4H-SiC single photon counting avalanche photodiodes(SPADs)are prior devices for weak ultraviolet(UV)signal detection with the advantages of small size,low leakage current,high avalanche multiplication gain,and high qu...4H-SiC single photon counting avalanche photodiodes(SPADs)are prior devices for weak ultraviolet(UV)signal detection with the advantages of small size,low leakage current,high avalanche multiplication gain,and high quantum efficiency,which benefit from the large bandgap energy,high carrier drift velocity and excellent physical stability of 4 H-SiC semiconductor material.UV detectors are widely used in many key applications,such as missile plume detection,corona discharge,UV astronomy,and biological and chemical agent detection.In this paper,we will describe basic concepts and review recent results on device design,process development,and basic characterizations of 4 H-SiC avalanche photodiodes.Several promising device structures and uniformity of avalanche multiplication are discussed,which are important for achieving high performance of 4 HSiC UV SPADs.展开更多
Two strains H2-410 and H2-419 were obtained from the chemically mutated survivors of wild Haematococcus pluvialis 2 by using ethyl methanesulphonate (EMS). Strains H2-410 and H2-419 showed a fast cell growth with 13% ...Two strains H2-410 and H2-419 were obtained from the chemically mutated survivors of wild Haematococcus pluvialis 2 by using ethyl methanesulphonate (EMS). Strains H2-410 and H2-419 showed a fast cell growth with 13% and 20% increase in biomass compared to wild type, respectively. Then H2-419-4, a fast cell growth and high astaxanthin accumulation strain, was obtained by exposing the strain H2-419 to ultraviolet radiation (UV) further. The total biomass, the astaxanthin content per cell, astaxanthin production of H2-419-4 showed 68%, 28%, and 120% increase compared to wild H. pluvialis 2, respectively. HPLC (High Performance Liquid Chromatography) data showed also an obvious proportional variation of different carotenoid compositions in the extracts of H2-419-4 and the wild type, although no peak of carotenoids appeared or disappeared. Therefore, the main compositions in strain H2-419-4, like its wild one, were free of astaxanthin, monoester, and diester of astaxanthin. The asexual reproduction in survivors after exposed to UV was not synchronous, and different from the normal synchronous asexual reproduction as the mother cells were motile instead of non-motile. Interestingly, some survivors from UV irradiation produced many mini-spores (or gamete?), the spores moved away from the mother cell gradually 4 or 5 days later. This is quite similar to sexual reproduction described by Elliot in 1934. However, whether this was sexual reproduction remains questionable, as no mating process has been observed.展开更多
The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes(APDs)in both linear and Geiger modes is extensively investigated.During the temperature-dependent measurements,a fixed bias voltage is adopt...The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes(APDs)in both linear and Geiger modes is extensively investigated.During the temperature-dependent measurements,a fixed bias voltage is adopted for the device samples,which is much more practical and important for high-temperature applications.The results show that the fabricated 4H-SiC APDs are very stable and reliable at high temperatures.As the temperature increases from room temperature to 425 K,the dark current at 95%of the breakdown voltage increases slightly and remains lower than40 pA.In Geiger mode,our 4H-SiC APDs can be self-quenched in a passive-quenching circuit,which is expected for highspeed detection systems.Moreover,an interesting phenomenon is observed for the first time:the single-photon detection efficiency shows a non-monotonic variation as a function of temperature.The physical mechanism of the variation in hightemperature performance is further analyzed.The results in this work can provide a fundamental reference for researchers in the field of 4H-SiC APD ultraviolet detectors.展开更多
The solar-blind ultraviolet(UV)wavelength is particularly interesting within the range of 200 nm–300 nm.Here,we propose a focusing metalens,focusing vortex beam(VB)metalens and metalens array that specifically work i...The solar-blind ultraviolet(UV)wavelength is particularly interesting within the range of 200 nm–300 nm.Here,we propose a focusing metalens,focusing vortex beam(VB)metalens and metalens array that specifically work in the UV band to focus a beam or VB.Firstly,a high numerical aperture(NA)focusing metalens working at a wavelength of 214.2 nm was designed,and the NA reached 0.83.The corresponding conversion efficiency of the unit structure reached as high as 94%,and the full width at half maximum was only 117.2 nm.Metalenses with large NA can act as optical tweezers and can be applied to trap ultracold atoms and molecules.Secondly,a focused VB metalens in the wavelength range of200 nm–300 nm was also designed,which can convert polarized light into a VB and focus the VB simultaneously.Finally,a metalens array was developed to focus VBs with different topological charges on the same focal plane.This series of UV metalenses could be widely used in UV microscopy,photolithography,photonics communication,etc.展开更多
It is well known that avian predators can use prey excretions such as urine and feces to track their prey, and the urine and feces of small mammalian herbivores can reflect ultraviolet (UV) light and emit fluorescent ...It is well known that avian predators can use prey excretions such as urine and feces to track their prey, and the urine and feces of small mammalian herbivores can reflect ultraviolet (UV) light and emit fluorescent light. There are still some debates as to whether UV visibility of small mammalian herbivores’ urine is used as a hunting cue by avian raptors. Some studies in Europe have demonstrated that diurnal raptors are capable of utilizing these cues to target key prey species. However, researchers in Australia have argued that raptors do not use the UV visibility of urine while hunting. To our knowledge, there are no reports from Asia concerning the ultraviolet spectral characteristics of small mammal herbivores’ urine. This study examined the UV spectral properties of urine from 6 small mammal herbivores species by comparing the UV reflectance and fluorescence spectra of urine from small mammalian herbivores living in plateau meadows, plateau shrubs, open marshland, farmland, and semi-desert grassland in China. In addition, we compared the UV spectral properties of urine from ground-dwelling species of rodents and subterranean species to determine whether ultraviolet visibility of small mammal herbivores’ urine could be used as a visual signal by Asian vole-eating raptors. The results showed that: 1) the SC<sub>370</sub> values of urine from four small mammal herbivores species were ordered as plateau pika (plateau meadow) > root voles (plateau bush) > reed voles (swampland) > Brandt’s vole (desert grassland);and 2) UV fluorescence peak intensity and the wavelengths of urine from ground-dwelling species (such as the root vole, plateau pika, or Brandt’s vole) were significantly higher than those of subterranean-dwelling species (mandarin vole and plateau zokor). These results indicate that UV visibility of small mammal herbivores’ urine may act as a visual cue for raptors.展开更多
基金supported in part by National Key R&D Program of China under Grant No. 2016YFB0400902in part by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘4H-SiC single photon counting avalanche photodiodes(SPADs)are prior devices for weak ultraviolet(UV)signal detection with the advantages of small size,low leakage current,high avalanche multiplication gain,and high quantum efficiency,which benefit from the large bandgap energy,high carrier drift velocity and excellent physical stability of 4 H-SiC semiconductor material.UV detectors are widely used in many key applications,such as missile plume detection,corona discharge,UV astronomy,and biological and chemical agent detection.In this paper,we will describe basic concepts and review recent results on device design,process development,and basic characterizations of 4 H-SiC avalanche photodiodes.Several promising device structures and uniformity of avalanche multiplication are discussed,which are important for achieving high performance of 4 HSiC UV SPADs.
基金the Innovation Program of the Institute of Oceanology,CAS (No.L86032523)the Project of Ministry of Sciences and Technology of China (No.02EFN216601213)
文摘Two strains H2-410 and H2-419 were obtained from the chemically mutated survivors of wild Haematococcus pluvialis 2 by using ethyl methanesulphonate (EMS). Strains H2-410 and H2-419 showed a fast cell growth with 13% and 20% increase in biomass compared to wild type, respectively. Then H2-419-4, a fast cell growth and high astaxanthin accumulation strain, was obtained by exposing the strain H2-419 to ultraviolet radiation (UV) further. The total biomass, the astaxanthin content per cell, astaxanthin production of H2-419-4 showed 68%, 28%, and 120% increase compared to wild H. pluvialis 2, respectively. HPLC (High Performance Liquid Chromatography) data showed also an obvious proportional variation of different carotenoid compositions in the extracts of H2-419-4 and the wild type, although no peak of carotenoids appeared or disappeared. Therefore, the main compositions in strain H2-419-4, like its wild one, were free of astaxanthin, monoester, and diester of astaxanthin. The asexual reproduction in survivors after exposed to UV was not synchronous, and different from the normal synchronous asexual reproduction as the mother cells were motile instead of non-motile. Interestingly, some survivors from UV irradiation produced many mini-spores (or gamete?), the spores moved away from the mother cell gradually 4 or 5 days later. This is quite similar to sexual reproduction described by Elliot in 1934. However, whether this was sexual reproduction remains questionable, as no mating process has been observed.
基金the National Natural Science Foundation of China(Grant No.61974134)Hebei Province Outstanding Youth Fund(Grant No.F2021516001).
文摘The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes(APDs)in both linear and Geiger modes is extensively investigated.During the temperature-dependent measurements,a fixed bias voltage is adopted for the device samples,which is much more practical and important for high-temperature applications.The results show that the fabricated 4H-SiC APDs are very stable and reliable at high temperatures.As the temperature increases from room temperature to 425 K,the dark current at 95%of the breakdown voltage increases slightly and remains lower than40 pA.In Geiger mode,our 4H-SiC APDs can be self-quenched in a passive-quenching circuit,which is expected for highspeed detection systems.Moreover,an interesting phenomenon is observed for the first time:the single-photon detection efficiency shows a non-monotonic variation as a function of temperature.The physical mechanism of the variation in hightemperature performance is further analyzed.The results in this work can provide a fundamental reference for researchers in the field of 4H-SiC APD ultraviolet detectors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60907003,61805278,61875168,and 22134005)Chongqing Science Funds for Distinguished Young Scientists(Grant No.cstc2021jcyj-jqX0027)+6 种基金Innovation Research 2035 Pilot Plan of Southwest University(Grant No.SWU-XDPY22012)China Postdoctoral Science Foundation(Grant No.2018M633704)Innovation Support Program for Overseas Students in Chongqing(Grant No.cx2021008)Foundation of NUDT(Grant Nos.JC13-02-13 and ZK17-0301)Hunan Provincial Natural Science Foundation of China(Grant No.13JJ3001)Program for New Century Excellent Talents in University(Grant No.NCET-12-0142)Chongqing Talents Program for Outstanding Scientists(Grant No.cstc2021ycjh-bgzxm0178)。
文摘The solar-blind ultraviolet(UV)wavelength is particularly interesting within the range of 200 nm–300 nm.Here,we propose a focusing metalens,focusing vortex beam(VB)metalens and metalens array that specifically work in the UV band to focus a beam or VB.Firstly,a high numerical aperture(NA)focusing metalens working at a wavelength of 214.2 nm was designed,and the NA reached 0.83.The corresponding conversion efficiency of the unit structure reached as high as 94%,and the full width at half maximum was only 117.2 nm.Metalenses with large NA can act as optical tweezers and can be applied to trap ultracold atoms and molecules.Secondly,a focused VB metalens in the wavelength range of200 nm–300 nm was also designed,which can convert polarized light into a VB and focus the VB simultaneously.Finally,a metalens array was developed to focus VBs with different topological charges on the same focal plane.This series of UV metalenses could be widely used in UV microscopy,photolithography,photonics communication,etc.
文摘It is well known that avian predators can use prey excretions such as urine and feces to track their prey, and the urine and feces of small mammalian herbivores can reflect ultraviolet (UV) light and emit fluorescent light. There are still some debates as to whether UV visibility of small mammalian herbivores’ urine is used as a hunting cue by avian raptors. Some studies in Europe have demonstrated that diurnal raptors are capable of utilizing these cues to target key prey species. However, researchers in Australia have argued that raptors do not use the UV visibility of urine while hunting. To our knowledge, there are no reports from Asia concerning the ultraviolet spectral characteristics of small mammal herbivores’ urine. This study examined the UV spectral properties of urine from 6 small mammal herbivores species by comparing the UV reflectance and fluorescence spectra of urine from small mammalian herbivores living in plateau meadows, plateau shrubs, open marshland, farmland, and semi-desert grassland in China. In addition, we compared the UV spectral properties of urine from ground-dwelling species of rodents and subterranean species to determine whether ultraviolet visibility of small mammal herbivores’ urine could be used as a visual signal by Asian vole-eating raptors. The results showed that: 1) the SC<sub>370</sub> values of urine from four small mammal herbivores species were ordered as plateau pika (plateau meadow) > root voles (plateau bush) > reed voles (swampland) > Brandt’s vole (desert grassland);and 2) UV fluorescence peak intensity and the wavelengths of urine from ground-dwelling species (such as the root vole, plateau pika, or Brandt’s vole) were significantly higher than those of subterranean-dwelling species (mandarin vole and plateau zokor). These results indicate that UV visibility of small mammal herbivores’ urine may act as a visual cue for raptors.
基金Project supported by National Innovation and Entrepreneurship Training Program Project for College Students,China(X202210166110X)Key Project of Education Department of Liaoning Province,China(LJKZZ20220116).