Vol. 67, No. 16 (2018)
2018-08-20
SPECIAL TOPIC—Physics in precise measurements
COVER ARTICLE
SPECIAL TOPIC—Physics in precise measurements
COVER ARTICLE
2018, 67 (16): 160401.
doi: 10.7498/aps.67.20180636
Abstract +
Many theoretical speculations assume that the Newtonian inverse square law (ISL) needs to be modified in short range, such as the modifications due to gravitation propagating in extra dimensions and the hypothetical interactions mediated by bosons predicted by the physics beyond the standard model. High precision tests of the non-Newtonian gravitational forces are important for verifying the proposed models and help us to further understand gravity. Scientists have performed many tests in different interaction ranges by using different techniques and have not find any nonNewtonian gravitational force up to now. Adopting a gap modulation scheme, the experimental group in Huazhong University of Science and Technology had accomplished the tests of ISL in the millimeter and submillimeter range with torsional balance. The experiment in the millimeter range set the strongest constraints on the Yukawa-type violation from ISL. Recently, they have conducted two other tests in the submillimeter and micrometer range by modulating the density of the source attractor. In the submillimeter range, torsional balance is used to measure the torque acting on the pendulum by a rotating density modulated source attractor. The Newtonian gravitational torque at the frequency of interest is suppressed below the thermal noise of the pendulum by a dual compensation design, whereas the nonNewtonian gravitational torque is preserved if it exists, so that a “Null” test can be realized. The experimental system is verified by comparing the theoretical torque with the measured one when intentionally shifting the attractor away from the position for “Null” test. The strongest constraints on the Yukawa-type violation are achieved in a range of 70-300 μm in this experiment. In the micrometer range, an isoelectronic test of the non-Newtonian forces is performed by sensing the lateral force between a gold sphere and a density modulated source attractor by using a soft cantilever. The attractor is fabricated based on silicon-on-insulator wafer to make its surface isoelectronic and possess a density modulated structure underneath. Two-dimensional (2D) mapping of the force signal indicates that the experimental sensitivity is mainly limited by the electrostatic force arising from the surface patch charges. We analyze the 2D mapping data by using maximum likelihood estimation method and set constraints on the Yukawa-type non-Newtonian gravitational forces without subtracting the model-dependent Casimir force or electrostatic force background. Both experiments show no sign of the non-Newtonian gravitational force, and further experiments with high precision are required to explore the unconstrained parameter space.
2018, 67 (16): 160402.
doi: 10.7498/aps.67.20180621
Abstract +
The equivalence principle is one of the two basic assumptions of general relativity. It is the extension of weak equivalence principle. At present, a lot of experiments have tested the weak equivalence principle within a certain accuracy. However, the new theories that unify the gravity and the standard model require the weak equivalence principle to be broken, so the highly accurate test of the weak equivalence principle has important scientific significance. The test of the weak equivalence principle using microscopic particles complements and extends that using macroscopic objects. In this paper, the principle of the atomic interferometer is introduced, and the history and status quo of experimental study on weak equivalence principle of microscopic particles using atomic interferometer are reviewed. The precision of experiments using different-mass atoms is improved from 10-7 to 10-8, the precision of experiment using different spin-orientation atoms reaches the level of 10-7, and the precision of quantum test using superposition-state atoms reaches the level of 10-9. The key problems in the weak equivalence principle test using dual-species atom interferometers are summarized. Advances have been made in vibration noise suppression, frequency shift and phase noise suppression of Raman laser, four-wave double-diffraction Raman-transition atom interference, signal detection and data processing. The development of long-baseline atom interferometers for improving the free evolution time of atoms has progressed. The precision of demonstration experiment of weak equivalence principle test using atom interferometers in weightlessness reaches 10-4 level. The space plan for atom interferometer based weak equivalence principle test is also gradually implemented. The test precision of microparticles' weak equivalence principle using long-baseline atom interferometers or space atom interferometers is expected to reach the level of 10-15-10-17 in the future.
2018, 67 (16): 164202.
doi: 10.7498/aps.67.20180876
Abstract +
With the development of the technologies in the lasers and the manipulation of cold atoms, the high precision optical frequency standards have been extensively studied and built in recent years. These high precision frequency standards may play an important role in establishing the new time reference, promoting the researches in the fundamental fields, fulfilling the national strategic needs, etc. In this paper, the research progress of high accuracy 40Ca+ optical frequency standard in Wuhan Institute of Physics and Mathematics (WIPM) of Chinese Academy of Sciences is presented. A new ULE super cavity is adopted for stabilizing the frequency of 729 nm clock laser, and the stability of the laser is improved now to 2×10-15 in a duration of 1-100 s. By controlling the external fields and other environmental influences, especially suppressing the micromotion effects of the trapped ion, the uncertainty of the optical frequency standard based on a single 40Ca+ is reduced to 5.5×10-17. The stability of 5×10-17 in a duration of 20000 s is achieved via the comparison between two 40Ca+ optical frequency standards. Several precision measurement experiments are performed, based on the high precision 40Ca+ optical frequency standard. The absolute value of the clock transition frequency of the 40Ca+ optical frequency standard is measured second time, using an optical comb referenced to a hydrogen maser which is calibrated via GPS referenced to UTC (NIM)) using the precise point positioning data-processing technique. The frequency offset of UTC (NIM) relative to the SI second can be evaluated through BIPM circular-T reports, and the newly measured value of m 4s 2S1/2-3m d 2D5/2 transition is adopted by CCTF-20, thus updating the recommended value of 40Ca+ optical clock transition. Besides the absolute frequency measurement, the magic wavelengths of 40Ca+ optical clock transition are measured precisely, and this work is a milestone for establishing all-optical trapped-ion clocks. The lifetime of the m 3 d 2D3/2 and m 3 d 2D5/2 state in 40Ca+ are precisely measured, too. The work mentioned above contributes to the researches of the precision measurements based on cold atomic systems.
2018, 67 (16): 160601.
doi: 10.7498/aps.67.20180581
Abstract +
Kilogram, the unit of mass, is the last one of seven base units in International System of Units (SI) which is still defined and kept by a material artifact. 1 kg is defined as the mass of the International Prototype of the Kilogram (IPK) kept at the Bureau International des Poids et Mesures (BIPM) in Paris. One of the major disadvantages of this definition is the fact that the amount of material constituting the IPK changes with time. Because a more stable mass reference does not exist, the variation of IPK is completely unknown so far. The International Committee for Weights and Measures (CIPM) recommended redefining the kilogram by fixing the numerical value of the Planck constant h and called on every national metrology institute to study the measurement of the h. To avoid possible system errors from one method, more experiments especially based on different principles are expected and encouraged for the final determination of the Planck constant. The CCM required that at least three consistent results should be obtained before the redefinition. Since 1970 s, the Kibble balance (also known as the Kibble balance) experiment has been used by a number of national metrology institutes such as NPL, NIST, METAS, LNE and BIPM. The IAC including the PTB, NMIJ and NMIA used the XRCD method to measure the Avogadro constant. To make contribution to the redefinition of kilogram, the National Institute of Metrology of China (NIM) proposed a joule balance method in 2006, which is also an electrical way but different from the watt balance method in that the dynamic phase is replaced with a static phase to avoid the trouble in the dynamic measurement. The progress of these approaches and the current situation of the redefinition of the kilogram are presented in this paper. In 2013, a model apparatus was built to verify the principle of the joule balance. Then NIM started to build its new joule balance aiming to obtain an uncertainty of 10-8 level since 2013. In Dec. 2016, the new apparatus was built and could be used to measure the Planck constant h in vacuum. In May 2017, the measurement result was submitted to the Metrologia and accepted by the CODATA TGFC as the input data. However, the measurement result has an uncertainty bigger than 10-8 and was not used for the final determination of the h value. At present, the joule balance group of NIM, together with the Harbin Institute of Technology, Tsinghua University and China Jiliang University is still making great efforts to improve the joule balance apparatus. The uncertainty of 10-8 level is expected to be achieved in the next two years.
2018, 67 (16): 160602.
doi: 10.7498/aps.67.20180751
Abstract +
With the progress of science and technology and the continuous improvement of the precision measurement application technology, the technical requirements for the stability and noise level of the ultra-stable microwave source are increasing. Its application range becomes more and more wide, including high performance frequency standard research, network radar development, deep space navigation system, etc. Up to now, the photonic microwave generators based on ultra-stable laser and femtosecond light comb are believed to be the highest microwave frequency source with the highest frequency stability and the relative frequency stability 10-16 in 1 s. This device is also the basis of the application for the next frequency standard (optical frequency standard). Whether the generation of time or most of the precision measurements, the output laser of the optical frequency standard should be transformed into a super stable baseband frequency signal. In this paper, we first introduce the development, current situation and application requirements of ultra-stable photonic microwave source, then we present the principle and structure of the ultra-stable photonic microwave source and the technical development of its components based on the first set of domestic-made ultra-stable microwave frequency sources developed by the National Time Service Center. For the ultra-stable laser, we mainly focus on the research and development of the ultra-stable cavity design, the Pound-Drever-Hall frequency locking technology, and the residual amplitude noise effect rejection. For the optical frequency combs, we mainly focus on the development of laser mode-locking and frequency control technology based on erbium-doped fiber combing system. For the low noise photonic-to-microwave detection and low noise synthesizer techniques, the noise effect rejection of wideband photoelectric detection and the microwave phase noise induced by the amplitude noise of the laser are emphatically introduced. Finally, we summarize and prospect the photonic ultra-stable microwave generation technique.
2018, 67 (16): 163202.
doi: 10.7498/aps.67.20180540
Abstract +
The principle and development of fountain frequency standard are introduced in this paper. Fountain frequency standard is an atomic clock technology developed in recent 20 years. It is based on laser cooling technology, and realizes the trapping and projection of the cold atom medium with laser cooling technology. In the process of launching upward and falling back, the cold atom medium first completes the preparation of atomic state, then passes through the microwave cavity twice to achieve the Ramsey interaction; between the two interactions it undergoes free evolution, and finally the Ramsey interference fringes are obtained by detecting the atomic interference probability with the two-level fluorescence detection method in the detection region, and the frequency is locked with a line width of the central fringe being about 1 Hz. The stability and uncertainty of the frequency are two important indexes of the fountain frequency standard. The factors influencing the stability of the fountain clock frequency mainly are quantum projection noise and electronic noise. At present, the short term stability of the fountain clock is (10-13-10-14)τ-1/2, and the long term stability is (10-16-10-17). The frequency uncertainty of the fountain frequency standard is mainly influenced by the two-order Zeeman frequency shift, the blackbody radiation frequency shift, the cold atom collisional frequency shift, and the frequency shift relating to the microwave. The uncertainty of the fountain clock is around 10-16 currently. As a reference frequency standard, the working media of the fountain clock mainly are 133Cs and 87Rb. All international metrology institutions have been developing the fountain frequency standard, and it plays a more and more important role in establishing the coordinated universal time and the calibration of the international atomic time. In addition, the fountain frequency standards are also used to study high-precision time-frequency reference and time comparison chain, and verify basic physical theories.
EDITOR'S SUGGESTION
2018, 67 (16): 160301.
doi: 10.7498/aps.67.20180788
Abstract +
Solid-state electronic spin system of the nitrogen-vacancy (NV) center in diamond is attractive as a nanoscale quantum sensor under room-temperature dueto its unique characteristics such as stable fluorescence, long coherent time, and near-atomic size under ambient conditions. Nowadays, the NV center plays a significant role in super-resolution microscopies. Different super-resolution microscopies have been used on NV center to archievenanoscale spatial resolution. Moreover, the spin state in NV center can be regraded as a solid-state qubit, which can be optically polarized and read out. The spin state can couple with electromagnetic fields and strain, which enables the NV center to be an excellent quantum sensor with high spatial resolution and high sensitivity. Such an NV-center based quantum sensing technique is being developed for applications in newmateriales, single protein nuclear spin dynamic field, life science, etc. This review will introduce the basic principle of such a nanoscale quantum sensor, the experimental realization, methods of enhancing the sensitivity, and some applications in high-spatial-resolution and high-sensitivity sensing.
EDITOR'S SUGGESTION
2018, 67 (16): 160303.
doi: 10.7498/aps.67.20181029
Abstract +
The highest precision achievable for a two-mode (two-path) classical interferometer is bounded by 1/√N (with NN
EDITOR'S SUGGESTION
2018, 67 (16): 160603.
doi: 10.7498/aps.67.20181381
Abstract +
The Newtonian gravitational constant G is the first fundamental physics constant introduced by human beings. It plays an important role in many fields, such as theoretical physics, astrophysics, and geophysics. Its precision measurement and related research is of great significance to the whole experimental physics. However, the measuring accuracy of G is the worst among all fundamental physical constants, which reflects the great complexity and difficulty in determining G. This paper briefly reviews the history of G measurement, and also introduces the current research progress in this field by a summary of the recent three precision measurements of G. At the end of the paper, the latest developments of the G measurement in the center of gravitational experiments at Huazhong University of Science and Technology are introduced.
2018, 67 (16): 160604.
doi: 10.7498/aps.67.20181097
Abstract +
The strontium optical lattice clock has experienced a rapid development since the beginning of the 21st century. Its relative frequency uncertainty, on the order of 10-18, has surpassed that of the cesium fountain clock, the current primary standard for time and frequency. This supreme level of precision reflects one of the most advanced measurement capabilities of mankind. This article reviews the current progress of the strontium optical lattice clock, and describes its key components and techniques, including high-resolution spectroscopy, close-loop operation, evaluation of systematic shifts, and absolute frequency measurement. The applications and future outlook of the strontium clock are also summarized.
2018, 67 (16): 163201.
doi: 10.7498/aps.67.20181021
Abstract +
In this paper, we report a precision measurement of hyperfine splitting and absolute frequency of D1 line in cold 6Li atoms. The gray molasses is realized in the experiment and the tempreature is cooled to about 50 μK, which is lower than the Doppler cooling limit, 140 μK. By use of an optical comb, the absolute frequencies and corresponding hyperfine splitting are measured. We obtain frequencies of 446789503.080(35) MHz, 446789529.198(36) MHz, 446789731.316(50) MHz and 446789757.476(29) MHz for the D1 line. The results are in reasonable agreement with the theoretical calculations and consistent with earlier measurements. They could provide an important foundation for future frequency measurement, α constant and nuclear radius.
2018, 67 (16): 164203.
doi: 10.7498/aps.67.20180914
Abstract +
Precision measurement in few-electron atomic systems played an important role in testing fundamental physics and determination of the fundamental physical constants throughout the past few decades.Atomic helium,as the simplest multi-electron system,its energy levels can be calculated with a very high precision by means of ab-initio calculations, and can be accurately determined using precision spectroscopy.Test of quantum theories can be achieved by comparing theoretical predictions with experimental results.In case of any disagreement,it might imply that there are some undiscovered systematic effects,or might signal physics beyond the standard model.Particularly,the 2 3PJ energy level in atomic helium is considered as one of the best atomic systems for determining the fine-structure constant α.High precision helium spectroscopy can also be used for setting constraints on exotic spin-dependent interactions,and may provide an accurate determination of the helium nuclear charge radius.Comparison of results from electronic and muonic helium may provide a sensitive test of universality in electromagnetic interactions of leptons,and may help solve the socalled “proton size puzzle”.In this paper,we summarize our recent progress on precision spectroscopy of atomic helium. By using transverse cooling and deflection,we are able to prepare a low-noise bright source of atoms in the metastable state 2 3S1.The initial state preparation is completed by optical pumping,followed by laser spectroscopy in the 2 3S-2 3P transition.The 2 3P0-2 3P2 and 2 3P1-2 3P2 fine-structure intervals are determined to be (31908130.98 ±0.13) kHz and (2291177.56 ±0.19) kHz,respectively.Compared with calculations including terms up to α7m,the deviation for the α-sensitive interval 2 3P0-2 3P2 is only 0.22 kHz,which paths way for further improvement of theoretical predictions and independent determination of α with a 2-ppb precision.The 2 3S-2 3P transition frequency is determined with an accuracy of 1.4 kHz by utilizing comb-linked spectroscopy and first-order Doppler cancellation technique.Our result is not only more accurate but also differs by as much as 50 kHz (20 σ) from the previously reported result.This discrepancy remains unsolved and indicates the need for further independent measurements.In combination with ongoing theoretical calculations,this new result may provide the most accurate determination of helium nuclear charge radius.Prospects for future improvements in relevant precision measurements,including simple molecules,are also discussed.
2018, 67 (16): 164204.
doi: 10.7498/aps.67.20180895
Abstract +
The measurement of physical quantities and measurement units standard promote the development of metrology. Especially, the developments of laser interference and atomic frequency standard bring a revolutionary leap for metrology. Many precision measurement techniques have been proposed and experimentally demonstrated, such as gravitational wave measurements and laser gyroscopes based on laser interferometry, and atomic clocks and atomic gyroscopes based on the atom interferometry. Recently, a new branch of science, quantum metrology, has grown up to further explore and exploit the quantum techniques for precision measurement of physical quantities.#br#This paper will focus on recent developments in quantum metrology and interference based on coherence and correlation of light and atom. Firstly, we briefly review the development of metrology. Then, we introduce our own researches in recent years, including quantum-correlation SU(1,1) optical interferometer based on four wave mixing process in atomic vapor and the atom-light hybrid interferometer based on Raman scattering in atomic vapor.#br#Interferometer is a powerful tool to measure physical quantities sensitive to the inference wave with high precision, and has been widely used in scientific research, industry test, navigation and guidance system. For example, the laser interferometer is able to measure optical phase sensitive quantities, including length, angular velocity, gravitational wave and so on. Meanwhile, the atom interferometer is sensitive to the change of atomic phase caused by the light, gravity, electric and magnetic fields. As a new type of interferometry, the atom-light hybrid interferometer, is sensitive to both the optical phase and atomic phase. Furthermore, SU(1,1) interferometer and nonlinear atom-light hybrid interferometer have the ability to beat the standard quantum limit of phase sensitivity. Quantum interference technology, whose phase measurement accuracy can break through the limit of standard quantum limit, is the core of quantum metrology and quantum measurement technology.
2018, 67 (16): 167601.
doi: 10.7498/aps.67.20181084
Abstract +
Magnetism is one of the most important physical phenomena. The precision measurement of magnetism gives impetus to science and technology. Various techniques, including Hall sensors, superconducting quantum interference devices, and magnetic resonance, are used for trying to improve the resolution and the sensitivity of magnetometry. In recent years, nitrogen-vacancy (NV) centers in diamond have been investigated extensively. This solid-state spin system is convenient to initialize, manipulate, and read out. It has been applied to the experimental study of quantum information and computation, and more importantly, it has displayed enormous potential applications in magnetometry. With various techniques such as dynamical decoupling and correlation spectroscopy that are being applied to NV centers, the microscopic magnetic resonance with high resolution and sensitivity has been implemented. Typical examples of these achievements are the nuclear magnetic resonance and electron paramagnetic resonance of nanoscale samples, and even of single molecules or single spins. The NV centers can also be used for precisely measuring the microwave and radiofrequency field. The issues mentioned above will be outlined in this review.
GENERAL
2018, 67 (16): 160502.
doi: 10.7498/aps.67.20172367
Abstract +
Terahertz radar research has attracted widely attention of researchers due to its advantages such as short wave length, wide bandwidth, no blind spot, low power, and low intercept rate. It is generally considered that the echo signal of terahertz radar system is a signal with noise. Therefore, it is necessary to reduce the noise in the process of the frequency spectrum analysis of different-frequency signals. The fast Fourier transform (FFT) and the filtering method are commonly used in radar signal processing. The FFT method has lower ability to estimate the frequency of signal due to the interference noise. The filtering method detects the signal from the angle of noise elimination, but at the same time, it weakens useful characteristics, blurs position information about the signal, and affects detection capability of terahertz radar system. Aiming at the problem above, a method of detecting terahertz radar signals based on adaptive stochastic resonance (SR) system is proposed in this paper due to a phenomenon that the noise can be suppressed while amplifying the weak signal by transferring the noise energy after going through the SR system. With the different-frequency signal processing method of the twice sampling, the adaptive SR system and the scale recovery, the optimal parameters can be obtained automatically and the ranging calculation can be completed. Comparing with the FFT method, the mean output signal-to-noise ratio (SNR) gain through the SR system is 9.6843 dB at different measuring distances. When the measuring distance is 1000 mm, the initial spectrum value increases from 110.1 to 7172, which is 64.1 times higher than original value. The initial SNR of the whole system is improved from -11.94 to -0.179 dB, the gain is 11.761 dB. Comparing with the filtering method, the largest SNR gain is 6.485 dB when the measuring distance is 1000 mm, which is increased by 70.56%. When the input noise intensity is between 0.5 V and 1 V, the output SNR of the adaptive SR system is higher than that of the traditional filter system, but the gain is small and the maximum SNR gain is 2.148 dB. When the noise intensity of the system is between 1 V and 5 V, the SNR of the adaptive SR system is obviously higher than that of the filter system, and the largest SNR gain is 14.018 dB when the noise intensity D=5 V. The SNR curve of the adaptive SR system tends to be smoother and the curvature is 0.507, while the SNR curvature of the filtering model is 3.765, which is reduced by 86.5%. The method proposed in this paper not only solves the problem of noise coverage in the different-frequency signal, but also uses the characteristic that the noise energy can be transferred to the signal, to improve the output SNR of terahertz radar system, which is beneficial to further signal processing. Experimental results demonstrate that the ranging capability of the THz radar system is greatly improved, which has high application value and wide prospect in practical engineering research.
2018, 67 (16): 160302.
doi: 10.7498/aps.67.20180315
Abstract +
Quantum information, as a comprehensive subject of quantum mechanics and information science, has a broad theoretical research value and application prospect. As a resource of quantum information, quantum entanglement has been studied thoroughly, which is not only significant to understand the features of quantum mechanics, but also of great value to the development of the method new quantum information processing. Therefore, the generation of entangled state is widely studied theoretically. In comparison to low-dimensional entangled states, multi-dimensional entangled states are not only safe but also efficient and error-tolerant for quantum computation. The adiabatic technique is one of the most widely used and proven techniques in quantum information science. The main advantages of this technique are that it is insensitive to the fluctuation of experimental parameters, and the interaction time of the system is not required to be controled accurately. However, limited by the adiabatic condition, it usually takes relatively long interaction time in scheme via adiabatic technique to achieve the target states. If the required evolution time is too long, the scheme may be useless. To overcome this problem, researchers have done a lot in the field of finding ways to shorten the long interaction time of adiabatic passage. Among these works, the technique named shortcuts to adiabatic passage is a successful work in this field and it has attracted a great deal of attention in recent years. In this paper, based on transitionless quantum driving to construct shortcuts to adiabatic passage, an efficient scheme to fast generate a four-dimensional entangled state of two-atom is proposed. The atoms are respectively trapped in the separate two-mode cavities which are connected by optical fiber. To achieve an alternative physically feasible system, the non-resonant dynamics is adopted to create a Hamiltonian which can exactly drive the system to evolve along the instantaneous eigenstates of the original Hamiltonian. As a result, if the system goes through adiabatic passage, it will evolve in the dark state, not transit to other states. Hence, using transitionless quantum driving to shortcuts to adiabatic passage, the evolutionary time in this scheme is much less than that in other schemes based on traditional adiabatic passage. The rigorous numerical simulations are conducted. The results show that with suitable pulsed laser parameters, this scheme is robust against decoherence arising from fiber decay, cavity decay and atomic spontaneous emission. Moreover, the scheme is more feasible in physics. That is, based on the proposed scheme, a high-fidelity four-dimensional entangled state of two-atom can be achieved.
2018, 67 (16): 160501.
doi: 10.7498/aps.67.20180250
Abstract +
In recent years, with the development of chemical study of complex systems, such as surface catalytic system, etc. the research of nonlinear dynamics problem of complex system has received much attention. These systems have high-degree complexity, and they are inevitably affected by intrinsic and extrinsic fluctuations (noise) and time delay. The combination of noise and time delay is ubiquitous in nature, and often changes fundamentally dynamical behavior of the system, and thus making the system produce more richer and complex dynamical behaviors. At present, in the theoretical studies of the nonlinear dynamic properties, the macroeconomic deterministic or stochastic dynamic equation is adopted most, and the time delay factor, especially the influences of combination of noise and time delay on complex system are rarely taken into account. Thus, the study of the character, mechanism and application has important realistic significance and scientific value. In this paper, we first introduce the Dimer-Monomer reaction model (DM model), where various dimer adsorption mechanisms in catalyst surface, namely, the local and random adsorption surface catalytic reaction models are considered. Then we use the stochastic delayed theory involved in this paper and its extension, including the analytical approximation and numerical simulation of complex systems under the action of noise and time delay. In this paper, we consider the effects of noise and time-delayed feedback in the surface catalytic reaction model, and construct a delayed monomer-dimer surface reaction model including correlated noise. According to the Langevin equation, applying small delay approximation, we obtain the delayed Fokker-Planck equation for calculating characteristic parameters of the non-equilibrium phase transition behavior (the extreme of the steady state probability distribution), analyzing the effect mechanism of noise and its correlation with the non-equilibrium phase transition. The MD model exhibits the first- and second-order phase transition, namely, the reactive window between first- and second-order phase transition. The MD models for various dimer adsorption mechanisms (namely, local and random adsorption models) are discussed. The results are indicated as follows. (1) The external noise and correlation between two noise signals cause the reactive window width to contract. (2) The influence of the internal noise on the behavior of non-equilibrium dynamical phase transition depends on the noise correlation, i.e., when the two noise signals are negatively correlated, the internal noise causes the reactive window width to expand. However when the two noise signals are positively correlated, the internal noise causes the reactive window width to contract. (3) The noise-caused changes of reaction window have important scientific significance in the first- and second-order phase transition of the MD surface reaction model.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2018, 67 (16): 164601.
doi: 10.7498/aps.67.20180451
Abstract +
As a rare metal material with low density, high strength and high melting point, beryllium (Be) is widely utilized in many fields including aerospace and vehicles. Dynamic loadings such as impact and high-rate compression often happen in the applications of Be materials in these fields. However, the dynamic behaviors of Be materials under high pressure and high-rate loading have not been fully investigated, although they are valuable for better applications of Be materials. articularly, the effect of twinning on dynamic behaviors of Be material is very important for better understanding the plasticity deformation mechanism of Be material. In this paper, a thermoelastic-viscoplastic crystal plasticity model is developed for dynamic behaviors of Be material under high pressure and high strain-rate loading based on the physical mechanism of plasticity deformation. Besides, the dislocation motion and work hardening are considered within the constitutive framework by the Orowan relation and the Taylor equation respectively, and the contribution of twinning to the plasticity deformation is also considered via twinning fraction evolution and fragmentation of crystal due to twinning deformation. With the model, dynamic behaviors of Be material are investigated, including effect of pressure on the dynamic yield strength, the quasi-elastic unloading behavior, and evolution of twinning in shock loading and unloading. Compared with the classical SG model, the model developed in this paper accords better with the experimental results in predicting yield strength of Be material under impact loading, especially with high pressure. Moreover, it is revealed that the condition of yield strength of the Be material is divided into three cases, namely the non-twinning under low pressure, the twinning deformation under moderate pressure, and the twinning fragmentation under high pressure. The unloading behavior of Be material under impact loading is also studied with the model, and the quasi-elastic unloading behavior observed in experiments many times, is faithfully predicted. It is found that the quasi-elastic unloading phenomenon of the material is closely related to the variation of the shear velocity of shock wave with the shear strain, which suggests that the non-linear elastic property of the material is an important reason for this phenomenon. Finally, the evolution of twinning of Be material in the shock loading is studied, showing that the increasing of twinning friction happens not only in the loading process but also in the unloading process of the shock waves. Some crystals break up into sub-crystals due to the fact that the volume fraction of twinning exceeds the critical fraction in the evolution of twinning.
2018, 67 (16): 164701.
doi: 10.7498/aps.67.20180349
Abstract +
The aim of the present paper is to investigate the gravity-driven draining process containing insoluble surfactants, with the coupling effects of surface elasticity and disjoining pressure taken into consideration. A set of evolution equations including liquid film thickness, surface velocity and surfactant concentration, is established based on the lubrication theory. Assuming that the top of the liquid film is attached to the wireframe and the bottom is connected to the reservoir, the drainage stability is simulated with the FreeFem software. The characteristics of film evolution under the coupled effects of surface elasticity and disjoining pressure are examined, respectively. The simulated results show that the surface elasticity and the disjoining pressure have significant influences on the vertical thin film draining process. Under the effect of the surface elasticity alone, the initial film thickness increases with the elasticity increasing and the black film only forms on the top of the liquid film, but cannot stably exist and breaks quickly. The addition of the surface elasticity can increase the liquid film thickness and the drainage time, reduce the surface velocity, and rigidify the interface. When the disjoining pressure is applied merely, the surfactant flows into the reservoir continuously; hardly can the liquid film form a surface tension gradient and thus cannot form a countercurrent phenomenon. Under the coupling effect of the surface elasticity and disjoining pressure, a more stable liquid film forms. In the early stage of drainage, surface elasticity increases the film thickness, reduces the surface speed and generates the liquid countercurrent to slow the drainage process. When the black film appears, the electrostatic repulsion of the disjoining pressure is notable and makes the black film stable. The results obtained in the paper are in agreement with some of the experimental results in the literature. However, the elasticity-related surface tension and surfactant concentration model used is a simplified model. The nonlinear relationship between surface tension and surfactant concentration should be further considered in future theoretical models.
2018, 67 (16): 164201.
doi: 10.7498/aps.67.20180486
Abstract +
High peak power, single frequency nanosecond fiber lasers have aroused the intense interest in their applications such as nonlinear frequency generation, LIDAR, and remote sensing. However, self-phase modulation (SPM) will induce a temporally dependent phase shift φNL (L, t)=|Ap (0, t)|2γLeff, where Ap is the amplitude of pump wave, γ is the nonlinear parameter, and Leff is the effective fiber length. The nonlinear phase shift will broaden the spectral linewidth of pulsed laser, which degrades the coherence of the laser and influences the performance of the laser. In order to obtain laser pulses with narrower linewidth, we can phase-modulate the pulsed laser with a value of-φNL(L,t). Thus, the SPM induced the nonlinear phase shift can be eliminated, and the spectra of pulsed laser can remain during the amplification and transmission in the fiber. Stimulated Brillouin scattering (SBS) has very low threshold and should be taken into consideration in narrow linewidth fiber lasers. The SBS threshold, which is dependent on the linewidth of laser, will be changed at the same time when the SPM is pre-compensated for. Because the SPM pre-compensation will change the linewidth of the pulsed laser. According to three coupled amplitude equations, we numerically analyze the influence of SPM pre-compensation on SBS threshold and spectral characteristics. The stimulation results show that in a master oscillator power amplifier structured fiber laser system, when SPM is completely compensated for (φM(t)=φNL(L,t)), the spectrum of the output pulsed laser can be maintained as that of the laser seed, but the SBS threshold usually decreases. When the SPM is compensated for incompletely (φM(t) φNL(L,t)), the spectral linewidth of the output laser cannot be compressed to that of the laser seed, and the SBS threshold in this situation is lower than the SBS threshold obtained when φM(t)=φNL(L,t). When the SPM is overcompensated for (φM(t) > φNL(L, t)), the spectral linewidth of the output laser cannot be compressed to that of the laser seed either, but the the SBS threshold in this situation is higher than the SBS threshold when φM(t)=φNL(L,t). We also build an experimental setup to verify the feasibility of SPM compensation. In our experiment, the linewidth of the pulsed laser is reduced from 1.4 GHz to 120 MHz when SPM is compensated for by phase modulation. The SBS threshold of the system are measured before and after SPM pre-compensation, and correctness of theoretical simulation is experimentally verified. This analysis method can provide the design guidelines for narrow-linewidth pulsed fiber laser systems.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2018, 67 (16): 165201.
doi: 10.7498/aps.67.20180374
Abstract +
Laser-induced breakdown spectroscopy (LIBS) is a well-known analytical technique based on the atomic emission spectroscopy.The elemental composition and relative abundance information can be obtained by analyzing the plasma radiation generated by focusing high-energy pulsed laser on the sample.It has a wide range of applications due to its many advantages,such as minimal-to-no sample preparation,broad applicability,and in-situ capability.But in LIBS,the self-absorption effect of the emitted line can reduce the spectral line intensity,and then affect the precision and accuracy of LIBS quantitative analysis.So there are many methods and researches to reduce or eliminate the adverse effects of selfabsorption on spectral lines.In this paper,a self-absorption quantification analysis method is proposed to characterize the laser-induced plasma quantitative parameters.This self-absorption quantification analysis method,which utilizes the intensity independent information in the self-absorbed spectral lines,is proposed to characterize the induced plasma and perform quantitative measurements.The plasma characteristics including electron temperature,elemental concentration ratio,and absolute species number density can be derived directly through quantifying the self-absorption degree of the analytical spectral lines.Compared with the traditional laser-induced breakdown spectroscopy,the new method is weakly related to the spectral intensity:neither the analysis results are affected by the self-absorption effects,nor the additional spectral efficiency calibration is required.The LIBS spectrum of an aluminum-lithium alloy (nominal weight compositions are Al 94.6%,Mg 1.8%,Li 0.8%,Cu 2.59%,and Mn 0.21%) is used to calculate the spatiallyaveraged electron temperature and the concentration ratio between Mg and Al,and the species number densities is obtained by using the proposed self-absorption quantification method.The results of experiment on aluminum-lithium alloy show that the mean electron temperatures obtained by the modified Saha-Boltzmann plots determined by Mg and Al are 0.96 eV and 0.97 eV,respectively.The weight ratio wMg/wAl in the plasma is calculated to be 0.0171,which is approximately coincident with the nominal value of 0.0169.The absolute singly ionized number density of matrix element Al is 1:65×1017 cm-3,which is comparable to the electron density calculated from the Hα line broadening (1:72×1017 cm-3).Evidently,the free electrons present in the plasma are mainly contributed by the singly ionized matrix element Al.These experimental results of aluminum-lithium alloy validate that the proposed method is qualified to realize accurate absolute quantitative measurements and fast diagnose the plasma characteristics,which verifies the practicability,advantages,and precision of this method.This self-absorption quantification method is of great significance for quantitative LIBS analysis,especially the CF-LIBS analysis.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2018, 67 (16): 166101.
doi: 10.7498/aps.67.20180829
Abstract +
Ferroelectric random access memory (FeRAM) has superior features such as low power consumption, short write access time, low voltage, high tolerance to radiation. Data about the total ionizing dose (TID) radiation effects of FeRAM have not been rich in the literature so far. Experimental study of the ionizing radiation effect of FeRAM is carried out based on Co-60 γ rays and 2 MeV electrons. And the TID radiation damages to the FeRAM in the dynamic biased, static biased and unbiased case are studied. The direct current and alternating current parameters are tested by J-750. The test results indicate that the stored information about the memory cell has no change before failure, the ferroelectric capacitors are still able to hold the data. Accordingly, the TID failure of the FeRAM should be mainly ascribed to the poor TID hardness of the peripheral complementary metal oxide semiconductor circuits. Besides, three types of electric fields from three working conditions can result in different generation and recombination rates of electronhole pairs. For static biased case, the internal electric field in the FeRAM is constant. It can lead to high net production of the electronhole pairs and a great number of trapped charges. Hence the radiation damage in the static biased case is most serious. With the increase of the total radiation dose, the electrical parameters of FeRAM have different degradations. Part of the parameters that can be detected by J-750, may lapse before they are detected online. Standby current, operating power supply current, leakage current and output low voltage are radiationsensitive parameters of FeRAM through analyzing the test data. And, other parameters, which have slight changes, have small effect on the degradation of the device. Furthermore, the electron accelerator is used in electron irradiation experiment. By comparing the results of the two kinds of radiation tests, it is discovered that the electrons tend to cause lighter TID degradation than Co-60 γ rays because of the high density of electrons in the electron irradiation environment and low net production rate of electronhole pairs. In addition, the electrons have weaker penetration than Co-60 γ rays due to low energy. The device packaging, the upper metal layers can also influence the experimental result of electron irradiation. The above conclusions provide a reference value for the total dose effect of FeRAM and will be of great significance for studying the radiation hardening of FeRAM.
2018, 67 (16): 166401.
doi: 10.7498/aps.67.20180626
Abstract +
The first-principles calculation method is used to systematically investigate the lattice structure, energy band, density of states of the bulk Cu2ZnSnS4, surface reconstruction, and mechanism of adsorption and passivation of F, Cl and H atoms on Cu2ZnSnS4 (112) surface. We find that the surface reconstruction occurs on the Cu-Zn-Sn-terminated Cu2ZnSnS4 (112) surface and this reconstruction introduces surface self-passivation. By analyzing the partial density of states of the atoms on the S-terminated Cu2ZnSnS4 (112) surface, it can be seen that surface states near the Fermi level are mainly contributed by 3d orbitals of Cu atoms and 3p orbits of S atoms at the top of the valence band. When a single F, Cl or H atom is adsorbed on the S-terminated Cu2ZnSnS4 (112) surface, all three kinds of atoms exhibit an optimal stability at a specific top adsorption site in comparison with at the bridge, hcp and fcc sites. And this top position is also the position of the S atom that has the greatest influence on the surface states. When two atoms of the same kind are adsorbed on the surface, H, Cl or F atoms occupy the top sites of two S atoms that cause surface states on the Cu2ZnSnS4 (112) surface, which have the lowest adsorption energy. And the surface states near the Fermi level are partially reduced. Therefore, two S atoms that cause the surface states are the main targets of S-terminated Cu2ZnSnS4 (112) surface passivation. It has also been found that the passivation effect of H atom for surface states is the most significant and the effect of Cl atom is better than that of F atom. Comparing the partial density of states, the Bader charge and the differential charge of the atoms before and after adsorption, we find that the main reason for the decrease of the surface states is that the adsorption atoms obtain electrons from the S atoms, and the state density peaks of the Cu and S atoms at the Fermi level almost disappear completely. In the surface model, the F atom obtains the same number of electrons from the two S atoms, while the two S atoms have different effects on the surface states. And the H and Cl atoms obtain fewer electrons from the S atoms, that have less influence on the surface states. It may be the reason why the passivation effect of F atom is slightly less than that of H and Cl atoms.
2018, 67 (16): 166801.
doi: 10.7498/aps.67.20180862
Abstract +
In recent years, with the rapid development of nanomedicine, the nanomaterials for bio-medical applications have received much attention. Although there are a variety of nanomaterials such as lipid, carbon nanotube, etc. that have been studied as drug carrier, they are restricted by the potential toxicity and high cost of production. So, it is necessary to find a good alternative for the future drug delivery applications. Detonation nanodiamond, as an important carbon nanomaterial, possesses many excellent properties such as facile functionalization, large specific surface area, low toxicity and high chemical stability and so on, which make them advantageous in bio-medical applications over many other nanomaterials. In this work, the carboxyl functionalized and well-dispersed nanodiamond (ND-COOH) is obtained through disintegration and chemical modification, and then the functionalized nanodiamond is characterized by transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, etc. to analyze its morphology and structure and the toxicity. Besides, the drug loading and release properties are also examined. The ND-COOH exhibits high zeta potential in aqueous solution, which enables them adsorb doxorubicin (dox) molecules onto the surface through electrostatic interaction, and the maximal loading reaches to 325 μg/mg, which is higher than most of reported results. It is because the bond between dox and ND-COOH origins from the electrostatic attraction between negatively charged-COO- on the ND and positively charged–NH3 in the dox. So, when the drug compounds are dispersed into low pH environment, the high H+ concentration would promote the transformation of –COO- into –COOH, which would weaken the electrostatic attraction between ND and dox and hence accelerate the drug release. This leads a drug release to reach 85% in pH 5.0 PBS and less than 40% in pH 7.4 PBS, exhibiting interesting pH-responsive drug release behavior. Finally, the toxicity and in vitro cancer cell killing results of ND-COOH and ND-dox preliminarily show that in the concentration range from 0 to 150 μg/mL, the functionalized ND-COOH does not inhibit the viability of SGC-7901 cells, exhibiting low toxicity. In contrast, the ND-dox shows obvious cytotoxicity towards SGC-7901 cells by strongly inhibiting their viability to lower than 40% in 150 μg/mL group. This work details and systematically discusses the disintegration, functionalization, drug loading and release properties of ND, which would be significant in promoting the biomedical application of ND.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2018, 67 (16): 167802.
doi: 10.7498/aps.67.20180663
Abstract +
Dye pollution,one of the most serious problems in water pollution,has attracted the attention of scientists.There are many methods,such as chemical oxidation,physical adsorption,biodegradation,photocatalysis,etc.,that have been adopted to handle the crisis of dye polultion. Compared with other strategies,photocatalysis has its unique advantages including low energy consumption,environment amicableness and high efficiency.Tungsten trioxide (WO3),a semiconductor with a band gap of 2.8 eV,has unique physical and chemical properties,and it has been applied to the area of photocatalysis to solve the problem of water pollution in recent years.However,the photocatalytic efficiency of bulk tungsten oxide fails to reach the expected.In this paper,a one-dimensional complex of tungstun trioxide and silver oxide (WO3/Ag2O) is synthesized via a simple hydrothermal method for photocatalytic degradation of methylene blue.The crystal structure,morphology and photocatalytic degradation ability towards methylene blue are characterized and analyzed via X-ray diffraction,scanning electron microscopy,transmission electron microscope,X-ray photoelectron spectroscopy,and UV-Vis spectrophotometer.Silver oxide (Ag2O),with a band gap of 1.2 eV,is found to be sensitive to visible light.The combination of tungsten trioxide and silver oxide promotes its photocatalytic efficiency dramatically under visible light illumination. Results show that WO3 nanorods in the composite possess a one-dimensional,hexagonal structure with an average length of 4μm and a diameter of 200 nm.The Ag2O attached to WO3 nanorods forms hexagonal nanoparticles and their average diameter reaches 20 nm.It is observed that WO3/Ag2O composite displays a loose structure and a high specific surface area,which provides more reactive sites.Comparing with single component,UV-Vis spectrophotometry shows that the composite has a highabsorbance in the range of visible light.The combination of tungsten trioxide and silver oxide can change the band gap of the photocatalyst whereas the photocatalytic efficiency of the composite reaches 98% in 60 min under visible light.Therefore,the synergistic effect of WO3 and Ag2O plays a vital role in enhancing the photocatalytic performance.Moreover,the stability of photocatalyst is one of the most important indicators of its recycling and long-term effectiveness,and the present WO3/Ag2O composite has good catalytic and chemical stability.This investigation proves that the combination of wide bandgap photocatalysts with visible-light sensitive metal oxide with large specific area will improve photocatalytic activity efficiently under visible light.
2018, 67 (16): 167101.
doi: 10.7498/aps.67.20180538
Abstract +
The structural stability, electronic and magnetic properties of semihydrogenated graphene and monolayer boron nitride (H-Gra@BN) composite system are studied by the first principles calculation. First, for the six possible stacked configurations of H-Gra@BN in three kinds of magnetic coupling manners, including the nonmagnetic, ferromagnetic and antiferromagnetic, the geometry optimization structures are calculated. The formation energies (Ef) are -28, -37, -40, -35, -28, and -34 meV/atom for AA-B, AA-N, AB-B, AB-B-H, AB-N and AB-N-H configurations of H-Gra@BN, respectively. The details of the six H-Gra@BN configurations are presented. The results show that the AB-B configuration of H-Gra@BN system is most stable with the largest formation energy in the six configurations. Its thickness is the smallest in all six configurations. The formation energies of all configurations are very close to each other and show that the combination of the interlayer between layers is very weak, The interaction between H-Gra and monolayer BN is van der Waals binding. Second, the band structure, total density of states (TDOS), partial density of states and polarization charge density of the most stable H-Gra@BN system are systematically analyzed. This material is ferromagnetic semiconductor. The band gaps for majority and minority spin electrons are 3.097 eV and 1.798 eV, respectively. Each physical cell has an about 1 μB magnetic moment, which is mainly derived from the contribution of the unhydrogenated C2 atom. Furthermore, while the pressure is applied along the z direction, we analyze the TDOS and band structure of H-Gra@BN system, and find that when the z axis strain is more than -10.48% (Δh=-0.45 Å), the valence band maximum of minority spin moves down. The conduction band minimum of minority spin moves from the high symmetry Γ position into a position between Γ and K. The electronic properties of the most stable H-Gra@BN system change from magnetic semiconductor into half metal. When the strain is increased by more than -11.65% (Δh=-0.5 Å), the most stable H-Gra@BN changes into a nonmagnetic metal. To analyze the effect caused by different strains, we analyze the difference in three-dimensional charge density, and find that with the decrease of the layer spacing, the interlayer interaction gradually increases and shows the obvious covalent bond characteristics. This paper predicts a new type of two-dimensional material of which the electronic and magnetic properties can be easily tuned by pressure, and it is expected to be used in nano-devices and serve as an intelligent building material.
2018, 67 (16): 167801.
doi: 10.7498/aps.67.20180271
Abstract +
Dynamic light scattering (DLS) technology has been employed to measure the hydrodynamic diameter of particle and liquid viscosity by detecting the translational diffusion coefficient of Brownian particle in the suspending liquid.The interaction between the particles in the suspension may lead to unpredictable deviations when the Stokes-Einstein equation is applied directly in the measurement.In order to solve this problem,this paper deduced the Stokes-Einstein's equation and introduced the One-Parameter Models to modify the existing DLS measurement principle.Based on the One-Parameter Models,the linear relation of collective translational diffusion coefficient with the single-particle translational diffusion coefficient and particles concentration was established and verified by the measurement under low particle concentration,which was introduced in the DLS principle.The improved method was able to obtain the single-particle translational diffusion coefficient,then the problem caused by the change of particle size in the suspension was solved.Compared with previous methods,the improved method can be used to measure the nominal diameter of nanoscale spherical particles and absolutely detect liquid viscosity.The fundamental principle of detection by light scattering was explained and a DLS experimental system was established for the measurement of viscosity and particle size.The two dispersed systems of polystyrene particles+water and silica particles+alcohol were considered as the samples for reference and measured to verify the reasonability of the improved method presented in this work.In addition,the influence of temperature and particles concentration on the collective translational diffusion coefficient was detected for this two dispersed systems.The interaction between the particles in the suspension was analyzed based on the experimental results. In a two-component system composed of rigid particles and liquid,three types of force act on a particle,which included the “Brownian” force,the direct interactions between the particles and the hydrodynamic interactions.The combined effects of the three forces can be qualitatively described as attractive or repulsive.The collective translational diffusion coefficient of the particles in the suspension increases with the increase of the particle volume concentration,indicating that the force between the particles in the suspension is repulsive,and vice versa.In addition,it was confirmed that in the ideal thin suspension,the Brownian motion of the particles increases with the temperature increases.The experimental results indicated the attractive forces among the polystyrene particles in water and the repulsive force among the silica particles in alcohol.The relationship between the second osmotic virial coefficient and the law of particles' collective translational diffusion coefficient with particles concentration is discussed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2018, 67 (16): 168201.
doi: 10.7498/aps.67.20180468
Abstract +
Monte Carlo simulation is performed to study the adsorption properties of polymers on an attractive surface. Annealing method is adopted to simulate the adsorption characteristics and conformational changes of polymer chains driven by an external driving force F. In simulations using cooperative motion algorithm, the ensembles of monomers located at lattice sites are connected by non-breakable bonds. When the external force is F=0, the finite-size scale method can be used to determine the critical adsorption temperature (Tc) of the polymer chain on the attractive surface, but when the external force is F>0, the dependence of the average number of surface contacts M> on the chain length N is unrelated to temperature T. Therefore, Tc cannot be obtained by the finite-size scale method. However, the pseudo-critical adsorption temperature Tc can be estimated by a function of the average number of surface contacts M> and the temperature T for the chain length N=200. And then Tc decreases with external force F increasing. The phase diagram is obtained for the polymer chain between the desorbed state and the adsorbed state under temperature T and external driving force F. Furthermore, the influence of the external driving force on the conformation of the polymer chain is analyzed by the mean square radius of gyration of polymer chains. The critical adsorption point Tc can be checked roughly by the minimum location of the mean square radius of gyration or by the variation of its components in the Y and Z direction perpendicular to the external force. With the increase of the external force F for adsorbed polymer, the temperature T can determine whether polymer is changed from the adsorption state to the desorption state and where the force is located at the transformation. There are two different cases, that is, the polymer can be desorbed at the temperature Tc* TTc and the polymer cannot be desorbed at T Tc*. In this paper, we discuss these two cases for the adsorption of polymer on the attractive surface:weak and strong adsorption. In the first case, the adsorption is strongly influenced by the external driving force. By contrast, in the strong adsorption, the adsorption is weakly influenced by the external force. Our results unravel the dependence of adsorption of polymer on external driving force, which is also consistent with the phase diagram of adsorption and desorption of polymer chains.
2018, 67 (16): 168501.
doi: 10.7498/aps.67.20172215
Abstract +
Bipolar junction transistors (BJTs) are generally employed in spacecraft, due to their current drive capability, linearity and excellent matching characteristics. High-energy particles and cosmic rays in space environment remarkably affect electronic devices, especially in BJTs producing total ionizing dose, displacement damage or single event effect. Among them, ionizing irradiation effects on BJTs dominates. For BJTs, ionization damage can induce the oxide trapped charges in SiO2 layer and interface traps in Si/SiO2, resulting in more recombination base current and the degradation of current gain. Consequently, the accumulation of both oxide charges and interface traps causes an increase in the base current.#br#Passivation layer is also an important factor of the irradiation effects of BJTs. Previous works only studied the degradation of electrical properties of the devices with/without passivation layer induced by irradiation, and did not give an influence mechanisms of passivation layer on the irradiation respond of devices. Therefore, the irradiation damage mechanisms of the BJTs with or without nitride passivation layer are not clear so far.#br#In this paper, the impact of Si3N4 passivation layer on ionizing irradiation damage on lateral PNP bipolar transistors (LPNP) was studied by using 60Co gamma irradiation source. The KEITHLEY 4200-SCS semiconductor parameter analyzer was used to measure the relationship between the electrical properties of LPNP transistors and ionization dose, including the Gummel characteristics, the degradation of current gain, etc. The irradiation defects of the LPNP transistors with/without passivation layer structure were analyzed by the deep level transient spectroscopy (DLTS). The experimental results show that the electrical properties of the LPNP transistors with and without passivation layer exhibit similar characteristics. For all samples, the base current increases with increasing the total dose, while the collector current does not almost change. Compared with the LPNP transistors without Si3N4 passivation layer, the degradation of LPNP transistor with Si3N4 passivation layer is severe.#br#Based on the excess base current as a function of base-emitter voltage for the LPNP transistors with/without nitride passivation layer, the degradation of bipolar transistors with nitride passivation layer is severe under the same irradiation conditions. The DLTS analyses show that compared with the bipolar transistors without nitride passivation layer, the signal peak located at about 300 K is shifted to low temperature for the bipolar transistors with nitride passivation layer. The above results show that the LPNP transistors with nitride passivation could produce a large number of interface states with the energy level is closer to the middle of the forbidden band during the irradiation, which is attributed to a large number of hydrogen presence during the processing of fabricated passivation layer.
2018, 67 (16): 168101.
doi: 10.7498/aps.67.20180356
Abstract +
The shape controlled growth of diamond is beneficial to its subsequent processing. The shape controlled growth for abrasive grade diamond, whose particle size is less than 1 mm, has been studied extensively, while the shape controlled growth of large diamond crystals, which have important commercial and scientific applications, has not been investigated in detail. Therefore, it is necessary to do further researches. In this study, we synthesize large type Ib diamond crystals and investigate their growth shapes at pressures of 5.3-5.9 GPa and temperatures of 1200-1370℃, by using Fe64Ni36 alloy as the catalyst and (100) or (111) face of seed as growth face. Experimental results show that for the diamond crystals grown along the (100) face, the crystal shapes presents plate shape at 1206-1215℃, tower shape at 1216-1260℃, and tower steeple shape at 1261-1360℃; in sequence while for those grown along the (111) face, the crystal shape is of tower at 1233-1238℃ and becomes plate at 1239-1364℃. The ratio of height to diameter, which can provide a standard to quantify the shape of a diamond, is used to describe the crystal shape in detail. For large diamond crystals growing along the (100) face, under a high pressure of 5.6 GPa, the ratio of height to diameter increases with temperature increasing but the ratio of height to diameter, when growing along the (111) face, decreases. The shape distributions of large diamond crystals in the V-shaped region can be determined in the experiments of large diamond crystal synthesis at different temperatures (1200-1370℃) and pressures (5.3 GPa, 5.6 GPa, 5.9 GPa). The lower limit temperature of large diamond crystal growing along the (111) face in the V-shape region is obviously higher than that growing along the (100) face, but the difference between the higher limit temperatures for growing along these two faces is not obvious. The difference between the lower temperature limits of large diamond crystals growing along the (100) and (111) face can be explained by the different energies of the crystal surface and diamond/graphite equilibrium line in the phase diagram of carbon/alloy. Therefore, it has been realized that the shapes for type Ib large diamond crystals are controlled.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2018, 67 (16): 169201.
doi: 10.7498/aps.67.20180505
Abstract +
The electrification within the thunderstorm, caused mainly by inductive and noninductive charging mechanism, can produce strong local electric field inside the thundercloud. Due to the resulting electric field force, the vertical velocity of the graupel and hail particles which are the main in-cloud charge carriers, would change. As a feedback, this variation could affect the original electrification and charge structure of the thunderstorm. In order to investigate such a feedback effect, a weather research forecasting (WRF) model coupled with explicit lightning physics including charging and discharge lightning scheme (hereafter WRF-Elec) is employed and modified in this study. We derive the formulas for calculating the mass-weighted mean terminal velocities of graupel and hail under the balance among gravity, resistance and electric field force. Then, the National Sever Storm Laboratory (NSSL) two-moment bulk microphysics scheme is modified by adding the calculating code with consideration of electric field force (EFF) acting on the fall speed of graupel and hail particles. Eventually, the two-coupled WRF-Elec is developed successfully.#br#Based on this modified WRF-Elec, sensitivity tests are conducted to quantitatively investigate the influences of EFF on the thunderstorm electrification and the corresponding charge structure in an idealized supercell case. The results show that during the rapid enhancement of the thunderstorm, the grid-scale mass-weighted mean fall speed of graupel and hail vary significantly in consideration of EFF, with the maximum values both exceeding 4 m/s, although this situation occurs within a local area and lasts a short time. The action of EFF tends to enhance the falling of graupel and weaken the falling of hail. The influences of EFF on those graupel and hail particles with smaller-size and lower number concentration are stronger, as determined by composite factors of the strength and polarity of electric field, the diameter and number concentration of graupel and hail, and their charge density and polarity as well. The adjustment of the terminal velocity of the graupel and hail in consideration of EFF, eventually results in increasing the rate of both inductive and noninductive charge separation, where the inductive charging is the much more significant one. This leads to a grid-scale total charge density variation of -0.6-1.2 nC/m3 and a redistribution of the charge structure in the thunderstorm, and correspondingly, an increase of the local vertical electric field by 5 kV/m, thus producing stronger lightning eventually. In addition, due to the effect of electric field force, the mass mixing ratio of four precipitation particles including graupel, hail, ice crystal and snow is changed in the ranges of -0.09-0.24, -0.16-0.04, -0.04-0.05, and -0.01-0.006 g/kg, respectively. Therefore, the electric field force in thunderstorm affects not only the electrification and charge structure, but also the microphysical process. Generally, the overall influence of EFF on electrification tends to be positive, and the feedback effect of EFF on the charge structure should not be neglected.
