Diffusion of diblock copolymer in periodical channels:a Monte Carlo simulation study
In recent years, the static and the dynamical properties of polymer confined in nano-channels have become a hot topic due to its potential applications in technology, such as genome mapping, DNA controlling and sequencing, DNA separation, etc. From the viewpoint of polymer physics, the properties of polymer confined in nano-channels are affected by many factors, such as the channel size, the channel geometry, the polymer-channel interaction, etc. Consequently, many researches have been extensively performed to uncover the underlying physical mechanisms of the static and the dynamical properties of polymer confined in nano-channels.
Although many conformations are forbidden as polymer is confined in channels, the static properties of polymer are found to be still complicated. For the simplest case, i.e., homo-polymer confined in homogeneous solid channels, there are several scaling regimes, in which polymer adopts different conformation modes and the extension of polymer shows different scaling relations with the channel diameter, the polymer length, the persistence length, etc. In addition, the dynamical properties of polymer, such as the diffusivity and the relaxation, have also been extensively studied.
Though the properties of polymer confined in homogeneous channels have been well studied, we know little about those of polymer inside compound channels. It is found that the dynamics of polymer in compound channels is quite different from that of polymer in homogeneous channels, and compound channel could be useful for DNA separation and DNA controlled movement.In this work, the diffusion of diblock copolymer(ANABNB) in periodical channels patterned alternately by part α and part β with the same length lp/2 is studied by using Monte Carlo simulation. The interaction between monomer A and channel α is attractive, while all other interactions are purely repulsive. Results show that the diffusion of polymer is remarkably affected by the length of block A(NA), and the diffusion constant D changes periodically with NA. Near the peaks of D, the projected length of block A along the channel is an even multiple of lp/2, and the diffusion is in consistence with that of homo-polymer in homogenous channels. While near the valleys of D, the projected length of block A is an odd multiple of lp/2, and polymer is in a state with long time trapping and rapid jumping to other trapped regions in the diffusion process. The physical mechanisms are discussed from the view of polymer-channel interaction energy landscape.
An in-situ real time study of the perovskite film micro-structural evolution in a humid environment by using synchrotron based characterization technique
heoretical model of influence of frequency on thermal breakdown in semiconductor device
Research on dual energy grating based X-ray phase contrast imaging
Latest studies on resistance switching of molecular thin films embedded with nanoparticles
The protection of qudit states by weak measurement
Investigation on the directed transport efficiency of feedback-control ratchet
Brownian motion in the environment of the thermal fluctuations is a long-study issue in nonequilibrium statistical physics. In recent years, the directed transport properties of Brownian ratchets attract the widespread attention of scholars. When a ratchet system possesses the spatio-temporal symmetry-breaking feature, the directed transport can be produced. Although the breakthrough progress in the directed transport of the Brownian ratchet has been made, the energy conversion efficiency of feedback ratchet is not clear. Therefore, the center-of-mass mean velocity and the energy conversion efficiency of coupled ratchet under the influences of the time asymmetry of external force and the spatial asymmetry of external potential are discussed in detail.
The overdamped coupled Brownian particles are investigated. Nevertheless, the optimized control of the coupled ratchet is the important for directed transport. Therefore, the closed-loop control which depends on the state of the system is adopted. The dynamic behavior of coupled particles can be described by the overdamped Langevin equation, and the equation is numerically solved by using the stochastic Runge-Kutta algorithm. Some properties of the directed transport can be obtained through this method, such as the center-of-mass mean velocity, the energy conversion efficiency, etc. It is interesting to find that the center-of-mass mean velocity can reach a maximum as the amplitude of external force increases. However, the mean velocity can show the quasi-periodic oscillations with the increase of the period of external force for different values of the spatial asymmetry of external potential. In addition, it can be found that the feedback ratchet needs strong noise to make the directed transport of the ratchet reach the maximum as the coupled strength increases. On the other hand, the energy conversion efficiencies of the feedback ratchet can achieve their corresponding maximum values with the increase of the amplitude of external force for different values of the time asymmetry, and the maximum increases as the time asymmetry increases. However, the efficiency can also show the quasi-periodic oscillations with the increase of the period of the external force for different values of the spatial asymmetry of external potential. Moreover, the energy conversion efficiency can achieve the maximum as the noise strength increases, but the maximum of the efficiency will decrease with the increase of coupling strength. From the discussion above, the optimal values of the time asymmetry, the spatial asymmetry, the period of the external force and the noise strength can promote the directed transport of the feedback coupled Brownian ratchet. These conclusions can provide some guidance in the enhancement of the energy conversion efficiency of a nanomachine.
Design and control of large-detuned optical lattice based on 87Rb atoms
An innovative and practical scheme of building far-detuned optical lattice for 87Rb atoms is proposed.The disposals of aligning the lattice beams,tuning the lattice frequency and controlling the tapered amplifier for output are described in detail.Alignment of optical lattices is quite difficult in principle,for several beams are required to hit the same atomic cloud.For the relatively near-detuned one-and two-dimensional lattices,the coarse alignment is accomplished by tuning the lattice laser onto resonance with the magnetic-optic trap(MOT) frequency,and then blowing away the MOT in real time.A more precision alignment is implemented at the end of the MOT loading,the atoms are first pumped into the lower hyperfine level by turning off the repumping for some time;then,the pulsed lattice beams are turned on for a short time at some reasonably large detuning.Finally,a fluorescent image of the MOT is taken without repumping,in order to detect only those atoms which are repumped by the lattice laser.For the purpose of controlling the detuning of the lattice easily and accurately,a home-made grating wavemeter with a resolution better than 1 GHz is used.This way allows the laser to be locked at any frequency by using a software PID and is experimentally simple to implement.The intensity of the lattice is controlled directly by pulsing the current through the tapered amplifier using a function generator and a laser diode driver.This technique has already been demonstrated before by Prof.M.Kasevich's group at Stanford.
Our experiment starts with a MOT capturing approximately 4×107 atoms in 200 ms.The lattice loading is overlap with the end of polarization gradient cooling(PGC),after that,the molasses laser beams are extinguished, and the adiabatic expansion is accomplished in the same time by a decrease in the lattice light intensity according to release function.On the basis of MOT and PGC,the dependences of atomic loading on such parameters as the intensity and frequency detuning of optical lattice are investigated experimentally.The vibration frequency is measured by intentionally modulating the trap intensity.Experimental results show that the lattice structure facilitates the cooling with the temperature of atoms cloud being reduced to 1/3 compared with free space polarization gradient cooling.The system design,experimental results and conclusions are of definite significance and can serve as a fine reference for other kinds of lattices designs or alkali atomic plans.
Observation of particle manipulation with axial plane optical microscopy
Optimization design of a Gamma-to-electron spectrometer for high energy gammas induced by fusion
Uncertainty quantification in the calculation of keff using sensitity and stochastic sampling method
Angle measurement uncertainty statistical distribution of pulsed laser quadrant photodetector
Moving target compressive imaging based on improved row scanning measurement matrix
Spontaneous emission from a V-type three-level atom in a dynamic photonic crystal
Manipulation of lattice vibration by ultrafast spectroscopy
One-dimensional magnetic photonic crystal structures with wide absolute bandgaps
Propagation properties of vortex beams in a ring photonic crystal fiber
High speed and high precision demodulation method of fiber grating based on dispersion effect
Ocean surface wave effect on the spatial characteristics of ambient noise
Influnece of nonspherical effects on the secondary Bjerknes force in a strong acoustic field
Noise source identification by using near field acoustic holograpy and focused beamforming based on spherical microphone array with random unifrom distribution of elements
With the development of techlology, noise controlling has received wide attention in recent years. Noise source identification is the key step for noise controlling. Spherical microphone array, which can locate the noise source of arbitrary direction in three-dimensional space, has been widely used for noise source identification in recent years. Conventional methods of locating noise source include spherical near field acoustic holography and spherical focused beamforming. The acoustic quantities are reconstructed by using spherical near field acoustic holography method to realize the noise source identification, while the noise source can also be located by using focused beamforming based on spherical harmonic wave decomposition. However, both these methods have their own limitations when they are used in identifying the noise source. Spherical near field acoustic holography has low resolution at high frequency with a far distance from noise source to measurement array for noise source identification, whereas the spherically focused beamforming has low localization resolution at low frequency.
Noise source identification is discussed here, and a 64-element microphone spherical array with randomly uniform distribution of elements is designed. The combination methods of noise source identification by using spherical near field acoustic holography and mode decomposition focused beamforming are investigated. The performance of the proposed combination method is simulated, and an experiment on noise source identification is carried out based on the designed spherical microphone array to test the validity of proposed method. Research results show that the high-resolution noise source identification can be achieved by using near field acoustic holography when reconstruction frequency is 100-1000 Hz with a distance 0.3-0.45 m from noise source to the center of spherical array, while high resolution of noise source localization can be achieved by using spherical wave decomposition beamforming when signal frequency is 1000-5000 Hz with a distance 0.5-3 m from noise source to the center of spherical array. Spherical array with random uniform distribution of elements maintains stable identification ability in all bearings. The spherical near field acoustic holography has high-resolution distinguishing ability in near field and at low frequency, while the focused beamforming method has high-resolution distinguishing ability in far field and at high frequency. Therefore the noise source can be efficiently identified by using the proposed combination method of near field holography and focused beamforming with less elements and small aperture spherical microphone array.
Principle and application of diagonal reducing method in the complex noise fields
Spatial correlation of underwater bubble clouds based on acoustic scattering
Ocean ambient noise model considering depth distribution of source and geo-acoustic inversion
A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonator
Cyclical pulsation properties of particles in cone silo
Variations of the electrical conductivity and the Fermi velocity of epitaxial graphene with temperature
DC electric field induced orientation of a graphene in water
Receptivity of the steady cross-flow vortices in three-dimensional boundary layer
Numerical analysis of hollow droplet impact on a flat surface
Simulation study of effect of cooling rate on evolution of microstructures during solidification of liquid Mg
Magnesium metal and its alloys are widely used in industry,especially,as biodegradable materials are highly suitable for biomedical applications.Since macroscopic properties and service behaviors of materials are mainly determined by their microstructures,it is very important to in depth understand the melting structure of pure magnesium and its evolution process in solidification process.In this work,a molecular dynamic simulation studyis performed with embedded atom method potential at different cooling rates to investigate the rapid solidification process of liquid magnesium,and the microstructure evolution and phase transition mechanisms are systematically analyzed by using E-T curves,pair distribution function g (r),Honeycutt-Anderson (HA) bond-type index method,cluster-type index method (CTIM-3) and three-dimentional (3D) visualization method,respectively.It is found that the cooling rate plays an important role in the evolution of microstructures,especially;from HA bond index method,CTIM-3 and 3D visualization method,the microstructure details of crystalline or amorphous structures in the system are displayed quite clearly with temperature decreasing.Meanwhile,it can be easily found how some basic clusters interconnect to form a larger one in the system. For short,some local configurations under different conditions at four typical temperatures are also given to show the difference in microstructure on a relatively large scale.At a lower cooling rate of 1×1011 K/s,the evolution of metastable bcc structure is obviously consistent with the Ostwald's step rule in the system,meaning that the bcc structure is first formed preferentially and then dissociated largely,and eventually the stable crystalline structures are formed mainly with the predominant hcp structure and fcc structure,and coexisting along with remaining partial bcc structure.At a middle cooling rate of 1×1012 K/s,the crystallization process is slower,the bcc initially is formed at lower temperature, suggesting that the crystalline process is postponed,and the coexisting structures is still formed with the predominant hcp structure and fcc,bcc structures,but lacking in the larger grains,due to the competitions among the hcp,fcc and bcc structures.Finally,for a higher cooling rate of 1×1013 K/s,amorphous magnesium is formed with basic amorphous clusters characterized by 1551,1441 and 1431 bond types and there is not a predominant structure,although a small number of medium or long range orders come out.In addition,there surely exists a critical cooling rate for forming amorphous structures in a range of 1×1012-1×1013 K/s.From the evolution of bcc,it is also suggested that short range orders in super-cooling liquid give birth to bcc structure and the process can be avoided by simply speeding up the cooling rate to a critical one.
Structural model of InSb IRFPAs including underfill curing process
InSb infrared focal plane array(IRFPA) detector, active in 3-5 μm range, has been widely used in military fields. Higher fracture probability appearing in InSb infrared focal plane arrays(IRFPAs) subjected to thermal shock test, restricts its final yield. In order to analyze and optimize the structure of InSb IRFPAs, it is necessary to create the three-dimensional structural model of InSb IRFPAs, which is employed to estimate its strain distribution appearing in the different fabricating processes. In this paper, the curing model of underfill is described by its volume contraction percentage combined with the elastic modulus of the completely cured underfill. Thus, both the von Mises stress and the Z-components of strain accumulated in the curing process of underfill are calculated. When InSb IRFPAs is naturally cooled to room temperature from the curing temperature of underfill, the Z-component of strain distribution appearing on the top surface of InSb IRFPAs is obtained with our structural model, which is identical to the deformation distribution on the top surface of InSb IRFPAs measured at room temperature. In the following thermal shock simulation, we find that the maximal von Mises stress appears at 100 K and the maximal Z-component of strain appears at 150 K, these two temperature points are located in the second half of the thermal shock process, these results indicate that the fracture of InSb chip happens more easily in liquid nitrogen shock test. This inference is consistent with the fact appearing in liquid nitrogen shock test. All these findings suggest that the proposed model is suitable to estimate the deformation distribution of InSb IRFPAs and its changing rule in its different fabricating stages.
Effects of the doping of Al and O interstitial atoms on thermodynamic properties of α-Al2O3:first-principles calculations
Al particles are widely used as a metal reductant in the thermite, and a native Al2O3 film always forms on the particle surface as a passivating oxide shell. The diffusions of Al and O atom through the oxide shell will influence the structure and thermodynamic properties of Al2O3, and thus the ignition process of the thermite. In this work, the thermodynamics properties of α-Al2O3, α-Al2O3 doped by Al interstitial atom and α-Al2O3 doped by O interstitial atom under high pressure and temperature are comparatively investigated by the first-principles calculations based on density-functional theory and quasi-harhmonic Debye model. The effects of the doping of Al and O interstitial atoms on the thermodynamic properties of α-Al2O3 are discussed. The results indicate that the doping of the Al and O interstitial atoms will reduce the bulk modulus, and increase the volume thermal expansion coefficient and constant volume heat capacity of α-Al2O3. Therefore, the diffusions of Al and O atom will make the oxide shell more ductile, and adverse to the spallation during the ignition of Al particles.
Fabrications and electrochemical properties of superlattice（Ce0.8SmO2-δ)/YSZ)N electrolyte films
The growing demand for the energy conversion and storage of miniaturized system has promoted extensive researches aiming at fabricating solid-state ionic devices in thin-film form. Recent developments in the field of thin-film growth technologies have controlled the films at an atomic level of deposited layers, thus opening new perspectives in the field of engineering of multilayers and heterostructures based on complex oxides. This work focuses on the characterizations of the low-temperature properties of Ce0.8Sm0.2O2-δ/Y2O3:ZrO2(SDC/YSZ)N superlattice films.(SDC/YSZ)N superlattice electrolytic films with various periods(N=4, 6, 10 and 20) are fabricated on monocrystal MgO substrates by the pulsed laser sputtering method. Here, SiTrO3(STO) is used as a buffer layer, SDC and YSZ are deposited alternately in the whole process. The total thickness values of samples are all fixed at 400 nm no matter how many periods the samples have. The surface morphologies, phase structures and electric properties of the as-deposited samples are characterized by scanning electron microscopy(SEM), X-ray diffraction and alternating current(AC) impedance spectroscopy. It is indicated that the films have excellent superlattice structures after STO has been used as a buffer layer and the substrate temperature has heated to 700℃. The interface between two layers are clearly observed by SEM. Moreover, neither cracks nor snaps are found at the interface. The grains uniformly grow on the surfaces of films and are arranged into cylinder structures, leading to compact films. Through AC impedance analysis, the samples which have more periods exhibit smaller activation energies. With increasing the number of interfaces, the activation energy of film decreases whereas the ionic conductivity increases. When the number of periods reaches 20, the activation energy is measured to be approximately 0.768 eV. The conductivity enhancement of(SDC/YSZ)N superlattice electrolyte film can be attributed to the large lattice mismatch near the interface between two different layers. That is to say, the interface between the highly dissimilar structures stabilizes a disordered oxygen sublattice with an increased number of oxygen vacancies, which promotes oxygen diffusion to increase the ionic conductivity of sample. Furthermore, the ionic conductivity of the(SDC/YSZ)20 film with a thickness ratio of m SDC: YSZ of 2:1 is much higher than that of the film witha thickness ratio of 1:1. Finally, it is noted that the STO buffer layer provides the proper lattice match for CeO2, inducing the good epitxial growth of superlattice electrolyte film(SDC/YSZ)20. And the conductivity enhancement could be attributed to the increase of SDC thickness in a bilayer. Therefore,(SDC/YSZ)20 superlattice electrolyte film is more ideal low-temperature fuel cell electrolyte material due to higher ionic conductivity.
Signal-to-noise ratio of spin noise spectroscopy in rubidium vapor
Spin noise spectroscopy is a non-demolition technique to detect the spin dynamics, and it is a good way to realize spin property under thermal equilibrium. Since spin noise arises from spin fluctuation at thermal equilibrium, it is a weak signal, therefore, various methods are used to enhance the signal-to-noise ratio(SNR) of the measurement system. To study the influence from different factors on the quality of spin noise spectroscopy, we report spin noise spectroscopy measurements in Rubidium vapor with three methods: a commercial frequency analyzer, a data acquisition card(DAC) with fast Fourier transform(FFT) done by a computer, and a DAC with real-time FFT based on FPGA(field-programmable gate array), respectively. According to the experimental results, we discuss several parameters and their influences on the SNR of the spectrum, including spectrum accumulation time, measurement efficiency and acquisition resolution. We find that the accumulation time is the most important factor for achieving high-quality spectrum. Measurement efficiency indicates how a good quality of the spin noise spectroscopy can be achieved in a finite time period, and we make a comparison of measurement efficiency among three methods. However, improvement of acquisition resolution does not make much more contribution to the quality of spin noise spectroscopy. Taken all into account, the DAC with real-time FFT performs best due to its bigger data utilization ratio, higher measurement efficiency and the multiplex advantage, thus it is more helpful for spin noise spectroscopy measurement in the study of spin dynamics.
Transmission characteristics of surface plasmon polaritons in “θ”-shaped resonator
To improve the efficiency of transmission, in this paper, we propose a structure of the surface plasmon polariton embedded in a sliver circular resonator with a sliver nanoellispod(“θ”-shaped resonator), and also investigate its optical properties by the finite element method. Firstly, we study the optical properties of “θ”-shaped resonator at a=120 nm and θ=0° with different values of b. The results show that the “θ”-shaped resonator structure has the narrow transmission peaks, and the transmittance spectrum can be tuned by modifying the structure parameters. So this nanostructure would find applications in the designing of the novel filter. Secondly, compared with the former Fano resonance which results from the localized plasmon resonance coupling, the Fano resonance which results from the resonance of the surface plasmon polaritons coupling is represented by this structure. When the symmetry of “θ”-shaped resonator is broken, the Fano resonance will be observed clearly. Like the Fano resonance which results from the localized plasmon resonance coupling between the bright mode of metallic nanostructure and the dark mode of metallic nanostructure, the results show that the dipolar, quadrupolar, and octupolar Fano resonances of “θ”-shaped resonator structure occur, which are caused by the destructive interference between the bright dipolar mode and the dark dipolar mode, quadrupolar mode, and octupolar mode. When we take the rotation angle θ as 0° and 90°, 15° and 75°, 30° and 90° respectively, the Fano asymmetric transmittance spectra of “θ”-shaped resonator are similar, which result from the same degree of asymmetry. The larger the degree of asymmetry of the “θ”-shaped resonator structure, the more obvious the Fano resonance is. Thirdly, the size of this structure has significant effects on the transmission peak positions, line width, and intensity of the Fano resonance, in particular, in the case that θ=0° corresponds to the generation of FR(FR on) and in the case corresponding to the vanishing of FR(FR off). therefore, this phenomenon of “θ”-shaped resonator will provide a new strategy for the surface plasmon polariton Fano switch. We hope that this nanostructure has potential applications in designing filter, biological sensors, and Fano switch.
Enhancement of tandem organic light-emitting diode performance by inserting an ultra-thin Ag layer in charge generation layer
White organic light-emitting diodes (WOLEDs) have attracted both scientific and industrial interest in the solidstate lighting and display applications due to their exceptional merits,such as high luminances,low power consumptions, high efficiencies,fast response times,wide-viewing angles,flexibilities and simple fabrications.The power efficiency of WOLED has been step-by-step improved in the last 20 years,however,the lifetime of WOLED is still unsatisfactory, which greatly restricts the further development of WOLED.In general,the tandem structure can be used to obtain high-efficiency and long-lifetime WOLED.One of the most important features of this kind of structure is that the different-colors emitting units can be connected by the charge generation layer.Therefore,the key to achieving a highperformance tandem device is how to design the charge generation layer.In this paper,we first develop a tandem green OLED by using an effective charge generation layer with an ultra-thin Ag layer between 4,7-diphenyl-1,10-phenanthroline:CsCO3 and hexaazatriphenylenehexacabonitrile,achieving high luminance,low voltage,high efficiency and long lifetime.The green tandem device with ultra-thin Ag layer (device C) obtains a highest luminance of 290000 cd/m2,which is 1.4 and 1.9 times higher than those of the tandem devices without ultra-thin Ag (device B) and singleunit device (device A),respectively.The driving voltage of device C is 7.2 V at 1000 cd/m2,1.4 V lower than that of device B.Besides,the maximum current efficiency of device C is 60.4 cd/A,which is 2.4% and 220% higher than those of device B (59 cd/A) and device A (18.7 cd/A),respectively.The power efficiency of device C is 26 lm/W,which is 21% higher than that of device B (21.5 lm/W).Moreover,the lifetime (T80) of device C reaches 250 h at an initial luminance of 10000 cd/m2,which is nearly 100 times higher than that of device B (2.7 h).Finally,we fabricate a white tandem device with the optimized charge generation layer,achieving a current efficiency and power efficiency of 75.9 cd/A and 36.1 lm/W at 1000 cd/m2,respectively.In addition,the lifetime (T80) is 77 h at an initial luminance of 10000 cd/m2.All the excellent performances are ascribed to the introduction of the ultra-thin Ag layer into the charge generation layer, which can effectively block the charge generation layer from diffusing.This exciting discovery can provide an effective way to design efficient and stable WOLED,which is beneficial to the solid-state lighting and display markets.
Ferromagnetism of Al-doped 6H-SiC and theoretical calculation
SiC with d0 ferromagnetism is thought to be one of the most important materials in the spintronics field, and it has received widespread attention. In this paper, Al: SiC magnetic powder is fabricated by high temperature calcination method with the protection of Ar gas. X-ray diffraction results show that the obtained powder is of 6H-SiC phase, and Al is proposed to enter into the 6H-SiC crystalline. Raman results show that Ar gas plays a crucial role in impeding the SiC from decomposing at high temperature. With the protection of Ar gas, it maintains round shape after calcination about 2200℃, no any other peakis detected in the Raman spectrum. Without the protection of Ar gas, SiC particle would decompose into graphite, and the instinct peak of graphite is detected in the Raman spectrum. Energy dispersive spectrometer results show that there is 0.96 at% Al in the powder. The obtained powder shows magnificent magnetic hysteresis loop and large coercive force. Its saturation magnetic moment reaches 0.07 emu/g after calcination at 1800℃. Its coercive force reaches a maximum after calcination at 2000℃, while the saturation magnetic moment is 0.012 emu/g. With the rise of calcination temperature, the magnetism of the powder changes from diamagnetism to ferromagnetism. But when the calcination temperature rises to 2200℃ or more, it would change back to diamagnetism. The phenomenon of ferromagnetism disappearing is similar to that in ZnO as reported. The total quantity of magnetic impurities(Fe, Co, Ni) is evaluated to be less than 5 ppm. Saturation magnetic moments arising from these impurities can be calculated to be less than 10-5 emu/g according to the reported results, which is impossible to affect the accuracy in the experiment. Thus it is proposed that the ferromagnetism originates from the doping of Al in SiC powder. To understand the origin of the observed magnetism, we carry out first principles calculations based on spin polarized density functional theory. All the calculations are performed by using the generalized gradient approximation in the form of the Perdew-Burke-Ernzerhof function, which is implemented in the Viemma ab initio simulation package. A supercell consisting of 3×3×1 unit cells of 6H-SiC containing one AlSi-VSi, corresponding to a defect concentration of 0.93 at%, is built for calculations. The origin of its ferromagnetism is studied, and its spin situation in the space is mapped. The results show that the combination of Al and vacancy leads to a local magnetic moment of 1.0 μB, and magnetic coupling is steady in the c axis direction. It is found that the p electron of carbon is the origin of the net spin.
Large enhanced perpendicular magnetic anisotropy and thermal stability in Ta/CoFeB/MgO films with excess boron
The discovery of perpendicular magnetic anisotropy(PMA) in Ta/CoFeB/MgO film and the demonstration of high performance perpendicular magnetic tunnel junction(p-MTJ) based on this material system have accelerated the development of the next-generation high-density non-volatile memories and other spintronic devices. Currently it is urgently needed to improve the interfacial PMA and thermal stability of the CoFeB/MgO system for practical applications. So far, the perpendicularly magnetized CoFeB/MgO films and the corresponding p-MTJs have been extensively explored with the B content of the CoFeB layer mostly fixed at about 20 atomic percent. In this paper, four sets of multilayered films Ta/(Co0.5Fe0.5)1-xBx/MgO(x=0.1, 0.2, 0.3) and MgO/(Co0.5Fe0.5)0.7B0.3/Ta with different CoFeB thickness are deposited on thermally oxidized Si substrates by magnetron sputtering at room temperature, and subsequently they are annealed in high vacuum at different temperatures ranging from 573 to 623 K. The room temperature magnetic properties of the annealed samples are characterized by using vibrating sample magnetometer and superconducting quantum interference device magnetometer.
With normal B content of 20% for the CoFeB layer, the Ta/CoFeB/MgO structure annealed at 573 K shows perpendicular magnetization when the CoFeB layer is no thicker than 1.2 nm. As the B content decreases to 10%, it has been found that PMA is achieved only in the sample with a 0.8 nm CoFeB layer under the same annealing condition. The result shows that the interfacial PMA appreciably falls off when the B content is reduced by half. On the other hand, when the B content of the CoFeB layers increases from 20% to 30%, the Ta/CoFeB/MgO structure annealed at 573 K exhibits PMA with the CoFeB layer as thick as 1.4 nm and the interfacial PMA(Ks) increases from 1.7×10-3 J·m-2 to 1.9×10-3 J·m-2 together with slightly improved thermal stability. Most remarkably, the MgO/CoFeB/Ta structure with 30% B shows optimum annealing temperature of about 623 K, at which Ks reaches 2.0×10-3J·m-2 and PMA is realized in the samples with the CoFeB thickness up to 1.5 nm. In contrast, the same structure with 20% B is magnetically destroyed completely under this annealing temperature. The present results suggest that the CoFeB layer with excess B can effectively improve the perpendicular magnetic properties and thermal stability for the Ta/CoFeB/MgO system, and one should take into account the B content effect to optimize the spintronic devices based on the perpendicularly magnetized CoFeB/MgO system.
Theory of very low frequency/extra low frequency radiation by dual-beam beat wave heating ionosphere