,Chinese Academy of Sciences for TEM characterizations.This study was supported by Nanyang Technological University under NAP award(M408050000)Singapore Ministry of Education Tier 1 program(2018-T1-001-051).We acknowledge Dr Hangjun Ying from Ningbo Institute of Materials Technology and Engineering,Chinese Academy of Sciences for TEM characterizations.This study was supported by Nanyang Technological University under NAP award(M408050000Singapore Ministry of Education Tier 1 program(2018-T1-001-051).
文摘Transition metal oxides hold great promise for lithium-ion batteries(LIBs)and electrocatalytic water splitting because of their high abundance and high energy density.However,designing and fabrication of efficient,stable,high power density electrode materials are challenging.Herein,we report rambutan-like hollow carbon spheres formed by carbon nanosheet decorated with nickel oxide(NiO)rich inmetal vacancies(denoted as h-NiO/C)as a bifunctional electrode material for LIBs and electrocatalytic oxygen evolution reaction(OER).When being used as the anode of LIBs,the h-NiO/C electrode shows a large initial capacity of 885mAh g−1,a robust stability with a high capacity of 817mAh g−1 after 400 cycles,and great rate capability with a high reversible capacity of 523mAh g−1 at 10Ag−1 after 600 cycles.Moreover,working as an OER electrocatalyst,the h-NiO/C electrode shows a small overpotential of 260mV at 10mAcm−2,a Tafel slope of 37.6mVdec−1 along with good stability.Our work offers a cost-effective method for the fabrication of efficient electrode for LIBs and OER.
基金Financial support from the National Natural Science Foundation of China(No.21273191)is acknowledged.
文摘This article describes a theory unifying the unusual performance of the undercoordinated adatoms,point defects,terrace edges,surfaces,and nanostructures of various shapes.The ideas of bond order-length-strength correlation and the associated nonbonding electron polarization(BOLS-NEP)feature that bonds between undercoordinated atoms contract spontaneously.Bond contraction raises the local density of charge and energy.Bond strength gain deepens the interatomic potential well to trap the core and bonding electrons deeply.In turn,the locally and densely entrapped electrons polarize those partially occupying the valence band and above pertaining to the lower-coordinated atoms.The BOLS-NEP theory reconciles the unusual behaviors of undercoordinated systems and the size dependency of nanostructures in their lattice oscillating dynamics,mechanical strength,thermal stability,photon emissivity,chemical reactivity,dielectric permeability,associated with generation of polarized Dirac fermions,serving as carriers for extraordinary catalysis,hydrophobicity,fluidity,lubricity,as well as monolayer high-TC superconductivity and topological insulator conductivity.
基金Q. H. X. gratefully thanks Singapore National Research Foundation via a Fellowship grant （No. NRF-RF2009-06） and an Investigatorship grant （No. NRF-NRFI2015-03）, Ministry of Education via a tier2 grant （No. MOE2012-T2-2-086） and a tier1 grant （No. 2013-T1-002-232）. S. Y. Q. and X. Luo gratefully acknowledge the Singapore National Research Foun- dation （NRF） for funding under the NRF Fellowship （No. NRF-NRFF2013-07）. Z. J. gratefully thanks National Natural Science Foundation of China （Nos. 11574305 and 51527901） and financial support from the National 1000 Talent Plan of China via a Young Project. The computations were performed on the cluster of NUS Graphene Research Centre. S. Y. Q. and X. Luo acknowledge the National Research Foundation, Prime Minister＇s Office, Singapore, under its Medium Sized Centre Programme.
文摘We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between ＂layers＂, while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials （MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus）, including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories： phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.
基金Fundamental Research Funds for the Central Universities,Grant/Award Numbers:31020190QD010,3102019PY004,3102019JC004Ministry of Education-Singapore,Grant/Award Numbers:MOE2015-T2-2-043,MOE2017-T2-2-136,Tier 1 RG7/18+2 种基金National Natural Science Foundation of China,Grant/Award Number:11904289Natural Science Foundation of Shaanxi Province,Grant/Award Number:2019JQ-613Start-up funds from Northwestern Polytechnical University,Grant/Award Numbers:19SH020159,19SH020123。
文摘Two-dimensional(2D)materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures.The study of the mechanical properties of 2D materials plays an important role in next-generation flexible mechanical electronic device applications.Unfortunately,traditional experiment models and measurement methods are not suitable for 2D materials due to their atomically ultrathin thickness,which limits both the theoretical research and practical value of the 2D materials.In this review,we briefly summarize the characterization of mechanical properties of 2D materials by in situ probe nanoindentation experiments,and discuss the effect of thickness,grain boundary,and interlayer interactions.We introduce the strain-induced effect on electrical properties and optical properties of 2D materials.Then,we generalize the mechanical sensors based on various 2D materials and their future potential applications in flexible and wearable electronic devices.Finally,we discuss the state of the art for the mechanical properties of 2D materials and their opportunities and challenges in both basic research and practical applications.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFA0205700)National Basic Research Program of China(Grant Nos.2015CB932403,2017YFA0206000)+4 种基金National Science Foundation of China(Grant Nos.11674012,61422501,11374023,61521004 and 21790364)Beijing Natural Science Foundation(Grant No.L140007)Foundation for the Author of National Excellent Doctoral Dissertation of PR China(Grant No.201420)National Program for Support of Top-notch Young Professionals(Grant No.W02070003)Ministry of Education Singapore under Grant No.MOE2015-T2-2-043.
文摘Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties.Here,we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grating array to an MoS_(2) monolayer in the strong coupling regime between localized surface plasmons(LSPs)and surface plasmon polaritons(SPPs).By means of femtosecond pump-probe spectroscopy,the measured hot electron transfer time is approximately 40 fs with a maximum external quantum yield of 1.65%.Our results suggest that strong coupling between LSPs and SPPs has synergetic effects on the generation of plasmonic hot carriers,where SPPs with a unique nonradiative feature can act as an‘energy recycle bin’to reuse the radiative energy of LSPs and contribute to hot carrier generation.Coherent energy exchange between plasmonic modes in the strong coupling regime can further enhance the vertical electric field and promote the transfer of hot electrons between the Au grating and the MoS_(2) monolayer.Our proposed plasmonic strong coupling configuration overcomes the challenge associated with utilizing hot carriers and is instructive in terms of improving the performance of plasmonic opto-electronic devices.
基金Financial supports from the National Natural Science Foundation of China(Nos.21273191 and 11502223)and inspiring discussion with Professor Ya-Pu Zhao are gratefully acknowledged.
文摘Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,the mechanism behind the superlubricity remains uncertain.This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice,self-lubrication of dry solids,and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation.The presence of nonbonding electron polarization,atomic or molecular undercoordination,and solute ionic electrification of the hydrogen bond as an addition,ensures the superlubricity.Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation.Molecular undercoordination shortens the covalent bond with local charge densification,which in turn polarizes the nonbonding electrons making them localized dipoles.The locally pinned dipoles provide force opposing contact,mimicking magnetic levitation and hovercraft.O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant.Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact.Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice,wet and dry frictions,which also reconciles the superhydrophobicity,superlubricity,and supersolidity at contacts.
基金the Singapore National Research Foundation-Agence Nationale de la Recherche(Grant No.NRF2017-NRF-ANR0052DCHIRAL).
文摘Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact differently with circularly polarized light exhibiting opposite handedness(left-handed and right-handed). However, the interaction between chiral molecules and chiral light is very weak. In contrast, artificial chiral plasmonic structures can generate "super-chiral" plasmonic near-field, leading to enhanced chiral light-matter(or chiroptical) interactions. The "super-chiral" near-field presents different amplitude and phase under opposite handedness incidence, which can be utilized to engineer linear and nonlinear chiroptical interactions. Specifically,in the interaction between quantum emitters and chiral plasmonic structures, the chiral hot spots can favour the emission with a specific handedness. This article reviews the state-of-the-art research on the design, fabrication and chiroptical response of different chiral plasmonic nanostructures or metasurfaces. This review also discusses enhanced chiral light-matter interactions that are essential for applications like chirality sensing, chiral selective light emitting and harvesting. In the final part, the review ends with a perspective on future directions of chiral plasmonics.
基金supported by the Joint BRFFR-CNRS Project (No. F15F-003)the Visby Program: scholarships for PhD studies and postdoctoral research in Sweden
文摘Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, forming stable MoS2-xOx ternary compounds, or adsorb on top of the sulfur atoms. The substituting oxygen provides a decrease of the band gap from 1.86 to 1.64 eV and transforms the material from a direct-gap to an indirect-gap semiconductor. The surface adsorbed oxygen atoms decrease the band gap up to 0.98 eV depending on their location tending to the metallic character of the electron energy bands at a high concentration of the adsorbed atoms. Oxygen plasma processing is proposed as an effective technology for such band-gap modifications.
文摘We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.
文摘The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.
基金the strong support from Singapore National Research Foundation through a Fellowship Grant(NRF-RF2009-06)an Investigatorship Award(NRF-NRFI2015-03)Singapore Ministry of Education via two Tier2 Grants(MOE2011-T2-2-051 and MOE2011-T2-2-085)
文摘In the conventional optical coating, the minimum thickness required to achieve anti-reflection should be quarter wavelength(λ/4n, where n is the refractive index). However, it was demonstrated that a lossy thin film with the thickness below quarter wavelength can also sustain the interference effect leading to a high absorption close to unity. In this paper we show that by depositing a phase change material Ge2Sb2Te5(GST) thin film(amorphous) on a metal reflector, unity absorption is attainable. We attribute the high absorption to the interference effect within the GST thin film even though its thickness is less than a quarter wavelength. The wavelength of the absorption peak can be tuned by adjusting the GST film thickness. In addition, the performance of this perfect absorber is insensitive to the incidence angle variation. Relying on the fact that GST is a phase change material, the absorption band can be tuned by inducing the phase transition of GST. The huge difference of the reflectivity between amorphous and crystalline phase leads to a high optical contrast ratio as high as 400 at the specific wavelength, suggesting the potential in the application of optical switch and rewritable data storage.
文摘Manipulation of valley pseudospins is crucial for future valleytronics. lhe emerging transition metal dichalcogenides （TMDs） provide new possibilities for exploring the interplay among the quantum degrees of freedom, including real spin, valley pseudospin, and layer pseudospin. For example, spin-valley coupling results in valley-dependent circular dichroism in which electrons with particular spin （up or down） can be selectively excited by chiral optical pumping in monolayer TMDs, whereas in few-layer TMDs, the interlayer hopping further affects the spin-valley coupling. In addition to valley and layer pseudospins, here we propose a new degree of freedom--stacking pseudospin--and demonstrate new phenomena correlated to this new stacking freedom that otherwise require the application of external electrical or magnetic field. We investigated all possible stacking configurations of chemical-vapor-deposition-grown trilayer MoS2 （AAA, ABB, AAB, ABA, and 3R）. Although the AAA, ABA, 3R stackings possess a sole peak with lower degree of valley polarization than that in monolayer samples, the AAB （ABB） stackings exhibit two distinct peaks, one similar to that observed in monolayer MoS2 and findings provide a more future valleytronics. an additional unpolarized complete understanding of peak at lower energy. Our valley quantum control for
基金This work was financially supported by the National Research Foundation Singapore programme(Grant Nos.NRF-CRP21-2018-0007 and NRF-CRP22-2019-0007)Singapore Ministry of Education via AcRF Tier 3 Programme’Geometrical Quantum Materials’(Grant No.MOE2018-T3-1-002)+8 种基金AcRF Tier 2(Grant No.MOE2016-T2-1-131)AcRF Tier 1 RG4/17 and RG7/18,the National Natural Science Foundation of China(Grant Nos.11904289 and 61974120)the Fundamental Research Funds for the Central Universities(Grant Nos.3102019PY004,31020190QD010,and 3102019JC004)the Key Program for International Science and Technology Cooperation Projects of Shanxi Province(Grant No.2018KWZ-08)the National Key Research and Development Program of China(Grant No.2019YFC1520904)Key Research and Development Project of Shanxi Province(Grant Nos.2020GXLH-Z-027 and 2020ZDLGY04-08)the Natural Science Foundation of Shanxi Province(Grant Nos.2019JQ-613)the Foundation of the Education Department of Shanxi Province(Grant Nos.18JK0780)the start-up funds from Northwestern Polytechnical University(Grant Nos.19SH020159 and 19SH020123).
文摘MoS_(2) nanomaterial with the micro-pompon structure was synthesized by a surfactant-assisted hydrothermal method.The morphologies and structures of as-prepared MoS_(2) micro-pompon were investigated by adding different types of surfactants such as cetyltrimethyl ammonium bromide(CTAB),sodium dodecylbenzene sulphonate(SDBS),and polyvinyl pyrrolidone(PVP).The results indicated that the morphology of MoS_(2) could be controlled and changed effectively by the cationic sur-factant of CTAB.A reasonable growth mechanism for hollow structured MoS_(2) micro-pompon by hydrothermal processes was proposed.Further,photocatalytic degradation properties of MoS_(2) micro-pompon under visible light were evaluated by degradation of common organic dyes,which include rhodamine B(RhB),congo red,methyl orange,and methylene blue.The results indicated that MoS_(2) micro-pompon owned the highly selective catalytic ability to RhB with degradation efficiency of 95%in 60 min and 68%in 30 min.With the additive of the surfactant,the MoS_(2)-CTAB sample exhibited an enhanced ability of photocatalytic activity where degradation efficiency was improved to 92%in 30 min.The method employed in this work could be expanded to fabricate other sulfides with the controllable morphology and structure to further regulate the photocatalytic performance.
文摘Thin-film electronics played an important role in flexible healthcare sensor applications.The common status of their constituent blocks are solid film and network structures.However,the solid film could only sustain bend in a narrow range due to cracks,and the network structure decreased the sensitivity of flexion sensors due to the strong interactions between nanowires.New materials and technologies are urgently required for flexible sensing electronics,to produce the reliable data for assessment of the human body.Here,we report on a novel three-dimensional(3D)carbon nanorods array(CNA)that is characterized as vertically aligned nanorods and self-cross-linked junctions.We also demonstrate the CNA-based flexible healthcare sensors in monitoring the Parkinsonian tremors.Comparing with two-dimensional(2D)carbon nanotube networks and solid thin films,such self-cross-linked geometries are highly resistant to crack and fragmentation under strain.In the meantime,it shows high sensitivity and good stability(~10,000 times)to detect the flexions.These CNA-based flexible devices are capable of recording low-frequency vibrations(<6 Hz)and make it excellent to monitor the rest tremor of the human body,which is an initial symptom of Parkinson’s disease.The 3D self-cross-linked CNA film shows great potential in the fabrication of cost-effective and durable flexible sensors for early diagnosis of disease by monitoring the health-related rest tremors.
