The evolution of cesium iodide band gap as a function of pressure is studied in the range from 0 to 60 GPa. Within this range, two structural phase transitions occurred, and the band gap was affected by the compressio...The evolution of cesium iodide band gap as a function of pressure is studied in the range from 0 to 60 GPa. Within this range, two structural phase transitions occurred, and the band gap was affected by the compression pressure and structural rearrangement. The band gap estimation under pressure, as obtained by the density functional theory methods, successfully reproduced the experimental trend of the optical gap and electrical resistivity, namely, a general decreasing tendency, an early maximum, and a discontinuous peak around 40 GPa.展开更多
The CRISPR-Cas revolution is taking place in virtually all fields of life sciences.Harnessing DNA cleavage with the CRISPR-Cas9 system of Streptococcus pyogenes has proven to be extraordinarily simple and efficient,re...The CRISPR-Cas revolution is taking place in virtually all fields of life sciences.Harnessing DNA cleavage with the CRISPR-Cas9 system of Streptococcus pyogenes has proven to be extraordinarily simple and efficient,relying only on the design of a synthetic single guide RNA（sgRNA） and its co-expression with Cas9.Here,we review the progress in the design of sgRNA from the original dual RNA guide for S.pyogenes and Staphylococcus aureus Cas9（SpCas9 and SaCas9）.New assays for genome-wide identification of offtargets have provided important insights into the issue of cleavage specificity in vivo.At the same time,the on-target activity of thousands of guides has been determined.These data have led to numerous online tools that facilitate the selection of guide RNAs in target sequences.It appears that for most basic research applications,cleavage activity can be maximized and off-targets minimized by carefully choosing guide RNAs based on computational predictions.Moreover,recent studies of Cas proteins have further improved the flexibility and precision of the CRISPR-Cas toolkit for genome editing.Inspired by the crystal structure of the complex of sgRNA-SpCas9 bound to target DNA,several variants of SpCas9 have recently been engineered,either with novel protospacer adjacent motifs（PAMs） or with drastically reduced off-targets.Novel Cas9 and Cas9-like proteins called Cpf 1 have also been characterized from other bacteria and will benefit from die insights obtained from SpCas9.Genome editing with CRISPR-Cas9 may also progress with better understanding and control of cellular DNA repair pathways activated after Cas9-induced DNA cleavage.展开更多
The structure of （E）-N-[（E）-3-[（lR,2R）-2-（3,4-dibromo-phenyl）-l-fluro-cyclopropyl]- allylidene]-2-0-tolyl-acetamide （C21HIsONFBrz, Mr = 479.18） has been determined by X-ray single- crystal diffraction and th...The structure of （E）-N-[（E）-3-[（lR,2R）-2-（3,4-dibromo-phenyl）-l-fluro-cyclopropyl]- allylidene]-2-0-tolyl-acetamide （C21HIsONFBrz, Mr = 479.18） has been determined by X-ray single- crystal diffraction and theoretical calculations to establish the configuration, stereochemistry and a stable conformation of the molecule. The compound crystallizes in the monoclinic space group P21/c, a = 28.3452（10）, b = 4.9311（10）, c = 14.257（2） A, fl = 102.7654（10）, V = 1943.5（5） A3 and Z = 4. The structure has been refined to the final R = 0.05 for the observed structure factors with 1 〉 30（/）. Theoretical calculations in the ground state have been carried out for the compound studied using the Hartree-Fock （HF） and density functional theory （DFT） （B3LYP） with 6-31G（d,p） basis sets. The results show that the studied compound prefers the keto form. The compound involves intra- and intermolecular hydrogen bonding of C-H.-.O and C-H-..F types, which further stabilize the structure and display a trans configuration for the C=N and C=C double bonds. The calculated results show that the predicted geometry can well reproduce the structural parameters.展开更多
Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers...Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics.This work demonstrates that a remanent polarization(P_(r))value of>5μC/cm^(2)can be obtained in asdeposited Hf_(0.5)Zr_(0.5)O_(2)(HZO)films that are fabricated by thermal atomic layer deposition(TALD)under low temperature of 250℃.The ferroelectric orthorhombic phase(o-phase)in the as-deposited HZO films is detected by scanning transmission electron microscopy(STEM).This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.展开更多
Thick GaN layer deposited by hydride vapor phase epitaxy (HVPE) on a metalorganic chemical vapor deposition (MOCVD) GaN template with a thin low temperature (LT) AlN intermediate layer was investigated. High resolutio...Thick GaN layer deposited by hydride vapor phase epitaxy (HVPE) on a metalorganic chemical vapor deposition (MOCVD) GaN template with a thin low temperature (LT) AlN intermediate layer was investigated. High resolution X-ray resolution diffraction (HRXRD) shows that the crystalline quality of thick GaN layer was improved compared with the template. As confirmed by atomic force microscopy (AFM) observations, the surface morphology of AlN intermediate layer helps to improve the nucleation of GaN epilayer. Photoluminescence (PL) spectra measurement shows its high optical quality and low compressive stress, and micro Raman measurement confirms the latter result. Thus, the deposition of the LT-AlN interlayer has promoted the growth of an HVPE-GaN layer with an excellent crystalline quality.展开更多
Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films ...Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers. The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process. Cl2/Ar and Cl2/He were employed as etching gas. Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions. Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.展开更多
A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer. A sample without interlayer was also grow...A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer. A sample without interlayer was also grown at the same time for comparison. Significant reductions of dislocation density in W-GaN film is confirmed by the result of high-resolution X-ray diffraction and transmission electron microscope (TEM) observation. The improvement of optical properties of the W-GaN is confirmed by photoluminescence (PL) result. A shift of PL peak suggests that the strain is lower in the W-GaN than the film without W interlayer. This technique offers a potential path to obtain high-quality GaN film as free-standing substrate.展开更多
X-ray powder diffraction, scanning electron microscopy （SEM）, energy dispersive X-ray, electrical resistivity and AC-magnetic susceptibility measurements have been performed for polycrystalline superconducting sampl...X-ray powder diffraction, scanning electron microscopy （SEM）, energy dispersive X-ray, electrical resistivity and AC-magnetic susceptibility measurements have been performed for polycrystalline superconducting samples of type TIBa2Ca2_xSCxCU309_δ （0.0 ≤ x 〈 0.6）. The powder X-ray diffractograms indicate that the tetragonal structure of T1-1223 is not affected by Sc-substitution whereas the lattice parameters are changed. The X-ray analysis indicates that the low-contents of scandium （x） enhance the formation of T1-1223 and reduce the secondary phases. The grain-size determined by SEM decreases as x increases. The electrical resistivity measurements show suppression in the superconducting transition temperature, Tc, and an increase in both the residual resistivity and the superconducting transition width as x increases. The suppression in Tc is attributed to the hole-filling mechanism.展开更多
Objective:To evaluate the antibacterial and antioxidant activities and to identify the volatile bioactive compounds present in different crude extracts of the seaweed Caulerpa racemosa var.cylindracea.Methods:Caulerpa...Objective:To evaluate the antibacterial and antioxidant activities and to identify the volatile bioactive compounds present in different crude extracts of the seaweed Caulerpa racemosa var.cylindracea.Methods:Caulerpa racemosa harvested from the intertidal zone of Mostaganem coast(N 35?54’37.94",E 0?3’17.37")was subjected to Soxhlet extraction using methanol,chloroform,and hexane solvents.Antioxidant properties were assessed by using 2,2’-diphenyl-1-picrylhydrazyl(DPPH),2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)andβ-carotene bleaching assays.The antibacterial activity was evaluated on six standard bacterial strains using the agar disc diffusion method.The GC-MS analysis was performed using non-polar and polar capillary columns.Results:The chloroform extract of Caulerpa racemosa exhibited higher contents of polyphenols[(123.91±1.46)mg gallic acid equivalent/g dry extract]and tannins[(59.28±5.43)mg catechin equivalent/g dry extract](P<0.001)and was the most effective in scavenging DPPH[(1.98±0.08)mg/m L]and ABTS[(1.66±0.05)mg/m L]radicals.The hexane extract displayed the best antibacterial activity against Staphylococcus aureus,Bacillus cereus,and Pseudomonas aeruginosa,producing inhibition zones of(11.16±0.76),(9.00±0.00)and(9.33±1.15)mm,respectively.The l-(+)-ascorbic acid 2,6-dihexadecanoate and 4-hydroxy-2 methylproline were among the most abundant volatile compounds.Besides conventional fatty acids,cis-10-heptadecenoic acid,nonahexacontanoic acid,and dodecanoic acid,3-hydroxy-were identified.Two phytosterols were identified:stigmast-5-en-3-ol-(12.9%)and stigmast-5-en-3.beta.-ol,(24 S)-(4.57%).Conclusions:The preliminary identification of the volatile compounds reveals the presence of some new bioactive components not reported previously in Caulerpa racemosa from other geographical areas.Some of these compounds possess an interesting potential for pharmaceutical/nutraceutical applications.展开更多
This work is part of an experimental contribution approach to the study of the incorporation of glass sand from the grinding of recycled glass waste in cement mortars and its influence on the physical and mechanical b...This work is part of an experimental contribution approach to the study of the incorporation of glass sand from the grinding of recycled glass waste in cement mortars and its influence on the physical and mechanical behavior of semi-rich mortars without adjuvants. For this purpose, after a physical characterization of the sands, eight (08) formulations of mortars based on cement CEM II B/L 32.5R and fine sands (0/2) of glass at mass contents of 0%, 10%, 20%, 30%, 40%, 50%, 75% and 100% of the silty sand (0/2) were made respectively to three (03) types of fine glass sand (white, brown, green) with water dosages on cement (W/C) of 0.50, 0.45, 0.40. The results obtained show that the fine sands of recycled glass have a higher water absorption than the silty sand and the physical properties of the mortars prepared are affected by the increase in the glass content. The mechanical performances are obtained for the ratio W/C = 0.50 and the formulation of glass mortars for an optimal compressive strength superior to glass-free mortar requires a substitution of 10% for fine white glass sand, 20% for sand fine green glass and 75% for fine brown glass sand. The comparative study between these different compositions of fine glass sand mortars shows that the mechanical performances of fine brown glass sand are better than other glass sands but generally remain inferior to the control mortar based on natural silty sand.展开更多
Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and...Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and electricstrain properties were investigated.The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3t and Zr4t doping levels.A large strain of 0.19%was obtained at relatively low electric fields of 30 kV/cm in the composition of x=0.04.The normalized large-signal d33*values were approximately 633 pm/V under a low driving electric field of 30 kV/cm,which were comparable or larger than the values reported for other lead-free families.The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls,which were confirmed by the observations of domain morphology using transmission electron microscopy(TEM)technique.Excellent temperature stability of the strain properties of the x=0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic.Theoretical simulations revealed that the Zr^(4t)produce the local stress at the BO6 octahedra and Bi3t could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons,which induced lattice expansion and local distortions in the sample.The local displacements are strongly anisotropic in heterovalent-ion doped system.It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution.Such heterovalent doping of Bi^(3t)and Zr^(4t)could destory simultaneously the orthorhombic symmetry and the short-range ferroelecctric order,leading to the formation of complex nanodomains and local structral hetergenenity.Heterovalent doping may,therefore,offer a new avenve to design novel K0.5Na0.5NbO3(KNN)-based materials for their mutifunctional applications.展开更多
La_(0.7)Ca_(0.3)MnO_(3)(LCMO)thin films have been grown on MgO substrate using the metal organic deposition process.The lattice mismatch between LCMO and MgO is relatively large around 8.14% imposing large inplane-ten...La_(0.7)Ca_(0.3)MnO_(3)(LCMO)thin films have been grown on MgO substrate using the metal organic deposition process.The lattice mismatch between LCMO and MgO is relatively large around 8.14% imposing large inplane-tensile strain and out-of-plane-compressive strain on the film.Hence the structural,microstructural and electrical properties have been found to be strongly correlated to the strain degree and relaxation.Cross-section transmission electron microscopy observations demonstrate the presence of microstructural defects due to the large lattice mismatch between the LCMO and MgO.In addition to structural and microstructural defects,X-ray diffraction and Raman spectroscopy measurements show the existence of a minor phase of MnO in the film.Magnetization versus temperature measurement show a relatively low Curie temperature around 75 K.The electrical behavior is found to be semiconducting over a large temperature interval.The electrical transport mechanisms have been investigated using the small polaron hopping and variable range hopping models and correlated to their microstructural properties.展开更多
1 Results Oxy-apatite materials are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well known difficulties related to their densification prevent them from b...1 Results Oxy-apatite materials are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well known difficulties related to their densification prevent them from being used as such. This study presents strategies to obtain oxy-apatite dense materials and the influence of elaboration route on transport properties. Particular emphasis is put on the microstructure effect on ion conduction. By the combined use of freeze-drying and conventional or spark p...展开更多
1 Results We study the synthesis,the structural and transport properties of acceptor-doped barium stannate BaSn0.75B0.25O3-d (B=La,Y…) compounds.Some of these materials were presented few years ago as good proton con...1 Results We study the synthesis,the structural and transport properties of acceptor-doped barium stannate BaSn0.75B0.25O3-d (B=La,Y…) compounds.Some of these materials were presented few years ago as good proton conductors with some interest for the fuel cell community[1-2].Nevertheless,these studies were only limited to two kinds of dopants and the elaboration was far from being optimised leading to poor properties.So the main objective of the present study is to extend the study of acceptor-doped bar...展开更多
In recent years,the emergence of numerous applications of artificial intelligence(AI)has sparked a new technological revolution.These applications include facial recognition,autonomous driving,intelligent robotics,and...In recent years,the emergence of numerous applications of artificial intelligence(AI)has sparked a new technological revolution.These applications include facial recognition,autonomous driving,intelligent robotics,and image restoration.However,the data processing and storage procedures in the conventional von Neumann architecture are discrete,which leads to the“memory wall”problem.As a result,such architecture is incompatible with AI requirements for efficient and sustainable processing.Exploring new computing architectures and material bases is therefore imperative.Inspired by neurobiological systems,in-memory and in-sensor computing techniques provide a new means of overcoming the limitations inherent in the von Neumann architecture.The basis of neural morphological computation is a crossbar array of high-density,high-efficiency non-volatile memory devices.Among the numerous candidate memory devices,ferroelectric memory devices with non-volatile polarization states,low power consumption and strong endurance are expected to be ideal candidates for neuromorphic computing.Further research on the complementary metal-oxide-semiconductor(CMOS)compatibility for these devices is underway and has yielded favorable results.Herein,we first introduce the development of ferroelectric materials as well as their mechanisms of polarization reversal and detail the applications of ferroelectric synaptic devices in artificial neural networks.Subsequently,we introduce the latest developments in ferroelectrics-based in-memory and in-sensor computing.Finally,we review recent works on hafnium-based ferroelectric memory devices with CMOS process compatibility and give a perspective for future developments.展开更多
Over the past two decades,flexible electronics have attracted numerous attentions for their potential use as flexible,stretchable,portable and conformable devices in various fields including computing,energy harvestin...Over the past two decades,flexible electronics have attracted numerous attentions for their potential use as flexible,stretchable,portable and conformable devices in various fields including computing,energy harvesting,robotics,sensors and transductors or health monitoring.展开更多
Negative capacitance in BaTiO_(3)/SrTiO_(3) superlattices is investigated by Monte Carlo simulations in an atomistic effective Hamiltonian model,using fluctuation formulas for responses to the local macroscopic field ...Negative capacitance in BaTiO_(3)/SrTiO_(3) superlattices is investigated by Monte Carlo simulations in an atomistic effective Hamiltonian model,using fluctuation formulas for responses to the local macroscopic field that incorporates depolarizing fields.We show that epitaxial strain can tune the negative capacitance of the BaTiO_(3) ferroelectric layer and the overall capacitance of the system.In addition,we predict and explain an original switching of the negative capacitance from the BaTiO3 layer to the SrTiO_(3) layer at low temperatures for intermediate strains.展开更多
For the last few years,the research interest in magnetoelectric(ME)effect,which is the cross-coupling between ferroelectric and magnetic ordering in multiferroic materials,has experienced a significant revival.The ext...For the last few years,the research interest in magnetoelectric(ME)effect,which is the cross-coupling between ferroelectric and magnetic ordering in multiferroic materials,has experienced a significant revival.The extensive recent studies are not only conducted towards the design of sensors,actuators,transducers,and memory devices by taking advantage of the cross-control of polarization(or magnetization)by magnetic(or electric)fields,but also aim to create a clearer picture in understanding the sources of ME responses and the novel effects associated with them.Here we derive analytical models allowing to understand the striking and novel dynamics of ME effects in multiferroics and further confirm it with atomistic simulations.Specifically,the role of strain is revealed to lead to the existence of electroacoustic magnons,a new quasiparticle that mixes acoustic and optical phonons with magnons,which results in resonances and thus a dramatic enhancement of magnetoelectric responses.Moreover,a unique aspect of the dynamical quadratic ME response under a magnetic field with varying frequencies,which is the second harmonic generation(SHG),has not been discussed prior to the present work.These SHGs put emphasis on the fact that nonlinearities should be considered while dealing with such systems.展开更多
基金A Lithuanian State Scholarship from the Education Exchanges Support Foundation was granted to A.C. Support from CONACYT grant 237045 and the hospitality of the SPMS Laboratory and Vilnius University were also acknowledged.
文摘The evolution of cesium iodide band gap as a function of pressure is studied in the range from 0 to 60 GPa. Within this range, two structural phase transitions occurred, and the band gap was affected by the compression pressure and structural rearrangement. The band gap estimation under pressure, as obtained by the density functional theory methods, successfully reproduced the experimental trend of the optical gap and electrical resistivity, namely, a general decreasing tendency, an early maximum, and a discontinuous peak around 40 GPa.
基金funded by ANR(ANR-II-INBS-0014)funded by grants NIH/NHGRI 5U41HG002371-15,NIH/NCI 5U54HG007990-02a grant from the California Institute of Regenerative Medicine,CIRM GC1R-06673C
文摘The CRISPR-Cas revolution is taking place in virtually all fields of life sciences.Harnessing DNA cleavage with the CRISPR-Cas9 system of Streptococcus pyogenes has proven to be extraordinarily simple and efficient,relying only on the design of a synthetic single guide RNA（sgRNA） and its co-expression with Cas9.Here,we review the progress in the design of sgRNA from the original dual RNA guide for S.pyogenes and Staphylococcus aureus Cas9（SpCas9 and SaCas9）.New assays for genome-wide identification of offtargets have provided important insights into the issue of cleavage specificity in vivo.At the same time,the on-target activity of thousands of guides has been determined.These data have led to numerous online tools that facilitate the selection of guide RNAs in target sequences.It appears that for most basic research applications,cleavage activity can be maximized and off-targets minimized by carefully choosing guide RNAs based on computational predictions.Moreover,recent studies of Cas proteins have further improved the flexibility and precision of the CRISPR-Cas toolkit for genome editing.Inspired by the crystal structure of the complex of sgRNA-SpCas9 bound to target DNA,several variants of SpCas9 have recently been engineered,either with novel protospacer adjacent motifs（PAMs） or with drastically reduced off-targets.Novel Cas9 and Cas9-like proteins called Cpf 1 have also been characterized from other bacteria and will benefit from die insights obtained from SpCas9.Genome editing with CRISPR-Cas9 may also progress with better understanding and control of cellular DNA repair pathways activated after Cas9-induced DNA cleavage.
文摘The structure of （E）-N-[（E）-3-[（lR,2R）-2-（3,4-dibromo-phenyl）-l-fluro-cyclopropyl]- allylidene]-2-0-tolyl-acetamide （C21HIsONFBrz, Mr = 479.18） has been determined by X-ray single- crystal diffraction and theoretical calculations to establish the configuration, stereochemistry and a stable conformation of the molecule. The compound crystallizes in the monoclinic space group P21/c, a = 28.3452（10）, b = 4.9311（10）, c = 14.257（2） A, fl = 102.7654（10）, V = 1943.5（5） A3 and Z = 4. The structure has been refined to the final R = 0.05 for the observed structure factors with 1 〉 30（/）. Theoretical calculations in the ground state have been carried out for the compound studied using the Hartree-Fock （HF） and density functional theory （DFT） （B3LYP） with 6-31G（d,p） basis sets. The results show that the studied compound prefers the keto form. The compound involves intra- and intermolecular hydrogen bonding of C-H.-.O and C-H-..F types, which further stabilize the structure and display a trans configuration for the C=N and C=C double bonds. The calculated results show that the predicted geometry can well reproduce the structural parameters.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFA1200700)the National Natural Science Foundation of China(Grant Nos.T2222025 and 62174053)+5 种基金the Open Research Projects of Zhejiang Laboratory(Grant No.2021MD0AB03)the Shanghai Science and Technology Innovation Action Plan(Grant Nos.21JC1402000 and 21520714100)the Guangdong Provincial Key Laboratory Program(Grant No.2021B1212040001)the Fundamental Research Funds for the Central Universitiessupport from the Zuckerman STEM Leadership ProgramPazy Research Foundation(Grant No.149-2020)。
文摘Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics.This work demonstrates that a remanent polarization(P_(r))value of>5μC/cm^(2)can be obtained in asdeposited Hf_(0.5)Zr_(0.5)O_(2)(HZO)films that are fabricated by thermal atomic layer deposition(TALD)under low temperature of 250℃.The ferroelectric orthorhombic phase(o-phase)in the as-deposited HZO films is detected by scanning transmission electron microscopy(STEM).This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.
基金The work was financially supported by the National High Technology Research and Development Program of China(No.2002AA305304),the CNRS/ASC2005:Project18152,Natural Science Foundation Project(05ZR14139)and International Cooperation Project(055207043) of ShanghaiGovernment,and Project ofthe National Natural Science Foundation ofChina(No.O62GJA1001).
文摘Thick GaN layer deposited by hydride vapor phase epitaxy (HVPE) on a metalorganic chemical vapor deposition (MOCVD) GaN template with a thin low temperature (LT) AlN intermediate layer was investigated. High resolution X-ray resolution diffraction (HRXRD) shows that the crystalline quality of thick GaN layer was improved compared with the template. As confirmed by atomic force microscopy (AFM) observations, the surface morphology of AlN intermediate layer helps to improve the nucleation of GaN epilayer. Photoluminescence (PL) spectra measurement shows its high optical quality and low compressive stress, and micro Raman measurement confirms the latter result. Thus, the deposition of the LT-AlN interlayer has promoted the growth of an HVPE-GaN layer with an excellent crystalline quality.
基金This work was financially supported by the National High Technology Research and Development Program of China(No.2001AA311100 and 2002AA305304)and the CNRS/ASC2005:Nproject18152andthe National Natural Science Foundation ofChina(No.O62GJA1001).
文摘Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers. The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process. Cl2/Ar and Cl2/He were employed as etching gas. Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions. Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.
基金This work was supportedbythe National High Technology Research and Development Program(No.2002AA305304)and CNRS/ASC2005:Project18152,Natural Science Foundation Project(05ZR14139),International Cooperation Project(055207043)of the Shanghai Government andtheNational Natural Science Foundation ofChina(No.O62GJA1001).
文摘A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer. A sample without interlayer was also grown at the same time for comparison. Significant reductions of dislocation density in W-GaN film is confirmed by the result of high-resolution X-ray diffraction and transmission electron microscope (TEM) observation. The improvement of optical properties of the W-GaN is confirmed by photoluminescence (PL) result. A shift of PL peak suggests that the strain is lower in the W-GaN than the film without W interlayer. This technique offers a potential path to obtain high-quality GaN film as free-standing substrate.
文摘X-ray powder diffraction, scanning electron microscopy （SEM）, energy dispersive X-ray, electrical resistivity and AC-magnetic susceptibility measurements have been performed for polycrystalline superconducting samples of type TIBa2Ca2_xSCxCU309_δ （0.0 ≤ x 〈 0.6）. The powder X-ray diffractograms indicate that the tetragonal structure of T1-1223 is not affected by Sc-substitution whereas the lattice parameters are changed. The X-ray analysis indicates that the low-contents of scandium （x） enhance the formation of T1-1223 and reduce the secondary phases. The grain-size determined by SEM decreases as x increases. The electrical resistivity measurements show suppression in the superconducting transition temperature, Tc, and an increase in both the residual resistivity and the superconducting transition width as x increases. The suppression in Tc is attributed to the hole-filling mechanism.
文摘Objective:To evaluate the antibacterial and antioxidant activities and to identify the volatile bioactive compounds present in different crude extracts of the seaweed Caulerpa racemosa var.cylindracea.Methods:Caulerpa racemosa harvested from the intertidal zone of Mostaganem coast(N 35?54’37.94",E 0?3’17.37")was subjected to Soxhlet extraction using methanol,chloroform,and hexane solvents.Antioxidant properties were assessed by using 2,2’-diphenyl-1-picrylhydrazyl(DPPH),2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)andβ-carotene bleaching assays.The antibacterial activity was evaluated on six standard bacterial strains using the agar disc diffusion method.The GC-MS analysis was performed using non-polar and polar capillary columns.Results:The chloroform extract of Caulerpa racemosa exhibited higher contents of polyphenols[(123.91±1.46)mg gallic acid equivalent/g dry extract]and tannins[(59.28±5.43)mg catechin equivalent/g dry extract](P<0.001)and was the most effective in scavenging DPPH[(1.98±0.08)mg/m L]and ABTS[(1.66±0.05)mg/m L]radicals.The hexane extract displayed the best antibacterial activity against Staphylococcus aureus,Bacillus cereus,and Pseudomonas aeruginosa,producing inhibition zones of(11.16±0.76),(9.00±0.00)and(9.33±1.15)mm,respectively.The l-(+)-ascorbic acid 2,6-dihexadecanoate and 4-hydroxy-2 methylproline were among the most abundant volatile compounds.Besides conventional fatty acids,cis-10-heptadecenoic acid,nonahexacontanoic acid,and dodecanoic acid,3-hydroxy-were identified.Two phytosterols were identified:stigmast-5-en-3-ol-(12.9%)and stigmast-5-en-3.beta.-ol,(24 S)-(4.57%).Conclusions:The preliminary identification of the volatile compounds reveals the presence of some new bioactive components not reported previously in Caulerpa racemosa from other geographical areas.Some of these compounds possess an interesting potential for pharmaceutical/nutraceutical applications.
文摘This work is part of an experimental contribution approach to the study of the incorporation of glass sand from the grinding of recycled glass waste in cement mortars and its influence on the physical and mechanical behavior of semi-rich mortars without adjuvants. For this purpose, after a physical characterization of the sands, eight (08) formulations of mortars based on cement CEM II B/L 32.5R and fine sands (0/2) of glass at mass contents of 0%, 10%, 20%, 30%, 40%, 50%, 75% and 100% of the silty sand (0/2) were made respectively to three (03) types of fine glass sand (white, brown, green) with water dosages on cement (W/C) of 0.50, 0.45, 0.40. The results obtained show that the fine sands of recycled glass have a higher water absorption than the silty sand and the physical properties of the mortars prepared are affected by the increase in the glass content. The mechanical performances are obtained for the ratio W/C = 0.50 and the formulation of glass mortars for an optimal compressive strength superior to glass-free mortar requires a substitution of 10% for fine white glass sand, 20% for sand fine green glass and 75% for fine brown glass sand. The comparative study between these different compositions of fine glass sand mortars shows that the mechanical performances of fine brown glass sand are better than other glass sands but generally remain inferior to the control mortar based on natural silty sand.
基金the Awards of Gates Cambridge Scholarship and British Academy Postdoctoral Fellowship(pf100022),which were awarded to the first author in 2006 and 2010 respectively,for their generous financial support throughout all stages of the current study
基金supported by National Science Foundation of China(NSFC No.52172125),the CSS project(YK2015-0602006),the Natural Science Foundation of Shandong Province of China(Grant No.ZR2018BA028),Quzhou Science and Technology Plan Project(2022K108)and General Research Project of Zhejiang Provincial Department of Education(Y202249978).
文摘Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and electricstrain properties were investigated.The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3t and Zr4t doping levels.A large strain of 0.19%was obtained at relatively low electric fields of 30 kV/cm in the composition of x=0.04.The normalized large-signal d33*values were approximately 633 pm/V under a low driving electric field of 30 kV/cm,which were comparable or larger than the values reported for other lead-free families.The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls,which were confirmed by the observations of domain morphology using transmission electron microscopy(TEM)technique.Excellent temperature stability of the strain properties of the x=0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic.Theoretical simulations revealed that the Zr^(4t)produce the local stress at the BO6 octahedra and Bi3t could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons,which induced lattice expansion and local distortions in the sample.The local displacements are strongly anisotropic in heterovalent-ion doped system.It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution.Such heterovalent doping of Bi^(3t)and Zr^(4t)could destory simultaneously the orthorhombic symmetry and the short-range ferroelecctric order,leading to the formation of complex nanodomains and local structral hetergenenity.Heterovalent doping may,therefore,offer a new avenve to design novel K0.5Na0.5NbO3(KNN)-based materials for their mutifunctional applications.
文摘La_(0.7)Ca_(0.3)MnO_(3)(LCMO)thin films have been grown on MgO substrate using the metal organic deposition process.The lattice mismatch between LCMO and MgO is relatively large around 8.14% imposing large inplane-tensile strain and out-of-plane-compressive strain on the film.Hence the structural,microstructural and electrical properties have been found to be strongly correlated to the strain degree and relaxation.Cross-section transmission electron microscopy observations demonstrate the presence of microstructural defects due to the large lattice mismatch between the LCMO and MgO.In addition to structural and microstructural defects,X-ray diffraction and Raman spectroscopy measurements show the existence of a minor phase of MnO in the film.Magnetization versus temperature measurement show a relatively low Curie temperature around 75 K.The electrical behavior is found to be semiconducting over a large temperature interval.The electrical transport mechanisms have been investigated using the small polaron hopping and variable range hopping models and correlated to their microstructural properties.
文摘1 Results Oxy-apatite materials are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well known difficulties related to their densification prevent them from being used as such. This study presents strategies to obtain oxy-apatite dense materials and the influence of elaboration route on transport properties. Particular emphasis is put on the microstructure effect on ion conduction. By the combined use of freeze-drying and conventional or spark p...
文摘1 Results We study the synthesis,the structural and transport properties of acceptor-doped barium stannate BaSn0.75B0.25O3-d (B=La,Y…) compounds.Some of these materials were presented few years ago as good proton conductors with some interest for the fuel cell community[1-2].Nevertheless,these studies were only limited to two kinds of dopants and the elaboration was far from being optimised leading to poor properties.So the main objective of the present study is to extend the study of acceptor-doped bar...
基金supported by National Key Research and Development Program of China(2021YFA1200700)The National Natural Science Foundation of China(T2222025 and 62174053)+2 种基金Open Research Projects of Zhejiang Lab(2021MD0AB03)Shanghai Science and Technology Innovation Action Plan(21JC1402000 and 21520714100)the Fundamental Research Funds for the Central Universities。
文摘In recent years,the emergence of numerous applications of artificial intelligence(AI)has sparked a new technological revolution.These applications include facial recognition,autonomous driving,intelligent robotics,and image restoration.However,the data processing and storage procedures in the conventional von Neumann architecture are discrete,which leads to the“memory wall”problem.As a result,such architecture is incompatible with AI requirements for efficient and sustainable processing.Exploring new computing architectures and material bases is therefore imperative.Inspired by neurobiological systems,in-memory and in-sensor computing techniques provide a new means of overcoming the limitations inherent in the von Neumann architecture.The basis of neural morphological computation is a crossbar array of high-density,high-efficiency non-volatile memory devices.Among the numerous candidate memory devices,ferroelectric memory devices with non-volatile polarization states,low power consumption and strong endurance are expected to be ideal candidates for neuromorphic computing.Further research on the complementary metal-oxide-semiconductor(CMOS)compatibility for these devices is underway and has yielded favorable results.Herein,we first introduce the development of ferroelectric materials as well as their mechanisms of polarization reversal and detail the applications of ferroelectric synaptic devices in artificial neural networks.Subsequently,we introduce the latest developments in ferroelectrics-based in-memory and in-sensor computing.Finally,we review recent works on hafnium-based ferroelectric memory devices with CMOS process compatibility and give a perspective for future developments.
基金supported by CAS Pioneer Hundred Talents Program(Y60707WR19)Zhejiang Province Qianjiang Talent Program(ZJ-QJRC-2020-32)+2 种基金the National Natural Science Foundation of China(51931011 and 52127803)K.C.Wong Education Foundation(GJTD-2020-11)“Pioneer”and“Leading Goose”R&D Program of Zhejiang(2022C01032)。
文摘Over the past two decades,flexible electronics have attracted numerous attentions for their potential use as flexible,stretchable,portable and conformable devices in various fields including computing,energy harvesting,robotics,sensors and transductors or health monitoring.
基金R.W.and L.B.acknowledge ARO Grant No.W911NF-16-1-0227C.P.and L.B.thank the DARPA Grant No.HR0011-15-2-0038(MATRIX program)+4 种基金S.P.and L.B.also acknowledge ONR Grant No.N00014-17-1-2818Some computations were made possible by MRI Grant No.0722625 from NSF,ONR Grant No.N00014-15-1-2881(DURIP)a Challenge grant from the Department of DefenseC.P.also acknowledges the support from a public grant overseen by the French National Research Agency(ANR)as part of the“Investissements d’Avenir”program(Labex NanoSaclay,reference:ANR-10-LABX-0035)S.P.appreciates support of the Russian Ministry of Science and Higher Education(State assignment in the field of scientific activity,Southern Federal University,2020).
文摘Negative capacitance in BaTiO_(3)/SrTiO_(3) superlattices is investigated by Monte Carlo simulations in an atomistic effective Hamiltonian model,using fluctuation formulas for responses to the local macroscopic field that incorporates depolarizing fields.We show that epitaxial strain can tune the negative capacitance of the BaTiO_(3) ferroelectric layer and the overall capacitance of the system.In addition,we predict and explain an original switching of the negative capacitance from the BaTiO3 layer to the SrTiO_(3) layer at low temperatures for intermediate strains.
基金S.O.S.,B.X.,and L.B.acknowledge the DARPA Grant Number HR0011-15-2-0038(under the MATRIX program)S.P.acknowledges ONR Grant Number N00014-17-1-2818 and also appreciates support of RFBR 19-52-53030 GFEN+3 种基金C.P.thanks the ARO grant W911NF-16-1-0227B.X.also acknowledges the startup fund from Soochow University and the support from Priority Academic Program Development(PAPD)of Jiangsu Higher Education InstitutionsWe appreciate the support of MRI Grant Number 0722625 from NSF,ONR Grant Number N00014-15-1-2881(DURIP)as well as a Challenge grant from the Department of Defense,and also acknowledge the High Performance Computing Center at the University of Arkansas.
文摘For the last few years,the research interest in magnetoelectric(ME)effect,which is the cross-coupling between ferroelectric and magnetic ordering in multiferroic materials,has experienced a significant revival.The extensive recent studies are not only conducted towards the design of sensors,actuators,transducers,and memory devices by taking advantage of the cross-control of polarization(or magnetization)by magnetic(or electric)fields,but also aim to create a clearer picture in understanding the sources of ME responses and the novel effects associated with them.Here we derive analytical models allowing to understand the striking and novel dynamics of ME effects in multiferroics and further confirm it with atomistic simulations.Specifically,the role of strain is revealed to lead to the existence of electroacoustic magnons,a new quasiparticle that mixes acoustic and optical phonons with magnons,which results in resonances and thus a dramatic enhancement of magnetoelectric responses.Moreover,a unique aspect of the dynamical quadratic ME response under a magnetic field with varying frequencies,which is the second harmonic generation(SHG),has not been discussed prior to the present work.These SHGs put emphasis on the fact that nonlinearities should be considered while dealing with such systems.
