Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_2 as the most typical 2D semiconductors has great application poten...Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_2 as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS_2 devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS_2 and graphite by conductive atom force microscope(C-AFM). It was found that at high pressure, the contact quality between graphite and MoS_2 is significantly improved. This pressure-mediated contact quality improvement between MoS_2 and graphite comes from the enhanced charge transfer between MoS_2 and graphite when MoS_2 is stretched. Our results provide a new way to enhance the contact quality between MoS_2 and graphite for further applications.展开更多
Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic pr...Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.展开更多
The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applica...The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applications beyond the bandgap limit,it is of great significance to study the light-matter interaction below the material bandgap.Here,we report the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region from-0.86 pm to 1.4 pm.Even though this spectral range is below the bandgap,we observe a significant absorbance enhancement up to-4.2%in the monolayer molybdenum disulfide(comparable to its absorption within the bandgap region)due to pump-induced absorption by the excited carrier states.The different rise times of the transient absorption at different wavelengths indicate the various contributions of the different carrier states(i.e.,real carrier states in the short-wavelength region of~<1μm,and exciton states in the long wavelength region of~>1μm).Our results elucidate the fundamental understanding regarding the optical properties,excited carrier states,and carrier dynamics in the technologically important near-infrared region,which potentially leads to various photonic and optoelectronic applications(e.g„excited-state-based photodetectors and modulators)of two-dimensional materials and their heterostructures beyond their intrinsic bandgap limitations.展开更多
Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detecti...Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detection,modulation,and switching,etc.Here,high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method.We thoroughly studied their nonlinear optical absorption properties at 1.06μm by the open-aperture Z-scan method.Interestingly,a transition phenomenon from satu-rable absorption(SA)to reverse saturable absorption(RSA)was observed with the increase of the incident laser intensity.In the analysis,we found that the effective nonlinear absorption cofficient(βeff-10^2 cm/MW)under the SA process was 3 orders of magnitude larger than that during the RSA processes.Furthermore,the SA proper-ties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q-switched Nd:YVO4 solid-state laser at 1.06μm,where the shortest pulse width of 462 ns and largest single pulse energy of 1.32μJ were obtained.Moreover,the ultrafast carrier relaxation dynamics were basically studied,and the intraband and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps,respectively,were measured by a degenerate pump-probe method with the probe laser of 800 nm.These results well demonstrate the nonlinear optical absorption properties,which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.展开更多
We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a ...We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a macroscopic oscillator,whose movements were accurately monitored by a Michelson interferometer.The laser light was propagating with variable optical powers and frequency modulations.Experimentally,we discovered that the driving force for the oscillator consisted of not only the optical force of the light exiting from the cleaved facets but also the tension along the fiber induced by the light guided therewithin.The net driving force was determined only by the optical power,refractive index of the fiber,and the speed of light,which pinpoints its fundamental origin.展开更多
Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties su...Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap.In this work,we synthesize In As P NWs and further explore their nonlinear optical properties.The ultrafast carrier dynamics and nonlinear optical response are thoroughly studied based on the nondegenerate pump probe and Z-scan experimental measurements.Two different characteristic carrier lifetimes(~2 and~15 ps)from In As P NWs are observed during the excited-carrier relaxation process.Based on the physical model analysis,the relaxation process can be ascribed to the carrier cooling process via carrier-phonon scattering and Auger recombination.In addition,based on the measured excited-carrier lifetime and Pauli-blocking principle,we discover that In As P NWs show strong saturable absorption properties at the wavelengths of 532 and 1064 nm.Last,we demonstrate for the first time a femtosecond(~426 fs)solid-state laser based on an In As P NWs saturable absorber at 1.04μm.We believe that our work provides a better understanding of the In As P NWs optical properties and will further advance their photonic applications in the near-infrared range.展开更多
As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster manageme...As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster management,as well as space science questions,thanks to their lower cost and faster development process CubeSats can benefit humanity and therefore,young scientists and engineers have been motivated to research and develop new CubeSat missions.Not very long after their inception,CubeSats have evolved to become accepted platforms for scientific and commercial applications.The last couple of years showed that they are a feasible tool for conducting scientific experiments,not only in the Earth orbit but also in the interplanetary space.For many countries,a CubeSat mission could prompt the community and young teams around the world to build the national capacity to launch and operate national space missions.This paper presents an overview of the key scientific and engineering gateways opened up to the younger scientific community by the advent and adaptation of new technology into CubeSat missions.The role of cooperation and the opportunities for capacity-building and education are also explored.Thus,the present article also aims to provide useful recommendations to scientists,early-career researchers,engineers,students,and anyone who intends to explore the potential and opportunities offered by CubeSats and CubeSats-based missions.展开更多
Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challen...Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challenge primarily stems from the substantial decline in electron mobility as silicon-based semiconductor thickness decreases,coupled with the pronounced emergence of short-channel effects upon FET miniaturization[1,2].展开更多
Excitons dominate the photonic and optoelectronic properties of a material.Although significant advancements exist in understanding various types of excitons,progress on excitons that are indirect in both real-and mom...Excitons dominate the photonic and optoelectronic properties of a material.Although significant advancements exist in understanding various types of excitons,progress on excitons that are indirect in both real-and momentum-spaces is still limited.Here,we demonstrate the real-and momentum-indirect neutral and charged excitons(including their phonon replicas)in a multi-valley semiconductor of bilayer MoS_(2),by performing electric-field/doping-density dependent photoluminescence.Together with first-principles calculations,we uncover that the observed real-and momentum-indirect exciton involves electron/hole from K/Γvalley,solving the longstanding controversy of its momentum origin.Remarkably,the binding energy of real-and momentum-indirect charged exciton is extremely large(i.e.,~59 meV),more than twice that of real-and momentum-direct charged exciton(i.e.,~24 meV).The giant binding energy,along with the electrical tunability and long lifetime,endows real-and momentum-indirect excitons an emerging platform to study many-body physics and to illuminate developments in photonics and optoelectronics.展开更多
Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent e...Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent electrode material,tin-doped indium-oxide(ITO)is brittle,less transparent and expensive,which limit its compatibility in flexible electronics as well as in low-cost devices.Here we review two large-area fabrication methods for graphene based transparent electrodes for industry:liquid exfoliation and low-pressure chemical vapor deposition(CVD).We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results.State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5,slightly over the minimum required for industry of 35,while CVD reaches as high as 419.展开更多
The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M–...The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M– K directions,the variations of resonant wavelengths,quality factors,and mode volumes in both fundamental and second-order resonant modes are calculated,implying optimal configurations for strong mode-NW couplings and light-NW interactions.For the fundamental(second-order)resonant mode,scanning an NW along the M– K(Γ– M)direction is preferred,which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously.The simulation results are confirmed experimentally with good agreements.展开更多
Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and r...Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and receiver.Parity-time-(PT-)symmetric systems,combining active and passive elements in a balanced form,provide an interesting route in this context.Here,we demonstrate a PT-symmetric microwave system operating in the extreme case in which the channel is shorted through a small reactance,which acts as a nearly impenetrable obstacle,and it is therefore expected to induce large reflections and poor transmission.After placing a gain element behind the obstacle,and a balanced lossy element in front of it,we observe full restoration of information and overall transparency to an external observer,despite the presence of the obstacle.Our theory,simulations,and experiments unambiguously demonstrate stable and robust wave tunneling and information transfer supported by PT symmetry,opening opportunities for efficient communication through channels with dynamic changes,active filtering,and active metamaterial technology.展开更多
Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization ...Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization selectivity. The concept is experimentally validated in monolayer materials (MoS2) with modulation depth approaching ~100%, ultra-fast modulation speed (<~130 fs), and wavelength-independence features. Moreover, the power and polarization of the incident optical beams can be used to tune the output chirality and modulation performance. Major performance of our demonstration reaches the fundamental limits of optical modulation: near-unity modulation depth, instantaneous speed (ultra-fast coherent interaction), compact footprint (atomic thickness), and unlimited operation bandwidth, which hold an ideal optical modulation solution for emerging and future nonlinear optical applications (e.g., interconnection, imaging, computing, and quantum technologies).展开更多
We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide in...We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide,which gives rise to a microcavity located on the NW section.Resonant modes with𝑄factors exceeding 103 are obtained.Leveraging on the high density of the electric field in the microcavity,the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion.Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts,showing a cavity-enhancement factor of 112.The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions,but also provides a compact platform to construct NW-based on-chip active devices.展开更多
In the article titled“Microwave Tunneling and Robust Information Transfer Based on Parity-Time-Symmetric Absorber-Emitter Pairs”[1],there were errors in Figure 2 which occurred during production.In panel(c),the red ...In the article titled“Microwave Tunneling and Robust Information Transfer Based on Parity-Time-Symmetric Absorber-Emitter Pairs”[1],there were errors in Figure 2 which occurred during production.In panel(c),the red line should be attributed to“Re(ZNIC/Z0)”and the blue line should be attributed to“Im(ZNIC/Z0).”In panel(d),the blue line should read“∣S 21∣=∣S12∣”and the black line should read“|S22|.”The corrected figure is shown as Figure 1 below.展开更多
Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies,further playing a paramount role in a host of nanotechnology applications.Nonetheles...Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies,further playing a paramount role in a host of nanotechnology applications.Nonetheless,the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density.Here,we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid.From the optical convoluted signal,we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density.It is shown,for the first time,that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects.Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces,thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.展开更多
Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is ...Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.展开更多
Rechargeable lithium-sulfur(Li-S)batteries have attracted significant research attention due to their high capacity and energy density.However,their commercial applications are still hindered by challenges such as the...Rechargeable lithium-sulfur(Li-S)batteries have attracted significant research attention due to their high capacity and energy density.However,their commercial applications are still hindered by challenges such as the shuttle effect of soluble lithium sulfide species,the insulating nature of sulfur,and the fast capacity decay of the electrodes.Various efforts are devoted to address these problems through questing more conductive hosts with abundant polysulfide chemisorption sites,as well as modifying the separators to physically/chemically retard the polysulfides migration.Two dimensional transition metal carbides,carbonitrides and nitrides,so-called MXenes,are ideal for confining the polysulfides shuttling effects due to their high conductivity,layered structure as well as rich surface terminations.As such,MXenes have thus been widely studied in Li-S batteries,focusing on the conductive sulfur hosts,polysulfides interfaces,and separators.Therefore,in this review,we summarize the significant progresses regarding the design of multifunctional MXene-based Li-S batteries and discuss the solutions for improving electrochemical performances in detail.In addition,challenges and perspectives of MXenes for Li-S batteries are also outlined.展开更多
Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties.In 3R-stacked transition metal dichalcogenides,the explicitly broken inversion symmetry enables valley-con...Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties.In 3R-stacked transition metal dichalcogenides,the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum,providing an unprecedented platform for valleytronics.Here,we study the valley coherence of 3R WS_(2) large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature.Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence.The valley coherence of direct A(B)excitons can reach 0.742(0.653)with excitation conditions on resonance with it.Such giant and thickness-independent valley coherence of large single-crystal 3R WS_(2) at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.展开更多
基金Project supported by the National Key R&D Program,China(Grant No.2016YFA0300904)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDB-SSW-SLH004)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDPB06 and XDB07010100)the National Natural Science Foundation of China(Grant Nos.61734001 and 51572289)
文摘Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_2 as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS_2 devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS_2 and graphite by conductive atom force microscope(C-AFM). It was found that at high pressure, the contact quality between graphite and MoS_2 is significantly improved. This pressure-mediated contact quality improvement between MoS_2 and graphite comes from the enhanced charge transfer between MoS_2 and graphite when MoS_2 is stretched. Our results provide a new way to enhance the contact quality between MoS_2 and graphite for further applications.
基金the National Key Research and Development Program of China(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.11834017,61888102,and 12074413)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0101340001)the Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11).
文摘Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.
基金support from Academy of Finland(Grant Nos.314810,333982,336144 and 336818)Academy of Finland Flagship Program(Grant No 320167,PREIN)+2 种基金the European Union's Horizon 2020 research and innovation program(Grant No.820423,S2QUIP)the EU H2020-MSCA-RISE-872049(IPN-Bio)ERC(Grant No 834742).
文摘The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applications beyond the bandgap limit,it is of great significance to study the light-matter interaction below the material bandgap.Here,we report the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region from-0.86 pm to 1.4 pm.Even though this spectral range is below the bandgap,we observe a significant absorbance enhancement up to-4.2%in the monolayer molybdenum disulfide(comparable to its absorption within the bandgap region)due to pump-induced absorption by the excited carrier states.The different rise times of the transient absorption at different wavelengths indicate the various contributions of the different carrier states(i.e.,real carrier states in the short-wavelength region of~<1μm,and exciton states in the long wavelength region of~>1μm).Our results elucidate the fundamental understanding regarding the optical properties,excited carrier states,and carrier dynamics in the technologically important near-infrared region,which potentially leads to various photonic and optoelectronic applications(e.g„excited-state-based photodetectors and modulators)of two-dimensional materials and their heterostructures beyond their intrinsic bandgap limitations.
基金National Natural Science Foundation of China(61575110,61675116,61975095)Department of Science and Technology of Shandong Province(2017WLJH48)+3 种基金Shandong University(2020QNQT)Academy of Finland Photonics Flagship PREIN(320167)Walter AhLströmin SäätiöNokia.
文摘Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detection,modulation,and switching,etc.Here,high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method.We thoroughly studied their nonlinear optical absorption properties at 1.06μm by the open-aperture Z-scan method.Interestingly,a transition phenomenon from satu-rable absorption(SA)to reverse saturable absorption(RSA)was observed with the increase of the incident laser intensity.In the analysis,we found that the effective nonlinear absorption cofficient(βeff-10^2 cm/MW)under the SA process was 3 orders of magnitude larger than that during the RSA processes.Furthermore,the SA proper-ties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q-switched Nd:YVO4 solid-state laser at 1.06μm,where the shortest pulse width of 462 ns and largest single pulse energy of 1.32μJ were obtained.Moreover,the ultrafast carrier relaxation dynamics were basically studied,and the intraband and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps,respectively,were measured by a degenerate pump-probe method with the probe laser of 800 nm.These results well demonstrate the nonlinear optical absorption properties,which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.
基金Ministry of Science and ICT,South Korea(2019R1A2C2011293)Research Executive Agency(846218).
文摘We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a macroscopic oscillator,whose movements were accurately monitored by a Michelson interferometer.The laser light was propagating with variable optical powers and frequency modulations.Experimentally,we discovered that the driving force for the oscillator consisted of not only the optical force of the light exiting from the cleaved facets but also the tension along the fiber induced by the light guided therewithin.The net driving force was determined only by the optical power,refractive index of the fiber,and the speed of light,which pinpoints its fundamental origin.
基金National Natural Science Foundation of China(61975095,61975097)Qilu Young Scholar of Shandong University,Youth Cross Innovation Group of Shandong University(2020QNQT)+7 种基金Self-made Equipment Cultivation Project of Shandong University(ZY202002)European Union(H2020-MSCA-RISE-872049(IPN-Bio))Aalto University Doctoral SchoolWalter Ahlstr?min S??ti?Elektroniikkainsin??rien S??ti?S?hk?insin??riliiton S??ti?Nokia FoundationAcademy of Finland(320167)。
文摘Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap.In this work,we synthesize In As P NWs and further explore their nonlinear optical properties.The ultrafast carrier dynamics and nonlinear optical response are thoroughly studied based on the nondegenerate pump probe and Z-scan experimental measurements.Two different characteristic carrier lifetimes(~2 and~15 ps)from In As P NWs are observed during the excited-carrier relaxation process.Based on the physical model analysis,the relaxation process can be ascribed to the carrier cooling process via carrier-phonon scattering and Auger recombination.In addition,based on the measured excited-carrier lifetime and Pauli-blocking principle,we discover that In As P NWs show strong saturable absorption properties at the wavelengths of 532 and 1064 nm.Last,we demonstrate for the first time a femtosecond(~426 fs)solid-state laser based on an In As P NWs saturable absorber at 1.04μm.We believe that our work provides a better understanding of the In As P NWs optical properties and will further advance their photonic applications in the near-infrared range.
文摘As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster management,as well as space science questions,thanks to their lower cost and faster development process CubeSats can benefit humanity and therefore,young scientists and engineers have been motivated to research and develop new CubeSat missions.Not very long after their inception,CubeSats have evolved to become accepted platforms for scientific and commercial applications.The last couple of years showed that they are a feasible tool for conducting scientific experiments,not only in the Earth orbit but also in the interplanetary space.For many countries,a CubeSat mission could prompt the community and young teams around the world to build the national capacity to launch and operate national space missions.This paper presents an overview of the key scientific and engineering gateways opened up to the younger scientific community by the advent and adaptation of new technology into CubeSat missions.The role of cooperation and the opportunities for capacity-building and education are also explored.Thus,the present article also aims to provide useful recommendations to scientists,early-career researchers,engineers,students,and anyone who intends to explore the potential and opportunities offered by CubeSats and CubeSats-based missions.
文摘Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challenge primarily stems from the substantial decline in electron mobility as silicon-based semiconductor thickness decreases,coupled with the pronounced emergence of short-channel effects upon FET miniaturization[1,2].
基金This work was supported by the National Natural Science Foundation of China(NSFC)(12274447,61888102,11834017,61734001,and 12074412)the National Key Research and Development Program(2021YFA1202900 and 2021YFA1400502)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB30000000)the Key-Area Research and Development Program of Guangdong Province(2020B0101340001).
文摘Excitons dominate the photonic and optoelectronic properties of a material.Although significant advancements exist in understanding various types of excitons,progress on excitons that are indirect in both real-and momentum-spaces is still limited.Here,we demonstrate the real-and momentum-indirect neutral and charged excitons(including their phonon replicas)in a multi-valley semiconductor of bilayer MoS_(2),by performing electric-field/doping-density dependent photoluminescence.Together with first-principles calculations,we uncover that the observed real-and momentum-indirect exciton involves electron/hole from K/Γvalley,solving the longstanding controversy of its momentum origin.Remarkably,the binding energy of real-and momentum-indirect charged exciton is extremely large(i.e.,~59 meV),more than twice that of real-and momentum-direct charged exciton(i.e.,~24 meV).The giant binding energy,along with the electrical tunability and long lifetime,endows real-and momentum-indirect excitons an emerging platform to study many-body physics and to illuminate developments in photonics and optoelectronics.
基金funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement GrapheneCore2 number 785219,and GrapheneCore3 number 881603the financial support from Academy of Finland(projects 298297 and 320167-PREIN Flagship).
文摘Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent electrode material,tin-doped indium-oxide(ITO)is brittle,less transparent and expensive,which limit its compatibility in flexible electronics as well as in low-cost devices.Here we review two large-area fabrication methods for graphene based transparent electrodes for industry:liquid exfoliation and low-pressure chemical vapor deposition(CVD).We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results.State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5,slightly over the minimum required for industry of 35,while CVD reaches as high as 419.
基金supported by the Key Research and Development Program(No.2017YFA0303800)the NSFC(Nos.61522507,61775183,and 11634010)+4 种基金the Key Research and Development Program in Shaanxi Province of China(No.2017KJXX-12)the Doctorate Foundation of Northwestern Polytechnical University(No.CX201924)the Academy of Finland(Nos.276376,284548,295777,304666,312297,312551,and 314810)TEKES(OPEC),he European Union Seventh Framework Program(No.631610)Aalto University Doctoral School,Walter Ahlstrom Foundation,Nokia Foundation
文摘The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M– K directions,the variations of resonant wavelengths,quality factors,and mode volumes in both fundamental and second-order resonant modes are calculated,implying optimal configurations for strong mode-NW couplings and light-NW interactions.For the fundamental(second-order)resonant mode,scanning an NW along the M– K(Γ– M)direction is preferred,which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously.The simulation results are confirmed experimentally with good agreements.
基金This work was supported by the Office of Naval Research,the National Science Foundationthe Air Force Office of Scientific Research.
文摘Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and receiver.Parity-time-(PT-)symmetric systems,combining active and passive elements in a balanced form,provide an interesting route in this context.Here,we demonstrate a PT-symmetric microwave system operating in the extreme case in which the channel is shorted through a small reactance,which acts as a nearly impenetrable obstacle,and it is therefore expected to induce large reflections and poor transmission.After placing a gain element behind the obstacle,and a balanced lossy element in front of it,we observe full restoration of information and overall transparency to an external observer,despite the presence of the obstacle.Our theory,simulations,and experiments unambiguously demonstrate stable and robust wave tunneling and information transfer supported by PT symmetry,opening opportunities for efficient communication through channels with dynamic changes,active filtering,and active metamaterial technology.
基金Aalto Centre for Quantum Engineering,Academy of Finland(grants:314810,333982,336144,and 336818)Academy of Finland Flagship Programme(320167,PREIN)+3 种基金the European Union’s Horizon 2020 research and innovation program(Grant agreement Nos.820423,S2QUIP,965124,FEMTOCHIP)the EU H2020-MSCA-RISE-872049(IPN-Bio)ERC advanced grant(834742)HORIZON-MSCA-2021-PF-01-01(680225).
文摘Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization selectivity. The concept is experimentally validated in monolayer materials (MoS2) with modulation depth approaching ~100%, ultra-fast modulation speed (<~130 fs), and wavelength-independence features. Moreover, the power and polarization of the incident optical beams can be used to tune the output chirality and modulation performance. Major performance of our demonstration reaches the fundamental limits of optical modulation: near-unity modulation depth, instantaneous speed (ultra-fast coherent interaction), compact footprint (atomic thickness), and unlimited operation bandwidth, which hold an ideal optical modulation solution for emerging and future nonlinear optical applications (e.g., interconnection, imaging, computing, and quantum technologies).
基金Key Research and Development Program(2017YFA0303800)National Natural Science Foundation of China(11634010,61775183,61905196,91950119)+5 种基金Key Research and Development Program in Shaanxi Province of China(2017KJXX-12,2018JM1058)Fundamental Research Funds for the Central Universities(310201911cx032,3102019JC008)Aalto University Doctoral School,Walter Ahlstrom Foundation,Nokia Foundation,Academy of Finland(298297)Academy of Finland Flagship Program(320167,PREIN)Horizon 2020 Framework Programme(820423)European Research Council(834742).
文摘We report an indium phosphide nanowire(NW)-induced cavity in a silicon planar photonic crystal(PPC)waveguide to improve the light–NW coupling.The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide,which gives rise to a microcavity located on the NW section.Resonant modes with𝑄factors exceeding 103 are obtained.Leveraging on the high density of the electric field in the microcavity,the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion.Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts,showing a cavity-enhancement factor of 112.The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions,but also provides a compact platform to construct NW-based on-chip active devices.
文摘In the article titled“Microwave Tunneling and Robust Information Transfer Based on Parity-Time-Symmetric Absorber-Emitter Pairs”[1],there were errors in Figure 2 which occurred during production.In panel(c),the red line should be attributed to“Re(ZNIC/Z0)”and the blue line should be attributed to“Im(ZNIC/Z0).”In panel(d),the blue line should read“∣S 21∣=∣S12∣”and the black line should read“|S22|.”The corrected figure is shown as Figure 1 below.
基金funding from CNPq(409403/2018-0,304738/2019-0)CAPES(Finance Code 001),Fundação Araucária,and FINEP+3 种基金Companhia Paranaense de Energia(COPEL)and Agência Nacional de Energia Elétrica(Aneel)the financial support through the contract P&D 2866-0466/2017the financial support from the Slovenian Research Agency(research core funding No.P2-0231)European Union’s Horizon 2020 Marie Skłodowska-Curie Actions(MSCA)individual fellowship under Contract No.846218.
文摘Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies,further playing a paramount role in a host of nanotechnology applications.Nonetheless,the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density.Here,we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid.From the optical convoluted signal,we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density.It is shown,for the first time,that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects.Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces,thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.
基金funding from the Adolf Messer Stiftungthe Friedrich-Ebert Stiftung+5 种基金the Rosa Luxemburg Stiftungthe EU-funded action H2020-MSCA-ITN-2015-ETN CELTAfunded by the Deutsche Forschungsgemeinschaft(DFG project RO 770/40)support via the BMBF projects 05K16ODA,05K16ODC,05K19ODA,and 05K19ODBfunding from the Swedish Research Council(grant no.2017.-04504)funding from the Academy of Finland(grant nos.325810,312297,320167,and 314810).
文摘Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.
基金the support from an Empa interal research grant.
文摘Rechargeable lithium-sulfur(Li-S)batteries have attracted significant research attention due to their high capacity and energy density.However,their commercial applications are still hindered by challenges such as the shuttle effect of soluble lithium sulfide species,the insulating nature of sulfur,and the fast capacity decay of the electrodes.Various efforts are devoted to address these problems through questing more conductive hosts with abundant polysulfide chemisorption sites,as well as modifying the separators to physically/chemically retard the polysulfides migration.Two dimensional transition metal carbides,carbonitrides and nitrides,so-called MXenes,are ideal for confining the polysulfides shuttling effects due to their high conductivity,layered structure as well as rich surface terminations.As such,MXenes have thus been widely studied in Li-S batteries,focusing on the conductive sulfur hosts,polysulfides interfaces,and separators.Therefore,in this review,we summarize the significant progresses regarding the design of multifunctional MXene-based Li-S batteries and discuss the solutions for improving electrochemical performances in detail.In addition,challenges and perspectives of MXenes for Li-S batteries are also outlined.
基金This work was supported financially by the NSFC(grants:11834017 and 61888102)the Strategic Priority Research Program of CAS(grant:XDB30000000)+5 种基金the Key Research Program of Frontier Sciences of CAS(grant:QYZDBSSW-SLH004)the National Key R&D program(grant:2016YFA0300904)the financial supports from Business Finland(A-Photonics)the Academy of Finland(grants:276376,284548,286920,295777,298297,304666,312297,312551,and 314810)the Academy of Finland Flagship Programme(320167,PREIN)the European Union’s Horizon 2020 research and innovation programme(820423,S2QUIP).
文摘Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties.In 3R-stacked transition metal dichalcogenides,the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum,providing an unprecedented platform for valleytronics.Here,we study the valley coherence of 3R WS_(2) large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature.Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence.The valley coherence of direct A(B)excitons can reach 0.742(0.653)with excitation conditions on resonance with it.Such giant and thickness-independent valley coherence of large single-crystal 3R WS_(2) at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.