Dual-metal gate and gate–drain underlap designs are introduced to reduce the ambipolar current of the device based on the C-shaped pocket TFET(CSP-TFET).The effects of gate work function and gate–drain underlap leng...Dual-metal gate and gate–drain underlap designs are introduced to reduce the ambipolar current of the device based on the C-shaped pocket TFET(CSP-TFET).The effects of gate work function and gate–drain underlap length on the DC characteristics and analog/RF performance of CSP-TFET devices,such as the on-state current(I_(on)),ambipolar current(I_(amb)),transconductance(g_(m)),cut-off frequency(f_(T))and gain–bandwidth product(GBP),are analyzed and compared in this work.Also,a combination of both the dual-metal gate and gate–drain underlap designs has been proposed for the C-shaped pocket dual metal underlap TFET(CSP-DMUN-TFET),which contains a C-shaped pocket area that significantly increases the on-state current of the device;this combination design substantially reduces the ambipolar current.The results show that the CSP-DMUN-TFET demonstrates an excellent performance,including high I_(on)(9.03×10^(-4)A/μm),high I_(on)/I_(off)(~10^(11)),low SS_(avg)(~13 mV/dec),and low I_(amb)(2.15×10^(-17)A/μm).The CSP-DMUN-TFET has the capability to fully suppress ambipolar currents while maintaining high on-state currents,making it a potential replacement in the next generation of semiconductor devices.展开更多
A new concentrated ternary salt ether-based electrolyte enables stable cycling of lithium metal battery(LMB)cells with high-mass-loading(13.8 mg cm^(−2),2.5 mAh cm^(−2))NMC622(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))cathodes ...A new concentrated ternary salt ether-based electrolyte enables stable cycling of lithium metal battery(LMB)cells with high-mass-loading(13.8 mg cm^(−2),2.5 mAh cm^(−2))NMC622(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))cathodes and 50μm Li anodes.Termed“CETHER-3,”this electrolyte is based on LiTFSI,LiDFOB,and LiBF4 with 5 vol%fluorinated ethylene carbonate in 1,2-dimethoxyethane.Commer-cial carbonate and state-of-the-art binary salt ether electrolytes were also tested as baselines.With CETHER-3,the electrochemical performance of the full-cell battery is among the most favorably reported in terms of high-voltage cycling stability.For example,LiNi_(x)Mn_(y)Co_(1-x-y)O_(2)(NMC)-Li metal cells retain 80%capacity at 430 cycles with a 4.4 V cut-off and 83%capacity at 100 cycles with a 4.5 V cut-off(charge at C/5,discharge at C/2).According to simulation by density functional theory and molecular dynamics,this favorable performance is an outcome of enhanced coordination between Li^(+)and the solvent/salt molecules.Combining advanced microscopy(high-resolution transmission electron microscopy,scanning electron microscopy)and surface science(X-ray photoelectron spectroscopy,time-of-fight secondary ion mass spectroscopy,Fourier-transform infrared spectroscopy,Raman spectroscopy),it is demonstrated that a thinner and more stable cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)are formed.The CEI is rich in lithium sulfide(Li_(2)SO_(3)),while the SEI is rich in Li_(3)N and LiF.During cycling,the CEI/SEI suppresses both the deleterious transformation of the cathode R-3m layered near-surface structure into disordered rock salt and the growth of lithium metal dendrites.展开更多
SrBi2-χNdχNb2O9(χ=0,0.1,0.2 and 0.4)bismuth layer-structured ferroelectric ceramics were prepared by the solid-state reaction sintering method.The accurate position of Nd element in SrBi2-χNdχNb2O9 ceramics was d...SrBi2-χNdχNb2O9(χ=0,0.1,0.2 and 0.4)bismuth layer-structured ferroelectric ceramics were prepared by the solid-state reaction sintering method.The accurate position of Nd element in SrBi2-χNdχNb2O9 ceramics was determined by the X-ray Rietveld method and Synchrotron radiation X-ray absorption fine structure(XAFS)technology.The partial substitution of Nd 3+ for Bi 3+ leads to the decrease in the distortion of NbO6 octahedron for SrBi2-χNdχNb2O9 ceramics and also lowers the piezoelectric properties of SrBi2-χNdχNb2O9 ceramics.Meanwhile,the temperature coefficient of resonant frequency(TCF)decreases when Nd element partially replaces Bi element in SrBi2-χNdχNb2O9 ceramics.展开更多
Temperature and excitation dependent photoluminescence(PL) of InGaN epilayer grown on c-plane Ga N/sapphire template by molecular beam epitaxy(MBE) has been systematically investigated. The emission spectra of the sam...Temperature and excitation dependent photoluminescence(PL) of InGaN epilayer grown on c-plane Ga N/sapphire template by molecular beam epitaxy(MBE) has been systematically investigated. The emission spectra of the sample consisted of strong multiple peaks associated with one stimulated emission(SE) located at 430 nm and two spontaneous emissions(SPE) centered at about 450 nm and 480 nm, indicating the co-existence of shallow and deep localized states.The peak energy of SE exhibiting weak s-shaped variation with increasing temperature revealed the localization effect of excitons. Moreover, an abnormal increase of the SPE intensity with increasing temperature was also observed, which indicated that the carrier transfer between the shallow and deeper localized states exists. Temperature dependent time-resolved PL(TRPL) demonstrated the carrier transfer processes among the localized states. In addition, a slow thermalization of hot carriers was observed in InGaN film by using TRPL and transient differential reflectivity, which is attributed to the phonon bottleneck effect induced by indium aggregation.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
A C-shaped pocket tunnel field effect transistor(CSP-TFET)has been designed and optimized based on the traditional double-gate TFETs by introducing a C-shaped pocket region between the source and channel to improve th...A C-shaped pocket tunnel field effect transistor(CSP-TFET)has been designed and optimized based on the traditional double-gate TFETs by introducing a C-shaped pocket region between the source and channel to improve the device performance.A gate-to-pocket overlapping structure is also examined in the proposed CSP-TFET to enhance the gate controllability.The effects of the pocket length,pocket doping concentration and gate-to-pocket overlapping structure on the DC and analog/RF characteristics of the CSP-TFET are estimated after calibrating the tunneling model in double-gate TFETs.The DC and analog/RF performance such as on-state current(Ion),on/off current ratio(Ion/Ioff),subthreshold swing(SS)transconductance(g;),cut-off frequency(f_(T))and gain-bandwidth product(GBP)are investigated.The optimized CSPTFET device exhibits excellent performance with high I_(off)(9.98×10^(-4)A/μm),high I_(on)/I_(off)(~10^(11)),as well as low SS(~12 m V/dec).The results reveal that the CSP-TFET device could be a potential alternative for the next generation of semiconductor devices.展开更多
Materials' properties may differ in the thin-film form, especially for epitaxial ultra-thin films, where the substrates play an important role in their deviation from the bulk quality. Here by molecular beam epita...Materials' properties may differ in the thin-film form, especially for epitaxial ultra-thin films, where the substrates play an important role in their deviation from the bulk quality. Here by molecular beam epitaxy(MBE) and scanning tunneling microscopy/spectroscopy, we investigate the growth kinetics of ultra-thin tellurium(Te) films on SrTiO_(3)(STO)(001). The MBE growth of Te films usually exhibits Volmer–Weber(VW) island growth mode and no a-few-monolayer film with full coverage has been reported. The absence of wetting-layer formation in the VW growth mode of Te on STO(001) is resulted from its low diffusion barriers as well as its relatively higher surface energy compared with those of the substrate and the interface. Here we circumvent these limiting factors and achieve the growth of ultra-thin β-Te films with near-complete coverages by driving the growth kinetics to the extreme condition. There is a critical thickness(3 monolayer) above which the two-dimensional Te films can form on the STO(001) substrate. In addition, the scanning tunneling spectra on the ultra-thin Te film grown on STO exhibits an enormously large forbidden gap compared with that grown on the graphene substrate. Our work establishes the necessary conditions for the growth of ultra-thin materials with similar kinetics and thermodynamics.展开更多
Concepts of the complex partition functions and the Fisher zeros provide intrinsic statistical mechanisms for finite temperature and real time dynamical phase transitions.We extend the utility of these complexificatio...Concepts of the complex partition functions and the Fisher zeros provide intrinsic statistical mechanisms for finite temperature and real time dynamical phase transitions.We extend the utility of these complexifications to quantum phase transitions.We exactly identify different Fisher zeros on lines or closed curves and elucidate their correspondence with domain-wall excitations or confined mesons for the one-dimensional transverse field Ising model.The crossover behavior of the Fisher zeros provides a fascinating picture for criticality near the quantum phase transition,where the excitation energy scales are quantitatively determined.We further confirm our results by tensor network calculations and demonstrate a clear signal of deconfined meson excitations from the disruption of the closed zero curves.Our results unambiguously show significant features of Fisher zeros for a quantum phase transition and open up a new route to explore quantum criticality.展开更多
Motivated by the mathematical beauty and the recent experimental realizations of fractal systems,we study the spin-1/2 antiferromagnetic Heisenberg model on a Sierpiński gasket.The fractal porous feature generates ne...Motivated by the mathematical beauty and the recent experimental realizations of fractal systems,we study the spin-1/2 antiferromagnetic Heisenberg model on a Sierpiński gasket.The fractal porous feature generates new kinds of frustration to exhibit exotic quantum states.Using advanced tensor network techniques,we identify a quantum gapless-spin-liquid ground state in fractional spatial dimension.This fractal spin system also demonstrates nontrivial nonlocal properties.While the extremely short-range correlation causes a highly degenerate spin form factor,the entanglement in this fractal system suggests a long-range scaling behavior.We also study the dynamic structure factor and clearly identify the gapless excitation with a stable corner excitation emerged from the ground-state entanglement.Our results unambiguously point out multiple essential properties of this fractal spin system,and open a new route to explore spin liquid and frustrated magnetism.展开更多
With the aid of photolithography, an array of one-dimensional porous silicon photonic crystai reflector islands for a far infrared image detector ranging from 10 μm to 14 μm is successfully fabricated. Silicon nitri...With the aid of photolithography, an array of one-dimensional porous silicon photonic crystai reflector islands for a far infrared image detector ranging from 10 μm to 14 μm is successfully fabricated. Silicon nitride formed by low pressure chemical vapor deposition (LPCVD) was used as the masking layer for the island array formation. After etching, the microstructures were examined by a scanning electron microscope and the optical properties were studied by Fourier transform infrared spectroscopy, the result indicates that the multilayer structure could be obtained in the perpendicular direction via periodically alternative etching current in each pre-pattern. At the same time, the island array has a well-proportioned lateral etching effect, which is very useful for the thermal isolation in lateral orientation of the application in devices. It is concluded that regardless of the absorption of the deposition layer on the substrate, the localized photonic crystalline islands have higher reflectivity. The designed islands structure not only prevents the cracking of the porous silicon layers but is also useful for the application in the cold part for the sensor devices and the iliterconnection of each pixel.展开更多
The spin-1/2 model system with antiferromagnetic(AF) couplings on a J1-J2checkerboard lattice, known as the planar pyrochlore model, is strongly frustrated and associated with a two-to-one dimensional crossover. Using...The spin-1/2 model system with antiferromagnetic(AF) couplings on a J1-J2checkerboard lattice, known as the planar pyrochlore model, is strongly frustrated and associated with a two-to-one dimensional crossover. Using the Projected Entangled Simplex States tensor network ansatz, we identify a large number of nearly degenerate states in the frustrated region(J_(1)<J_(2)).Specifically, we find the long-sought crossed-dimer valence bond solid(VBS) state to be the ground state at J_(1)≤J_(2), while various 1D AF correlated states take over the rest. We verify the stability of the VBS state against nematic perturbation. The corresponding bosonic picture provides an intuitive understanding of the low-energy physics. Particularly, it predicts weaker VBS states in the easy-plane limit, which we confirm numerically. Our results clarify the most essential ground state properties of this interesting system and demonstrate the usefulness of bosonic picture in dealing with frustrated magnetism.展开更多
Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition t...Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.展开更多
The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical ...The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH3NH3PbI3 solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH3NH3PbI3 is thermodynamically unstable with respect to the phase separation into CH3NH3I + PbI2, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombie phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH3NH3PbI3 is unchanged. When I is replaced by Br or CI, Pb by Sn, or the organic cation CH3NH3 by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH3NH3PbI3 and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.展开更多
The beneficial effect of the alkali metals such as Na and K on the Cu(In.Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe) solar cells has been extensively investigated in the past two decades, however, in most of the...The beneficial effect of the alkali metals such as Na and K on the Cu(In.Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe) solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum (VBM) level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.展开更多
Using first-principles calculations,we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair.15 defect-pairs with short defect–defect dist...Using first-principles calculations,we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair.15 defect-pairs with short defect–defect distances are found to be stable during structural relaxation,so they can exist in the GaN lattice once formed during the irradiation of high-energy particles.9 defect-pairs have formation energies lower than 10 eV in the neutral state.The vacancy-pair VN–VN is found to have very low formation energies,as low as 0 eV in p-type and Ga-rich GaN,and act as efficient donors producing two deep donor levels,which can limit the p-type doping and minority carrier lifetime in GaN.VN–VN has been overlooked in the previous study of defects in GaN.Most of these defect-pairs act as donors and produce a large number of defect levels in the band gap.Their formation energies and concentrations are sensitive to the chemical potentials of Ga and N,so their influences on the electrical and optical properties of Ga-rich and N-rich GaN after irradiation should differ significantly.These results about the defect-pairs provide fundamental data for understanding the radiation damage mechanism in GaN and simulating the defect formation and diffusion behavior under irradiation.展开更多
The multiple ferroelectric polarization tuned by external electric field could be used to simulate the biological synaptic weight. Ferroelectric synaptic devices have two advantages compared with other reported ones: ...The multiple ferroelectric polarization tuned by external electric field could be used to simulate the biological synaptic weight. Ferroelectric synaptic devices have two advantages compared with other reported ones: One is that the intrinsic switching of ferroelectric domains without invoking of defect migration as in resistive oxides, contributes reliable performance in these ferroelectric synapses. Another tremendous advantage is the extremely low energy consumption because the ferroelectric polarization is manipulated by electric field which eliminates the Joule heating by current as in magnetic and phase change memories. Ferroelectric synapses have potential for the construction of low-energy and effective brain-like intelligent networks. Here we summarize recent pioneering work of ferroelectric synapses involving the structure of ferroelectric tunnel junctions (FTJs), ferroelectric diodes (FDs), and ferroelectric field effect transistors (FeFETs), respectively, and shed light on future work needed to accelerate their application for efficient neural network.展开更多
In this work, a Fe-based nanocrystalline microwire of 20 mm in length and 25 μm in diameter was placed in the center of a 316 stainless steel pipe. The pipe was 500 μm in diameter and a little shorter than the micro...In this work, a Fe-based nanocrystalline microwire of 20 mm in length and 25 μm in diameter was placed in the center of a 316 stainless steel pipe. The pipe was 500 μm in diameter and a little shorter than the microwire. A series of voltages were applied on the pipe to study the influence of the electrical field on the Giant-Magneto-Impedance(GMI) effect of the microwire. Experimental results showed that the electronic field between the wire and the pipe reduced the hysteresis of the GMI effect. The results were explained based on equivalent circuit and eddy current consumptions analysis.展开更多
Radiation damage in 4H-SiC samples implanted by 70 keV oxygen ion beams was studied using photoluminescence and electron spin resonance techniques. ESR peak of g = 2.0053 and two zero-phonon lines were observed with t...Radiation damage in 4H-SiC samples implanted by 70 keV oxygen ion beams was studied using photoluminescence and electron spin resonance techniques. ESR peak of g = 2.0053 and two zero-phonon lines were observed with the implanted samples. Combined with theoretical calculations, we found that the main defect in the implanted 4H-Si C samples was oxygen-vacancy complex. The calculated defect formation energies showed that the oxygen-vacancy centers were stable in n-type 4H-Si C.Moreover, the V_(Si)O_C^0 and V_(Si)O_C^(-1) centers were optically addressable. The results suggest promising spin coherence properties for quantum information science.展开更多
Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are re...Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are reviewed, including the defects and defect levels of intrinsic V_(Hg) and the extrinsic amphoteric arsenic(As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level,conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.展开更多
The kesterite thin film solar cells based on the quaternary Cu2ZnSnS4 and Cu2ZnSnSe4 and their alloys Cu2ZnSn(S,Se)4 have been considered as environment-friendly and non-toxic alternatives to the currently commercia...The kesterite thin film solar cells based on the quaternary Cu2ZnSnS4 and Cu2ZnSnSe4 and their alloys Cu2ZnSn(S,Se)4 have been considered as environment-friendly and non-toxic alternatives to the currently commercialized CdTe and Cu(In,Ga)Se2 thin film solar cells. From the theoretical point of view, we will review how the group I2-II-IV-VI4 quaternary compound semiconductors are derived from the binary CdTe and the ternary CuInSe2 or CuGaSe2 through the cation mutation, and how the crystal structure and electronic band structure evolve as the component elements change. The increased structural and chemical freedom in these quaternary semiconductors opens up new possibility for the tailoring of material properties and design of new light-absorber semiconductors. However, the increased freedom also makes the development of high-efficiency solar cells more challenging because much more intrinsic point defects, secondary phases, surfaces, and grain-boundaries can exist in the thin films and influence the photovoltaic performance in a way different from that in the conventional CdTe and Cu(In,Ga)Se2 solar cells. The experimental characterization of the properties of defects, secondary phase, and grain-boundaries is currently not very efficient and direct, especially for these quaternary compounds. First-principles calculations have been successfully used in the past decade for studying these properties. Here we will review the theoretical progress in the study of the mixed-cation and mixed-anion alloys of the group I2-II-IV- VI4 semiconductors, defects, alkaline dopants, and grain boundaries, which provided very important information for the optimization of the kesterite solar cell performance.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52177185 and 62174055)。
文摘Dual-metal gate and gate–drain underlap designs are introduced to reduce the ambipolar current of the device based on the C-shaped pocket TFET(CSP-TFET).The effects of gate work function and gate–drain underlap length on the DC characteristics and analog/RF performance of CSP-TFET devices,such as the on-state current(I_(on)),ambipolar current(I_(amb)),transconductance(g_(m)),cut-off frequency(f_(T))and gain–bandwidth product(GBP),are analyzed and compared in this work.Also,a combination of both the dual-metal gate and gate–drain underlap designs has been proposed for the C-shaped pocket dual metal underlap TFET(CSP-DMUN-TFET),which contains a C-shaped pocket area that significantly increases the on-state current of the device;this combination design substantially reduces the ambipolar current.The results show that the CSP-DMUN-TFET demonstrates an excellent performance,including high I_(on)(9.03×10^(-4)A/μm),high I_(on)/I_(off)(~10^(11)),low SS_(avg)(~13 mV/dec),and low I_(amb)(2.15×10^(-17)A/μm).The CSP-DMUN-TFET has the capability to fully suppress ambipolar currents while maintaining high on-state currents,making it a potential replacement in the next generation of semiconductor devices.
基金National Natural Science Foundation of China,Grant/Award Numbers:21905265,52072322,U1930402,61974042National Science Foundation,Civil,Mechanical and Manufacturing Innovation,Grant/Award Number:1911905+3 种基金Fundamental Research Funds for the Central Universities,Grant/Award Number:WK2060140026Department of Science and Technology of Sichuan Province,Grant/Award Numbers:2019‐GH02‐00052‐HZ,2019YFG0220Scientific and Technological Innovation Foundation of Shunde Graduate School,Grant/Award Number:BK19BE024National Key Research and Development Program of China,Grant/Award Number:2017YFA0303403。
文摘A new concentrated ternary salt ether-based electrolyte enables stable cycling of lithium metal battery(LMB)cells with high-mass-loading(13.8 mg cm^(−2),2.5 mAh cm^(−2))NMC622(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))cathodes and 50μm Li anodes.Termed“CETHER-3,”this electrolyte is based on LiTFSI,LiDFOB,and LiBF4 with 5 vol%fluorinated ethylene carbonate in 1,2-dimethoxyethane.Commer-cial carbonate and state-of-the-art binary salt ether electrolytes were also tested as baselines.With CETHER-3,the electrochemical performance of the full-cell battery is among the most favorably reported in terms of high-voltage cycling stability.For example,LiNi_(x)Mn_(y)Co_(1-x-y)O_(2)(NMC)-Li metal cells retain 80%capacity at 430 cycles with a 4.4 V cut-off and 83%capacity at 100 cycles with a 4.5 V cut-off(charge at C/5,discharge at C/2).According to simulation by density functional theory and molecular dynamics,this favorable performance is an outcome of enhanced coordination between Li^(+)and the solvent/salt molecules.Combining advanced microscopy(high-resolution transmission electron microscopy,scanning electron microscopy)and surface science(X-ray photoelectron spectroscopy,time-of-fight secondary ion mass spectroscopy,Fourier-transform infrared spectroscopy,Raman spectroscopy),it is demonstrated that a thinner and more stable cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)are formed.The CEI is rich in lithium sulfide(Li_(2)SO_(3)),while the SEI is rich in Li_(3)N and LiF.During cycling,the CEI/SEI suppresses both the deleterious transformation of the cathode R-3m layered near-surface structure into disordered rock salt and the growth of lithium metal dendrites.
基金Project(20080440083)supported by China Postdoctoral Science FoundationProject(2007CB924901)supported by the National Basic Research Program of China+1 种基金Project(60677022)supported by the National Natural Science Foundation of ChinaProject(09ZR1409200)supported by the Natural Science Foundation of Shanghai,China
文摘SrBi2-χNdχNb2O9(χ=0,0.1,0.2 and 0.4)bismuth layer-structured ferroelectric ceramics were prepared by the solid-state reaction sintering method.The accurate position of Nd element in SrBi2-χNdχNb2O9 ceramics was determined by the X-ray Rietveld method and Synchrotron radiation X-ray absorption fine structure(XAFS)technology.The partial substitution of Nd 3+ for Bi 3+ leads to the decrease in the distortion of NbO6 octahedron for SrBi2-χNdχNb2O9 ceramics and also lowers the piezoelectric properties of SrBi2-χNdχNb2O9 ceramics.Meanwhile,the temperature coefficient of resonant frequency(TCF)decreases when Nd element partially replaces Bi element in SrBi2-χNdχNb2O9 ceramics.
基金Project supported by the National Key Research Program of China(Grant No.2016YFB0501604)the National Natural Science Foundation of China(Grant Nos.10874127 and 61227902)
文摘Temperature and excitation dependent photoluminescence(PL) of InGaN epilayer grown on c-plane Ga N/sapphire template by molecular beam epitaxy(MBE) has been systematically investigated. The emission spectra of the sample consisted of strong multiple peaks associated with one stimulated emission(SE) located at 430 nm and two spontaneous emissions(SPE) centered at about 450 nm and 480 nm, indicating the co-existence of shallow and deep localized states.The peak energy of SE exhibiting weak s-shaped variation with increasing temperature revealed the localization effect of excitons. Moreover, an abnormal increase of the SPE intensity with increasing temperature was also observed, which indicated that the carrier transfer between the shallow and deeper localized states exists. Temperature dependent time-resolved PL(TRPL) demonstrated the carrier transfer processes among the localized states. In addition, a slow thermalization of hot carriers was observed in InGaN film by using TRPL and transient differential reflectivity, which is attributed to the phonon bottleneck effect induced by indium aggregation.
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Project supported by the National Natural Science Foundation of China(Grant Nos.52177185 and 62174055)Open Fund of Shanghai Key Laboratory of Multidimensional Information Processing,East China Normal University(Grant No.2019MIP002)。
文摘A C-shaped pocket tunnel field effect transistor(CSP-TFET)has been designed and optimized based on the traditional double-gate TFETs by introducing a C-shaped pocket region between the source and channel to improve the device performance.A gate-to-pocket overlapping structure is also examined in the proposed CSP-TFET to enhance the gate controllability.The effects of the pocket length,pocket doping concentration and gate-to-pocket overlapping structure on the DC and analog/RF characteristics of the CSP-TFET are estimated after calibrating the tunneling model in double-gate TFETs.The DC and analog/RF performance such as on-state current(Ion),on/off current ratio(Ion/Ioff),subthreshold swing(SS)transconductance(g;),cut-off frequency(f_(T))and gain-bandwidth product(GBP)are investigated.The optimized CSPTFET device exhibits excellent performance with high I_(off)(9.98×10^(-4)A/μm),high I_(on)/I_(off)(~10^(11)),as well as low SS(~12 m V/dec).The results reveal that the CSP-TFET device could be a potential alternative for the next generation of semiconductor devices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61804056 and 92065102)the National Key R&D Program of China (Grant No. 2022YFA1403100)。
文摘Materials' properties may differ in the thin-film form, especially for epitaxial ultra-thin films, where the substrates play an important role in their deviation from the bulk quality. Here by molecular beam epitaxy(MBE) and scanning tunneling microscopy/spectroscopy, we investigate the growth kinetics of ultra-thin tellurium(Te) films on SrTiO_(3)(STO)(001). The MBE growth of Te films usually exhibits Volmer–Weber(VW) island growth mode and no a-few-monolayer film with full coverage has been reported. The absence of wetting-layer formation in the VW growth mode of Te on STO(001) is resulted from its low diffusion barriers as well as its relatively higher surface energy compared with those of the substrate and the interface. Here we circumvent these limiting factors and achieve the growth of ultra-thin β-Te films with near-complete coverages by driving the growth kinetics to the extreme condition. There is a critical thickness(3 monolayer) above which the two-dimensional Te films can form on the STO(001) substrate. In addition, the scanning tunneling spectra on the ultra-thin Te film grown on STO exhibits an enormously large forbidden gap compared with that grown on the graphene substrate. Our work establishes the necessary conditions for the growth of ultra-thin materials with similar kinetics and thermodynamics.
基金the National Natural Science Foundation of China(Grant No.12274126)。
文摘Concepts of the complex partition functions and the Fisher zeros provide intrinsic statistical mechanisms for finite temperature and real time dynamical phase transitions.We extend the utility of these complexifications to quantum phase transitions.We exactly identify different Fisher zeros on lines or closed curves and elucidate their correspondence with domain-wall excitations or confined mesons for the one-dimensional transverse field Ising model.The crossover behavior of the Fisher zeros provides a fascinating picture for criticality near the quantum phase transition,where the excitation energy scales are quantitatively determined.We further confirm our results by tensor network calculations and demonstrate a clear signal of deconfined meson excitations from the disruption of the closed zero curves.Our results unambiguously show significant features of Fisher zeros for a quantum phase transition and open up a new route to explore quantum criticality.
基金the National Natural Science Foundation of China(Grant No.12274126)carried out during the virtual program“Tensor Networks in Many Body and Quantum Field Theory”held at the Institute for Nuclear Theory,University of Washington,Seattle(INT 21–1c)。
文摘Motivated by the mathematical beauty and the recent experimental realizations of fractal systems,we study the spin-1/2 antiferromagnetic Heisenberg model on a Sierpiński gasket.The fractal porous feature generates new kinds of frustration to exhibit exotic quantum states.Using advanced tensor network techniques,we identify a quantum gapless-spin-liquid ground state in fractional spatial dimension.This fractal spin system also demonstrates nontrivial nonlocal properties.While the extremely short-range correlation causes a highly degenerate spin form factor,the entanglement in this fractal system suggests a long-range scaling behavior.We also study the dynamic structure factor and clearly identify the gapless excitation with a stable corner excitation emerged from the ground-state entanglement.Our results unambiguously point out multiple essential properties of this fractal spin system,and open a new route to explore spin liquid and frustrated magnetism.
基金Supported by the National Natural Science Foundation of China under Grant No 50672027 and the Shanghai Fundamental Key Project under Grant No 08JC1408900.
文摘With the aid of photolithography, an array of one-dimensional porous silicon photonic crystai reflector islands for a far infrared image detector ranging from 10 μm to 14 μm is successfully fabricated. Silicon nitride formed by low pressure chemical vapor deposition (LPCVD) was used as the masking layer for the island array formation. After etching, the microstructures were examined by a scanning electron microscope and the optical properties were studied by Fourier transform infrared spectroscopy, the result indicates that the multilayer structure could be obtained in the perpendicular direction via periodically alternative etching current in each pre-pattern. At the same time, the island array has a well-proportioned lateral etching effect, which is very useful for the thermal isolation in lateral orientation of the application in devices. It is concluded that regardless of the absorption of the deposition layer on the substrate, the localized photonic crystalline islands have higher reflectivity. The designed islands structure not only prevents the cracking of the porous silicon layers but is also useful for the application in the cold part for the sensor devices and the iliterconnection of each pixel.
基金supported by the National Natural Science Foundation of China(Grant No.12274126)supports from the National Natural Science Foundation of China(Grant Nos.12074031,and 12234016)+1 种基金supports from the National Natural Science Foundation of China(Grant Nos.12274287,and 12042507)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301900)。
文摘The spin-1/2 model system with antiferromagnetic(AF) couplings on a J1-J2checkerboard lattice, known as the planar pyrochlore model, is strongly frustrated and associated with a two-to-one dimensional crossover. Using the Projected Entangled Simplex States tensor network ansatz, we identify a large number of nearly degenerate states in the frustrated region(J_(1)<J_(2)).Specifically, we find the long-sought crossed-dimer valence bond solid(VBS) state to be the ground state at J_(1)≤J_(2), while various 1D AF correlated states take over the rest. We verify the stability of the VBS state against nematic perturbation. The corresponding bosonic picture provides an intuitive understanding of the low-energy physics. Particularly, it predicts weaker VBS states in the easy-plane limit, which we confirm numerically. Our results clarify the most essential ground state properties of this interesting system and demonstrate the usefulness of bosonic picture in dealing with frustrated magnetism.
基金Project supported by the the National Key Research and Development Program of China (Grant No. 2022YFA1402902)the National Natural Science Foundation of China (Grant Nos. 12074119, 12204171, 12134003, and 12374145)+1 种基金the Chenguang Program Foundation of Shanghai Education Development Foundation and Shanghai Municipal Education Commission, ECNU (East China Normal University) Multifunctional Platform for Innovation (006)the Fundamental Research Funds for the Central Universities。
文摘Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.
基金supported by the Special Funds for Major State Basic ResearchNational Natural Science Foundation of China(NSFC)+6 种基金Project of Shanghai Municipality(16520721600)supported by NSFC under Grant No 91233121Shanghai Rising-Star Program(14QA1401500)CC of ECNUsupported by the Royal Society,the ERC and EPSRC under Grant Nos EP/M009580/1 and EP/K016288/1supported by the National Key Research and Development Program of China under Grant No 2016YFB0700700the National Natural Science Foundation of China under Grant Nos 51672023,11634003 and U1530401
文摘The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH3NH3PbI3 solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH3NH3PbI3 is thermodynamically unstable with respect to the phase separation into CH3NH3I + PbI2, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombie phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH3NH3PbI3 is unchanged. When I is replaced by Br or CI, Pb by Sn, or the organic cation CH3NH3 by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH3NH3PbI3 and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.
基金supported by the National Natural Science Foundation of China(NSFC)under grant nos.61574059 and 61722402the National Key Research and Development Program of China(2016YFB0700700)+1 种基金Shu-Guang program(15SG20)CC of ECNU
文摘The beneficial effect of the alkali metals such as Na and K on the Cu(In.Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe) solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum (VBM) level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.
基金supported by the Science Challenge Project (TZ2018004)National Natural Science Foundation of China (NSFC) under grant Nos. 61722402 and 91833302+3 种基金National Key Research and Development Program of China (2016YFB0700700)Shanghai Academic/Technology Research Leader (19XD1421300)Fok Ying Tung Education Foundation (161060)the Fundamental Research Funds for the Central Universities
文摘Using first-principles calculations,we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair.15 defect-pairs with short defect–defect distances are found to be stable during structural relaxation,so they can exist in the GaN lattice once formed during the irradiation of high-energy particles.9 defect-pairs have formation energies lower than 10 eV in the neutral state.The vacancy-pair VN–VN is found to have very low formation energies,as low as 0 eV in p-type and Ga-rich GaN,and act as efficient donors producing two deep donor levels,which can limit the p-type doping and minority carrier lifetime in GaN.VN–VN has been overlooked in the previous study of defects in GaN.Most of these defect-pairs act as donors and produce a large number of defect levels in the band gap.Their formation energies and concentrations are sensitive to the chemical potentials of Ga and N,so their influences on the electrical and optical properties of Ga-rich and N-rich GaN after irradiation should differ significantly.These results about the defect-pairs provide fundamental data for understanding the radiation damage mechanism in GaN and simulating the defect formation and diffusion behavior under irradiation.
基金Project supported by the National Natural Science Foundation of China(Grant No.61804055)"Chenguang Program"supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission,China(Grant No.17CG24)Shanghai Science and Technology Innovation Action Plan,China(Grant No.19JC1416700).
文摘The multiple ferroelectric polarization tuned by external electric field could be used to simulate the biological synaptic weight. Ferroelectric synaptic devices have two advantages compared with other reported ones: One is that the intrinsic switching of ferroelectric domains without invoking of defect migration as in resistive oxides, contributes reliable performance in these ferroelectric synapses. Another tremendous advantage is the extremely low energy consumption because the ferroelectric polarization is manipulated by electric field which eliminates the Joule heating by current as in magnetic and phase change memories. Ferroelectric synapses have potential for the construction of low-energy and effective brain-like intelligent networks. Here we summarize recent pioneering work of ferroelectric synapses involving the structure of ferroelectric tunnel junctions (FTJs), ferroelectric diodes (FDs), and ferroelectric field effect transistors (FeFETs), respectively, and shed light on future work needed to accelerate their application for efficient neural network.
文摘In this work, a Fe-based nanocrystalline microwire of 20 mm in length and 25 μm in diameter was placed in the center of a 316 stainless steel pipe. The pipe was 500 μm in diameter and a little shorter than the microwire. A series of voltages were applied on the pipe to study the influence of the electrical field on the Giant-Magneto-Impedance(GMI) effect of the microwire. Experimental results showed that the electronic field between the wire and the pipe reduced the hysteresis of the GMI effect. The results were explained based on equivalent circuit and eddy current consumptions analysis.
基金supported by the National Science Foundation of China(Nos.61076089,11505265 and 61227902)the Ministry of Education of China(SRF for ROCS,SEM)
文摘Radiation damage in 4H-SiC samples implanted by 70 keV oxygen ion beams was studied using photoluminescence and electron spin resonance techniques. ESR peak of g = 2.0053 and two zero-phonon lines were observed with the implanted samples. Combined with theoretical calculations, we found that the main defect in the implanted 4H-Si C samples was oxygen-vacancy complex. The calculated defect formation energies showed that the oxygen-vacancy centers were stable in n-type 4H-Si C.Moreover, the V_(Si)O_C^0 and V_(Si)O_C^(-1) centers were optically addressable. The results suggest promising spin coherence properties for quantum information science.
基金Project supported by the Major Program of the National Natural Science Foundation of China(Grant Nos.61790583,61874043,61874045,and 61775060)the National Key Research and Development Program,China(Grant No.2016YFB0501604)
文摘Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are reviewed, including the defects and defect levels of intrinsic V_(Hg) and the extrinsic amphoteric arsenic(As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level,conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0700700)the National Natural Science Foundation of China(Grant Nos.61574059 and 61722402)+1 种基金Shu-Guang Program,China(Grant No.15SG20)CC of ECNU,China
文摘The kesterite thin film solar cells based on the quaternary Cu2ZnSnS4 and Cu2ZnSnSe4 and their alloys Cu2ZnSn(S,Se)4 have been considered as environment-friendly and non-toxic alternatives to the currently commercialized CdTe and Cu(In,Ga)Se2 thin film solar cells. From the theoretical point of view, we will review how the group I2-II-IV-VI4 quaternary compound semiconductors are derived from the binary CdTe and the ternary CuInSe2 or CuGaSe2 through the cation mutation, and how the crystal structure and electronic band structure evolve as the component elements change. The increased structural and chemical freedom in these quaternary semiconductors opens up new possibility for the tailoring of material properties and design of new light-absorber semiconductors. However, the increased freedom also makes the development of high-efficiency solar cells more challenging because much more intrinsic point defects, secondary phases, surfaces, and grain-boundaries can exist in the thin films and influence the photovoltaic performance in a way different from that in the conventional CdTe and Cu(In,Ga)Se2 solar cells. The experimental characterization of the properties of defects, secondary phase, and grain-boundaries is currently not very efficient and direct, especially for these quaternary compounds. First-principles calculations have been successfully used in the past decade for studying these properties. Here we will review the theoretical progress in the study of the mixed-cation and mixed-anion alloys of the group I2-II-IV- VI4 semiconductors, defects, alkaline dopants, and grain boundaries, which provided very important information for the optimization of the kesterite solar cell performance.