Impacts of hydrogen annealing on the carrier lifetimes in p-type 4H-SiC after thermal oxidation

Thermal oxidation and hydrogen annealing were applied on a 100μm thick Al-doped p-type 4H-Si C epitaxial wafer to modulate the minority carrier lifetime,which was investigated by microwave photoconductive decay(μ-PCD).The minority carrier lifetime decreased after each thermal oxidation.On the contrary,with the hydrogen annealing time increasing to3 hours,the minority carrier lifetime increased from 1.1μs(as-grown)to 3.14μs and then saturated after the annealing time reached 4 hours.The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes.Moreover,the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed.The average minority carrier lifetime was up to 1.94μs and non-uniformity of carrier lifetime reached 38%after 4-hour hydrogen annealing.The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms.

AFF4 regulates osteogenic differentiation of human dental follicle cells

As a member of the AFF(AF4/FMR2)family,AFF4 is a transcription elongation factor that is a component of the super elongation complex.AFF4 serves as a scaffolding protein that connects transcription factors and promotes gene transcription through elongation and chromatin remodelling.Here,we investigated the effect of AFF4 on human dental follicle cells(DFCs)in osteogenic differentiation.In this study,we found that small interfering RNA-mediated depletion of AFF4 resulted in decreased alkaline phosphatase(ALP)activity and impaired mineralization.In addition,the expression of osteogenic-related genes(DLX5,SP7,RUNX2 and BGLAP)was significantly downregulated.In contrast,lentivirus-mediated overexpression of AFF4 significantly enhanced the osteogenic potential of human DFCs.Mechanistically,we found that both the mRNA and protein levels of ALKBH1,a critical regulator of epigenetics,changed in accordance with AFF4 expression levels.Overexpression of ALKBH1 in AFF4-depleted DFCs partially rescued the impairment of osteogenic differentiation.Our data indicated that AFF4 promoted the osteogenic differentiation of DFCs by upregulating the transcription of ALKBH1.

A 4H-SiC semi-super-junction shielded trench MOSFET: p-pillar is grounded to optimize the electric field characteristics

A 4H-SiC trench gate metal-oxide-semiconductor field-effect transistor(UMOSFET)with semi-super-junction shiel-ded structure(SS-UMOS)is proposed and compared with conventional trench MOSFET(CT-UMOS)in this work.The advantage of the proposed structure is given by comprehensive study of the mechanism of the local semi-super-junction structure at the bottom of the trench MOSFET.In particular,the influence of the bias condition of the p-pillar at the bottom of the trench on the static and dynamic performances of the device is compared and revealed.The on-resistance of SS-UMOS with grounded(G)and ungrounded(NG)p-pillar is reduced by 52%(G)and 71%(NG)compared to CT-UMOS,respectively.Additionally,gate ox-ide in the GSS-UMOS is fully protected by the p-shield layer as well as semi-super-junction structure under the trench and p-base regions.Thus,a reduced electric-field of 2 MV/cm can be achieved at the corner of the p-shield layer.However,the quasi-intrinsic protective layer cannot be formed in NGSS-UMOS due to the charge storage effect in the floating p-pillar,resulting in a large electric field of 2.7 MV/cm at the gate oxide layer.Moreover,the total switching loss of GSS-UMOS is 1.95 mJ/cm2 and is reduced by 18%compared with CT-UMOS.On the contrary,the NGSS-UMOS has the slowest overall switching speed due to the weakened shielding effect of the p-pillar and the largest gate-to-drain capacitance among the three.The proposed GSS-UMOS plays an important role in high-voltage and high-frequency applications,and will provide a valuable idea for device design and circuit applications.

A Study on the Funding Management of Agricultural Scientific Research Project in the New Situation

The agricultural scientific research project funding is an important prerequisite for the implementation of agricultural scientific research project,and an essential basic condition to support agricultural research. In recent years,China has paid great attention to the development of scientific research,and increased the input of scientific research funds,but there are some shortcomings in funding management during the implementation of the project. Based on many years of practice,this paper expounds the main problems in the current funding management for agricultural scientific research project,and brings forward the relevant recommendations,in order to provide a reference for the scientific management of agricultural scientific research project funding in the new situation.

3D printing of fine-grained aluminum alloys through extrusion-based additive manufacturing:Microstructure and property characterization

Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based metal AM method(refer to“SoftTouch”depositionin thefiledpatent)thatis suitablefor making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures.The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties.Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment,avoiding pricy powders and costly inert or vacuum conditions.The resulting multi-layer de-posited 6061 aluminum alloys yield strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment.The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites,adding novel features to existing parts,repairing damaged metal parts,and welding advanced metals for supporting sustainable manufac-turing,in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.

Scientific objectives of the Hot Universe Baryon Surveyor(HUBS) mission

The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view,the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, difuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.

宇宙中“隐藏”物质的X射线层析成像

Great strides have been made towards our understanding of the Universe over the past few decades.Surprisingly,only roughly 5%of what the Universe is made of is in the form of matter that is composed of the elements in the periodic table.The other 95% is,at present,completely unknown,and is conveniently referred to as dark matter and dark energy,which certainly represents new physics at work(see,e.g.,Ref.[1]for a review).

SDS-modified Nanoporous Silver as an Efficient Electrocatalyst for Selectively Converting CO2 to CO in Aqueous Solution

Selectively electrochemical conversion of CO2 into organic fuel using renewable electricity is one of the most sought-after processes.In this paper,we report the electrochemical reduction of CO2(CO2RR)on the nanoporous Ag electrodes made of compacted Ag nanoparticles(AgNPs),which were prepared by one-step reduction in the water phase with or without the surfactant sodium dodecyl sulfate(SDS).The scanning electron microscope(SEM)characterizations show that the compacted Ag electrodes have the nanoporous morphology formed by stacking AgNPs.Compared with the nanoporous Ag electrode without SDS modification(C-AgNPs),the SDS-modified AgNPs electrode(C-AgNPs-SDS)is highly effective in improving selective CO production in a wide range of potentials(-0.69 V--1.19 V,vs.RHE),with a Faradaic efficiency of 92.2% and a current density of -8.23 mA·cm^-2 for CO production at -0.79 V(vs.RHE).C-AgNPs-SDS is also catalytically stable with only less than 7% deactivation after 8 h of continuous electrolysis.

载阿奇霉素-鼠李糖脂胶束制备工艺优化及性能表征

采用薄膜水化法制备载阿奇霉素-鼠李糖脂(AZI-RHL)胶束,以包封率、载药量为评价指标,通过单因素试验和正交试验优化制备工艺,并考察其理化性质。制备载药胶束前先测定RHL水溶液的临界胶束浓度(CMC)。结果表明,RHL水溶液的CMC值约为0.25 mg/mL。优化后的最佳制备工艺条件为:RHL投料量100 mg,甲醇用量12 mL,搅拌时长20 min。在此条件下制备的AZI-RHL胶束呈球形,水动力学直径为136.3±68.5 nm,Zeta电位为-23.1±6.8 mV,包封率为80.34%±0.60%,载药量为19.42%±0.48%。红外光谱证明AZI包埋在胶束中。体外释放试验表明AZI-RHL胶束具有一定的缓释作用,其体外累计释放曲线符合Ritger-Peppas方程,释放药物以Fick扩散为主。综上所述,AZI-RHL胶束的制备工艺稳定可靠,胶束粒径小,且包封率、载药量高,是一种有潜力的新型制剂。