Synthesis and nitrogen content regulation of diamond in a high-pressure hydrogen-rich environment

The regulating nitrogen content of diamond in a hydrogen-rich high-temperature and high-pressure(HPHT) growth environment was systematically investigated in this work by developing three growth systems,namely, "FeNi+Ti", "FeNi+G_(3)N_(6)H_(6)",and "FeNi+Ti+C_(3)N_(6)H_(6)".Optical microscopy,infrared spectroscopy,and photoluminescence(PL)spectroscopy measurements were conducted to analyze the spectroscopic characteristics of diamonds grown in these three systems.From our analysis,it was demonstrated that the presence of hydrogen in the sp^(3) hybrid C-H does not directly affect the color of the diamond and facilitates the increase of the nitrogen-vacancy(NV) center concentration in a highnitrogen-content diamond.In addition,titanium plays an important role in nitrogen removal,while its impact on hydrogen doping within the diamond lattice is insignificant.Most importantly,by regulating the ratio of nitrogen impurities that coexist in the nitrogen and hydrogen HPHT environment,the production of hydrogenous Ⅱa-type diamond,hydrogenous Ib-type diamond,and hydrogenous high-nitrogen-type diamonds was achieved with a nitrogen content of less than 1 ppm to 1600 ppm.

Preparation of fluorescence starch-nanoparticle and its application as plant transgenic vehicle

Starch-nanoparticles were synthesized in water-in-oil microemusion at room temperature, and the starch-nanoparticles were coated with poly-L-lysine. The surface of the starch-nanoparticles was combined with fluorescence material Ru(bpy)32+·6H2O, and then the particles were characterized via transmission electron microscope. The fluorescence nanoparticles were conjugated with plasmid DNA to form complexes, and then treated with ultrasound and DNase I. pEGAD plasmid DNA-nanoparticle complexes were co-cultured with plant suspension cells of Dioscrea Zigiberensis G H Wright, and treated with ultrasound. The results show that the diameter of the fluorescence starch-nanoparticles is 50-100 nm. DNA-nanoparticle complexes can protect DNA from ultrasound damage as well as from DNase I cleavage. Mediated by ultrasound, pEGAD plasmid DNA-nanoparticle complexes can pierce into the cell wall, cell membrane and nucleus membrane of plant suspension cells. The green fluorescence protein(GFP) gene at a high frequency exceeds 5%. This nano-biomaterial can efficiently solve the problem that exterior genes cannot traverse the plant cell wall easily.

Simulation and test of the SLEGS TOF spectrometer at SSRF

The Shanghai laser electron gamma source(SLEGS)is a powerful tool for exploring photonuclear physics,such as giant dipole resonance(GDR)and pygmy dipole resonance,which are the main mechanisms of collective nuclear motion.The goal of the SLEGS neutron time-of-flight(TOF)spectrometer is to measure GDR and specific nuclear structures in the energy region above the neutron threshold.The SLEGS TOF spectrometer was designed to hold 20 sets of EJ301 and LaBr3 detectors.Geant4 was used to simulate the efficiency of each detector and the entire spectrometer,which provides a reference for the selection of detectors and layout of the SLEGS TOF spectrometer.Under the events of 208Pb,implementations of coincidence and time-of-flight technology for complex experiments are available;thus,and neutron decay events can be separated.The performance of SLEGS TOF spectrometer was systematically evaluated using offline experiments,in which the time resolution reached approximately 0.9 ns.

Fabrication of PdSe2/GaAs Heterojunction for Sensitive Near-Infrared Photovoltaic Detector and Image Sensor Application

In this study,we have developed a high-sensitivity,near-infrared photodetector based on PdSe2/GaAs heterojunction,which was made by transferring a multilayered PdSe2 film onto a planar GaAs.The as-fabricated PdSe2/GaAs heterojunction device exhibited obvious photovoltaic behavior to 808 nm illumination,indicating that the near-infrared photodetector can be used as a self-driven device without external power supply.Further device analysis showed that the hybrid heterojunction exhibited a high on/off ratio of 1.16×10^5 measured at 808 nm under zero bias voltage.The responsivity and specific detectivity of photodetector were estimated to be 171.34 mA/W and 2.36×10^11 Jones,respectively.Moreover,the device showed excellent stability and reliable repeatability.After 2 months,the photoelectric characteristics of the near-infrared photodetector hardly degrade in air,attributable to the good stability of the PdSe2.Finally,the PdSe2/GaAs-based heterojunction device can also function as a near-infrared light sensor.

Analysis and simulation of lateral PIN photodiode gated by transparent electrode fabricated on fully-depleted SOI film

A novel device, lateral PIN photodiode gated by transparent electrode （LPIN PD-GTE） fabricated on fully-depleted SOI film was proposed. ITO film was adopted in the device as gate electrode to reduce the light absorption. Thin Si film was fully depleted under gate voltage to achieve low dark current and high photo4o-dark current ratio. The model of gate voltage was obtained and the numerical simulations were presented by ATLAS. Current-voltage characteristics of LPIN PD-GTE obtained in dark （dark current） and under 570 nm illumination （photo current） were studied to achieve the greatest photo-to-dark current ratio for active channel length from 2 to 12 /am. The results show that the photo-to-dark current ratio is 2.0×10^7, with dark current of around 5×10^-4 pA under VGK=0.6 V, PrN=5 mW/cm2, for a total area of 10μm×10μm in fully depleted SOI technology. Thus, the LPIN PD-GTE can be suitable for high-grade photoelectric systems such as blue DVD.

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.

Surface rumples and band gap reductions of cubic BaZrO_3 (001) surface studied by means of first-principles calculations

Electronic properties of the （001） surface of cubic BaZrO3 with BaO and ZrO2 terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO2-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO2-terminated surface. Results of surface energy calculations reveal that the BaZrO3 surface is likely to be more stable than the PbZrO3 surface.

Effect of platform temperature on microstructure and corrosion resistance of selective laser melted Al-Mg-Sc alloy plate

The Al-3.40Mg-1.08Sc alloy plates were manufactured by selective laser melting(SLM) at platform temperatures of 35 ℃ and 200 ℃, respectively, and the corrosion performance of them was studied along height direction. The results show that the corrosion resistance of the alloy plate built at platform temperature of 35 ℃ along height direction is basically the same due to a uniform microstructure;While the corrosion resistance of the alloy plate built at platform temperature of 200 ℃ along height direction is different. The evolution of microstructure and the distribution of secondary phases are investigated, and the results show that the Cu-rich phases in alloy play a key role on corrosion performance. At higher platform temperature, the cooling rate is relative slow and a certain degree of in situ ageing leads to the significantly different distribution of Cu-rich phases along grain boundary. Specimens built at the platform temperature of 200 ℃ are inclined to locate at the crossed grain boundary, rather than continuous segregation of Cu-rich phases along grain boundary that is built at platform temperature of 35 ℃. Therefore, the corrosion resistance of Al-3.40Mg-1.08Sc alloy plate manufactured at platform temperature of 200 ℃ is higher, and presents a gradually decreasing trend along height direction.

Magnetic and Transport Properties of La_(0.5-x)Nd_xBa_(0.5) CoO_3 Compounds

Substituting effects of Nd for La in La 0.5 Ba 0.5 CoO 3 compounds were studied systematically. The results show that Nd doping does not change the itinerant properties of the Co3d electrons. The molecular magnetic moment of the materials decreases monotonically with increasing Nd dopant. When Nd content x ≥0.45, a magnetic phase separation appears in the materials. When x ≤0.45, the Curie temperature decreases monotonically with increasing Nd dopant. This is due to the size effects of the rare earth ions. The electric resistance measurements show that in the studied temperature range, the conduction of the materials belongs to the thermo diffusion conduction below the Curie temperature, while it belongs to the variable range hopping conduction of polarons over the Curie temperature.

Nonlinear Electrical Characteristics of Antimony and Copper Doped Tin Oxide Based Varistor Ceramics

The novel CuO-doped dense tin oxide varistor ceramics are investigated. The densification of tin oxide varistor ceramics could be greatly improved by doping copper oxide additives. The introduction of antimony additives into a SnO2. CuO ceramic system would make it possess excellent nonlinearity. The sample doped with 0.05 mol% Sb2 03 possesses the highest nonlinearity coefficient （α = 17.9） and the lowest leakage current density （ JL = 52μA cm^-2） among all the samples. A modified defect barrier model is introduced to explain the formation of the grainboundary barrier. The nonlinear behaviour of （Cu, Sb）-doped SnO2 varistor system could be explained by the barrier model.

Synthesis and biochemical properties of fluorescent/magnetic bifunctional starch particles

Magnetic starch particles （MSPs） were synthesized in water-in-oil mieroemulsion at room temperature. MSPs were characterized by transmission electron microscopy （TEM）, Fourier transform infrared spectrometry （FTIR）, zeta potential system, thermogravimetric analysis （TGA） and vibrating sample magnetometry （VSM）. The average diameter of the MSPs was 220 nm, dispersed with well-proportioned size and magnetic resonance, the saturation magnetization was 3.64 A.mR/kg. MSP was coated with poly-L-lysine （PLL）, and then the surface of PLL-MSP was combined with fluorescein isothiocynate （FITC）. Results show that fluorescent/magnetic starch particles （FMSPs） are of stable photo-bleaching capability compared with free FITC, with low bio-toxicity and certain function of magnetic separation. It is expected that FMSPs are bifimctional nano-materials including fluorescence labelling and magnetic separation.

Synthesis and Field Emission of ZnO Nanostructures on CuO Catalyzed Porous Silicon Substrate

Mass production of ZnO nanobelts and hexagonal nanorods has been successfully synthesized on CuO catalyzed porous silicon （PS） using a simple vapour-solid （VS） growth method. A comparison of their morphologies is investigated by scanning electron microscopy （SEM）. The transmission electron microscopy （TEM） confirms that ZnO nanobelts and nanorods are single crystalline with the growth direction of （0110） and （0001）, respectively. Field emission tests indicate that the ZnO nanostructures on porous silicon have low turn-on field of about 3.6 V/μm （at 1.0μA/cm^2） and the threshold field of about 8.3 V/μm （at 1.0mA/cm^2）, high emission site density （ESD） of approximately 104 cm^-2.

Microstructures and corrosion behaviors of Al−6.5Si−0.45Mg−xSc casting alloy

The microstructures and corrosion behaviors of the Al−6.5Si−0.45Mg casting alloys with the addition of Sc were investigated by using scanning electron microscopy,X-ray diffraction,electrochemical measurement techniques and immersion corrosion tests and compared with those of Sr-modified alloy.The results show that Sc has evident refining and modifying effects on the primaryα(Al)and the eutectic Si phase of the alloy,and the effects can be enhanced with the increase of Sc content.When the Sc content is increased to 0.58 wt.%,its modifying effect on the eutectic Si is almost same as that of Sr.Sc can improve the corrosion resistance of the test alloy in NaCl solution when compared with Sr,but the excessively high Sc content cannot further increase the corrosion resistance of the alloy.The corrosion of the alloys mainly occurs in the eutectic region of the alloy,and mostly the eutecticα(Al)is dissolved.This confirms that Si phase is more noble thanα(Al)phase,and the galvanic couplings can be formed between the eutectic Si andα(Al)phases.

Effect of the codoping of N-H-O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N-H-O at 5.5 GPa-7.1 GPa and 1370℃-1450℃. With the increase in the N-H-O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds;surface morphology became block-like;and growth texture,stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N-H-O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N-H-O impurity contents of the synthesis system.

Low-dimensional phases engineering for improving the emission efficiency and stability of quasi-2D perovskite films

The two-dimensional(2 D) Ruddlesden–Popper-type perovskites, possessing tunable bandgap, narrow light emission,strong quantum confinement effect, as well as a simple preparation method, are identified as a new generation of candidate materials for efficient light-emitting diodes. However, the preparation of high-quality quasi-2 D perovskite films is still a challenge currently, such as the severe mixing of phases and a high density of defects within the films, impeding the further promotion of device performance. Here, we prepared the quasi-2 D PEA_(2) MA_(n-1) Pbn Br_(3 n+1) perovskite films by a modified spin-coating method, and the phases with large bandgap were effectively suppressed by the vacuum evaporation treatment. We systematically investigated the optical properties and stability of the optimized films, and the photoluminescence(PL) quantum yield of the treated films was enhanced from 23% to 45%. We also studied the emission mechanisms by temperature-dependent PL spectra. Moreover, the stability of films against moisture, ultraviolet light, and heat was also greatly improved.

Synergistic influences of titanium,boron,and oxygen on large-size single-crystal diamond growth at high pressure and high temperature

The synergistic influences of boron,oxygen,and titanium on growing large single-crystal diamonds are studied using different concentrations of B_(2)O_(3) in a solvent-carbon system under 5.5 GPa-5.7 GPa and 1300℃-1500℃.It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B_(2)O_(3) without the addition of Ti atoms.However,high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti.Additionally,boron-oxygen complexes are found on the surface of the crystal,and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi-C system.The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal.This has important scientific significance not only for understanding the synergistic influence of boron,oxygen,and titanium atoms on the growth of diamond in the earth,but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.

Diamond growth in a high temperature and high pressure Fe–Ni–C–Si system:Effect of synthesis pressure

Pressure is one of the necessary conditions for diamond growth.Exploring the influence of pressure on growth changes in silicon-doped diamonds is of great value for the production of high-quality diamonds.This work reports the morphology,impurity content and crystal quality characteristics of silicon-doped diamond crystals synthesized under different pressures.Fourier transform infrared spectroscopy shows that with the increase of pressure,the nitrogen content in the C-center inside the diamond crystal decreases.X-ray photoelectron spectroscopy test results show the presence of silicon in the diamond crystals synthesized by adding silicon powder.Raman spectroscopy data shows that the increase in pressure in the Fe-Ni-C-Si system shifts the Raman peak of diamonds from 1331.18 cm^(-1)to 1331.25 cm^(-1),resulting in a decrease in internal stress in the crystal.The half-peak width decreased from 5.41 cm^(-1)to 5.26 cm^(-1),and the crystallinity of the silicon-doped diamond crystals improved,resulting in improved quality.This work provides valuable data that can provide a reference for the synthesis of high-quality silicon-doped diamonds.

Uncertainty evaluation and correlation analysis of single-particle energies in phenomenological nuclear mean field:an investigation into propagating uncertainties for independent model parameters

Based on the Monte Carlo approach and conventional error analysis theory,taking the heaviest doubly magic nucleus 208Pb as an example,we first evaluate the propagated uncertainties of universal potential parameters for three typical types of single-particle energy in the phenomenological Woods–Saxon mean field.Accepting the Woods–Saxon modeling with uncorrelated model parameters,we found that the standard deviations of singleparticle energy obtained through the Monte Carlo simulation and the error propagation rules are in good agreement.It seems that the energy uncertainty of the single-particle levels regularly evoluate with certain quantum numbers to a large extent for the given parameter uncertainties.Further,the correlation properties of the single-particle levels within the domain of input parameter uncertainties are statistically analyzed,for example,with the aid of Pearson’s correlation coefficients.It was found that a positive,negative,or unrelated relationship may appear between two selected single-particle levels,which will be extremely helpful for evaluating the theoretical uncertainty related to the single-particle levels(e.g.,K isomer)in nuclear structural calculations.

Computational Prediction of a Novel Superhard sp^(3) Trigonal Carbon Allotrope with Bandgap Larger than Diamond

Searching for new carbon allotropes with superior properties has been a longstanding interest in material sciences and condensed matter physics.Here we identify a novel superhard carbon phase with an 18-atom trigonal unit cell in a full-sp^(3) bonding network,termed tri-C_(18) carbon,by first-principles calculations.Its structural stability has been verified by total energy,phonon spectra,elastic constants,and molecular dynamics simulations.Furthermore,tri-C_(18) carbon has a high bulk modulus of 400 GPa and Vickers hardness of 79.0 GPa,comparable to those of diamond.Meanwhile,the simulated x-ray diffraction pattern of tri-C_(18) carbon matches well with the previously unexplained diffraction peaks found in chimney soot,indicating the possible presence of tri-C_(18) carbon.Remarkably,electronic band structure calculations reveal that tri-C_(18) carbon has a wide indirect bandgap of 6.32 eV,larger than that of cubic diamond,indicating its great potential in electronic or optoelectronic devices working in the deep ultraviolet region.

Structure and Photoluminescence of Polycrystalline MgxZn1-xO Films

Different photoluminescence （PL） spectra are observed for rf magnetron sputtered polycrystalline Mg0.25Zn0.75O and Mg0.37Zn0.63O films on silicon substrates when excited by different wavelengths. When the excitation wavelength is 280nm, a UV emission peak at 370nm and a blue peak at 462nm are generated for the Mg0.25Zn0.75O film, and those two peaks for the Mg0.37Zn0.63O film shift to 366nm and 466nm, respectively. The wavelengths of the PL peaks are related to the excitation wavelength. The stronger peak is obtained in the blue band due to a large number of oxygen vacancies caused by excess Zn and Mg atoms, while the weaker peak is obtained in the ultraviolet band.