Manipulating magnetic anisotropy and ultrafast spin dynamics of magnetic nanostructures
We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TRMOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials.
Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface
Observation of mode-like features in tunneling spectra of iron-based superconductors
We report scanning tunneling microscopy/spectroscopy (STM/STS) studies on iron-based superconductors of Ba1-xKxFe2As2 and nearly optimally doped Fe(Te,Se). Mode-like features were observed universally outside the superconducting gaps in the tunneling spectra, which are similar to our previous observations in other samples and can be ascribed to the interaction between electrons and spin excitations. Furthermore, an almost linear relationship between the superconducting gaps and the superconducting transition temperatures was noted and should also be taken into account in understanding the mechanism of iron-based superconductors.
Temperature dependence of multi-jump magnetic switching process in epitaxial Fe/MgO (001) films
Characterizing silicon intercalated graphene grown epitaxially on Ir films by atomic force microscopy
An efficient method based on atomic force microscopy (AFM) has been developed to characterize silicon intercalated graphene grown on single crystalline Ir(111) thin films. By combining analyses of the phase image, force curves, and friction–force mapping, acquired by AFM, the locations and coverages of graphene and silicon oxide can be well distinguished. We can also demonstrate that silicon atoms have been successfully intercalated between graphene and the substrate. Our method gives an efficient and simple way to characterize graphene samples with interacted atoms and is very helpful for future applications of graphene-based devices in the modern microelectronic industry, where AFM is already widely used.
Improved performance of microcrystalline silicon solar cell with graded-band-gap silicon oxide buffer layer
Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer
A novel transient rotor current control scheme of a doubly-fed induction generator equipped with superconducting magnetic energy storage for voltage and frequency support
Stochastic stability of the derivative unscented Kalman filter
An efficient locally one-dimensional finite-difference time-domain method based on the conformal scheme
Quantum nonlocality of generic family of four-qubit entangled pure states
We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states |Gabcd> [Phys. Rev. A 65 052112 (2002)] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called “four-qubit the maximally entangled state |Gm>” and it is also violated by four-qubit W state and a special family of states |Gab00>. Moreover, a useful entanglement-nonlocality relationship for the family of states |Gab00> is derived. Finally, we present a scheme of preparation of the state |Gm ightangle with linear optics and cross-Kerr nonlinearities.
Detection of the ideal resource for multiqubit teleportation
A compact Einstein–Podolsky–Rosen entangled light source
Explicit solution of diffusion master equation under the action of linear resonance force via the thermal entangled state representation
Quantum mechanical operator realization of the Stirling numbers theory studied by virtue of the operator Hermite polynomials method
Time evolution of a squeezed chaotic field in an amplitude damping channel when used as a generating field for a squeezed number state
Nonlocal multi-target controlled—controlled gate using Greenberger–Horne–Zeilinger channel and qutrit catalysis
Multi-user quantum key distribution with collective eavesdropping detection over collective-noise channels
Direct measurement of the concurrence for two-qubit electron spin entangled pure state based on charge detection
Quantum state transfer between atomic ensembles trapped in separate cavities via adiabatic passage
Nonlinear tunneling through a strong rectangular barrier
Hawking radiation of stationary and non-stationary Kerr–de Sitter black holes
Rotational stretched exponential relaxation in random trap-barrier model
The relaxation behavior of complex-disordered systems, such as spin glasses, polymers, colloidal suspensions, structural glasses,and granular media, has not been clarified. Theoretical studies show that relaxation in these systems has a topological origin. In this paper, we focus on the rotational stretched exponential relaxation behavior in complex-disordered systems and introduce a simple phase space model to understand the mechanism of the non-exponential relaxation of these systems. By employing the Monte Carlo simulation method to the model, we obtain the rotational relaxation function as a function of temperature. We show that the relaxation function has a stretched exponential form under the critical temperature while it obeys the Debye law above the critical temperature.
Multifractal analysis of white matter structural changes on 3D magnetic resonance imaging between normal aging and early Alzheimer's disease
Applications of multifractal analysis to white matter structure changes on magnetic resonance imaging (MRI) have recently received increasing attentions. Although some progresses have been made, there is no evident study on applying multifractal analysis to evaluate the white matter structural changes on MRI for Alzheimer's disease (AD) research. In this paper, to explore multifractal analysis of white matter structural changes on 3D MRI volumes between normal aging and early AD, we not only extend the traditional box-counting multifractal analysis (BCMA) into the 3D case, but also propose a modified integer ratio based BCMA (IRBCMA) algorithm to compensate for the rigid division rule in BCMA. We verify multifractal characteristics in 3D white matter MRI volumes. In addition to the previously well studied multifractal feature, Δα, we also demonstrated Δf as an alternative and effective multifractal feature to distinguish NC from AD subjects. Both Δα and Δf are found to have strong positive correlation with the clinical MMSE scores with statistical significance. Moreover, the proposed IRBCMA can be an alternative and more accurate algorithm for 3D volume analysis. Our findings highlight the potential usefulness of multifractal analysis, which may contribute to clarify some aspects of the etiology of AD through detection of structural changes in white matter.
Compression and stretching of ring-vortex solitons in a bulk nonlinear medium
Compression and stretching of ring-vortex solitons, which is a novel self-similar solution of (2+1)-dimensional diffraction decreasing waveguide, is investigated analytically and numerically. We obtain the ring-vortex solitons via the similarity transformation method. The distance modulation for the width, the diffraction, and the nonlinear response, strongly affects the form and the behavior of the self-similar vortex, and facilitates the efficient compression of optical waves. This approximate ring-vortex solitons can reflect the real properties of self-similar optical vortex beams during propagation under certain parameter window selection. Specific examples and figures are given to illustrate discussed features. The results obtained in this paper may have potential values for all-optical data-processing schemes and the design of beam compressors and amplifiers.
Effects of evacuation assistant's leading behavior on the evacuation efficiency: Information transmission approach
Synthesis mechanism of heterovalent Sn2O3 nanosheets in oxidation annealing process
Output power analyses of an endoreversible Carnot heat engine with irreversible heat transfer processes based on generalized heat transfer law
Recent improvements on the atomic fountain clock at SIOM
Optimal migration path of Ag in HfO2: A first-principles study
Dependence of above-threshold ionization spectrum on polarization directions of two-color laser fields
Using the frequency-domain theory, we investigate the above-threshold ionization (ATI) process of an atom in two-color laser fields. When both photon energies of the two-color laser fields are much smaller than the atomic ionization threshold, the ATI spectrum depends on the angle between the two lasers' polarization directions. While when the photon energy of one laser is comparable with or larger than the atomic ionization threshold, the ATI spectrum is independent of the angle, and only several dips appear at certain angles. By analyzing the contributions of different quantum channels, we find that, for the case that both frequencies of the two color lasers are low, the quantum interferences between the channels are strong, and hence the spectrum changes with the angle between the two lasers' polarization directions. While for the case that the frequency of one of the two color lasers is high, the contributions of the channels to the ATI spectrum decrease dramatically with increasing channel order, hence the interferences between the channels disappear, and the ATI spectrum has a step-like structure, which is independent of the angle between the two lasers' polarizations. These results can shed light on the study of the corresponding relation between classical and quantum mechanisms of the matter–laser interaction in high-frequency laser fields.
Quantum path control and isolated attosecond pulse generation in the combination of near-infrared and terahertz pulses
We present an efficient and realizable scheme for the generation of an ultrashort single attosecond (as) pulse from H atom with a 800-nm fundamental laser field combined with a terahertz (THz) field. The high-order harmonic generation (HHG) can be obtained by solving the time-dependent Schrödinger equation accurately and efficiently with time-dependent generalized pseudo-spectral (TDGPS) method. The result shows that the plateau of high-order harmonics is extended and the broadband spectra can be produced by the combined laser pulse, which can be explained by the corresponding ionization probability. The time–frequency analysis and semi-classical three-step model are also presented to further investigate this mechanism. Besides, by the superposition of the harmonics near the cutoff region, an isolated 133-as pulse can be obtained.
Assignment of terahertz vibrational modes of L-glutamine using density functional theory within generalized-gradient approximation
Influence of electron correlations on double-capture process in proton helium collisions
Theoretical study on photorecombination of C V ion
Giant transmission Goos–Hänchen shift in surface plasmon polaritons excitation and its physical origin
Coherence transfer from 1064 nm to 578 nm using an optically referenced frequency comb
A laser at 578 nm is phase-locked to an optical frequency comb (OFC) which is optically referenced to a subhertz-linewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavity-stabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3× 10-15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.
Relationship between electromagnetically-induced transparency and Autler–Townes splitting in a Doppler-broadened system
Image information transfer via electromagnetically induced transparency-based slow light
Multi-level effects in the high-order harmonic generation driven by intense frequency-comb laser fields
High harmonic generation (HHG) driven by intense frequency-comb laser fields can be dramatically enhanced via multiphoton resonance by tuning the carrier-envelope phase (CEP) shift, without increasing the driving intensity. However, the multiphoton-resonant enhancement (MRE) factor in the realistic atomic hydrogen is much smaller than that in a two-level system. To study the deviation, we present a theoretical investigation of the multiphoton resonance dynamics of three-level systems driven by intense frequency-comb laser fields. The many-mode Floquet theorem (MMFT) is employed to provide a nonperturbative and exact treatment of the interaction between the quantum system and the laser fields. The investigations show that the dipole interaction of a two-level system with the third level affects the multiphoton resonance dynamics and enhances the HHG spectra. It is the dipole interaction of the excited level of the two-level system with other levels that results in the smaller MRE factor in the realistic atomic system.
Absorption enhancement and sensing properties of Ag diamond nanoantenna arrays
Influences of cavity dispersion distribution on the output pulse properties of an all-normal-dispersion fiber laser
In this paper, the influences of the dispersion distribution in the cavity on the output pulse properties of the all-normal-dispersion (ANDi) fiber laser are investigated. Our simulations show that, as the relative length of the dispersion fiber increases, the temporal width and the spectral bandwidth of the output pulse for an ANDi fiber laser with fixed total cavity dispersion or fiber length are decreased, while the pulse energy is enhanced and the compressed pulse width is increased. These simulation predictions have been proved by our experimental results. The reason may be that the nonlinear phase shift accumulated in the nonlinear fiber is more than that in the dispersion fiber if they have the same length.
An accurate and stable method of array element tiling for high-power laser facilities
Grazing bifurcation analysis of a relative rotation system with backlash non-smooth characteristic
Stabilizing effect of plasma discharge on bubbling fluidized granular bed
Fluidized beds have been widely used for processing granular materials. In this paper, we study the effect of plasma on the fluidization behavior of a bubbling fluidized bed with an atmospheric pressure plasma discharger. Experiment results show that the bubbling fluidized bed is stabilized with the discharge of plasma. When the discharge current reaches a minimum stabilization current Cms, air bubbles in the bed will disappear and the surface fluctuation is completely suppressed. A simplified model is proposed to consider the effect of electric Coulomb force generated by the plasma. It is found that the Coulomb force will propel the particles to move towards the void area, so that the bubbling fluidized bed is stabilized with a high enough plasma discharge.
A new mixed subgrid-scale model for large eddy simulation of turbulent drag-reducing flows of viscoelastic fluids
A mixed subgrid-scale (SGS) model based on coherent structures and temporal approximate deconvolution (MCT) is proposed for turbulent drag-reducing flows of viscoelastic fluids. The main idea of the MCT SGS model is to perform spatial filtering for the momentum equation and temporal filtering for the conformation tensor transport equation of turbulent flow of viscoelastic fluid, respectively. The MCT model is suitable for large eddy simulation (LES) of turbulent drag-reducing flows of viscoelastic fluids in engineering applications since the model parameters can be easily obtained. The LES of forced homogeneous isotropic turbulence (FHIT) with polymer additives and turbulent channel flow with surfactant additives based on MCT SGS model shows excellent agreements with direct numerical simulation (DNS) results. Compared with the LES results using the temporal approximate deconvolution model (TADM) for FHIT with polymer additives, this mixed SGS model MCT behaves better, regarding the enhancement of calculating parameters such as the Reynolds number. For scientific and engineering research, turbulent flows at high Reynolds numbers are expected, so the MCT model can be a more suitable model for the LES of turbulent drag-reducing flows of viscoelastic fluid with polymer or surfactant additives.
Nano watermill driven by revolving charge
A novel nanoscale watermill for the unidirectional transport of water molecules through a curved single-walled carbon nanotube (SWNT) is proposed and explored by molecular dynamics simulations. In this nanoscale system, a revolving charge is introduced to drive a water chain confined inside the SWNT, the charge and the tube together serving as a nano waterwheel and nano engine. A resonance-like phenomenon is found, and the revolving frequency of the charge plays a key role in pumping the water chain. The water flux across the SWNT increases with respect to the revolving frequency of the external charge and it reaches its maximum when the frequency is 4 THz. Correspondingly, the number of hydrogen bonds in the water chain inside the SWNT decreases dramatically as the frequency increases from 4 THz to 25 THz. The mechanism behind the resonance phenomenon has been investigated systematically. Our findings are helpful for the design of nanoscale fluidic devices and energy converters.
Dynamics of laser beams in inhomogeneous electron—positron—ion plasmas
Effects of N2/O2 flow rate on the surface properties and biocompatibility of nano-structured TiOxNy thin films prepared by high vacuum magnetron sputtering
NiTi shape memory alloys (SMA) have many biomedical applications due to their excellent mechanical and biocompatible properties. However, nickel in the alloy may cause allergic and toxic reactions, which limit some applications. In this work, titanium oxynitride films were deposited on NiTi samples by high vacuum magnetron sputtering for various nitrogen and oxygen gas flow rates. The x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) results reveal the presence of different phases in the titanium oxynitride thin films. Energy dispersive spectroscopy (EDS) elemental mapping of samples after immersion in simulated body fluids (SBF) shows that Ni is depleted from the surface and cell cultures corroborate the enhanced biocompatibility in vitro.
Continuous operation of 2.45-GHz microwave proton source for 306 hours with more than 50 mA DC beam
This paper describes a long-term operation of the 2.45-GHz microwave proton source at Peking University. The DC proton beam of 50–55 mA with energy of 35 keV has been run for 306 hours continuously. Total beam availability, defined as 35-keV beam-on time divided by elapsed time, is higher than 99%. Water cooling machine failures cause all the downtime, and no plasma generator failure or high voltage breakdown is observed. The longest uninterrupted run time is 122 hours.
Modeling of the nanoparticle coagulation in pulsed radio-frequency capacitively coupled C2H2 discharges
Using a Mach–Zehnder interferometer to deduce nitrogen density mapping
Helix unwinding in ferroelectric liquid crystals induced by tilted electric field
Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.
Visible to deep ultraviolet range optical absorption of electron irradiated borosilicate glass
Microstructure evolution of Cu atomic islands on liquid surfaces in the ambient atmosphere
Electric field effect in ultrathin zigzag graphene nanoribbons
Subthreshold behavior of AlInSb/InSb high electron mobility transistors
Theoretical investigation of sulfur defects on structural, electronic, and elastic properties of ZnSe semiconductor
Load-redistribution strategy based on time-varying load against cascading failure of complex network
Effects of energy dissipation on anisotropic materials
A model and its simulations are presented to describe the effects of energy dissipation on anisotropic systems. When the current electromigration is constant, energy dissipation depends on lattice constants, resistivity, and the angles along the longitudinal and transversal directions. It is shown that an orientation variation of the grain can significantly influence the energy dissipation for some anisotropic materials. Based on calculations for the grain model, the mechanism of grain growth and microstructure evolution under electromigration is explained. Theoretical implications about material selection and reliability are derived.
Nondestructive measurement of thermal contact resistance for the power vertical double-diffused metal-oxide-semiconductor
Phase diagram and collective modes in Rashba spin–orbit coupled BEC: Effect of in-plane magnetic field
We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave (PW) phase, striped wave (SW) phase, and zero momentum (ZM) phase. It was shown that with a growing in-plane field, both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.
Unusual structural properties of polymers confined in a nanocylinder
Structural properties of polymers confined in nanocylinders are investigated by Monte Carlo simulation, which is successfully used to consider the conformational property of constrained polymers. The conformational properties of the polymers close to the walls exhibit different features. The density profiles of polymers are enhanced near the wall of the nanocylinder, which shows that the packing densities differ near the wall and far from the wall. The highest densities near the wall of the nanocylinder decrease with increasing radius of the nanocylinder. Furthermore, the density excess is not only near the wall of the nanocylinder, but also shifts to the center of the nanocylinder at lower temperatures. The radius of gyration and the bond length of polymers in the nanocylinder show that the polymer chains tend to extend along the axis of the nanocylinder in highly confined nanocylinder and contract at lower temperature. Our results are very helpful in understanding the packing induced physical behaviors of polymers in nanocylinders, such as glass transition, crystallization, etc.
New method for fast morphological characterization of organic polycrystalline films by polarized optical microscopy
A new method to visualize the large-scale crystal grain morphology of organic polycrystalline films is proposed. First, optical anisotropic transmittance images of polycrystalline zinc phthalocyanine (ZnPc) films vacuum deposited by weak epitaxial growth (WEG) method were acquired with polarized optical microscopy (POM). Then morphology properties including crystal grain size, distribution, relative orientation, and crystallinity were derived from these images by fitting with a transition dipole model. At last, atomic force microscopy (AFM) imaging was carried out to confirm the fitting and serve as absolute references. This method can be readily generalized to other organic polycrystalline films, thus providing an efficient way to access the large-scale morphologic properties of organic polycrystalline films, which may prove to be useful in industry as a film quality monitoring method.
Structure-dependent metal—insulator transition in one-dimensional Hubbard superlattice
Stacking fault energy, yield stress anomaly, and twinnability of Ni3Al: A first principles study
Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of Ni3Al. The antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies, and twinning energies decrease slightly with temperature. Temperature dependent anomalous yield stress of Ni3Al is predicted by the energy-based criterion based on elastic anisotropy and antiphase boundary energies. It is found that p increases with temperature and this can give a more accurate description of the anomalous yield stress in Ni3Al. Furthermore, the predicted twinnablity of Ni3Al is also decreasing with temperature.
Enhanced coercivity and remanence of PrCo5 nanoflakes prepared by surfactant-assisted ball milling with heat-treated starting powder
PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly in the ranges of 50–100 nm and 0.5–3 μm, respectively. The x-ray diffraction patterns demonstrate that the heat treatment can increase the single phase and crystallinity of the PrCo5 compound, and combined with the demagnetization curves, indicate that the single phase and crystallinity are important for preparing high-coercivity and strong-textured rare earth permanent magnetic nanoflakes. In addition, the coercivity mechanism of the as-milled PrCo5 nanoflakes is studied by the angle dependence of coercivity for an aligned sample and the field dependence of coercivity, isothermal (IRM) and dc demagnetizing (DCD) remanence curves for an unaligned sample. The results indicate that the coercivity is dominated by co-existing mechanisms of pinning and nucleation. Furthermore, exchange coupling and dipolar coupling also co-exist in the sample.
Electronic and optical properties of lithium niobate under high pressure: A first-principles study
High performance trench MOS barrier Schottky diode with high-k gate oxide
A novel trench MOS barrier Schottky diode (TMBS) device with a high-k material introduced into the gate insulator is reported, which is named high-k TMBS. By simulation with Medici, it is found that the high-k TMBS can have 19.8% lower leakage current while maintaining the same breakdown voltage and forward turn-on voltage compared with the conventional regular trench TMBS.
Au and Ti induced charge redistributions on monolayer WS2
Coherent and tunable radiation with power enhancement from surface plasmon polaritons
A low-threshold nanolaser based on hybrid plasmonic waveguides at the deep subwavelength scale
Energy distribution extraction of negative charges responsible for positive bias temperature instability
A new method is proposed to extract the energy distribution of negative charges, which results from electron trapping by traps in the gate stack of nMOSFET during positive bias temperature instability (PBTI) stress based on the recovery measurement. In our case, the extracted energy distribution of negative charges shows an obvious dependence on energy, and the energy level of the largest energy density of negative charges is 0.01 eV above the conduction band of silicon. The charge energy distribution below that energy level shows strong dependence on the stress voltage.
A novel physical parameter extraction approach for Schottky diodes
Modulation of WNx/Ge Schottky barrier height by varying N composition of tungsten nitride
Temperature-dependent bias-stress-induced electrical instability of amorphous indium-gallium-zinc-oxide thin-film transistors
The time and temperature dependence of threshold voltage shift under positive-bias stress (PBS) and the following recovery process are investigated in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors. It is found that the time dependence of threshold voltage shift can be well described by a stretched exponential equation in which the time constant τ is found to be temperature dependent. Based on Arrhenius plots, an average effective energy barrier Eτstress= 0.72 eV for the PBS process and an average effective energy barrier Eτrecovery= 0.58 eV for the recovery process are extracted respectively. A charge trapping/detrapping model is used to explain the threshold voltage shift in both the PBS and the recovery process. The influence of gate bias stress on transistor performance is one of the most critical issues for practical device development.
Effect of interfacial coupling on rectification in organic spin rectifiers
The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases.
Optimization of intergrain connection in high-temperature superconductor Bi2Sr2CaCu2Ox
Tuning the magnetic anisotropy of CoFeB grown on flexible substrates
The magnetic properties of CoFeB thin films grown on flexible polyimide substrates were investigated using a magneto-optical Kerr effect magnetometer. In-plane uniaxial magnetic anisotropy was observed in the virgin state. The strain induced by bending the flexible substrate was applied on the sample to change the magnetic properties of CoFeB. The strain induced uniaxial magnetic anisotropy changed linearly with the deformation by about 8.41×104 erg/cm3 at 1% of deformation. Our results prove the magnetic properties of CoFeB grown on flexible polyimide substrate can be tuned effectively by bending, which could be important for future flexible spintronics.
Anomalous microstructure and magnetocaloric properties in off-stoichiometric La–Fe–Si and its hydride
FePt nano-stripes fabricated on anodic aluminum oxide templates
Equivalent circuit model including magnetic and thermo sources for the thermo–magneto–electric coupling effect in magnetoelectric laminates
Piezoelectric and electro—optic properties of tetragonal (1-x)Pb(Mg1/3Nb2/3)O3—xPbTiO3 single crystals by phenomenological theory
An eighth-order Landau–Devonshire theory is constructed to investigate the piezoelectric and electro–optic properties of tetragonal (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals (x=0.38 and x=0.4). The dielectric stiffness coefficients of the Landau potential are obtained by fitting to the dielectric properties and the phase transition temperature between cubic phase and tetragonal phase. It is indicated that tetragonal (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the first-order cubic-tetragonal phase transitions. The dielectric constants are in great agreement with the experimental results. The piezoelectric coefficients d33 and d31 at room temperature are about 145 pC/N and -62 pC/N respectively which are smaller than that of (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals around the morphotropic phase boundary. Moreover, tetragonal (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the linear electro–optic coefficients rc=33.7 pm/V and rc=28.8 pm/V for x=0.38 and x=0.4, respectively which are in accordance with the measurements.
Theoretical analysis of semi/non-polar InGaN/GaN light-emitting diodes grown on silicon substrates
Linear optical properties of defective KDP with oxygen vacancy: First-principles calculations
The linear optical properties of potassium dihydrogen phosphate (KDP) with oxygen vacancy are investigated with first-principles density functional theory calculations. We use Heyd–Scuseria–Ernzerhof (HSE06) functional to calculate the linear optical properties because of its accuracy in the band gap calculation. Compared with the perfect KDP, we found that due to the defect states located at the band gap, the defective KDP with oxygen vacancy has new optical adsorption within the energy region from 4.8 eV to 7.0 eV (the corresponding wavelength region is from 258 nm to 177 nm). As a result, the oxygen vacancy can decrease the damage threshold of KDP crystal. It may give a direction to the KDP production for laser system.
Real-time quantitative optical method to study temperature dependence of crack propagation process in colloidal photonic crystal film
A real-time quantitative optical method to characterize crack propagation in colloidal photonic crystal film (CPCF) is developed based on particle deformation models and previous real-time crack observations. The crack propagation process and temperature dependence of the crack propagation rate in CPCF are investigated. By this method, the crack propagation rate is found to slow down gradually to zero when cracks become more numerous and dense. Meanwhile, with the temperature increasing, the crack propagation rate constant decreases. The negative temperature dependence of the crack propagation rate is due to the increase of van der Waals attraction, which finally results in the decrease of resultant force. The findings provide new insight into the crack propagation process in CPCF.
Doping inhomogeneity and staging of ultra-thin graphite intercalation compound flakes probed by visible and near-infrared Raman spectroscopy
When ultra-thin graphite intercalation compounds (GICs) are deposited on the SiO2/Si substrate, it is found that their colors are dependent on the thickness of GIC flakes. The sample colors of ultrathin GIC flakes can no longer provide qualitative information on the stage index. Here, multi-wavelength Raman spectroscopy is thus applied to study the doping inhomogeneity and staging of ultra-thin GICs by FeCl3 intercalation. The G band intensity of stage-1 GIC flakes is strongly enhanced by 532-nm laser excitation, while that of stage-2 and stage-3 flakes exhibits strong intensity enhancement for 785-nm laser excitation. The near-infrared lasers are suggested to probe the doping inhomogeneity and staging of ultra-thin GIC flakes.
Influence of vacuum degree on growth of Bi2Te3 single crystal
Bi2Te3 single crystals were prepared by the solid-state reaction method. The effect of the vacuum on the growth of Bi2Te3 single crystals was studied with varying the oxygen content by controlling the air pressure in the silica tube. High quality Bi2Te3 single crystals have been obtained and there is no influence on the growth by an extremely small amount of oxygen in a high vacuum at 1.0 × 10-3 Pa. As the air pressure is increased at 1.0 × 10-2 Pa, oxygen only mainly impacts on the growth of the surface for the prepared samples. Micron-sized rod-like structure and flower-like clusters are observed on the surface. For the samples prepared at 1.0 × 10-1 Pa, x-ray diffraction data show that the yellow part on the surface is Bi2TeO5, while the Bi2Te3 single crystal is still the major phase as the inside part. More interestingly, various crystal morphologies are observed by scanning electron microscope for Bi2Te3 near the boundary between Bi2Te3 and Bi2TeO5. Possible growth mechanisms for Bi2Te3 with different morphologies are discussed in detail.
Normally-off metamorphic AlInAs/AlInAs HEMTs on Si substrates grown by MOCVD
Influence of Ag and Sn incorporation in In2S3 thin films
Preparation and characterization of PTFE coating in new polymer quartz piezoelectric crystal sensor for testing liquor products
Tip-splitting instability in directional solidification based on bias field method
Tip splitting instability of cellular interface morphology in directional solidification is analyzed based on the bias field method proposed recently by Glicksman. The physical mechanism of tip instability is explained by analyzing the interface potential, the tangential energy flux, and the normal energy flux. A rigorous criterion for tip-splitting instability is established analytically, i.e., the ratio of the cellular tip radius to the cellular width α > √3/2/π≈0.3899, which is in good agreement with simulation results. This study also reveals that the cellular tip splitting instability is attributable to weak Gibbs–Thomson energy acting on the interface.
Effects of physical parameters on the cell-to-dendrite transition in directional solidification
Synthesis of graphene-supported monodisperse AuPd bimetallic nanoparticles for electrochemical oxidation of methanol
Monodisperse AuPd bimetallic nanoparticles (NPs) with different compositions are synthesized by using oleylamine (OAm) as reducing reagent, stabilizer, and solvent. To obtain AuPd solid solution NPs, Pd–OAm and Au–OAm precursors are firstly prepared by mixing OAm with Palladium (II) acetylacetonate (Pd(acac)2) and HAuCl4, respectively. Then Pd–OAm and Au–OAm precursor solutions are injected into a hot oleylamine solution to form AuPd NPs. The size of these NPs ranges from 6.0 to 8.0 nm and the composition is controlled by varying the precursor ratio. The AuPd NPs are loaded onto reduced graphene oxide (RGO) sheets to make catalysts. Alloy NPs show high electrocatalytic activity and stability toward methanol oxidation in the alkaline media. Their catalytic activity for methanol oxidation is found to be dependent on the NP composition. As the Pd component increases, the peak current densities during the forward scan gradually increase and reach the maximum at AuPd2. The enhancement of alloy NPs for methanol oxidation can be attributed to a synergistic effect of Au and Pd on the surface of alloy NPs.
Instability of lithium bis(fluorosulfonyl)imide (LiFSI)–potassium bis(fluorosulfonyl)imide (KFSI) system with LiCoO2 at high voltage
Redox-mediated reversible modulation of the photoluminescence of single quantum dots
Nano structure evolution in P3HT:PC61BM blend films due to the effects of thermal annealing or by adding solvent
Crystallographic dynamics of blend films of regioregular poly(3-hexylthiophene) (P3HT) mixed with [6-6-]-phenyl-C61-butyric acid methyl ester (PC61BM) treated by thermal annealing or by adding solvent 1,8-diiodooctane (DIO) are characterized by 2D-grazing incidence x-ray diffraction (2D-GIXRD). The results show that the P3HT chains are primarily oriented with the thiophene ring edge-on to the substrate, with a small fraction of chains oriented plane-on. The interplanar spacing becomes narrow after being treated by DIO, and the coherence length of the P3HT crystallites increases after being treated by thermal annealing or DIO, which is accompanied by a change in the orientation angle of the P3HT lamellae. The increased ordering of P3HT packing induced by thermal annealing or adding DIO contributes to enhanced photovoltaic performance.
Low-Tc direct current superconducting quantum interference device magnetometer-based 36-channel magnetocardiography system in a magnetically shielded room
Characteristics of drain-modulated generation current in n-type metal-oxide-semiconductor field-effect transistor
Bandwidth improvement of high power uni-traveling-carrier photodiodes by reducing the series resistance and capacitance
A backside illuminated mesa-structure InGaAs/InP modified uni-traveling-carrier photodiode (MUTC-PD) with wide bandwidth and high saturation power is fabricated and investigated. The device structure is optimized to reduce the capacitance and resistance. For the 22-μm-diameter device, the maximum responsivity at 1.55 μm is 0.5 A/W, and the 3-dB cutoff frequency reaches up to 28 GHz. The output photocurrent at the 1-dB compression point is measured to be 54 mA at 25 GHz, with a corresponding output radio frequency (RF) power of up to 15.5 dBm. The saturation characteristics of the MUTC-PD are also verified by the electric field simulation, and electric field collapse is found to be the cause of the saturation phenomenon.
An improved recommendation algorithm viaweakening indirect linkage effect
Effect of body biasing on single-event induced charge collection in deep N-well technology
A novel multi-pin rectangular waveguide slow-wave structure based backward wave amplifier at 340 GHz