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7Li cold atoms manipulation based ultra-high vacuum measurement
Cheng Yong-Jun, Dong Meng, Sun Wen-Jun, Wu Xiang-Min, Zhang Ya-Fei, Jia Wen-Jie, Feng Cun, Zhang Rui-Fang
Abstract +
The redefinition of the International System of Units (SI) promotes the transformation of the vacuum measurement system toward quantization, and the quantization of vacuum parameters is one of the most leading, prospective and subversive research directions in the field of international vacuum metrology, and the quantum vacuum measurement is based on the quantum effect of the microscopic particle system, and the use of optical means and the theory of quantum mechanics to realize the precision measurement of the vacuum parameters. We develop a lithium-cooled atom vacuum measurement apparatus, which mainly consists of a 7Li atom trap system and a continuous expansion vacuum system. In this work, an experimental study of ultrahigh vacuum measurement is carried out by manipulating 7Li atoms and utilizing the loss characteristics of lithium cold atoms in magneto-optical and magnetic traps, and the results show that for the four commonly used gas molecules in vacuum, namely N2, Ar, He, and H2, in the vacuum range of (3×10–8–4×10–5) Pa, the maximum measurement uncertainty is 7.6%–6.0% (k = 2) based on 7Li cold atoms, and the cold atom vacuum measurement results are in good agreement with those of the traditional ionization vacuum gauges, and their relative sensitivities are in good agreement with those of the ionization vacuum gauges, and the maximal deviation of the relative sensitivity factor is less than 8%, which verifies the accuracy and reliability of the cold-atom quantum vacuum measurements. The research results are of great significance in promoting the development of new cross-generation vacuum measurement technology and meeting the needs of space science exploration, ultra-precision measurement and high-end equipment manufacturing.
Photo-emission electron gun and electron optical simulation for ultrafast scanning electron microscope
Yang Dong, Li Zhong-Wen, Tian Yuan, Sun Shuai-Shuai, Tian Huan-Fang, Yang Huai-Xin, Li Jian-Qi
Abstract +
Ultrafast scanning electron microscope (USEM) integrates pump-probe technique with microscopic imaging, enabling the visualizing of photon-induced surface charge dynamics with high spatial and temporal resolution. This capability is crucial for high-resolution detection of semiconductor surface states and optoelectronic devices. This work discusses the parametric design of a thermionic emission electron gun that has been modified into a photoemission electron gun, based on a home-built ultrafast scanning electron microscope. Given that the dose of the photoemitting electron beam is usually much lower than that of thermionic emission, the transition to photoemission requires the removal of the self-bias voltage function of the original electron microscope power supply to ensure the normal operation of the Wehnelt electrode. We quantitatively analyze the dependence of bias voltage, cathode, Wehnelt electrode, and anode on the position, size and divergence angle of crossover, which helps to improve the parameter adjustment of the modified electron gun. The analysis results indicate that if the distance between the Wehnelt electrode and the anode is adjusted from 8 to 23 mm, the distance between the filament and wehnelt can be changes from 0.65 to 0.45 mm to cooperate with the bias adjustment, so that the normal use of high-resolution thermionic emission mode, low voltage mode and photoemission mode can be realized. Subsequently, the effect of the mirror’s position on the electron optical path is analyzed. It is found that when the anode is raised 1.4 mm above the mirror, the influence on the electron optical path can be ignored. Additionally, the zero-of-time and temporal broadening of the photo-electron pulse are further simulated. The results indicate that with the increase of bias voltage, the time zero of photoemission will be delayed and the temporal broadening will become larger. This study lays a foundation for the future development of ultrafast electron microscope and the design of photoemission electron sources.
High-order cavity coupled plasmon polaritons in resonant cavity-monolayer MoS2 system
Hou Lei, Guan Shu-Yang, Yin Jun, Zhang Yu-Jun, Xiao Yi-Ming, Xu Wen, Ding Lan
Abstract +
Compared with graphene, two-dimensional (2D) transition metal sulfides, represented by mono-/few-layer MoS2, have tunable non-zero bandgap, and thus their applications in optoelectronic devices are more advantageous. By using classical electromagnetic theory and finite element method (FEM), we investigate the cavity coupled plasmon polaritons (CCPPs) formed through the coupling between cavity modes in a resonator and plasmons in monolayer MoS2, particularly calculate and verify the properties of the high-order CCPPs. In previous work, it was demonstrated that the substrates, defects, and polycrystalline grains of the CVD grown monolayer MoS2 usually induce weak electron localization, which leads to the deviation from the Drude model based on the approximation of free electron gas. Therefore, here we use the Drude-Smith model with characteristic parameters obtained experimentally to describe the optical conductivity of monolayer MoS2 in our theoretical calculation and simulation. Then, we not only derive and solve the dispersion equations of the high-order CCPPs, but also verify the existence and analyze the properties of these high-order modes. Specifically, there are three types of CCPPs in the asymmetric cavity-monolayer MoS2 system, i.e. the FP-like-modes (FPLMs), the surface-plasmon-like modes (SPLMs), and the quasi-localized modes (QLMs). Among them, the FPLMs and QLMs can support high-order modes whereas the SPLMs only support the fundamental modes. According to our model, we calculate the wave localization properties for the 7th-order and 8th-order FPLM, the 3rd-order and 6th-order QLM, and the SPLM. These theoretical results are in good agreement with the simulation results. Moreover, the effects of weak electron localization are also shown by comparing the field distributions of the CCPPs based on the Drude model with those based on the Drude-Smith model. It is found that weak electron localization can reduce the coupling between the cavity modes and the plasmons in monolayer MoS2. These results can deepen our understanding of the excitation of plasmons in 2D materials as well as the modulation of their properties. Furthermore, the theoretical model can also be extended to other plasmonic systems related to low-dimensional and topological quantum materials.
Investigation of partial parity- time reversal symmetry in cesium atomic system
Xue Yong-Mei, He Yun-Hui, Han Xiao-Xuan, Bai Jing-Xu, Jiao Yue-Chun, Zhao Jian-Ming
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Parity-time reversal (PT) in atomic systems is of great significance for exploring exotic phenomena in non-Hermitian physics and non-Hermitian systems. It has been found that if PT symmetry is satisfied only in a certain spatial direction, then the Hamiltonian of the system still has a spectrum with eigenvalues of real numbers, which is called partial PT symmetry. In this paper, we use a Λ-type three-level atomic system, which is composed of two ground states $\left| {6{{\mathrm{S}}_{1/2}}, F = 3} \right\rangle $,$\left| {6{{\mathrm{P}}_{3/2}}, F' = 4} \right\rangle $and an excited state $\left| {6{{\mathrm{P}}_{3/2}}, F' = 4} \right\rangle $of cesium atom, to investigate the partial PT symmetry. A probe laser with the detuning of Δ3 = 607 MHz and a couple laser satisfy the condition of two-photon Raman absorption of cesium atom, forming a loss channel. In order to construct the gain channel, we add the repumping laser that resonates during the transition of $\left| {6{{\mathrm{S}}_{1/2}}, F = 3} \right\rangle $to $\left| {6{{\mathrm{P}}_{3/2}}, F' = 4} \right\rangle $, changing the population of the two ground state energy levels, thus reducing the absorption of the Λ level system and forming the gain channel of the atomic system under certain conditions. In order to obtain the equilibrium condition of the partial PT-symmetric system, firstly, the light spot of the repumping laser in the experiment is covered by the probe laser, and then the repumping laser is moved to overlap with half of the probe laser of the detection light. When the gain and loss are balanced, the partial PT-symmetric system is in equilibrium.By changing the beam-waist ratio σ of the coupling laser to the probe laser, the transition from symmetry to broken phase is observed in partial PT-symmetric systems. By measuring the asymmetry of the detection-beam intensity distribution Dasym, we can accurately determine the partial PT symmetry breaking point, and the breaking point is located at $\sigma = {\sigma _{cr}} \approx 3.8$. The theoretical calculations are in good agreement with the experimental measurements. The results of partial PT symmetry and its phase transition, reported in this study, open up a way to actively manipulate multidimensional laser beams in non-Hermitian systems and have potential applications in the design of optical devices for laser amplification and attenuation in different parts of the laser.
Influence of assisted electric field on the microstructure evolution and direct current electrical properties of low-density polyethylene
Li Yong-Jun, Han Yong-Sen, Zhang Wen-Jiang-Qi, Guo Wen-Min, Sun Yun-Long, Li Zhong-Hua
Abstract +
Low-density polyethylene (LDPE) is the basic material of the high-voltage direct current (DC) power cable insulation. The assisted electric field is a common way to regulate the microstructure of polymers, but its application in the field of electrical insulating polymers is rarely reported. In order to study the influence of the assisted electric field on the microstructure evolution and DC electrical properties of LDPE, the LDPEs without and with being treated with assisted electric field are prepared in the melting stage, cooling stage, and the whole stage (i.e. the melting stage and cooling stage), respectively. The influence of the assisted electric field applied in the different stages on the microstructure evolution of LDPE is characterized by the scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The DC electrical properties of the untreated LDPE and the treated LDPE are investigated via measuring their breakdown strengths, conductivities, space charges and surface potential decays. The results show that, compared with the untreated LDPE, the LDPE treated with the assisted electric field in the whole stage has the smallest spherulite size and the largest spherulite number, followed by the LDPE treated in the cooling stage and the melting stage. The assisted electric field applied in different stages can significantly improve the DC electrical properties of LDPE. Compared with the untreated LDPE, the LDPE treated in the melting stage, the cooling stage and the whole stage increases the breakdown strength but greatly reduces the conductivity and space charge accumulation. The DC electrical properties of LDPE treated with the assisted electric field in the whole-stage are the best. Compared with untreated LDPE, the LDOE treated in whole stage increases the breakdown field strength by 35.8%, reduces the conductivity by 72.0%, and the space charge accumulation by 20.2%. More and smaller spherulites lead to the formation of more interface paths and introduce more deep-traps, which contributes to improving the DC electrical characteristics of the electric field assisted LDPE. This work provides a new idea for improving the DC electrical properties of polymers.
Perovskite-based two-dimensional ferromagnet Sr2RuO4 monolayer
Zhang Jun-Ting, Ji Ke, Xie Yu, Li chao
Abstract +
At present, the research on two-dimensional (2D) ferromagnets is mainly concentrated in the field of van der Waals materials, while the successful preparation of strain-free freestanding 2D perovskite films provides a great opportunity for the design of 2D ferromagnets beyond van der Waals materials. Perovskite oxide SrRuO3, as a typical perovskite itinerant ferromagnet, has broad application prospects in many fields. In this paper, the lattice dynamics, ground-state structure, electronic and magnetic properties of its perovskite monolayer with formula Sr2RuO4, as well as the effect of external electric field, are studied by combining first-principles calculation, symmetry analysis and Monte Carlo simulation. The influence of the Hubbard parameter U is also revealed. The results indicate that the ground-state structure under all U values is the structural phase (space group $P4/mbm$) generated by octahedral rotation distortion. Similar to the SrRuO3 bulk, the ground-state phase of the Sr2RuO4 monolayer exhibits ferromagnetism, which is independent of the U value and thus robust. Density functional theory calculation with Hubbard parameter U predicts the ground-state phase of the monolayer to be a ferromagnetic half metal with out-of-plane easy-magnetization axis, while excluding the U parameter predicts the ground-state phase to be a ferromagnetic metallic state. The ferromagnetism mainly originates from the strong ferromagnetic exchange interaction between the nearest neighbor spin pairs. The simulated Curie temperature of the Sr2RuO4 monolayer is 177 K, which is close to the value (150 K) of its bulk phase. The out-of-plane electric field does not change the ground-state structure and ferromagnetism of the Sr2RuO4 monolayer, but can significantly modulate its electronic and magnetic properties. When an external electric field exceeding 0.3 V/Å is applied, the system undergoes a transition from a ferromagnetic half-metal state to a ferromagnetic metallic state. This work indicates the potential application of Sr2RuO4 monolayer in low-dimensional spintrnic devices, and provides a reference for the development of perovskite-based 2D ferromagnets and the realization of controlling 2D magnetism by electric field.
Research on acoustic control of coupled vibration system of transducers using acoustic surface and topological defect structures
Lin Ji-Yan, Chen Cheng, Guo Lin-Wei, Li Yao, Lin Shu-Yu, Sun Jiao-Xia, Xu Jie
Abstract +
How to regulate the sound waves in the coupled vibration system of complex power ultrasonic transducers and design high-performance transducer systems has always been an urgent problem in the field of power ultrasound. Research has found that introducing various defects within the transducer system can improve the performance of the transducer coupled vibration system to a certain extent. However, the drawbacks of high loss, narrow frequency band, and sensitivity to structural parameters limit the further practical application of defect type phononic crystal transducer coupled vibration systems.In order to improve the limitations of the coupled vibration system of defect-type phononic crystal transducers, effectively reduce energy loss, and enhance the efficiency of energy transmission, this paper introduces a topological defect structure with energy localization effect and a sound surface structure with high energy transmission efficiency into the coupled vibration system of the transducer. In this study, the acoustic surface structure and topological defect structure are used to excite defect states with energy localization effects and high energy transmission efficiency surface states, effectively regulating the vibration of the transducer coupled vibration system, and constructing a transducer coupled vibration system with high quality factor, low loss, and high energy transmission efficiency. By flexibly designing the geometric size parameters of the acoustic surface structure and defects, the vibration of the transducer coupled vibration system can be effectively controlled, thereby meeting the different functional requirements of the transducer coupled vibration system.However, due to the excessive design parameters of surface structure and topological defect structure, the complexity of the design will be multiplied, greatly reducing the success rate of the design. Therefore, this study uses data analysis technology to establish a performance prediction model for the transducer coupled vibration system, in order to achieve the accurate prediction of system performance and change the shortcomings of low design efficiency and low success rate brought by traditional empirical trial and error methods.In order to verify the effectiveness of the research, the coupled vibration system of the transducer is studied in simulation and experiment in this work. The simulation and experimental results indicate that the acoustic surface structure and topological defect structure can effectively regulate sound waves to improve the performance of the transducer coupled vibration system.
Perovskite solar cells prepared by processing CsPbBr3 nanocrystalline films in low temperature solution
Zhang Xi-Sheng, Yan Chun-Yu, Hu Li-Na, Wang Jing-Zhou, Yao Chen-Zhong
Abstract +
In the process of preparing perovskite polycrystalline films by solution method, toxic solvents are used, and heat treatment is still the main way to induce perovskite grain growth, which not only increases energy consumption, but also hinders the development of flexible solar cells. In order to avoid the use of toxic solvents and high-temperature process, CsPbBr3 nanocrystal films are treated with low temperature solution to obtain corresponding polycrystalline thin films, which are applied to solar cells. Firstly, CsPbBr3 nanocrystalline (nanocrystalline NC) ink precursor is prepared by hot injection method, and nanocrystalline film is prepared by spinning coating method. In atmospheric environment, CsPbBr3 nanocrystalline films are prepared by saturated solution of Pb(SCN)2 and NH4Br methyl acetate. Using the CsPbBr3 nanocrystalline film as an absorbing layer, the perovskite solar cell is prepared and the performance of the cell is effectively improved, and the efficiency of the cell reaches 8.43%. The results show that the saturated solution of Pb(SCN)2 and NH4Br methyl acetate (MA) can not only continue the nanocrystalline crystallization, but also effectively passivate the defects in the perovskite films. In the process of preparing CsPbBr3 polycrystalline films, neither high temperature treatment nor the high boiling point toxic solvent is used, which is suitable for the preparation rigid and flexible solar cells.The inorganic halide perovskite nanocrystals are developed and used as “ink” to fabricate fully air-processed, electrically stable solar cells. Although the prepared film is composed of mosaic nanocrystals capped with a large number of organic ligands and surface traps, this method provides a new approach for single-step, large-scale fabrication of inorganic perovskite devices. Moreover, the flexible control of the material composition provides a platform for uncovering the optimal conditions for optoelectronics and photonics.
Cascade overlap simulation of formation of dislocation loops in Ti-V-Ta multi-principal element alloy
Zhao Yong-Peng, Dou Yan-Kun, He Xin-Fu, Yang Wen
Abstract +
Among the currently developed multi-principal element alloys (MPEAs), Ti-V-Ta MPEA stands out because of its good high-temperature strength, good room-temperature plasticity, stable organizational structure, and low neutron activation, and becomes a first option for cladding material of special power reactors. The radiation resistance of Ti-V-Ta MPEA is the focus of current research. Dislocation loops are the main irradiation defects in Ti-V-Ta MPEA, which can significantly affect the mechanical properties. Therefore, clarifying the formation mechanism of dislocation loops in Ti-V-Ta HEA can help to understand its radiation resistance. The formation behavior of dislocation loops in Ti-V-Ta MPEA is studied based on molecular dynamics method in this work. Cascade overlap simulations with vacancy clusters and interstitial clusters are carried out. The cascade overlap formation mechanism of dislocation loops is analyzed and discussed. In Ti-V-Ta MPEA, the cascade overlap with defect clusters can directly produce different types of dislocation structures. The defect configuration after cascade overlap is determined by the primary knock-on atom (PKA) energy and the type and size of the preset defect clusters. Cascade overlap can improve the formation probability of $ \left\langle {100} \right\rangle $ dislocation loops in Ti-V-Ta MPEA. Cascade overlap with vacancy clusters is an important mechanism for the formation of $ \left\langle {100} \right\rangle $ vacancy dislocation loops, and the size of vacancy clusters is the dominant factor for the formation of $ \left\langle {100} \right\rangle $ vacancy dislocation loops. When the PKA energy is enough to dissolve the defect clusters, $ \left\langle {100} \right\rangle $ vacancy dislocation loops are more likely to form. Furthermore, cascade overlap with interstitial clusters in Ti-V-Ta MPEA is a possible mechanism for the formation of $ \left\langle {100} \right\rangle $ interstitial dislocation loops. This study can contribute to understanding the evolution behavior of irradiation defects in Ti-V-Ta MPEA, and provide theoretical support for designing the composition and optimizing the high-entropy alloys.
Prediction of hysteresis model at different external conditions for giant magnetostrictive materials
Yan Hong-Bo, Huang Hai-Tao, Wang Jian-Xin, Huang Jian, Xie Kai
Abstract +
The hysteresis model of giant magnetostrictive materials (GMMs) changes with model parameters: the excitation amplitude, bias condition and excitation frequency. The existing hysteresis model is unable to predict the effects of simultaneous changes in the three external conditions. In this paper, the hysteresis loss mechanism is explained by using the traditional Jiles-Atherton (J-A) dynamic model, and the relation equation is established according to the operating conditions and material properties to respond to the changes of external conditions. For the J-A model, the relationship equation related to the excitation amplitude is established, and the relationship equation relating the residual loss coefficient to the excitation amplitude and the bias condition is established for the residual loss, while the eddy current loss of the system is redefined by using the fractional order to obtain the modified hysteresis model. In the paper, the genetic algorithm is used to identify the model parameters of the test data under different operating conditions, and the corresponding correction coefficients are obtained according to the model parameters and the operating conditions. The accuracy of the modified model is verified by simulating the model and analyzing the influences of eddy currents and residual losses and their effects on the model predictions. The hysteresis model is evaluated to compare the hysteresis curves with the hysteresis losses in terms of errors. The results show that the modified model is capable of predicting various excitations with high accuracy, and that neglecting dynamic losses at low frequencies results in large errors. If the model order of the eddy current loss is smaller than the actual order of the material, the predicted hysteresis curve will be contracted inward and the predicted eddy current loss will be small; on the contrary, the predicted hysteresis curve will be expanded outward and the predicted eddy current loss will be large, and with the increase of the excitation frequency, both cases will cause the prediction error to become larger and larger. When the bias magnetic field is zero, the residual loss coefficient is unchanged; when the bias magnetic field is kept constant, the excitation amplitude increases and the residual loss coefficient decreases; when the excitation amplitude is unchanged, the bias magnetic field increases and the residual loss coefficient also increases. When both the bias magnetic field and the excitation amplitude change at the same time, it is necessary to conduct an actual analysis of their corresponding residual loss coefficients. Using hysteresis curves to evaluate hysteresis is more accurate.
Electrical stress of graphene field effect transistor under different bias voltages Reliability studies
Wang SongWen, Guo HongXia, Ma Teng, Lei ZhiFeng, Ma WuYing, Zhong XiangLi, Zhang Hong, Lu XiaoJie, Li JiFang, Fang JunLin, Zeng TianXiang
Abstract +
In this paper, graphene field effect transistors (GFET) with the top-gate structure are taken as the research object. Conducted electrical stress reliability studies under different bias voltage conditions. The electrical pressure conditions are Gate Electrical Stress (VG=-10V, VD=0V, VS=0V), drain electric stress (VG=0V, VD=-10V, VS=0V), and Electrical stresses applied simultaneously by gate and drain voltages (VG=-10V, VD= -10V, VS=0V). Using a semiconductor parameter analyzer, the transfer characteristic curves of GFETs before and after electrical stress are obtained. At the same time, the carrier migration and the Dirac voltage VDirac degradation are extracted from the transfer characteristic curves. The test results show that under different electrical pressure conditions, the carrier mobility of GFETs degrades continuously with the increase of electric stress time. Different electrical pressure conditions affect the drift direction and degradation of VDirac differently: Gate electrical stress and drain electrical stress cause VDirac drift of the device in opposite directions, and the gate electrical stress is greater than the electrical stress applied by both gate and drain voltages leading to VDirac degradation of GFETs. An analysis of the causes suggests that different electrical stress conditions produce different electric field directions in the device, which can affect the carrier concentration and direction of movement. Electrons and holes in the channel are induced to tunnel into the oxide layer and are captured by trap charge in the oxide layer and at the graphene\oxide interface, forming oxide trap charges and interface trap charges. This is the main reason for the reduced carrier mobility of GFETs. Different electric field directions under different electric stress conditions produce positively charged and negatively charged trap charges. The difference in the type of trap charge banding is the main reason for the different directions of VDiracdrift in GFETs. When both trap charges are present at the same time, they have a canceling effect on the amount of VDiracdrift of the GFETs. Finally, the paper combines TCAD simulation, further revealing the simulation model of the impact of electrical stress induced trap charge on the VDiracgeneration of GFETs. The result demonstrates that differences in the type of trap charge banding have different degradation effects on the VDirac of GFETs. The related research provides data and theoretical support for the practical application of graphene devices.
Quantum Enhancement Solution Method Based on Quantum K-means for Platform Clustering Grouping
He Yi, Zheng Kouquan, Jing Feng, Zhang Yijun, Wang Xun, Liu Ying, Zhao Le
Abstract +
The paper proposes a quantum enhanced solution method based on quantum K-means for platform clustering and grouping in joint operations campaigns. The method first calculates the number of categories for platform clustering based on the determined number of task clusters, and sets the number of clustering categories in the classical K-means algorithm. By using the location information of the tasks, the clustering center points are calculated and derived. Secondly, the Euclidean distance is used as an indicator to measure the distance between the platform data and each cluster center point. The platform data is quantized and transformed into the corresponding quantum state representation. According to theoretical derivation, the Euclidean distance solution is transformed into the quantum state inner product solution. By designing and constructing a universal quantum state inner product solution quantum circuit, the Euclidean distance solution is completed. Then, based on the sum of squared errors of the clustering dataset, the corresponding quantum circuits are constructed through calculation and deduction. The experimental results show that the proposed method not only effectively solves the platform clustering and grouping problem under such action scales, but also significantly reduces the time and space complexity of the algorithm compared to the classical K-means algorithm.
Composable security analysis of linear optics cloning machine enhanced discretized polar modulation continuous-variable quantum key distribution
He Ying, Wang TianYi, Li YingYing
Abstract +
In experimental setups of continuous-variable quantum key distribution (CVQKD) independently modulating the amplitude and phase of coherent states, the ideal Gaussian modulation will be degraded into discretized polar modulation (DPM) due to the finite resolution of the driving voltages of electro-optical modulators. To compensate for the performance degradation induced by the joint effect of amplitude and phase discretization, linear optics cloning machine (LOCM) can be introduced at the receiver side to reduce the impact of channel excess noise. Implemented by linear optical elements, homodyne detection and controlled displacement, LOCM introduces extra noise that can be transformed into an advantageous one to combat channel excess noise by dynamically adjusting the relevant parameters into a suitable range. In this paper, the prepare-and-measure version of LOCM DPM-CVQKD is presented, where the incoming signal state enters a tunable LOCM before being measured by the nonideal heterodyne detector. The equivalent entanglement-based model is also established to perform security analysis, where the LOCM is reformulated into combining the incoming signal state and a thermal state on a beam splitter. The composable secret key rate is derived to investigate the security of LOCM DPM-CVQKD. Simulation results demonstrate that the secret key rate is closely related to the tuning gain and the transmittance of LOCM. Once the two parameters are set to appropriate values, LOCM allows the promotion of the secret key rate of DPM-CVQKD, as well as its resistance to excess noise. Meanwhile, taking finite-size effect into consideration, LOCM can also effectively reduce the requirement for the block size of the exchanged signals, which is beneficial to the feasibility and practicability of CVQKD. Since the performance of LOCM DPM-CVQKD is heavily reliant on the calibrate selection of relevant parameters, further research may concentrate on the optimization of LOCM in experimental implementations, where machine learning related methods may be exploited.
Anisotropic energy funneling effect in wrinkled monolayer GeSe
Liu JunJie, Zuo HuiLing, Tan Xin, Dong JianSheng
Abstract +
Two-dimensional materials with tunable wrinkled structures opening up new avenue to modulate their electronic and optoelectronic properties. However, the formation mechanisms of wrinkles and their influences on the band structures and associated properties remains unclear. Here, we investigate the strain distributions, bandgap, and anisotropic energy funneling of wrinkled monolayer GeSe and their evolution with the wrinkle wavelength based on the atomic-bond-relaxation approach and continuum medium mechanics. We find that the top and valley regions of wrinkled monolayer GeSe exhibit tensile and compressive strains, respectively, and the strain increases with decreasing wrinkle wavelength. Moreover, the periodic undulation strain in the wrinkles can lead to continuously adjustable bandgaps and band edges in wrinkled monolayer GeSe. For zigzag wrinkled monolayer GeSe, when the wrinkle wavelength is large, the conduction band minimum (valence band maximum) continuously decreases (increases) from the top to the valley, forming an energy funneling. As a result, the excitons accumulate in the valley of wrinkles, and their accumulation ability increases with decreasing wrinkle wavelength. However, as the wavelength further decreases, the energy funneling will disappear, resulting in the excitons to part accumulate at the top of wrinkles and another part to accumulate at the valley of wrinkles. The critical wavelength for disappearance of energy funneling of zigzag wrinkled GeSe is 106nm. The physical origin is that when the top strain exceeds 4%, the bandgap will decrease. Due to the monotonic variation of bandgap with strain, the energy funneling effect of armchair wrinkled monolayer GeSe is still retained when the wavelength is reduced to 80 nm, and the accumulation of excitons is further enhanced. Our results demonstrate that the energy funneling effect induced by nonuniform can realize excitons accumulation in one material without the need for p-n junctions, which is of great benefit to collection of photogenerated excitons. Therefore, the proposed theory not only clarifies the physical mechanism regarding the anisotropic energy funneling effect of wrinkled monolayer GeSe, but also provides a new avenue to design next-generation optoelectronic devices.
Phase field simulation of intra/intergranular pore morphology evolution in neutron-irradiated austenitic stainless steel
Cheng Da-Zhao, Liu Cai-Yan, Zhang Chao-Ran, Qu Jia-Hui, Zhang Jing
Abstract +
Intergranular or intragranular anisotropic pores can be easily observed in the FCC structure of nuclear reactor core structural materials, such as austenitic stainless steel or nickel-based alloys. Austenitic stainless steel contains a certain amount of nickel (Ni), and Ni undergoes transmutation reaction under neutron irradiation to produce helium. Helium combines with vacancy and continuously absorbs more helium and vacancy, evolving into under pressure pores filled with a small amount of helium. The morphology of pores is influenced by both the surface anisotropy of the crystal and grain boundary characteristic because pore nucleation predominantly occurs at grain boundary. The swelling effect caused by pores and the embrittlement effect of high temperature helium are related to the morphology, size and distribution of pores. The phase field method can couple multiple physical fields and accurately describe the effects of material microscopic defects on pores. In this study, we use the phase field method to simulate the evolution and morphology of pores, establishing a free energy functional coupling between crystal plane anisotropy and pore-grain boundary interactions. Our results demonstrate that helium gas induces pore nucleation, with higher concentrations leading to shorter incubation period, faster nucleation rate, and greater growth rate. Grain boundaries act as heterogeneous nucleation sites for helium pores, leading to the formation of pores along these boundaries and high-density diffusion pores within the grains. The intragranular pores exhibit anisotropic characteristics regulated by interfacial energy's anisotropic modulus, the strength of the anisotropy, and crystal orientation. The high-density intergranular pores interact with each other significantly and are influenced by grain boundaries, while the anisotropic morphology is negligible. Additionally, it has been observed that the pores located in the middle of grain boundaries tend to become an elliptical. The stress inside the pores that contain a small amount of helium gas is negative, which is lower than the value in the matrix. These findings presented herein align well with experimental results, which inspires the prediction of service life of core components and the design of core materials.
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