Study of the time-resolved emission spectra of the ejected plume generated by ultrashort laser ablation of graphite
First-principles study on the hydrogenation of the O2 on TiN4 embedded graphene
Simulation on surface morphology evolution of metal targets irradiated by intense pulsed electron beam
Angular dependence of proton single event multiple-cell upsets in nanometer SRAM
Micro-damage characteristics of incipient spall in high-purity copper
Dynamic damage of material is a complex process that is dependent on lots of effects on a mesoscale, including grain size, morphology and micro-voids. In order to study the shocked lead micro-damage characteristics in oxygen-free high-purity copper, the variational thickness values of flyers and samples are designed to vary pulse duration and strain rate in plate-impact experiment, and the special recovery chamber and surface profile measurement system are used for soft-recovery and cross-section measure respectively. Based on the reconstruction, quantitative and statistical analysis, it is found that the longer pulse duration and higher shock loading stress bring about more serious local damage in oxygen-free high-purity copper. The mensurable damage width of sample cross-section results from the damage evolution on a sub-micron scale. Critical evolution time of sub-micron is observed to decrease with strain rate increasing, suggesting that damage evolution speed of sub-micron becomes faster as strain rate increases. The void size distribution of recovered sample is presented, and the topological characteristic transition accompanied with nucleation, growth, and coalescence processes of microscopic voids is also discussed. Through a comparison of difference between this work and the literature of previous research, a physical explanation of voids size distribution characteristics of oxygen-free high-purity copper is presented.
Thermal rectification of heterojunction nanotubes
The Influence of Co binding phase on adhesive strength of diamond coating with cemented carbide substrate
Molecular dynamics simulation on the wetting characteristic of micro-droplet on surfaces with different free energies
Study on controlling the stress in flexible Al/PI film by interface alloying
Effect of low As pressure annealing on the morphology and reconstruction of GaAs (001)
In-situ investigation on the growth of Cu-Al intermetallic compounds in Cu wire bonding
According to Moore's Law, as the feature size of semiconductor devices becoming smaller and smaller, the chip integration degree keeps increasing. In particular, accompanying with the development of high chip integration and unit size reduction, the metal interconnects, i. e. the wire bonding, are becoming a challenging problem. Copper wire is believed to be an excellent metal for wire bonding, instead of gold wire, due to its attractive advantages such as low cost, favorable electrical and thermal conductivities etc. However, the excess Cu/Al intermetallic compounds (IMC) at the interface of copper wire and aluminum pad will increase the contact resistance and reduce bonding strength. This can affect the properties and reliability of devices. Currently, the evolutions of the interfacial microstructures as well as the growth mechanism of Cu/Al IMC at the bonding interface under thermal condition are still unclear.In-situ transmission electron microscope (TEM) has high spatial resolution and strong analysis ability. With fast CCD cameras, TEM can also record the dynamic structure evolution of the sample in real time. Combined with multi-function holders, TEM can also exert diverse fields and loads on the sample and synchronously monitor their structures and component evolutions. Hence, in situ TEM provides an advanced technique to explore the structural evolution and growth mechanism of Cu/Al IMC.In this paper, the growth mechanism of Cu/Al IMC is investigated during the annealing temperature from 50-220 ℃ based on the in-situ high resolution transmission electron microscopy (in-situ HRTEM). Specifically, the dynamic growth and structural evolution of Cu/Al IMC during annealing are recorded in real time. Results show that the isolated Cu/Al IMC is distributed in the bonding interface before annealing. The main component of IMC is Cu9Al4, whereas the minor one of IMC is CuAl2. After annealing at 50-220 ℃ for 24 h, Cu/Al IMC near the Cu layer is Cu9Al4, while Cu-Al IMC apart from the Cu layer is CuAl2. Meanwhile, the reaction rates and the activation energy of Cu/Al IMC at different temperatures are calculated. Furthermore, the more accurate growth equation of Cu/Al IMC is also proposed based on the in-situ experimental results, which will benefit the optimization of bonding process and the reliability of Cu/Al wire bonding.
Azimuthal spin wave modes in an elliptical nanomagnet with single vortex configuration
Effects of Co-doping on multiferroic properties of Bi6Fe2-xCoxTi3O18 ceramics
Multiferroic materials have drawn increasing interest due to the coexistence of ferromagnetism (FM) and ferroelectricity (FE), which provides significant potentials for applications in spintronics, information storage, and sensors, etc. In this paper, the multiferroic Bi6Fe2-xCoxTi3O18 (BFCT-x,x=0-2.0) ceramics are prepared by the solid-state reaction. The BFCT-x samples belong to Aurivillius structure containing five perovskite layers clapped between two Bi-O layers. The lattice constants a, b, and c of BFCT-x samples increase simultaneously with increasing cobalt content up to 0.6 and then decrease with further addition of cobalt. The magnetic and ferroelectric properties, and their corresponding Curie temperatures are measured. At room temperature (RT), the magnetism of the BFCT-0, BFCT-1.8 and BFCT-2.0 samples can be understood by the presence of the antiferromagnetic (AFM) interaction with the dominant paramagnetism (PM) state, which is consistent with the linear behavior of the M-H plot. The Fe3+-O-Fe3+ and Co3+-O-Co3+ interactions present in the BFCT-x samples lead to AFM. The BFCT-0.2–1.0 samples show saturated magnetic loops, while the BFCT-1.2 sample is far from saturation even under an applied magnetic field of 10 kOe. The M-H curve of BFCT-1.6 sample shows a weak ferromagnetism. The Co content (x=0.2-1.6) dependences of 2Ms and 2Mr have been recorded. Both the 2Ms and 2Mr experience first-increase-then-decrease variation tendency with their maximal values of ～ 4.49 emu/g and ～ 0.89 emu/g located at x =0.6 and x =1.0, respectively. As the cobalt content varies from x=0.2 to x=1.2, the paramagnetic-ferromagnetic phase transition temperature (TMC) decreases from 752 to 372 K. At RT, the BFCT-x samples are ferroelectric, and the maximum and minimum values of remnant polarization (2Pr) are about 8.0 μup C/cm2 (x=0.6) and 1.1 μup C/cm2(x=1.2), respectively. The 2Pr of the BFCT-0.6 is about three times larger than that of Bi5Fe2Ti3O18 (x=0) sample. Furthermore, the dependence of 2Pr on Co content first increases with Co doping when x ≤qslant 0.6, and decreases from x=0.8 to x=1.2, and then increases again. The ferroelectric Curie temperature Tc of the BFCT-x samples increases with increasing x up to 0.8 and then decreases with further increasing cobalt content. It is noteworthy that the Tc of BFCT-1.0 is 2 K lower than that of BFCT-0.6, while the 2Pr decreases by 63%. It is seen that the 2Pr and 2Mr increase simultaneously with increasing Co content (below 0.6). When 0.8 < x ≤qslant 1.0, the 2Mr increases while 2Pr decreases with increasing Co content. After x>1.2, the 2Mr decreases while 2Pr increases with increasing Co content. The repelling between the FE and FM as discussed above may result from the magnetic-crystalline and ferroelectric-crystalline anisotropy. The mechanism of this phenomenon is not quite clear and needs further investigation.
First-principle study of electronic structure and optical properties of Ba(Mg1/3Nb2/3)O3
High temperature thermoelectric performance of Ca2+ doped CdO ceramics
Design and fabrication of broadband radar metamaterial absorber based on the resistor FSS
Effect of interfacial hydrogen bonds on the structure and dynamics of confined water
Terminating the spiral wave and spatiotemporal chaos in cardiac tissue using the low-pass filtering scheme
Robust cubature Kalman filter target tracking algorithm based on genernalized M-estiamtion
Community detection based on joint matrix factorization in networks with node attributes
First-principles study of electron-phonon coupling and superconductivity in compound Li2C2
Phase string effect and mutual Chern-Simons theory of Hubbard model
Electron correlations and orbital selectivities in multiorbital models for iron-based superconductors
Heavy-fermion superconductivity and competing orders
One of the most salient features of heavy fermion superconductivity is its coexistence with various competing orders. Superconductivity often emerges near or at the border of these exotic orders and their interplay may give rise to many interesting quantum phenomena. In this paper, we give a brief review of the various heavy fermion superconductors discovered so far and show there may exist an intimate connection between their superconducting pairing and quantum critical spin/charge/orbital fluctuations. We classify these superconductors into three categories:(A) CeM2X2, CenMmIn3n+2m, CePt3Si, CeMX3, CeNiGe3, Ce2Ni3Ge5 and CePd5Al2, in which superconductivity emerges at the border of antiferromagnetic phase; YbRh2Si2, in which superconductivity was very recently found inside the antiferromagnetic phase at 2 mK; UX2Al3 and UPt3, in which superconductivity occurs inside the antiferromagnetic phase; and UBe13 and U6Fe, in which the connection between magnetism and superconductivity is not yet clear. Among them, CePt3Si and CeMX3 are noncentrosymmetric, while UPt3 exhibits spin triplet pairing inside an antiferromagnetic phase.(B) UGe2, URhGe, UCoGe, UIr and U2PtC2, are spin triplet superconductors under the influence of ferromagnetic order or fluctuations.(C) URu2Si2, PrOs4Sb12, PrT2X20, Pu-115, NpPd5Al2 and β-YbAlB4, in which superconductivity may be related to other exotic quantum states or fluctuations such as hidden order, valence fluctuations and quadrupolar fluctuations.In these compounds, f-electrons may participate in both superconductivity and other competing orders and often behave simultaneously itinerant and localized. These could be described by a phenomenological two-fluid theory, in which two coexisting fluids–an itinerant heavy electron fluid (the Kondo liquid) and a spin liquid of unhybridized local f-moments–compete to give rise to the various low temperature orders as well as superconductivity. Combining the two-fluid picture and the idea of spin-fluctuation-induced superconducting pairing, a BCS-like formula is proposed for calculating the superconducting transition temperature, and the results are found to be in good agreement with the experimental data for Ce-115. This model can explain naturally the microscopic coexistence of superconductivity and antiferromagnetism in these materials, and provides a promising guidance to other heavy fermion superconductors to achieve a systematic examination of the interplay between superconductivity and other exotic orders.
A brief analysis of annealing process for electron-doped cuprate superconductors
Order parameters of non-centrosymmetric superconductors
Quantum criticalities in carrier-doped iron-based superconductors
In the past several decades, quantum phase transition and the associated fluctuations have emerged as a major challenge to our understanding of condensed matter. Such transition is tuned by an external parameter such as pressure, chemical doping or magnetic field. The transition point, called quantum critical point (QCP), is only present at absolute zero temperature (T), but its influence (quantum criticality), is spread to nonzero temperature region. Quite often, new stable orders of matter, such as superconductivity, emerge around the QCP, whose relationship with the quantum fluctuations is one of the most important issues.
Iron-pnictide superconductors are the second class of high-temperature superconductor family whose phase diagram is very similar to the first class, the copper-oxides. Superconductivity emerges in the vicinity of exotic orders, such as antiferromagnetic, structural or nematic order. Therefore, iron-pnictides provide us a very good opportunity to study quantum criticality. Here we review nuclear magnetic resonance (NMR) study on the coexistence of states and quantum critical phenomena in both hole-doped system Ba1-xKxFe2As2 as well as electron-doped systems BaFe2-xNixAs2 and LaFeAsO1-xFx. Firstly, we found that the 75As NMR spectra split or are broadened for H//c-axis, and shift to a higher frequency for H//ab-plane below a certain temperature in the underdoped region of both hole-doped Ba1-xKxFe2As2 and electron-doped BaFe2-xNixAs2, which indicate that an internal magnetic field develops along the c-axis due to an antiferromagnetic order. Upon further cooling, the spin-lattice relaxation rate 1/T1 measured at the shifted peak shows a distinct decrease below the superconducting critical temperature Tc. These results show unambiguously that the antiferromagnetic order and superconductivity coexist microscopically, which is the essential condition of magnetic QCP. Moreover, the much weaker T-dependence of 1/T1 in the superconducting state compared with the optimal doping sample suggests that the coexisting region is an unusual state and deserves further investigation. Secondly, we conducted transport measurements in electron-doped BaFe2-xNixAs2 system, and found a T-linear resistivity at two critical points. One is at the optimal doping xc1 = 0.10, while the other is in the overdoped region xc2 = 0.14. We found that 1/T1 is nearly T-independent above Tc at xc1 where TN =0, which indicates that xc1 is a magnetic QCP and the observed T-linear resistivity is due to the quantum fluctuation. We find that 1/T1 close to the optimal doping in both Ba1-xKxFe2As2 and LaFeAsO1-xFx also shows a similar behavior as in BaFe2-xNixAs2. The results suggest that superconductivity in these compounds is strongly tied to the quantum antiferromagnetic spin fluctuation. We further studied the structural transition in BaFe2-xNixAs2 by NMR. Since the a-axis and b-axis are not identical below the nematic structural transition temperature Ts, the electric field-gradient becomes asymmetric. Therefore the NMR satellite peaks associated with nuclear spin I=3/2 of 75As split for a twinned single crystal, when the external magnetic field is applied along a- or b-axis. We were able to track the nematic structural transition up to x=0.12. The Ts extrapolates to zero at x=0.14 which suggests that xc2 is a QCP associated with a nematic structural phase transition and the T-linear resistivity at xc2 is therefore due to the QCP. No existing theories can explain such behavior of the resistivity and we call for theoretical investigations in this regard.
Recent experimental progress in low-dimensional superconductors
Phenomena and findings in pressurized alkaline iron selenide superconductors
Magnetic and electrical properties of K2NiF4-type Sr2CrO4
Application status and future of multi-scale numerical models for lithium ion battery
Lithium ion battery is nowadays one of the most popular energy storage devices due to its high energy, power density and cycle life characteristics. It has been known that the overall performance of battery depends on not only electrolyte and electrode materials, but also operation condition and choice of physical parameters. Designers need to understand the thermodynamic and kinetic characteristics of battery, which is costly and time-consuming by experimental methods. However, lithium ion battery is a complicated electrochemical system with multi physicochemical processes including the mass, charge, and energy conservations as well as the electrochemical kinetics. It not only has a typical multiple level arrangement: across the electrode level, cell level, and extending to the battery module level, which is different from the basic active material particle level arrangement, but also confronts the challenges to meeting the requirements for sorting and consistency method for battery. These facts increase the difficulties in designing the battery and evaluating the overall performance. Owing to the rapid development of multi-scale numerical simulation technology, the multi-scale mathematical models for lithium ion battery are developed to help battery designer comprehensively and systematically gain the interaction mechanisms between different physicochemical fields in the battery working process and analyze the regulations of these interaction mechanisms, which is significant in providing theoretical supports for designing and optimizing the battery systems. At present, multi-type lithium ion battery models coupled with many physicochemical processes have been developed on different scales to study different issues, such as thermal behavior, inner polarization, micro structure, inner stress and capacitance fading, etc. In this paper, we review the research statuses and development trends of multi-scale mathematical models for lithium ion battery. The primary theoretical models for lithium ion battery are systemized and their features, application ranges and limitations are also summarized. Furthermore, the future research area and the difficulty in industry application are discussed. All of these are helpful for the theoretic research and engineering application of the multi-scale numerical models for lithium ion battery.
Numerical simulation of a hybrid magnetic refrigeration combined with high pressure Stirling regenerative refrigeration effect
Research on extended micro-motion target echo simulation and characteristic extraction
Phenomena of limit cycle oscillations for non-Markovian dissipative systems undergoing long-time evolution
Transmission protocol and its performance analysis of quantum communication network based on packet switching
Vibration energy harvesting from a piezoelectric bistable system with two symmetric stops
Attitude estimation and three-axis magnetometer on-line calibration based on moving horizon estimation
Pulse response of a monostable system
Study on dynamical characteristics of a meminductor model and its meminductor-based oscillator
Numerical simulations of hexagonal grid state patterns
Improved averaged model and stability analysis of voltage-mode controlled positive output super-lift Luo converter
Chaotic circuit of ion migration memristor and its application in the voice secure communication
Chaos synchronization of coronary artery system based on higher order sliding mode adaptive control
Study of erosion and deposition characteristics of Li during liquid Li limiter experiment in HT-7
Theoretical study on the photodissociation reaction of α-cyclohexanedione in ground state
Research of data retention for charge trapping memory by first-principles
Theoretical and experimental study on line intensities of CO2 and CO transitions near 1.5 μm at high temperatures
Numerical simulation of heat transfer and natural convection of the indirect-driven cryogenic target
Experimental optimization in ion source configuration of a miniature electron cyclotron resonance ion thruster
High-resolution laser frequency scanning interferometer based on fiber dispersion phase compensation
The laser frequency scanning interferometer has several advantages, such as non-contact, high accuracy and low signal to noise ratio in detection. In order to achieve higher resolution of the laser frequency scanning interferometer, increasing the tuning range of the light source and reducing the tuning non-linearity have become the key factors. The commonly used method is to correct the non-linearity of the wide bandwidth external cavity tuning laser by a fiber optical auxiliary interferometer constructed external frequency sampling clock. When using the broadband external cavity tuning laser and the auxiliary interferometer with an optical path difference of 220 m, it is found experimentally that the single-mode fiber dispersion makes the frequency of sampled signals change over time, causing the spectrum to broaden and resolution to decline. This paper has established the dispersion mismatch model which shows that the fiber dispersion of the auxiliary interferometer causes linear chirp frequency changes during the measurement of signals. The linear chirp frequency is proportional to the tuning bandwidth and measured distance. The phenomenon and theoretical model of dispersion mismatch is verified by experiments. The results for targets in the air are shown to linearly decrease as the tuning range increases with the maximum offset of 156.3 m for the 20 nm tuning bandwidth. The experiment also proves the peak broadening intensifies with increasing distance measured, and thus verifies as the time delay of free space increase, and the peak broadening and distortion also increases. This result means that it will limit the ranging distance and make large errors in measurement result for long distance targets. The dispersion of the auxiliary interferometer should be compensated in the laser frequency scanning interferometer for large-sized high resolution measurements. In this paper, phase dispersion compensation method based on the evolution of peak variation distortion elimination is proposed, by taking the peak amplitude variation as the criterion; the phase compensation can offset the dispersion and improve the resolution. The original signal is multiplied by the complex phase compensation term, then regulating the phase compensation factor, the chirp becomes smaller as the phase compensation factor is approaching the distortion factor. Under the condition that the phase compensation factor is equal to the distortion factor, the chirp is offset. Then, the relationship between the amplitude and the peak FWHM is studied. It is found that the peak FWHM decreases while the amplitude shows a gradually increasing trend. Therefore, the amplitude can be referred to in order to determine whether the peak FWHM reaches the minimum. The resolution for target's peak can be improved by searching for the maximum amplitude of the spectrum and adjusting the phase distortion coefficient. The experiment shows that the peak FWHM of the target is obviously narrowed after dispersion compensation. The peak value becomes close to the theoretical resolution, and the static target at a distance of 975.216254 mm from the laser frequency scanning interferometer is measured. Results show the measurement accuracy of the interferometer is 584 nm. To further verify the accuracy of the laser frequency scanning interferometer, the laser frequency scanning interferometer is compared with the Renishaw laser interferometer in the measurement range of 0–692 mm. The standard deviation between them is 4.5 m. The proposed method is put forward to provide basis for future studies on the large size high resolution laser frequency scanning interferometer.
A new simulation method of X-ray pulsar signals
Multiple harmonic X-ray pulsar signal phase estimation method