By using atmospheric wind data in the mesopause and lower thermosphere(MLT)region,features of seasonal variations in the quasi-6-day wave(6DW)at different latitudes are analyzed,and modulation of the 6DW by the diurna...By using atmospheric wind data in the mesopause and lower thermosphere(MLT)region,features of seasonal variations in the quasi-6-day wave(6DW)at different latitudes are analyzed,and modulation of the 6DW by the diurnal tide and solar 27-day period is discussed.The data used in the analysis are extracted from a wind dataset collected by a meteor radar chain from December 2008 to November 2017.The meteor radar chain includes four stations,in Mohe,Beijing,Wuhan,and Sanya.Features of seasonal variations in the 6DW indicate that in summer the 6DW is usually strongest during July and August,followed by stronger variations in January and April.At certain altitudes over Wuhan and Sanya,the 6DW is slightly different in different years and altitudes.In our analysis of seasonal variations in the 6DW,we find that it is generally affected by annual oscillations and semiannual oscillations.The annual oscillations of the 6DW in the mid-low latitudes are modulated by the quasibiennial oscillation in the diurnal tide,resulting in seasonal features that are different from those at other latitudes.In addition,the 6DW amplitude at mid-high latitudes has a significant 27-day solar rotation variation,which was prominent in 2016.展开更多
We report a theoretical study of a broadband Si/graded-SiGe/Ge/Ge0.9Sn0.1 p–i–n photodetector with a flat response based on modulating thickness of the layers in the active region.The responsivity of the photodetect...We report a theoretical study of a broadband Si/graded-SiGe/Ge/Ge0.9Sn0.1 p–i–n photodetector with a flat response based on modulating thickness of the layers in the active region.The responsivity of the photodetector is about 0.57 A/W in the range of 700 to 1800 nm.This structure is suitable for silicon-based epitaxial growth.Annealing is technically applied to form the graded-SiGe.The photodetector reaches a cut-off wavelength at^2300 nm and a low dark-current density under 3 V reverse bias about 0.17 mA/cm^2 is achieved theoretical at room temperature.This work is of great significance for silicon-based detection and communication,from visible to infrared.展开更多
It has been successfully demonstrated can be widely used in nano-photonics applications owing to their flexible wavefront manipulation in a limited physical profile.However,how to improve the efficiency for the transm...It has been successfully demonstrated can be widely used in nano-photonics applications owing to their flexible wavefront manipulation in a limited physical profile.However,how to improve the efficiency for the transmission light is still a challenge.We experimentally demonstrate that the sine-shaped metallic meanderline fabricated by focus ion beam technology converts circularly polarized(CP)light to its opposite handedness and sends them into different propagation directions depending on the polarization states in near-infrared and visible frequency regions.The beam splitting behavior is well characterized by a simple geometry relation,following the rule concluded from other works on the wavefront manipulation of metasurface with phase discontinuity.Importantly,the meanderline is demonstrated to be more efficient in realizing the same functions due to the suppressed high order diffractions resulted from the absence of interruption in phase profile.The theoretical efficiency reaches 67%.Particularly,potential improvements are feasible by changing or optimizing shape of the meanderline,offering high flexibility in applications for optical imaging,communications and other phase-relative techniques.Additionally,since the continuous phase provided by the meanderline can improve the sampling efficiency of the phase function,it is helpful in realizing high quality hologram.展开更多
This paper proposes an air-coupled piezoelectric micromachined ultrasonic transducer(PMUT)for detection and imaging of surface stains.A 508 kHz PMUT array is designed,fabricated,and characterized in terms of its elect...This paper proposes an air-coupled piezoelectric micromachined ultrasonic transducer(PMUT)for detection and imaging of surface stains.A 508 kHz PMUT array is designed,fabricated,and characterized in terms of its electrical and acoustic properties,and it is used in a pulse echo validation test.Imaging of stains on metal blocks is successfully demonstrated.Compared with existing optical methods for stain detection,the proposed approach can work in a dark environment without color requirements.This work provides a new and promising route for the development of miniaturized stain detection systems.展开更多
An interlayer is usually employed to tackle the interfacial instability issue between solid electrolytes(SEs)and Li metal caused by the side reaction.However,the failure mechanism of the ionic conductor interlayers,es...An interlayer is usually employed to tackle the interfacial instability issue between solid electrolytes(SEs)and Li metal caused by the side reaction.However,the failure mechanism of the ionic conductor interlayers,especially the influence from electron penetration,remains largely unknown.Herein,using Li1.3Al0.3Ti1.7(PO4)3(LATP)as the model SE and LiF as the interlayer,we use metal semiconductor contact barrier theory to reveal the failure origin of Li/LiF@LATP interface based on the calculation results of density functional theory(DFT),in which electrons can easily tunnel through the LiF grain boundary with F vacancies due to its narrow barrier width against electron injection,followed by the reduction of LATP.Remarkably,an Al-LiF bilayer between Li/LATP is found to dramatically promote the interfacial stability,due to the highly increased barrier width and homogenized electric field at the interface.Consequently,the Li symmetric cells with Al-LiF bilayer can exhibit excellent cyclability of more than 2,000 h superior to that interlayered by LiF monolayer(~860 h).Moreover,the Li/Al-LiF@LATP/LiFePO4 solid-state batteries deliver a capacity retention of 83.2%after 350 cycles at 0.5 C.Our findings emphasize the importance of tuning the electron transport behavior by optimizing the potential barrier for the interface design in high-performance solid-state batteries.展开更多
The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calc...The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of 'lamellar-anomalous-divorced' eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si.展开更多
An amorphous Ge(a-Ge) intermediate layer is introduced into the Si bonded interface to lower the annealing temperature and achieve good electrical characteristics. The interface and electrical characteristics of nSi...An amorphous Ge(a-Ge) intermediate layer is introduced into the Si bonded interface to lower the annealing temperature and achieve good electrical characteristics. The interface and electrical characteristics of nSi/n-Si and p-Si/n-Si junctions manufactured by low-temperature wafer bonding based on a thin amorphous Ge are investigated. It is found that the bubble density tremendously decreases when the a-Ge film is not immersed in DI water. This is due to the decrease of the –OH groups. In addition, when the samples are annealed at 400 °C for20 h, the bubbles totally disappear. This can be explained by the appearance of the polycrystalline Ge(absorption of H;) at the bonded interface. The junction resistance of the n-Si/n-Si bonded wafers decreases with the increase of the annealing temperature. This is consistent with the recrystallization of the a-Ge when high-temperature annealing is conducted. The carrier transport of the Si-based PN junction annealed at 350 °C is consistent with the trap-assisted tunneling model and that annealed at 400 °C is related to the carrier recombination model.展开更多
Eye blinking is closely related to human physiology and psychology.It is an effective method of communication among people and can be used in human-machine interactions.Existing blink monitoring methods include videoo...Eye blinking is closely related to human physiology and psychology.It is an effective method of communication among people and can be used in human-machine interactions.Existing blink monitoring methods include videooculography,electro-oculograms and infrared oculography.However,these methods suffer from uncomfortable use,safety risks,limited reliability in strong light or dark environments,and infringed informational security.In this paper,we propose an ultrasound-based portable approach for eye-blinking activity monitoring.Low-power pulse-echo ultrasound featuring biosafety is transmitted and received by microelectromechanical system(MEMS)ultrasonic transducers seamlessly integrated on glasses.The size,weight and power consumption of the transducers are 2.5 mm by 2.5 mm,23.3 mg and 71μW,respectively,which provides better portability than conventional methods using wearable devices.Eye-blinking activities were characterized by open and closed eye states and validated by experiments on dfferent volunteers.Finally,real-time eye-blinking monitoring was successfully demonstrated with a response time less than 1 ms.The proposed solution paves the way for ultrasound-based wearable eye-blinking monitoring and offers miniaturization,light weight,low power consumption,high informational security and biosafety.展开更多
The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes(PDs) was studied.Due to a two-step growth method,there are high defect densities in...The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes(PDs) was studied.Due to a two-step growth method,there are high defect densities in low-temperature buffer Ge layer.It is shown that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field,leading to the increase of the total dark current for p-Ge/i-Ge/n-Si PDs,whereas these defects have no influence on the dark current for n-Ge/i-Ge/p-Ge PDs.As a complement,a three-dimensional simulation of the total current under illumination was also performed.展开更多
基金supported by the USTC Research Funds of the Double First-Class Initiative(YD3420002004)the National Natural Science Foundation of China(42125402,41974174,42188101,41831071,42174183,and 41904135)+4 种基金the B-type Strategic Priority Program of CAS(XDB41000000)the Project of Stable Support for Youth Team in Basic Research Field,CAS(YSBR-018)the Fundamental Research Funds for the Central Universitiesthe Anhui Provincial Natural Science Foundation(2008085MD113)the Joint Open Fund of Mengcheng National Geophysical Observatory(MENGO202209).
基金the National Natural Science Foundation of China(41774158,41974174,41674150,41831071 and 41904135)the Open Research Project of Large Research Infrastructures of CAS—“Study on the interaction between low/mid-latitude atmosphere and ionosphere based on the Chinese Meridian Project”.
文摘By using atmospheric wind data in the mesopause and lower thermosphere(MLT)region,features of seasonal variations in the quasi-6-day wave(6DW)at different latitudes are analyzed,and modulation of the 6DW by the diurnal tide and solar 27-day period is discussed.The data used in the analysis are extracted from a wind dataset collected by a meteor radar chain from December 2008 to November 2017.The meteor radar chain includes four stations,in Mohe,Beijing,Wuhan,and Sanya.Features of seasonal variations in the 6DW indicate that in summer the 6DW is usually strongest during July and August,followed by stronger variations in January and April.At certain altitudes over Wuhan and Sanya,the 6DW is slightly different in different years and altitudes.In our analysis of seasonal variations in the 6DW,we find that it is generally affected by annual oscillations and semiannual oscillations.The annual oscillations of the 6DW in the mid-low latitudes are modulated by the quasibiennial oscillation in the diurnal tide,resulting in seasonal features that are different from those at other latitudes.In addition,the 6DW amplitude at mid-high latitudes has a significant 27-day solar rotation variation,which was prominent in 2016.
基金This work was supported by National Basic Research Program of China(No.2013CB632103)National Natural Science Foundation of China(Nos.61534005 and 61474081)Scientific Research Project of Fujian Provincial Department of Education(No.JA15651).
文摘We report a theoretical study of a broadband Si/graded-SiGe/Ge/Ge0.9Sn0.1 p–i–n photodetector with a flat response based on modulating thickness of the layers in the active region.The responsivity of the photodetector is about 0.57 A/W in the range of 700 to 1800 nm.This structure is suitable for silicon-based epitaxial growth.Annealing is technically applied to form the graded-SiGe.The photodetector reaches a cut-off wavelength at^2300 nm and a low dark-current density under 3 V reverse bias about 0.17 mA/cm^2 is achieved theoretical at room temperature.This work is of great significance for silicon-based detection and communication,from visible to infrared.
基金supported by National Natural Science Funds (61601367, 61601375)the Fundamental Research Funds for the Central Universities (3102016 ZY028)
文摘It has been successfully demonstrated can be widely used in nano-photonics applications owing to their flexible wavefront manipulation in a limited physical profile.However,how to improve the efficiency for the transmission light is still a challenge.We experimentally demonstrate that the sine-shaped metallic meanderline fabricated by focus ion beam technology converts circularly polarized(CP)light to its opposite handedness and sends them into different propagation directions depending on the polarization states in near-infrared and visible frequency regions.The beam splitting behavior is well characterized by a simple geometry relation,following the rule concluded from other works on the wavefront manipulation of metasurface with phase discontinuity.Importantly,the meanderline is demonstrated to be more efficient in realizing the same functions due to the suppressed high order diffractions resulted from the absence of interruption in phase profile.The theoretical efficiency reaches 67%.Particularly,potential improvements are feasible by changing or optimizing shape of the meanderline,offering high flexibility in applications for optical imaging,communications and other phase-relative techniques.Additionally,since the continuous phase provided by the meanderline can improve the sampling efficiency of the phase function,it is helpful in realizing high quality hologram.
基金This work is supported by funding from the Natural Science Foundation of China(NSFC Grant No.62001322)the Tianjin Municipal Science and Technology Project(No.20JCQNJC011200)+1 种基金the National Key Research and Development Program(No.2020YFB2008801)the Nanchang Institute for Microtechnology of Tianjin University。
文摘This paper proposes an air-coupled piezoelectric micromachined ultrasonic transducer(PMUT)for detection and imaging of surface stains.A 508 kHz PMUT array is designed,fabricated,and characterized in terms of its electrical and acoustic properties,and it is used in a pulse echo validation test.Imaging of stains on metal blocks is successfully demonstrated.Compared with existing optical methods for stain detection,the proposed approach can work in a dark environment without color requirements.This work provides a new and promising route for the development of miniaturized stain detection systems.
基金This research was supported by the National Natural Science Foundation of China(Nos.52072323,52172240,and 11874307)Natural Science Foundation of Jiangxi Province(No.20192ACBL20048)+3 种基金Natural Science Foundation of Jiangsu Province(No.BK20200800)Scientific Research Project of Fujian Provincial Department of Education(No.JAT191150)the Fundamental Research Funds for the Central Universities(No.20720200075)the Double-First Class Foundation of Materials and Intelligent Manufacturing Discipline of Xiamen University.
文摘An interlayer is usually employed to tackle the interfacial instability issue between solid electrolytes(SEs)and Li metal caused by the side reaction.However,the failure mechanism of the ionic conductor interlayers,especially the influence from electron penetration,remains largely unknown.Herein,using Li1.3Al0.3Ti1.7(PO4)3(LATP)as the model SE and LiF as the interlayer,we use metal semiconductor contact barrier theory to reveal the failure origin of Li/LiF@LATP interface based on the calculation results of density functional theory(DFT),in which electrons can easily tunnel through the LiF grain boundary with F vacancies due to its narrow barrier width against electron injection,followed by the reduction of LATP.Remarkably,an Al-LiF bilayer between Li/LATP is found to dramatically promote the interfacial stability,due to the highly increased barrier width and homogenized electric field at the interface.Consequently,the Li symmetric cells with Al-LiF bilayer can exhibit excellent cyclability of more than 2,000 h superior to that interlayered by LiF monolayer(~860 h).Moreover,the Li/Al-LiF@LATP/LiFePO4 solid-state batteries deliver a capacity retention of 83.2%after 350 cycles at 0.5 C.Our findings emphasize the importance of tuning the electron transport behavior by optimizing the potential barrier for the interface design in high-performance solid-state batteries.
基金supported by the National Natural Science Foundations of China (Grant Nos. 50871090, 50971104 and 50901060)the NPU Foundations for Fundamental Research (JC20110279)the financial support from the National Aerospace Science Foundation of China (Grant Nos. 2008ZF53052 and 2010ZF53059)
文摘The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of 'lamellar-anomalous-divorced' eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si.
基金Project supported by the National Natural Science Foundation of China(Nos.61534005,61474081)
文摘An amorphous Ge(a-Ge) intermediate layer is introduced into the Si bonded interface to lower the annealing temperature and achieve good electrical characteristics. The interface and electrical characteristics of nSi/n-Si and p-Si/n-Si junctions manufactured by low-temperature wafer bonding based on a thin amorphous Ge are investigated. It is found that the bubble density tremendously decreases when the a-Ge film is not immersed in DI water. This is due to the decrease of the –OH groups. In addition, when the samples are annealed at 400 °C for20 h, the bubbles totally disappear. This can be explained by the appearance of the polycrystalline Ge(absorption of H;) at the bonded interface. The junction resistance of the n-Si/n-Si bonded wafers decreases with the increase of the annealing temperature. This is consistent with the recrystallization of the a-Ge when high-temperature annealing is conducted. The carrier transport of the Si-based PN junction annealed at 350 °C is consistent with the trap-assisted tunneling model and that annealed at 400 °C is related to the carrier recombination model.
基金the Natural Science Foundation of China(NSFC Grant No.62001322)the Tianjin Municipal Science and Technology Project(No.20JCQNJCo11200)+1 种基金the National Key Research and Development Program(No.2020YFB2008800)the Nanchang Institute for Microtechnology of Tianjin University for funding.
文摘Eye blinking is closely related to human physiology and psychology.It is an effective method of communication among people and can be used in human-machine interactions.Existing blink monitoring methods include videooculography,electro-oculograms and infrared oculography.However,these methods suffer from uncomfortable use,safety risks,limited reliability in strong light or dark environments,and infringed informational security.In this paper,we propose an ultrasound-based portable approach for eye-blinking activity monitoring.Low-power pulse-echo ultrasound featuring biosafety is transmitted and received by microelectromechanical system(MEMS)ultrasonic transducers seamlessly integrated on glasses.The size,weight and power consumption of the transducers are 2.5 mm by 2.5 mm,23.3 mg and 71μW,respectively,which provides better portability than conventional methods using wearable devices.Eye-blinking activities were characterized by open and closed eye states and validated by experiments on dfferent volunteers.Finally,real-time eye-blinking monitoring was successfully demonstrated with a response time less than 1 ms.The proposed solution paves the way for ultrasound-based wearable eye-blinking monitoring and offers miniaturization,light weight,low power consumption,high informational security and biosafety.
基金Project supported by the Key Project of Natural Science Foundation of China(No.61534005)the National Science Foundation of China(No.61474081)+2 种基金the National Basic Research Program of China(No.2013CB632103)the Natural Science Foundation of Fujian Province(No.2015D020)the Science and Technology Project of Xiamen City(No.3502Z20154091)
文摘The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes(PDs) was studied.Due to a two-step growth method,there are high defect densities in low-temperature buffer Ge layer.It is shown that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field,leading to the increase of the total dark current for p-Ge/i-Ge/n-Si PDs,whereas these defects have no influence on the dark current for n-Ge/i-Ge/p-Ge PDs.As a complement,a three-dimensional simulation of the total current under illumination was also performed.