Electron beam pumping improves the conversion efficiency of low-frequency photons radiated by perovskite quantum dots

This research argues that using an electron beam with high kinetic energy to pump perovskite quantum dots can significantly boost the efficiency of the low-frequency photon radiation conversion.Firstly,we measure the random lasing threshold and luminescence threshold of CsPbX_(3)films pumped by an electron beam.Then,we simulate the spatial distribution of the electron beams in CsPbX_(3)films.Combined with the above data,a low-frequency photon radiation conversion model based on the electron pumped perovskite quantum dots is presented.This could be a way to create a terahertz source with a high-power output or to multiply the terahertz power.

Capillary gas chromatographic determination of dimethachlon residues in fresh tobacco leaves and cut-tobacco

Simple procedures for extraction and chromatographic determination of dimethachlon residues in fresh tobacco leaves and cut-tobacco are described.The determination was carried out by capillary gas chromatography(GC) with electron capture detection(ECD) and confirmed by GC-MS.The mean recoveries and relative standard deviation(RSD) were 93.2%～112.9% and 3.5%～6.7%,respectively at levels ranging from 0.01 to 0.1 mg/kg.The limit of determination was 0.001 mg/kg.Tobacco samples in routine check were successfully analyzed using the proposed method.

Preparation and photoelectric properties of cadmium sulfide quantum dots

Cadmium sulfide quantum dots(CdS QDs) are widely used in solar cells, light emitting diodes, photocatalysis, and biological imaging because of their unique optical and electrical properties. However, there are some drawbacks in existing preparation techniques for CdS QDs, such as protection of inert gas, lengthy reaction time, high reaction temperature, poor crystallinity, and non-uniform particle size distribution. In this study, we prepared CdS QDs by liquid phase synthesis under ambient room temperature and atmospheric pressure using sodium alkyl sulfonate, CdCl_2, and Na_2S as capping agent, cadmium, and sulfur sources respectively. This technique offers facile preparation, efficient reaction, low-cost, and controllable particle size. The as-prepared CdS QDs exhibited good crystallinity, excellent monodispersity, and uniform particle size. The responsivity of CdS QDs-based photodetector is greater than 0.3 μA/W, which makes them suitable for use as ultra-violet(UV) detectors.

Optimum Indium Concentration for Growth of 1.3 μm InAs/InxGa1-xAs Quantum Dots in a Well

Five InAs/InxGa1-xAs quantum dots in a well （DWELL） with different indium concentration x are grown by solid source molecular beam epitaxy. The high quantum dot density is observed in the InAs/In0.3Ga0.7As DWELL. The photoluminescence （PL） experiments indicate that the ground state peaks of InAs/In0.15 Ga0.85As and InAs/In0.22 Ga0.78As DWELLs shift to 1.31 and 1.33μm, respectively. The optical properties are investigated by using the PL and piezoreflectance spectroscope methods. An abnormal blue shift has been observed with the further increase of x from 0.22 to 0.30.

A theoretical and experimental evaluation of Ⅲ–nitride solar-blind UV photocathode

We have developed a superior solar-blind ultraviolet （UV） photocathode with an AlxGa1_xrN photocathode （x ～ 0.45） in semi-transparent mode, and assessed spectra radiant sensitivity related to practical use. Betbre being grown over a basal plane sapphire substrate by low-pressure metal organic chemical vapor deposition （MOCVD）, a reasonable design was made to the photocathode epitaxy structure, focusing on the AlxGa1_xN： Mg active layer, then followed by a comprehen- sive analysis of the structural and optical characterization. The spectra radiant sensitivity is peaked of 41.395 mA/W at wavelength 257 nm and then decreases by about 3 to 4 decades at 400 nm demonstrating the ability of this photocathode for solar-blind application prospects.

Long-term hemispheric variation of the flare index

The long-term hemispheric variation of the flare index is investigated. It is found that, （1） the phase difference of the flare index between the northern and southern hemispheres is about 6-7 months, which is near the time delay between flare activity and sunspot activity; （2） both the dominant and phase-leading hemisphere of the flare index is the northern hemisphere in the considered time interval, implying that the hemispheric asynchrony of solar activity has a close connection with the N-S asymmetry of solar activity.

Synthesis and Spectral Properties of Nd^(3+)∶Gd_3Ga_5O_(12) Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.

The estimate of sensitivity for large infrared telescopes based on measured sky brightness and atmospheric extinction

In order to evaluate the ground-based infrared telescope sensitivity affected by the noise from the atmosphere,instruments and detectors,we construct a sensitivity model that can calculate limiting magnitudes and signal-to-noise ratio(S/N).The model is tested with tentative measurements of M’-band sky brightness and atmospheric extinction obtained at the Ali and Daocheng sites.We find that the noise caused by an excellent scientific detector and instruments at-135℃can be ignored compared to the M’-band sky background noise.Thus,when S/N=3 and total exposure time is 1 second for 10 m telescopes,the magnitude limited by the atmosphere is 13.01^(m)at Ali and 12.96^(m)at Daocheng.Even under lessthan-ideal circumstances,i.e.,the readout noise of a deep cryogenic detector is less than 200 e-and the instruments are cooled to below-87.2℃,the above magnitudes decrease by 0.056^(m)at most.Therefore,according to observational requirements with a large telescope in a given infrared band,astronomers can use this sensitivity model as a tool for guiding site surveys,detector selection and instrumental thermal-control.

Piezoresponse Force Microscopy Imaging of Ferroelectric Domains in Bi(Zn_(1/2)Ti_(1/2))O_(3)−Pb(Mg_(1/3)Nb_(2/3))O_(3)−PbTiO_(3) Piezoelectric Ceramics

Bismuth zinc titanate dopied lead magnesium niobate-lead titanate[Bi(Zn_(1/2)Ti_(1/2))O_(3)−Pb(Mg_(1/3)Nb_(2/3))O_(3)−PbTiO_(3)(BZT-PMN-PT)]piezoelectric ceramics are synthesized by the conventional solid state reaction method.Ferroelectric domain structures and the evolutionary behavior of BZT-PMN-PT ceramics under an external in-plane electric field are investigated by piezoresponse force microscopy(PFM).It is found that the BZT doping has a significant effect on the domain configurations and the domain kinetic behavior of the piezoelectric BZT-PMN-PT solid solution ceramics.Microdomains embedded in the macrodomains,induced by the BZT dopant in the solid solution ceramics,are clearly observed by PFM and their volume increases with increasing amounts of BZT doping.The microdomains of BZT-PMN-PT piezoelectric ceramics exhibit better domain dynamic behavior stability than macrodomains under an external in-plane electric field.

Preparation and Performance of CdZnTe Ray Detector

γ-ray and x-ray detectors made by Cd1-xZnxTe alloy can gain high energy resolution and detect efficiency at room temperature due to its high atomic number,large energy gap and high density,which were well-developed recently.By well controlled of Cadmium partial pressure and compensatory doping technique,Ф90 mm Cd1-xZnxTe alloy obtained successfully(ρ≥1011Ω·cm)by an improved-Bridgman method.3 mm×3 mm×3 mm CZT de­tector was made at Kunming Institute of Physics,which has energy resolu­tion of 3.52%(FWHM)at room temperature when detect 59.54 KeV Am241γ-ray source.

Fully-Differential Multichannel Integrated Neural Signal Recording Front-End

Neural signal can be used for clinical disease diagnosis,data analysis and real-time life signal monitoring.Its analysis requires high-performance signal processors.Based on the 180 nm standard CMOS technology,a16-channel fully-differential neural recording chip is designed.The chip consists of 16-channel low-noise pre-amplifiers,a multiplexer and a successive approximation register（SAR）ADC.The result shows that the equivalent input-referred noise of recording amplifier is 3.63μV,bringing down noise efficiency factor to 4.24.At 8.5 bits effective number of bit（ENOB）,the analog-to-digital converter（ADC）has an SNR of 52.6dB.The core area of the proposed neural recording front-end is about 2.46 mm^2.

SnS_2 quantum dots: Facile synthesis, properties,and applications in ultraviolet photodetector

Tin sulfide quantum dots(SnS_2 QDs) are n-type wide band gap semiconductor. They exhibit a high optical absorption coefficient and strong photoconductive property in the ultraviolet and visible regions. Therefore, they have been found to have many potential applications, such as gas sensors, resistors, photodetectors, photocatalysts, and solar cells. However, the existing preparation methods for SnS_2 QDs are complicated and require a high temperature and high pressure environments; hence they are unsuitable for large-scale industrial production. An effective method for the preparation of monodispersed SnS_2 QDs at normal temperature and pressure will be discussed in this paper. The method is facile, green,and low-cost. In this work, the structure, morphology, optical, electrical, and photoelectric properties of SnS_2 QDs are studied. The synthesized SnS_2 QDs are homogeneous in size and exhibit good photoelectric performance. A photoelectric detector based on the SnS_2 QDs is fabricated and its J–V and C–V characteristics are also studied. The detector responds under λ = 365 nm light irradiation and reverse bias voltage. Its detectivity approximately stabilizes at 1011 Jones at room temperature. These results show the possible use of SnS_2 QDs in photodetectors.

Molecular-beam epitaxy-grown HgCdTe infrared detector:Material physics, structure design, and device fabrication

Infrared(IR) detectors have important applications in numerous civil and military sectors. Hg Cd Te is one of the most important materials for IR detector manufacture. This review systematically discusses the progress of Hg Cd Te materials grown via molecular-beam epitaxy(MBE) for IR detection in terms of material physics, structure design, and fabrication. The material physics of Hg Cd Te includes crystal information, band structure, and electrical and optical properties. The characterization methods of the As-grown Hg Cd Te materials are also summarized. Then, four design structures of Hg Cd Te for IR detectors, with multilayer, superlattice, double-layer heterojunction, and barrier properties, which significantly improve the device performance,are discussed. The third section summarizes the studies on Hg Cd Te MBE-grown on different substrates, including Cd Zn Te, Si,and Ga Sb, in recent decades. This review discusses the factors influencing the growth of the Hg Cd Te film and their relationships and optimal conditions. Finally, we present the prospects and challenges associated with the fabrication and applications of Hg Cd Te materials for IR detectors.

TEC Colling Shortwave Infrared 320×256 Focal Plane Detector

The short-wave HgCdTe thin film material was grown by liquid phase epitaxy on CdTe substrate,Adopt n on p injection bonding and function and flip-flop mixing process,With a low noise readout circuit,sealed with a high airtightness cellular-metal shell,Using a four-stage Thermo Electric Cooler(TEC),320×256 Short Wave Infrared Focal Plane Cooling Detecto r available to operate at near room temperature(210K).Its main photoelectric performance are signal-to-noise ratio greater than 400,nonuniformity equivalent to 4.69%,operability equivalent to 99.76%,frame rate equivalent to 115Hz,component weight less than 150grams.

Ge-based Medium Wave Infrared MCT 1280×1024 Focal Plane Detector

Medium-wave HgCdTe thin films grown on germanium-based substrates by molecular beam epitaxy were treated by large area n-on-p injection junction and flip-flop mixing process.The chips interconnected with low-noise and multimodal options readout circuit composed a 1280×1024 Medium-wave Infrared Focal Plane Cooling Detector whose pixel spacing was 15 microns.Its main photoelectric properties are average NETD equivalent to 18.5 mK,non-uniformity equivalent to 7.5%,operability equivalent to 98.97%.The paper also studies the substrate-removal technique on Germanium-based chip,which improves the stability and reliability of detector.

A Photodetector based on ZnO Nanorods

In this work,a photodetector based on ZnO nanorods array was vertically grown on the nanoZnO film.ZnO nanorods playing two roles in the photodetector,as the materials of absorbing UV light and carrier transport path.We used the solgel method to prepare the ZnO seed solution and annealed to get nano-ZnO film.Then,ZnO nanorods array were fabricated by

Graphene quantum dots:preparations,properties,functionalizations and applications

Zero-dimensional graphene quantum dots(GQDs)exhibit many different properties,such as strong fluorescence,nonzero bandgap and solubility in solvents,compared to two-dimensional graphene.GQDs are biocompatible and have low toxicity;hence,they are widely used in the biomedical field.The edge effect of GQDs is of particular interest because edge modification can regulate the performance of nanomaterials.In this review,various preparation methods for GQDs,which can be divided into three main categories,namely top-down,bottom-up and chemical methods,are discussed.The unique optical,electrical,thermal and magnetic properties of GQDs are reviewed.The functionalization of GQDs by doping with heteroatoms and forming composites with other materials is studied,and the characteristics of these GQDs are also discussed.The applications of these GQDs in the fields of optics,electricity,optoelectronics,biomedicine,energy,agriculture and other emerging interdisciplinary fields are reviewed to highlight the enormous potential of nanomaterials.This review reports on the recent advancement in GQD research and suggests future directions for the development of GQDs.

Effect of power variation on microstructure and surface morphology of HgCdTe films deposited by RF magnetron sputtering

Mercury cadmium telluride films were grown by the RF magnetron sputtering technique at different sputtering powers.In experiment,X-ray diffraction（XRD） and atomic force microscopy（AFM） have been used to characterize the microstructure of HgCdTe films.The experimental results showed that when the growth power increased,the growth rate of HgCdTe films increased;when the growth power was less than 30 W,the HgCdTe film deposited by RF magnetron sputtering was amorphous;when the growth power was more than 30 W,the films exhibited polycrystalline structure.Films deposited at different growth rates were found to have characteristically different formations and surface morphologies;as observed through AFM,the surface morphology is composed of longitudinal islands forming a maze-like pattern in the high deposition rate.AFM analysis also illustrated that a significant reduction in the areal density of large islands and characteristically smoother films was achieved using a low deposition rate.

Dark conductivity and photoconductivity of amorphous Hg_(0.78)Cd_(0.22)Te thin films

This paper reports the dark conductivity and photoconductivity of amorphous HgCdTe thin films deposited on an AlOsubstrate by RF magnetron sputtering.It is determined that dark conduction activation energy is 0.417 eV for the as-grown sample.Thermal quenching is absent for the as-grown sample during the testing temperature zone,but the reverse is true for the polycrystalline sample.Photosensitivity shows the maximum at 240 K for amorphous thin films,while it is higher for the as-grown sample than for polycrystalline thin films in the range from 170 to 300 K.The recombination mechanism is the monomolecular recombination process at room temperature,which is different from the low temperature range.Theμτ-product is low in the range of 10-10cm~2/V,which indicates that some defect states exist in the amorphous thin films.

INFLUENCE OF SURFACE CONDUCTANCE ON PYROELECTRIC PROPERTIES OF FERROELECTRIC CRYSTALS

The bound surface charges generated by the spontaneous polarization of ferroelectric crystals are neutralized by the free charges coming from crystals or the stray charges at constant temperature, so it cannot be detected. The mean time of neutralization by the free charges is τ=ε/σ, where ε is the dielectric constant and σ is the bulk conductivity. The value of τ for the most of pyroelectric materials is about from 1 to 1000 sec. The spontaneous polarization of ferroelectric crystals