One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epita...One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy(HVPE)and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [1120] GaN and [1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film(~1%)reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μm Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.展开更多
The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of ...The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of an antenna-coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) terahertz detector are evaluated at temperatures elevated from 300 K to 473 K. Noise spectrum measurement and a simultaneous measurement of the source–drain conductance and the terahertz photocurrent allow for detailed analysis of the electrical characteristics, the photoresponse, and the noise behavior. The responsivity is reduced from 59 mA/W to 11 mA/W by increasing the detector temperature from 300 K to 473 K. However,the noise spectral density maintains rather constantly around 1–2 pA/Hz^(1/2) at temperatures below 448 K, above which the noise spectrum abruptly shifts from Johnson-noise type into flicker-noise type and the noise density is increased up to one order of magnitude. The noise-equivalent power(NEP) is increased from 22 pW/Hz^(1/2) at 300 K to 60 pW/Hz^(1/2) at 448 K mainly due to the reduction in mobility. Above 448 K, the NEP is increased up to 1000 pW/Hz^(1/2) due to the strongly enhanced noise. The sensitivity can be recovered by cooling the detector back to room temperature.展开更多
Antenna-coupled field-effect-transistors(FETs) offer high sensitivity for terahertz detection. Both the magnitude and the polarity of the response signal are sensitive to the localized terahertz field under the gate. ...Antenna-coupled field-effect-transistors(FETs) offer high sensitivity for terahertz detection. Both the magnitude and the polarity of the response signal are sensitive to the localized terahertz field under the gate. The ability of accurate sensing the intensity pattern is required for terahertz imaging systems. Here, we report artefacts in the intensity pattern of a focused terahertz beam around 1 THz by scanning a silicon-lens and antenna coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) detector. The origin of the image distortion is found to be connected with one of the antenna blocks by probing the localized photocurrents as a function of the beam location and the frequency. Although the exact distortion is found with our specific antenna design, we believe similar artefacts could be commonplace in antenna-coupled FET terahertz detectors when the beam spot becomes comparable with the antenna size. To eliminate such artefacts, new antenna designs are welcomed to achieve strong asymmetry in the terahertz field distribution under the gate while maintaining a more symmetric radiation pattern for the whole antenna.展开更多
Power electronic devices are of great importance in modern society.After decades of development,Si power devices have approached their material limits with only incremental improvements and large conversion losses.As ...Power electronic devices are of great importance in modern society.After decades of development,Si power devices have approached their material limits with only incremental improvements and large conversion losses.As the demand for electronic components with high efficiency dramatically increasing,new materials are needed for power device fabrication.Betaphase gallium oxide,an ultra-wide bandgap semiconductor,has been considered as a promising candidate,and variousβ-Ga_(2)O_(3)power devices with high breakdown voltages have been demonstrated.However,the realization of enhancement-mode(E-mode)β-Ga_(2)O_(3)field-effect transistors(FETs)is still challenging,which is a critical problem for a myriad of power electronic applications.Recently,researchers have made some progress on E-modeβ-Ga_(2)O_(3)FETs via various methods,and several novel structures have been fabricated.This article gives a review of the material growth,devices and properties of these E-modeβ-Ga_(2)O_(3)FETs.The key challenges and future directions in E-modeβ-Ga_(2)O_(3)FETs are also discussed.展开更多
The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold c...The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.展开更多
Efficient coupling of terahertz electromagnetic wave with the active region in a terahertz detector is required to enhance the optical sensitivity.In this work,we demonstrate direct integration of a field-effect-trans...Efficient coupling of terahertz electromagnetic wave with the active region in a terahertz detector is required to enhance the optical sensitivity.In this work,we demonstrate direct integration of a field-effect-transistor(FET)terahertz detector chip at the waveguide port of a horn antenna.Although the integration without a proper backshot is rather preliminary,the noise-equivalent power is greatly reduced from 2.7 nW/Hz^(1/2)for the bare detector chip to 76 pW/Hz^(1/2)at340 GHz.The enhancement factor of about 30 is confirmed by simulations revealing the effective increase in the energy flux density seen by the detector.The simulation further confirms the frequency response of the horn antenna and the onchip antennas.A design with the detector chip fully embedded within a waveguide cavity could be made to further enhance the coupling efficiency.展开更多
Electrocatalytic reduction of carbon dioxide is one of the most effective strategies to achieve carbon neutrality and energy sustainability.Although high-value multi-carbon products have been widely studied,limited el...Electrocatalytic reduction of carbon dioxide is one of the most effective strategies to achieve carbon neutrality and energy sustainability.Although high-value multi-carbon products have been widely studied,limited electrocatalysts have been reported for the selective conversion of ethane.More importantly,the factors tuning the selectivity between ethane and ethylene have not been clarified.Here,Zn@Cu nanowire arrays(Zn@Cu-NWAs) catalyst is proposed to stimulate the maintenance of efficient CO_(2)-to-C_(2)H_(6) conversion at high current densities.Meanwhile,in order to investigate the factors affecting the interconversion between ethane and ethylene,the counterpart catalyst that facilitates C–C coupling to ethylene was also synthesized.Time-of-flight secondary-ion mass spectroscopy(TOF-SIMS),in-situ Raman spectroscopy,and simulation results show that Zn@Cu-NWAs can provide a localized proton corridor environment for the formation of ethane,accelerating the further proton-coupled CO_(2) reduction reaction(CO_(2)RR)kinetics.Hence,this catalyst delivered an ethane Faraday efficiency of over 65% at-1.14 V vs.RHE with a total current density of 142.3 mA/cm^(2).This work provides a new perspective on regulating the local microenvironment to modify the selectivity of multi-carbon products.展开更多
Monochiral single-walled carbon nanotubes(SWCNTs)can enable high-performance carbon-based electronic devices and integrated circuits.However,their fabrication often requires complex SWCNT purification and enrichment.H...Monochiral single-walled carbon nanotubes(SWCNTs)can enable high-performance carbon-based electronic devices and integrated circuits.However,their fabrication often requires complex SWCNT purification and enrichment.Herein,we showed that isoindigo-based polymer derivatives(PDPPIID and PFIID)directly enriched(9,8)nanotubes from as-synthesized SWCNT powders selectively and efficiently to yield high concentration(9,8)nanotube inks.The selective wrapping mechanism was elucidated by classical full-atomistic molecular dynamic(MD)simulations.Thin-film transistors(TFTs)were fabricated by depositing the SWCNT ink into device channels using aerosol jet printing.TFT performance was strongly influenced by polymer residues,the deposition condition(humidity),and ink concentration.Optimized TFTs showed excellent device-to-device uniformity with 108 on/off ratios.Further,optoelectronic transistors were fabricated,and their photoelectrical neuromorphic characteristics,storage,memory,and logic functions were characterized under the pulsed light and voltage stimulations,demonstrating excellent application potentials.展开更多
Real-time tracking drug release behavior is fundamentally important for avoiding adverse effects or unsuccessful treatment in personalizemedical treatment.However,the development of a non-invasive drug reporting platf...Real-time tracking drug release behavior is fundamentally important for avoiding adverse effects or unsuccessful treatment in personalizemedical treatment.However,the development of a non-invasive drug reporting platform still remains challenging.Herein the design of a novelsyn thetic magnetic resonance imaging(MRI)agent for drug release tracking(SMART)is reported,which integrates photothermal core andparamagnetic ion/drug loading shell with a thermal valve in a hybrid structure.Through near-infrared(NIR)-II photothermal effect originatingfrom inner Au-Cu9S5 nanohybrid core,burst release of drugs loaded in the mesoporous silica shell is achieved.The concomitant use of aphase change material not only prevents premature drug release,but also regulates heating effect,keeping local temperature below 45℃,enabling synergistic chemotherapy and mild hyperthermia in vitro and in vivo.Furthermore,the drug release from SMART facilitates protonaccessibility to the paramagnetic ions anchored inside mesopores channels,enhancing Iongitudinal T1 relaxation rate and displaying positivesignal correlation to the amount of released drug,thus allowing norvinvasive real-time monitoring of drug release event.The current studyhighlights the potential of designed MRI nanophores such as SMART for real-time and in-situ monitoring of drug delivery for precisionthera nostic applications.展开更多
Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defe...Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of^5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.展开更多
Air-breathing proton exchange membrane fuel cells(PEMFCs) are very promising portable energy with many advantages. However, its power density is low and many additional supporting parts affect its specific power. In t...Air-breathing proton exchange membrane fuel cells(PEMFCs) are very promising portable energy with many advantages. However, its power density is low and many additional supporting parts affect its specific power. In this paper, we aim to improve the air diffusion and fuel cell performance by employing a novel condensing-tower-like curved flow field rather than an additional fan, making the fuel cell more compact and has less internal power consumption. Polarization curve test and galvanostatic discharge test are carried out and proved that curved flow field can strengthen the air diffusion into the PEMFC and improve its performance. With appropriate curved flow field, the fuel cell peak power can be 55.2%higher than that of planar flow field in our study. A four-layer stack with curved cathode flow field is fabricated and has a peak power of 2.35 W(120 W/kg).展开更多
The synthesis of atomic-scale metal catalysts is a promising but very challenging project. In this work, we successfully fabricated a hybrid catalyst of PL/Ni（OH）2 with atomic-scale Pt clusters uniformly decorated o...The synthesis of atomic-scale metal catalysts is a promising but very challenging project. In this work, we successfully fabricated a hybrid catalyst of PL/Ni（OH）2 with atomic-scale Pt clusters uniformly decorated on porous Ni（OH）2 nanowires （NWs） via a facile room-temperature synthesis strategy. The as-obtained Ptc/Ni（OH）2 catalyst exhibits highly efficient hydrogen evolution reaction （HER） performance under basic conditions. In 0.1moll-1 KOH, the Ptc/Ni（OH）2 has an onset overpotential of -0 mV vs. RHE, and a significantly low overpotential of 32 mV at a current density of 10mAcm-2, lower than that of the com- mercial 20% Pt/C （58 mV）. The mass current density data illustrated that the PL/Ni（OH）2 reached a high current den- sity of 6.34Amg^-1i at an overpotential of 50 mV, which was approximately 28 times higher than that of the commercial Pt/C （0.223Amg^-1i） at the same overpotential, proving the high-efficiency electrocatalytic activity of the as-obtained Ptc/Ni（OH）2 for HER under alkaline conditions.展开更多
Extensive efforts have recently been devoted to the construction of aqueous rechargeable sodium-ion batteries(ARSIBs)for large-scale energy-storage applications due to their desired properties of abundant sodium resou...Extensive efforts have recently been devoted to the construction of aqueous rechargeable sodium-ion batteries(ARSIBs)for large-scale energy-storage applications due to their desired properties of abundant sodium resources and inherently safer aqueous electrolytes.However,it is still a significant challenge to develop highly flexible ARSIBs ascribing to the lack of flexible electrode materials.In this work,nanocube-like KNiFe(CN)6(KNHCF)and rugby balllike NaTi2(PO4)3(NTP)are grown on carbon nanotube fibers via simple and mild methods as the flexible binder-free cathode(KNHCF@CNTF)and anode(NTP@CNTF),respectively.Taking advantage of their high conductivity,fast charge transport paths,and large accessible surface area,the as-fabricated binder-free electrodes display admirable electrochemical performance.Inspired by the remarkable flexibility of the binder-free electrodes and the synergy of KNHCF@CNTF and NTP@CNTF,a high-performance quasi-solid-state fiber-shaped ARSIB(FARSIB)is successfully assembled for the first time.Significantly,the as-assembled FARSIB possesses a high capacity of 34.21 mAh cm?3 and impressive energy density of 39.32 mWh cm?3.More encouragingly,our FARSIB delivers superior mechanical flexibility with only 5.7%of initial capacity loss after bending at 90°for over 3000 cycles.Thus,this work opens up an avenue to design ultraflexible ARSIBs based on all binder-free electrodes for powering wearable and portable electronics.展开更多
High-performance green InGaN laser diodes(LDs)are highly demanded in laser display,medical instruments,and quantum technology[1-4].However,the fabrication of green LDs is challenging,and GaN-based green LDs(λ>500 ...High-performance green InGaN laser diodes(LDs)are highly demanded in laser display,medical instruments,and quantum technology[1-4].However,the fabrication of green LDs is challenging,and GaN-based green LDs(λ>500 nm)were realized by Osram Corp until 2009[5],which was 15 years after the first violet InGaN LDs.The greatest challenge is the growth of InGaN/(In)GaN multiple-quantum-well(MQW)active regions with high potential homogeneity.The potential fluctuation becomes pronounced as the indium composition increases in InGaN quantum wells(QWs)[6]due to the composition and interface fluctuation.展开更多
Graphene, with its zero-bandgap electronic structure, is a highly promising ultra-broadband light absorbing material.However, the performance of graphene-based photodetectors is limited by weak absorption efficiency a...Graphene, with its zero-bandgap electronic structure, is a highly promising ultra-broadband light absorbing material.However, the performance of graphene-based photodetectors is limited by weak absorption efficiency and rapid recombination of photoexcited carriers, leading to poor photodetection performance. Here, inspired by the photogating effect, we demonstrated a highly sensitive photodetector based on graphene/WSe_(2) vertical heterostructure where the WSe_(2) layer acts as both the light absorption layer and the localized grating layer. The graphene conductive channel is induced to produce more carriers by capacitive coupling. Due to the strong light absorption and high external quantum efficiency of multilayer WSe_(2), as well as the high carrier mobility of graphene, a high photocurrent is generated in the vertical heterostructure. As a result, the photodetector exhibits ultra-high responsivity of 3.85×10~4A/W and external quantum efficiency of 1.3 × 10~7%.This finding demonstrates that photogating structures can effectively enhance the sensitivity of graphene-based photodetectors and may have great potential applications in future optoelectronic devices.展开更多
High-quality InSb epilayers are grown on semi-insulting GaAs substrates by metalorganic chemical vapor deposition using an indium pre-deposition technique. The influence of Ⅴ/Ⅲ ratio and indium pre-deposition time o...High-quality InSb epilayers are grown on semi-insulting GaAs substrates by metalorganic chemical vapor deposition using an indium pre-deposition technique. The influence of Ⅴ/Ⅲ ratio and indium pre-deposition time on the surface morphology, crystalline quality and electrical properties of the InSb epilayer is systematically investigated using Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction, Hall measurement and contactless sheet resistance measurement. It is found that a 2-μm-thick InSb epilayer grown at 450℃ with a Ⅴ/Ⅲ ratio of 5 and an indium pre-deposition time of 2.5s exhibits the optimum material quality, with a root-meansquare surface roughness of only 1.2 nm, an XRD rocking curve with full width at half maximum of 358 arcsec and a room-temperature electron mobility of 4.6 × 10~4 cm^2/V·s. These values are comparable with those grown by molecular beam epitaxy. Hall sensors are fabricated utilizing a 600-nm-thick InSb epilayer. The output Hall voltages of these sensors exceed 10 mV with the input voltage of 1 V at 9.3 mT and the electron mobility of 3.2 × 10~4 cm^2/V·s is determined, which indicates a strong potential for Hall applications.展开更多
Recently,it has been proposed that spin torque oscillators(STOs)and spin torque diodes could be used as artificial neurons and synapses to directly process microwave signals,which could lower latency and power consump...Recently,it has been proposed that spin torque oscillators(STOs)and spin torque diodes could be used as artificial neurons and synapses to directly process microwave signals,which could lower latency and power consumption greatly.However,one critical challenge is to make the microwave emission frequency of the STO stay constant with a varying input current.In this work,we study the microwave emission characteristics of STOs based on magnetic tunnel junction with MgO cap layer.By applying a small magnetic field,we realize the invariability of the microwave emission frequency of the STO,making it qualified to act as artificial neuron.Furthermore,we have simulated an artificial neural network using STO neuron to recognize the handwritten digits in the Mixed National Institute of Standards and Technology database,and obtained a high accuracy of 92.28%.Our work paves the way for the development of radio-frequency-oriented neuromorphic computing systems.展开更多
Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity,structure versatility and environmental benignity.However,the poor intrinsic electric conductivit...Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity,structure versatility and environmental benignity.However,the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs.A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework.The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction.As a result,the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g^-1 at 1 C (175 mA·g^-1),remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate),and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C.Last but not least,a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode,showing a discharge capacity exceeding 300 mAh·g^-1 at a current of 175 mA·g^-1.展开更多
In a perfect security case of symmetric encryption,the secure key is generated from a true random number generator and cannot be reused.Moreover,it has the same code length as the total message.Furthermore,we require ...In a perfect security case of symmetric encryption,the secure key is generated from a true random number generator and cannot be reused.Moreover,it has the same code length as the total message.Furthermore,we require the secure key to be distributed by employing unconditionally secure methods.Apart from quantum secure direct communication(QSDC)that directly achieves the confidential transmission of secure information over a quantum channel without key distribution procedure[1–3],secure key generation and secure key distribution(SKD)are the two most remarkable challenges restricting the efficiency and security of a cryptosystem[4]in conventional secure communication systems.展开更多
Clean energy technologies such as water splitting and fuel cells have been intensively pursued in the last decade for their free pollution. However, there is plenty of fossil energy consumed in the preparation of the ...Clean energy technologies such as water splitting and fuel cells have been intensively pursued in the last decade for their free pollution. However, there is plenty of fossil energy consumed in the preparation of the catalysts,which results in a heavy pollution. Therefore, it is much desired but challenging to fabricate high-efficiency catalysts without extra energy input. Herein, we used a facile one-pot room-temperature method to synthesize a highly efficient electrocatalyst of nickel iron layered double hydroxide grown on Ni foam(NiFe LDH/NF) for oxygen evolution reaction(OER). The formation of the NiFe LDH follows a dissolutionprecipitation process, in which the acid conditions by hydrolysis of Fe^3+ combined with NO3^- could etch the NF to form Ni^2+. Then, the obtained Ni^2+ was co-precipitated with the hydrolysed Fe^3+ to in situ generate NiFe LDH on the NF. The NiFe LDH/NF exhibits excellent OER performance with a low potential of about 1.411 V vs. reversible hydrogen electrode(RHE) at a current density of 10 m A cm^-2, a small Tafel slope of 42.3 mV dec^-1 and a significantly low potential of ~1.452 V vs. RHE at 100 mA cm^-2 in 1 mol L^-1 KOH. Moreover, the material also keeps its original morphology and structure over 20 h. This energy-efficient strategy to synthesize NiFe LDH is highly promising for widespread application in OER catalyst industry.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0403002)the National Science Fund for Distinguished Young Scholars,China(Grant No.Y3CHC11001)the National Natural Science Foundation of China(Grant No.11604368)
文摘One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy(HVPE)and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [1120] GaN and [1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film(~1%)reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μm Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFF0100501)the National Natural Science Foundation of China(Grant Nos.61771466,61775231,and 61611530708)+1 种基金the Six Talent Peaks of Jiangsu Province,China(Grant No.XXRJ-079)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017372)
文摘The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of an antenna-coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) terahertz detector are evaluated at temperatures elevated from 300 K to 473 K. Noise spectrum measurement and a simultaneous measurement of the source–drain conductance and the terahertz photocurrent allow for detailed analysis of the electrical characteristics, the photoresponse, and the noise behavior. The responsivity is reduced from 59 mA/W to 11 mA/W by increasing the detector temperature from 300 K to 473 K. However,the noise spectral density maintains rather constantly around 1–2 pA/Hz^(1/2) at temperatures below 448 K, above which the noise spectrum abruptly shifts from Johnson-noise type into flicker-noise type and the noise density is increased up to one order of magnitude. The noise-equivalent power(NEP) is increased from 22 pW/Hz^(1/2) at 300 K to 60 pW/Hz^(1/2) at 448 K mainly due to the reduction in mobility. Above 448 K, the NEP is increased up to 1000 pW/Hz^(1/2) due to the strongly enhanced noise. The sensitivity can be recovered by cooling the detector back to room temperature.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFF0100501)the National Natural Science Foundation of China(Grant Nos.61771466,61775231,and 61611530708)+3 种基金the Six Talent Peaks Project of Jiangsu Province,China(Grant No.XXRJ-079)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017372)the Russian Foundation for Basic Research(Grant No.17-52-53063)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20160400)
文摘Antenna-coupled field-effect-transistors(FETs) offer high sensitivity for terahertz detection. Both the magnitude and the polarity of the response signal are sensitive to the localized terahertz field under the gate. The ability of accurate sensing the intensity pattern is required for terahertz imaging systems. Here, we report artefacts in the intensity pattern of a focused terahertz beam around 1 THz by scanning a silicon-lens and antenna coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) detector. The origin of the image distortion is found to be connected with one of the antenna blocks by probing the localized photocurrents as a function of the beam location and the frequency. Although the exact distortion is found with our specific antenna design, we believe similar artefacts could be commonplace in antenna-coupled FET terahertz detectors when the beam spot becomes comparable with the antenna size. To eliminate such artefacts, new antenna designs are welcomed to achieve strong asymmetry in the terahertz field distribution under the gate while maintaining a more symmetric radiation pattern for the whole antenna.
基金supported in part by the National Basic Research Program of China(Grant No.2021YFB3600202)Key Laboratory Construction Project of Nanchang(Grant No.2020-NCZDSY-008)the Suzhou Science and Technology Foundation(Grant No.SYG202027)。
文摘Power electronic devices are of great importance in modern society.After decades of development,Si power devices have approached their material limits with only incremental improvements and large conversion losses.As the demand for electronic components with high efficiency dramatically increasing,new materials are needed for power device fabrication.Betaphase gallium oxide,an ultra-wide bandgap semiconductor,has been considered as a promising candidate,and variousβ-Ga_(2)O_(3)power devices with high breakdown voltages have been demonstrated.However,the realization of enhancement-mode(E-mode)β-Ga_(2)O_(3)field-effect transistors(FETs)is still challenging,which is a critical problem for a myriad of power electronic applications.Recently,researchers have made some progress on E-modeβ-Ga_(2)O_(3)FETs via various methods,and several novel structures have been fabricated.This article gives a review of the material growth,devices and properties of these E-modeβ-Ga_(2)O_(3)FETs.The key challenges and future directions in E-modeβ-Ga_(2)O_(3)FETs are also discussed.
基金supported by the National Key Research and Development Program of China(Grant Nos.2017YFB0405000,2016YFB0401803)the National Natural Science Foundation of China(Grant Nos.61834008,61574160,and 61704184)support of the Chinese Academy of Science Visiting Professorship for Senior International Scientists (Grant No.2013T2J0048)
文摘The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.
基金supported by the National Key Research and Development Program of China(Grant Nos.2016YFF0100501 and 2016YFC0801203)the National Natural Science Foundation of China(Grant Nos.61611530708,11403084,61401456,61401297,and 61505242)+2 种基金the Six Talent Peaks Project of Jiangsu Province,China(Grant No.XXRJ-079)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017372)the Russian Foundation for Basic Research(Grant No.17-52-53063)
文摘Efficient coupling of terahertz electromagnetic wave with the active region in a terahertz detector is required to enhance the optical sensitivity.In this work,we demonstrate direct integration of a field-effect-transistor(FET)terahertz detector chip at the waveguide port of a horn antenna.Although the integration without a proper backshot is rather preliminary,the noise-equivalent power is greatly reduced from 2.7 nW/Hz^(1/2)for the bare detector chip to 76 pW/Hz^(1/2)at340 GHz.The enhancement factor of about 30 is confirmed by simulations revealing the effective increase in the energy flux density seen by the detector.The simulation further confirms the frequency response of the horn antenna and the onchip antennas.A design with the detector chip fully embedded within a waveguide cavity could be made to further enhance the coupling efficiency.
基金financially supported by the Outstanding Youth Project of Guangdong Natural Science Foundation (2021B1515020051)the financial support from the Basic and Applied Basic Research Foundation of Guangdong Province (2021B1515120024, 2022A1515011804)。
文摘Electrocatalytic reduction of carbon dioxide is one of the most effective strategies to achieve carbon neutrality and energy sustainability.Although high-value multi-carbon products have been widely studied,limited electrocatalysts have been reported for the selective conversion of ethane.More importantly,the factors tuning the selectivity between ethane and ethylene have not been clarified.Here,Zn@Cu nanowire arrays(Zn@Cu-NWAs) catalyst is proposed to stimulate the maintenance of efficient CO_(2)-to-C_(2)H_(6) conversion at high current densities.Meanwhile,in order to investigate the factors affecting the interconversion between ethane and ethylene,the counterpart catalyst that facilitates C–C coupling to ethylene was also synthesized.Time-of-flight secondary-ion mass spectroscopy(TOF-SIMS),in-situ Raman spectroscopy,and simulation results show that Zn@Cu-NWAs can provide a localized proton corridor environment for the formation of ethane,accelerating the further proton-coupled CO_(2) reduction reaction(CO_(2)RR)kinetics.Hence,this catalyst delivered an ethane Faraday efficiency of over 65% at-1.14 V vs.RHE with a total current density of 142.3 mA/cm^(2).This work provides a new perspective on regulating the local microenvironment to modify the selectivity of multi-carbon products.
基金supported by the National Key Research and Development Program of China(No.2020YFA0714700)the National Natural Science Foundation of China(No.61874132)+5 种基金Key Research Program of Frontier Science of Chinese Academy of Sciences(No.QYZDB-SSWSLH031)the Shaanxi Province Natural Science Foundation(No.2017JM5063)Cooperation Project of Vacuum Interconnect Nano X Research Facility(No.NANO-X)of Suzhou nanotechnology and Nano-Bionics Institute,Chinese Academy of Sciences(No.E20045)China scholarship fund(No.201708615046)Y.C.acknowledges the Australian Research Council under the Future Fellowships scheme(No.FT160100107)M.T.thanks Prof.T.Okazaki(National Institute of Advanced Industrial Science and Technology)for experimental help.
文摘Monochiral single-walled carbon nanotubes(SWCNTs)can enable high-performance carbon-based electronic devices and integrated circuits.However,their fabrication often requires complex SWCNT purification and enrichment.Herein,we showed that isoindigo-based polymer derivatives(PDPPIID and PFIID)directly enriched(9,8)nanotubes from as-synthesized SWCNT powders selectively and efficiently to yield high concentration(9,8)nanotube inks.The selective wrapping mechanism was elucidated by classical full-atomistic molecular dynamic(MD)simulations.Thin-film transistors(TFTs)were fabricated by depositing the SWCNT ink into device channels using aerosol jet printing.TFT performance was strongly influenced by polymer residues,the deposition condition(humidity),and ink concentration.Optimized TFTs showed excellent device-to-device uniformity with 108 on/off ratios.Further,optoelectronic transistors were fabricated,and their photoelectrical neuromorphic characteristics,storage,memory,and logic functions were characterized under the pulsed light and voltage stimulations,demonstrating excellent application potentials.
基金This work was funded by the National Natural Science Foundation of China(No.21473243)Six Talent Peaks Project in Jiangsu Province(No.SWYY-243).
文摘Real-time tracking drug release behavior is fundamentally important for avoiding adverse effects or unsuccessful treatment in personalizemedical treatment.However,the development of a non-invasive drug reporting platform still remains challenging.Herein the design of a novelsyn thetic magnetic resonance imaging(MRI)agent for drug release tracking(SMART)is reported,which integrates photothermal core andparamagnetic ion/drug loading shell with a thermal valve in a hybrid structure.Through near-infrared(NIR)-II photothermal effect originatingfrom inner Au-Cu9S5 nanohybrid core,burst release of drugs loaded in the mesoporous silica shell is achieved.The concomitant use of aphase change material not only prevents premature drug release,but also regulates heating effect,keeping local temperature below 45℃,enabling synergistic chemotherapy and mild hyperthermia in vitro and in vivo.Furthermore,the drug release from SMART facilitates protonaccessibility to the paramagnetic ions anchored inside mesopores channels,enhancing Iongitudinal T1 relaxation rate and displaying positivesignal correlation to the amount of released drug,thus allowing norvinvasive real-time monitoring of drug release event.The current studyhighlights the potential of designed MRI nanophores such as SMART for real-time and in-situ monitoring of drug delivery for precisionthera nostic applications.
基金supported by the Key Research and Development Plan of Ministry of Science and Technology(No.2016YFB0402303)the National Natural Science Foundation of China(No.61575222)+1 种基金the open project of the State Key Laboratory of Luminescence and ApplicationsChina Postdoctoral Science Foundation(No.2017M621858)
文摘Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of^5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.
基金financial support granted by National Key R&D Program of China from Ministry of Science and Technology of China (Nos. 2020YFB1505700, 2016YFA0200700)China Postdoctoral Science Foundation (No. 2021M702408)+4 种基金the National Natural Science Foundation of China (No. 22172191)Dongyue Polymer Material Company of Dongyue FederationState Key Laboratory of Fluorinated Functional Membrane Materials(Dongyue Group institute)Dongyue Future Hydrogen Energy Materials Companysponsored by the Collaborative Innovation Center of Suzhou Nano Science and Technology。
文摘Air-breathing proton exchange membrane fuel cells(PEMFCs) are very promising portable energy with many advantages. However, its power density is low and many additional supporting parts affect its specific power. In this paper, we aim to improve the air diffusion and fuel cell performance by employing a novel condensing-tower-like curved flow field rather than an additional fan, making the fuel cell more compact and has less internal power consumption. Polarization curve test and galvanostatic discharge test are carried out and proved that curved flow field can strengthen the air diffusion into the PEMFC and improve its performance. With appropriate curved flow field, the fuel cell peak power can be 55.2%higher than that of planar flow field in our study. A four-layer stack with curved cathode flow field is fabricated and has a peak power of 2.35 W(120 W/kg).
基金financial support from the National Natural Science Foundation of China(21425103,21673280 and 11374039)
文摘The synthesis of atomic-scale metal catalysts is a promising but very challenging project. In this work, we successfully fabricated a hybrid catalyst of PL/Ni（OH）2 with atomic-scale Pt clusters uniformly decorated on porous Ni（OH）2 nanowires （NWs） via a facile room-temperature synthesis strategy. The as-obtained Ptc/Ni（OH）2 catalyst exhibits highly efficient hydrogen evolution reaction （HER） performance under basic conditions. In 0.1moll-1 KOH, the Ptc/Ni（OH）2 has an onset overpotential of -0 mV vs. RHE, and a significantly low overpotential of 32 mV at a current density of 10mAcm-2, lower than that of the com- mercial 20% Pt/C （58 mV）. The mass current density data illustrated that the PL/Ni（OH）2 reached a high current den- sity of 6.34Amg^-1i at an overpotential of 50 mV, which was approximately 28 times higher than that of the commercial Pt/C （0.223Amg^-1i） at the same overpotential, proving the high-efficiency electrocatalytic activity of the as-obtained Ptc/Ni（OH）2 for HER under alkaline conditions.
基金supported by the Fundamental Research Funds for the Central Universities(No.020514380183)the National Natural Science Foundation of China(No.51703241)+1 种基金the Key Research Program of Frontier Science of Chinese Academy of Sciences(No.QYZDB-SSW-SLH031)the Thousand Youth Talents Plan,and the Science and Technology Project of Nanchang(2017-SJSYS-008).
文摘Extensive efforts have recently been devoted to the construction of aqueous rechargeable sodium-ion batteries(ARSIBs)for large-scale energy-storage applications due to their desired properties of abundant sodium resources and inherently safer aqueous electrolytes.However,it is still a significant challenge to develop highly flexible ARSIBs ascribing to the lack of flexible electrode materials.In this work,nanocube-like KNiFe(CN)6(KNHCF)and rugby balllike NaTi2(PO4)3(NTP)are grown on carbon nanotube fibers via simple and mild methods as the flexible binder-free cathode(KNHCF@CNTF)and anode(NTP@CNTF),respectively.Taking advantage of their high conductivity,fast charge transport paths,and large accessible surface area,the as-fabricated binder-free electrodes display admirable electrochemical performance.Inspired by the remarkable flexibility of the binder-free electrodes and the synergy of KNHCF@CNTF and NTP@CNTF,a high-performance quasi-solid-state fiber-shaped ARSIB(FARSIB)is successfully assembled for the first time.Significantly,the as-assembled FARSIB possesses a high capacity of 34.21 mAh cm?3 and impressive energy density of 39.32 mWh cm?3.More encouragingly,our FARSIB delivers superior mechanical flexibility with only 5.7%of initial capacity loss after bending at 90°for over 3000 cycles.Thus,this work opens up an avenue to design ultraflexible ARSIBs based on all binder-free electrodes for powering wearable and portable electronics.
基金financially supported by the National Key Research and Development Program of China(2017YFE0131500)the National Natural Science Foundation of China(61834008,61704184 and 61804164)+2 种基金the Key Research and Development Program of Jiangsu province(BE2020004)the Natural Science Foundation of Jiangsu Province(BK20180254)Guangdong Basic and Applied Basic Research Foundation(2019B1515120091)。
文摘High-performance green InGaN laser diodes(LDs)are highly demanded in laser display,medical instruments,and quantum technology[1-4].However,the fabrication of green LDs is challenging,and GaN-based green LDs(λ>500 nm)were realized by Osram Corp until 2009[5],which was 15 years after the first violet InGaN LDs.The greatest challenge is the growth of InGaN/(In)GaN multiple-quantum-well(MQW)active regions with high potential homogeneity.The potential fluctuation becomes pronounced as the indium composition increases in InGaN quantum wells(QWs)[6]due to the composition and interface fluctuation.
基金Project supported by the National Natural Science Foundation of China (Grant No.11974379)the National Key Basic Research and Development Program of China (Grant No.2021YFC2203400)Jiangsu Vocational Education Integrated Circuit Technology “Double-Qualified” Famous Teacher Studio (Grant No.2022-13)。
文摘Graphene, with its zero-bandgap electronic structure, is a highly promising ultra-broadband light absorbing material.However, the performance of graphene-based photodetectors is limited by weak absorption efficiency and rapid recombination of photoexcited carriers, leading to poor photodetection performance. Here, inspired by the photogating effect, we demonstrated a highly sensitive photodetector based on graphene/WSe_(2) vertical heterostructure where the WSe_(2) layer acts as both the light absorption layer and the localized grating layer. The graphene conductive channel is induced to produce more carriers by capacitive coupling. Due to the strong light absorption and high external quantum efficiency of multilayer WSe_(2), as well as the high carrier mobility of graphene, a high photocurrent is generated in the vertical heterostructure. As a result, the photodetector exhibits ultra-high responsivity of 3.85×10~4A/W and external quantum efficiency of 1.3 × 10~7%.This finding demonstrates that photogating structures can effectively enhance the sensitivity of graphene-based photodetectors and may have great potential applications in future optoelectronic devices.
基金Supported by the Hundred Talents Program of Chinese Academy of Sciencesthe CAS Interdisciplinary Innovation Team+1 种基金the National Natural Science Foundation of China under Grant Nos 61874179,61804161 and 61605236the Key Frontier Scientific Research Program of Chinese Academy of Sciences under Grant No QYZDB-SSW-JSC014
文摘High-quality InSb epilayers are grown on semi-insulting GaAs substrates by metalorganic chemical vapor deposition using an indium pre-deposition technique. The influence of Ⅴ/Ⅲ ratio and indium pre-deposition time on the surface morphology, crystalline quality and electrical properties of the InSb epilayer is systematically investigated using Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction, Hall measurement and contactless sheet resistance measurement. It is found that a 2-μm-thick InSb epilayer grown at 450℃ with a Ⅴ/Ⅲ ratio of 5 and an indium pre-deposition time of 2.5s exhibits the optimum material quality, with a root-meansquare surface roughness of only 1.2 nm, an XRD rocking curve with full width at half maximum of 358 arcsec and a room-temperature electron mobility of 4.6 × 10~4 cm^2/V·s. These values are comparable with those grown by molecular beam epitaxy. Hall sensors are fabricated utilizing a 600-nm-thick InSb epilayer. The output Hall voltages of these sensors exceed 10 mV with the input voltage of 1 V at 9.3 mT and the electron mobility of 3.2 × 10~4 cm^2/V·s is determined, which indicates a strong potential for Hall applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974379 and 12204357)K.C.Wong Education Foundation(Grant No.GJTD2019-14)+2 种基金Jiangxi Province“Double Thousand Plan”(Grant No.S2019CQKJ2638)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.22KB140017)Wuxi University Research Start-up Fund for Introduced Talents(Grant No.2022r006)。
文摘Recently,it has been proposed that spin torque oscillators(STOs)and spin torque diodes could be used as artificial neurons and synapses to directly process microwave signals,which could lower latency and power consumption greatly.However,one critical challenge is to make the microwave emission frequency of the STO stay constant with a varying input current.In this work,we study the microwave emission characteristics of STOs based on magnetic tunnel junction with MgO cap layer.By applying a small magnetic field,we realize the invariability of the microwave emission frequency of the STO,making it qualified to act as artificial neuron.Furthermore,we have simulated an artificial neural network using STO neuron to recognize the handwritten digits in the Mixed National Institute of Standards and Technology database,and obtained a high accuracy of 92.28%.Our work paves the way for the development of radio-frequency-oriented neuromorphic computing systems.
基金the "Strategic Priority Research Program:of the CAS (No.XDA09010600)the National Natural Science Foundation of China (Nos.21473242,21625304 and 21733012).
文摘Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity,structure versatility and environmental benignity.However,the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs.A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework.The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction.As a result,the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g^-1 at 1 C (175 mA·g^-1),remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate),and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C.Last but not least,a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode,showing a discharge capacity exceeding 300 mAh·g^-1 at a current of 175 mA·g^-1.
基金This work was supported by the National Key Research and Development Program of China(2016YFE0129400)Youth Innovation Promotion Association(2016290)+1 种基金Strategic Priority Research Program of the Chinese Academy of Sciences(XDC02010800)National Cryptography Development Fund during the 13th Five-Year Plan Period(MMJJ20180112).
文摘In a perfect security case of symmetric encryption,the secure key is generated from a true random number generator and cannot be reused.Moreover,it has the same code length as the total message.Furthermore,we require the secure key to be distributed by employing unconditionally secure methods.Apart from quantum secure direct communication(QSDC)that directly achieves the confidential transmission of secure information over a quantum channel without key distribution procedure[1–3],secure key generation and secure key distribution(SKD)are the two most remarkable challenges restricting the efficiency and security of a cryptosystem[4]in conventional secure communication systems.
基金financially supported by the National Natural Science Foundation of China (21425103 and 21501192)
文摘Clean energy technologies such as water splitting and fuel cells have been intensively pursued in the last decade for their free pollution. However, there is plenty of fossil energy consumed in the preparation of the catalysts,which results in a heavy pollution. Therefore, it is much desired but challenging to fabricate high-efficiency catalysts without extra energy input. Herein, we used a facile one-pot room-temperature method to synthesize a highly efficient electrocatalyst of nickel iron layered double hydroxide grown on Ni foam(NiFe LDH/NF) for oxygen evolution reaction(OER). The formation of the NiFe LDH follows a dissolutionprecipitation process, in which the acid conditions by hydrolysis of Fe^3+ combined with NO3^- could etch the NF to form Ni^2+. Then, the obtained Ni^2+ was co-precipitated with the hydrolysed Fe^3+ to in situ generate NiFe LDH on the NF. The NiFe LDH/NF exhibits excellent OER performance with a low potential of about 1.411 V vs. reversible hydrogen electrode(RHE) at a current density of 10 m A cm^-2, a small Tafel slope of 42.3 mV dec^-1 and a significantly low potential of ~1.452 V vs. RHE at 100 mA cm^-2 in 1 mol L^-1 KOH. Moreover, the material also keeps its original morphology and structure over 20 h. This energy-efficient strategy to synthesize NiFe LDH is highly promising for widespread application in OER catalyst industry.
