Search

The topological insulator has attracted increasing attention as a new state of quantum matter featured by the symmetry-protected edge states. Although the qualitative robustness of the edge states against local perturbations has been well established, it is not clear how these topological edge states respond quantitatively to a global perturbation. Here, we study the response of topological edge states in a HgTe quantum dot to an external in-plane electric field--a paradigmatic global perturbation in solid-state environments. We find that the stability of the topological edge state could be larger than that of the ground bulk state by several orders of magnitudes. This robustness may be verified by standard transport measurements in the Coulomb blockage regime. Our work may pave the way towards utilizing these topological edge states as stable memory devices for charge and/or spin information and stable emitter of single terahertz photons or entangled terahertz photon pairs for quantum communication. [ABSTRACT FROM AUTHOR]

The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS0, FS+, and FS2+ centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS 0 center) than that for electron-poor oxygen vacancies (FS+ and FS2+ centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster. [ABSTRACT FROM AUTHOR]

We investigated composite gratings for their sound transmission properties induced by phase resonances. Each periodic unit of the composite grating consisted of a rectangular slit and a triangular slit. The triangular slit showed special properties in generating enhanced phase resonance and in restraining sound transmission. By adjusting the triangular slit's opening, we could regulate the frequency and sound transmission at phase resonance. These features of the composite grating can be used in designing acoustic filters for sound reduction. [ABSTRACT FROM AUTHOR]

This work investigates the unsteady magnetohydrodynamic flow of generalized second grade fluid through a porous medium with Hall effects on heat and mass transfer. The second grade fluid with a fractional derivative is used for the constitutive equation. A second-order fractional backward difference formula in the temporal direction and a spectral collocation method in the spatial direction are proposed to solve the model numerically. In the numerical implementation, a fast method is applied to decrease the memory requirement and computational cost. The velocity, temperature, and concentration profiles are discussed through graphs. The effects of various parameters on the velocity profiles, temperature field, and concentration field are shown. Results indicate that as the fractional derivative γ increases and the Hall parameter m decreases, the amplitudes of the velocity components decrease. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have many potential applications, while the performances of TMDs are generally limited by the less surface active sites and the poor electron transport efficiency. Here, a novel three-dimensional (3D) structure of molybdenum disulfide (MoS2) with larger surface area was proposed based on first-principle calculations. 3D layered MoS2 structure contains the basal surface and joint zone between the different nanoribbons, which is thermodynamically stable at room temperature, as confirmed by first principles molecular dynamics calculations. Compared the two-dimensional layered structures, the 3D MoS2 not only owns the large surface areas but also can effectively avoid the aggregation. Interestingly, although the basal surface remains the property of the intrinsic semiconductor as the bulk MoS2, the joint zone of 3D MoS2 exhibits semimetallic, which is derived from degenerate 3d orbitals of the Mo atoms. The high stability, large surface area, and high conductivity make 3D MoS2 have great potentials as high performance catalyst [ABSTRACT FROM AUTHOR]

An acoustic sensor with composited transmission and reflecting structure is investigated for detection in liquid medium, in which a temperature compensational layer is deposited on the Si wafer to create a low temperature coefficient of frequency. This type of structure regulates most acoustic energy into the substrate, i.e., Si wafer and the compensational layer. Consequently, the standing resonant vibrations in the substrate are induced, as its thickness is integer multiples of a half wavelength. The acoustic sensor shows a low frequency shift with temperature, and the temperature coefficient of frequency can be controlled to about zero at the room temperature. Additionally, the acoustic sensor for the liquid detection on the viscosity and mass can be estimated 35 kHz/Pa . s and 23.25 kHz cm2/ng, respectively. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

Magnetostriction and its inverse effect (also referred to as a magnetomechanical effect) in the Tb0.3Dy0.7Fe2 alloy have been investigated based on the three dimensional Stoner–Wohlfarth model in this paper. The solutions of direction cosines of magnetization under a compressive stress and a field both applied along the [112] axis have been obtained by following a conventional minimization procedure in which the nonlinear equations for equilibrium conditions have been solved numerically. With a more accurate computation presented here, some new theoretical results have been achieved. These results are in good agreement with experimental observations reported previously. In the demagnetized state the resultant anisotropy for the alloy is determined by the combination of the magnetocrystalline and stress-induced anisotropy energies, and degenerates from cubic into uniaxial at a critical stress. When a field is applied to the alloy along the [112] axis, the alloy under the compressive stress is more difficult to magnetize and can attain a maximum change in bulk magnetostriction at the critical stress. The main reason for the large bulk magnetostriction is that the fractional occupancy of the [111] or [111]-oriented domains increases from 1/8 to 1/2 with the stress. This more accurate computation has been proposed for similar investigations and the results will also be helpful for a better understanding of the magnetostriction in materials such as the FeGa alloys. [ABSTRACT FROM AUTHOR]

Coherent control of two-photon fluorescence (TPF) of 2′,7′-dichlorofluorescein in methanol solution was experimentally investigated by shaping the femtosecond pulse with the phase jump. The experimental results indicated that the TPF intensity induced by the shaped femtosecond pulses with certain phase jump could be coherently enhanced. The physical mechanisms for TPF enhancement in the molecular system were explicitly discussed and analyzed, which could be attributed to the wave-packet constructive interference in the excited states. Finally, two phase-locked femtosecond pulses were used to explore the wave-packet constructive interference in the excited states of 2′,7′-dichlorofluorescein, which validate experimentally the proposed mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we present a feasible method to realize and improve the selective excitation of femtosecond coherent anti-Stokes Raman scattering (CARS) in a mixture. We theoretically show that, by shaping both the pump and probe pulses with the π phase step, the CARS signal from one quantum system can be enhanced and simultaneously that from the other quantum system is effectively suppressed. Comparing with only shaping the probe pulse [D. Oron, N. Dudovich, D. Yelin, and Y. Silberberg, Phys. Rev. Lett., 88, 063004 (2002)], the selectivity of femtosecond CARS by shaping both pump and probe pulses can be greatly improved. Finally, we experimentally compare two shaping schemes by investigating the selective excitation of the femtosecond CARS in the mixture of dibromomethane (CH2Br2) and chloroform (CHCl3). [ABSTRACT FROM AUTHOR]

Polycrystalline EuZn2Sb2 is prepared by direct reaction of the elements. Its composition, structure, magnetism, heat capacity, and thermoelectric properties have been investigated. EuZn2Sb2 crystallizes in p3m space group with a=4.4932(7) Å and c=7.6170(10) Å. Antiferromagnetic ordering is detected at the Nèel temperature of 13.06 K, and the saturation magnetization reaches 6.87μB/Eu at 2 K and 7 T. Eu ion has +2 valence. Its Hall effects are characterized by a high positive Hall coefficient of +0.226 cm3/C, proper carrier concentration of 2.77×1019/cm3, and high carrier mobility of 257 cm2/V s at 300 K. This compound shows high p-type Seebeck coefficient (+122 to +181 μV/K), low lattice thermal conductivity (1.60–0.40 W/m K), and high electrical conductivity (1137–524 S/cm). The obtained figure of merit and powder factor reach 0.92 and 20.72 μW/cm K2, respectively. The thermoelectric properties of EuZn2Sb2 are encouraging. [ABSTRACT FROM AUTHOR]

We report a coupling structure to realize tunable sound transmission in various frequency ranges. The structure, consisting of a flexible Helmholtz resonator and a waveguide, excites three main coupling modes that generate bandpass and bandstop filter effects. Importantly, the coupling modes are controlled by membrane tension or the device structure. These properties show that a tunable filter can be realized simply by regulating the coupling vibration states by changing the membrane tension with different electromagnetic forces. In applications, the flexible Helmholtz resonator operating at its multiple resonances can be fabricated on the sub-wavelength scale, making it easy to achieve acoustic devices with small size for noise suppression or sound control at low frequencies. [ABSTRACT FROM AUTHOR]

Due to the limitation of the hole injection, p-type doping is essential to improve the performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs). In this work, we propose and show a depletion-region Mg-doping method. Here we systematically analyze the effectiveness of different Mg-doping profiles ranging from the electron blocking layer to the active region. Numerical computations show that the Mg-doping decreases the valence band barrier for holes and thus enhances the hole transportation. The proposed depletion-region Mg-doping approach also increases the barrier height for electrons, which leads to a reduced electron overflow, while increasing the hole concentration in the p-GaN layer. Experimentally measured external quantum efficiency indicates that Mg-doping position is vitally important. The doping in or adjacent to the quantum well degrades the LED performance due to Mg diffusion, increasing the corresponding nonradiative recombination, which is well supported by the measured carrier lifetimes. The experimental results are well numerically reproduced by modifying the nonradiative recombination lifetimes, which further validate the effectiveness of our approach. [ABSTRACT FROM AUTHOR]

Cyanoketene (OCCHCN) has been reported as a potential alternative insulation gas for SF6 in Patent US0135817. Stationary point equilibrium geometries on the ground state have been optimized at the B3LYP/6-311+G(d,p) level, and the harmonic vibration frequencies are calculated at the same level. The HOMO-LUMO energy gaps (Eg), ionization potentials (IP), and electron affinities (EA) of the studied molecules are obtained. The minimum energy path (MEP) is obtained by the intrinsic reaction coordinate (IRC) theory, and the energetic information is further refined by QCISD(T) (single-point) method. The results show that OCCHCN can be used as SF6 alternative insulation gas in high voltage equipment according to potential energy surface analysis. As the isomerization and the cleavage reactions potential barriers are lower than the Eg and IP values, resulting in OCCHCN is not easy to be ionized and excited. [ABSTRACT FROM AUTHOR]

In this paper, the fractional Schrödinger equation is studied. The Bayesian method is put forward to estimate some relevant parameters of the equation. Results show that the estimated values can fit well with the exact solution. The varying initial values and maximum iterations have little effect on the estimated results. It indicates that the Bayesian method is efficient for the multi-parameter estimation for the fractional Schrödinger equation. This method can also be used to estimate parameters for the fractional Schrödinger equation in other potential field. [ABSTRACT FROM AUTHOR]

In this work, we systematically conduct parametric studies revealing the sensitivity of the hole injection on the hole accelerator (a hole accelerator is made of the polarization mismatched p-electron blocking layer (EBL)/p-GaN/p-AlxGa1-xN heterojunction) with different designs, including the AlN composition in the p-AlxGa1-xN layer, and the thickness for the p-GaN layer and the p-AlxGa1-xN layer. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-AlxGa1-xN layer increases. Meanwhile, with p-GaN layer or p-AlxGa1-xN layer thickening, the energy that the holes gain increases and then reaches a saturation level. Thus, the hole injection efficiency and the device efficiency are very sensitive to the p-EBL/p-GaN/p-AlxGa1-xN design, and the hole accelerator can effectively increase the hole injection if properly designed. [ABSTRACT FROM AUTHOR]

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO2 insulator layer on the p+-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p+-GaN and SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p+-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs. [ABSTRACT FROM AUTHOR]

Fully leaky optical-guided mode was employed to determine the difference in the splay and bend flexoelectric coefficient (e1-e3) in negative nematic liquid crystal MS-N01300-000. The experimental curves of reflectivity versus internal angle (angle of incident light to the liquid crystal) were obtained when a laser beam passed through the hybrid-aligned nematic in-plane switching liquid crystal cell; the cell was embedded in pyramid-coupled waveguide with different alternating current (AC) and direct current (DC) voltages. The curves of the applied DC with voltage similar to that of AC shift to the left or the right. Experimental results were then compared with theoretical results derived from elastic continuum theory and multi-layer optical theory of liquid crystals. The approximate value of the flexoelectric coefficient (e1-e3) of MS-N01300-000 is 9.0 x 10-11 C/m. [ABSTRACT FROM AUTHOR]

Both Raman spectroscopy and the photoluminescence (PL) spectroscopy are intensively used in studying the characteristics of monolayer MoS2. However, the substrate-related interference effect will influence the optical signal intensities collected from monolayer MoS2. In this work, we investigated the influence of multilayer film interference on the optical signal intensity of monolayer MoS2 on SiO2/Si substrate. Based on our results, the most commonly used substrate for monolayer MoS2, SiO2/Si with SiO2 thickness around 280-300 nm, is not the optimized choice. By considering the interference effect caused by the Air-MoS2-SiO2 multilayers, we can now enhance the optical signal intensity of monolayer MoS2 greatly by selecting proper SiO2 thickness for any chosen incident light wavelength. [ABSTRACT FROM AUTHOR]

In this paper, we are concerned with superlinear fractional Schrödinger equation (-Δ)su + V(x)u = f (x,u), x ∈ RN, where f is continuous. When V and f are asymptotically periodic in x, we show the existence of ground states. When V and f are periodic in x, we obtain infinitely many geometrically distinct solutions. The method used here is based on the method of Nehari manifold and Lusternik-Schnirelmann category theory. [ABSTRACT FROM AUTHOR]

Transport of noninteracting self-propelled particles is numerically investigated in a two-dimensional horizontally asymmetrical channel with nonstraight midline which can be controlled by the phase shift between the top and bottom walls. From numerical simulations, we found that self-propelled particles can be rectified by the self-propelled velocity. The direction of the average velocity is determined by the horizontally asymmetrical parameter of the channel. The average velocity is very sensitive to the phase shift and its behaviors can be manipulated by changing the phase shift. As the phase shift is increased, the average velocity decreases and its peak position moves (to right or left). Remarkably, the average velocity is zero when the phase shift is in the interval [ 3π/5, 4π/5 ]. The small phase shift may facilitate the rectification process for the large horizontal asymmetry of the channel. [ABSTRACT FROM AUTHOR]

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ~332 meV to ~294 meV at 80 A/cm² and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs. [ABSTRACT FROM AUTHOR]

The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED. [ABSTRACT FROM AUTHOR]

We report an acoustic dual filter to realize the sound regulation in the audio frequency range, in which resonant vibrations of two membrane-air and metal-elastomer systems generate two sound transmission peaks and a sound blocking below 3000 Hz. The local vibrational profiles manifest that the transmission peak at lower frequency is mainly dependent on the resonant vibration of the membrane-air system, and the coupling vibrations of two systems generate the blocking frequency and transmission peak at higher frequency. Importantly, two transmission peaks can be controlled independently. It is feasible to realize the acoustic device in sound shield and dual filters. [ABSTRACT FROM AUTHOR]

In conventional InGaN/GaN light-emitting diodes (LEDs), thin InGaN quantum wells are usually adopted to mitigate the quantum confined Stark effect (QCSE), caused due to strong polarization induced electric field, through spatially confining electrons and holes in small recombination volumes. However, this inevitably increases the carrier density in quantum wells, which in turn aggravates the Auger recombination, since the Auger recombination scales with the third power of the carrier density. As a result, the efficiency droop of the Auger recombination severely limits the LED performance. Here, we proposed and showed wide InGaN quantum wells with the InN composition linearly grading along the growth orientation in LED structures suppressing the Auger recombination and the QCSE simultaneously. Theoretically, the physical mechanisms behind the Auger recombination suppression are also revealed. The proposed LED structure has experimentally demonstrated significant improvement in optical output power and efficiency droop, proving to be an effective solution to this important problem of Auger recombination. [ABSTRACT FROM AUTHOR]

The coupling acoustic matching is investigated to realize acoustic sensors with a microfluidic channel, in which two overlap layers couple three local quarter-wavelength transmission elements. Provided that the reflecting waves from both sides of each overlap layer satisfy destructive interferences, most acoustic energy can be transmitted. Especially, the microfluidic channel is sensitive to realize a function of the acoustic matching, which could induce effects of an approximate halfwavelength transmission and much acoustic dissipation. With an optimized design, the detections of liquid properties with a high quality factor 300 in liquid environment, and a mass sensitivity of 95 kHz mm2/ng are obtained. [ABSTRACT FROM AUTHOR]

China's photovoltaic (PV) enterprises have experienced difficulties under the influence of the growth slowdown of international market and trade protectionism since 2012. In this paper, from a new perspective of building a hierarchical network model, by using the minimum spanning tree (MST) technique, the market characteristics of China's PV enterprises was researched. The economic distance in the MST was calculated by using PV enterprises' daily closing price of stocks during the years 2007-2013. With the analysis of the topology of hierarchical network, the community structures of the network are derived and some influential enterprises are identified. It is necessary for PV enterprises to deeply connect and cooperate with each other to cope with market risk. What's more, the key factors that affect the hierarchical network were also studied; the result indicates that assets expansion and the core technology competitiveness are important factors for the development of PV enterprises. In the end, some suggestions are put forward to promote sustainable development of China's PV industry. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) grown along the [0001] orientation inherit very strong polarization induced electric fields. This results in a reduced effective conduction band barrier height for the p-type AlGaN electron blocking layer (EBL) and makes the electron blocking effect relatively ineffective and the electron injection efficiency drops. Here, we show the concept of polarization self-screening for improving the electron injection efficiency. In this work, the proposed polarization self-screening effect was studied and proven through growing a p-type EBL with AlN composition partially graded along the [0001] orientation, which induces the bulk polarization charges. These bulk polarization charges are utilized to effectively self-screen the positive polarization induced interface charges located at the interface between the EBL and the last quantum barrier when designed properly. Using this approach, the electron leakage is suppressed and the LED performance is enhanced significantly. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the dependence of both the electromechanical effect and the electrostriction on the compressive stress in PMN-30%PT single crystal on the basis of single domain polarization rotation model. In the model, the electroelastic energy induced by the compressive stress is taken into account. The results have demonstrated that the compressive stress can lead to a significant change in the initial polarization state in the crystal. The reason lies in the stress induced anisotropy which is the coupling between the compressive stress and the electrostrictive coefficients. Thus, the initial polarization state in single crystal is determined by the combination of both electrocrystalline anisotropy and the stress induced anisotropy. The compressive stress along the [100] axis can make the polarization in the crystal be perpendicular to the stress direction, and make it difficult to be polarized to the saturation. This model is useful for better understanding both the polarization rotation and electromechanical effect in ferroelectric crystals with the compressive stress present. [ABSTRACT FROM AUTHOR]

A three-step graded undoped-InGaN layers embedded between the GaN last quantum barrier layer and the p-AlGaN electron blocking layer was proposed and its effect on the performance of InGaN/GaN light-emitting diodes was investigated both experimentally and theoretically. In the proposed structure, the electron leakage is found to be effectively reduced, while the hole injection efficiency is simultaneously increased significantly, hence enabling a greatly enhanced radiative recombination rate within the active region. As a result, improvements of 12.25% in the optical output power and 11.98% in the external quantum efficiency are obtained from the proposed device with the respect to the reference device. [ABSTRACT FROM AUTHOR]

We demonstrate the possibility of forming long-range ordered self-assembled arrays of 5-nmdiameter nanodots with pitch of 10×7.5 nm² using guide line templates and low molecular weight (MW) (4700-1200 g/mol) poly(styrene)-poly(dimethylsiloxane) (PS-PDMS) for application in ultrahigh density patterned magnetic recording media. We propose a three-dimensional control which involves control of the height of the guide lines, the thickness of the PS-PDMS films, and the gap between the guide lines in order to produce 5-nm-diameter, sub-10 nm pitched nanodots with long-range order along the guide lines. Adopting a 13-nm-thick PS-PDMS film and 14-nm-high resist guide lines, the 5-nm-diameter and 10×7.5 nm²-pitched self-assembled nanodots were ordered in 4-7 dot arrays with long-range order. The experimental results demonstrate that the method is suitable for the production of patterned media with magnetic recording densities of 8.6 Tbit/in². using low MW PS-PDMS and slim guide lines. [ABSTRACT FROM AUTHOR]

In this work, the origin of electron blocking effect of n-type Al0.25Ga0.75N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes. [ABSTRACT FROM AUTHOR]

The effects of mechanical losses and elastic properties of the electrodes on the performance figures of a thin film bulk acoustic resonator (FBAR) are analyzed by numerical simulation. Results indicate that the material loss of the electrode has no visible effect on the characterization of the effective electromechanical coupling factor, keff2. The acoustic impedance ratio of the electrode to the piezo-film dominantly determines the behaviors of the keff2 variation with the electrode thickness. The resonance Q value, Qs, of the FBAR closely relies on the material Q values of film and of electrodes as expected. Besides, the variation of Qs versus the thickness of the electrodes crucially depends on the acoustic impedance ratio as well. Especially, three characteristic parameters, i.e., the maximum value of keff2, the sectional mass ratio of the electrode to the piezo film corresponding to the maximum keff2, and the tolerance range of the ratio to keep keff2 near the maximum, are calculated for some typical samples. These results would be useful for optimizing FBAR designs and performances. [ABSTRACT FROM AUTHOR]

In this letter, on the basis of Stoner-Wohlfarth model, the changes in magnetization of Tb0.3Dy0.7Fe2 alloy have been calculated with a compressive stress along the [111] and [112] axes. The results have shown that the significant change in magnetization for Tb0.3Dy0.7Fe2 alloy can be induced by the compressive stress. A feasible application of power generation floor which can convert the energy from the vibration created by a walking person on it into electric energy has been proposed, and its structure and performance also have been revealed. [ABSTRACT FROM AUTHOR]

Based on the analysis of the photocurrent behavior of Pt sandwiched Pb(Zr0.2Ti0.8)O3 (PZT) films, the experimental evidence of top Pt/PZT interface layer thickness effect on the photocurrent is reported. It was well established before that the photocurrent of metal/ferroelectric film is attributed to the height of Schottky contact barrier. However, our results suggest that the photocurrent of Pt/PZT interface contact is determined not only by the barrier height but also by the interface layer thickness, namely, by the built-in electrical field at the interface layer. The mechanism behind such photocurrent phenomenon is proposed. [ABSTRACT FROM AUTHOR]

We report a simple and robust magnetomechanical system for direct visual observation of the DNA packaging behavior of the bacteriophage phi29 in real time. The system comprises a micron-sized magnetic bead attached to the free end of the viral DNA, a magnet and a bright-field microscope. We show that the phi29 DNA packaging activity can be observed and dynamically analyzed at the single molecular level in bright field with a relatively simple system. With this system we also visually demonstrate the phi29 motor transporting a cargo 10 000 times the viral size. [ABSTRACT FROM AUTHOR]

The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials exhibit different electronic properties than their bulk materials. Here, we present a systematic study of 2D tetragonal materials of ScN and YN using density functional theory calculations. Several thermodynamically stable 2D tetragonal structures were determined, and such novel tetragonal structures have good electronic and optical properties. Both bulk ScN and YN are indirect band gap semiconductors while the electronic structures of 2D ScN and YN are indirect gap semiconductors, with band gaps of 0.62-2.21 eV. The calculated optical spectra suggest that 2D tetragonal ScN and YN nanosheets have high visible light absorption efficiency. These electronic properties indicate that 2D ScN and YN have great potential for applications in photovoltaics and photocatalysis. [ABSTRACT FROM AUTHOR]

We report a three-dimensional ab initio potential energy surface for He–N2O using a supermolecular method at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. Besides the intermolecular stretching and bending modes, we included the Q3 normal mode for the ν3 antisymmetric stretching vibration of N2O molecule in order to simulate the observed infrared spectra in the ν3 region of N2O, especially to explain the frequency shift of the band origin in the infrared spectra. The harmonic oscillator approximation is used for the potential curve of the Q3 mode of the isolate N2O molecule. The intermolecular potential energy surfaces are calculated for five potential-optimized discrete variable representation grid points of the Q3 mode. The three-dimensional discrete variable representation method was employed to calculate the rovibrational states without separating the inter- and intramolecular nuclear motions. The calculated transition frequencies and line intensities of the rotational transitions in the ν3 region of N2O for the van der Waals ground vibrational state are in good agreement with the observed infrared spectra. The calculated band shifts are found to be 0.1704 and 0.1551 cm-1 for 4He–N2O and 3He–N2O, respectively, which agree well with the observed values of 0.2532 and 0.2170 cm-1. [ABSTRACT FROM AUTHOR]

A new global potential-energy surface for the ground electronic state of HO2(X2A″) has been developed by three-dimensional cubic spline interpolation of more than 15 000 ab initio points, which were calculated at the multireference configuration-interaction level with Davidson correction using the augmented correlation-consistent polarized valence quadruple zeta basis set. Low-lying vibrational states were obtained in this new potential using the Lanczos method and assigned. The calculated vibrational frequencies are in much better agreement with the available experimental band origins than those obtained from a previous potential. In addition, rate constants for the H+O2↔O+OH reactions were obtained using a wave-packet-based statistical model. Reasonably good agreement with experimental data was obtained. These results demonstrate the accuracy of the potential. [ABSTRACT FROM AUTHOR]

We present a detailed study of the transport and the efficiency of a ratchet system in a periodic potential in the presence of correlated noises. The current and the efficiency of the system are investigated. It is found that, when the potential is spatially symmetric, the correlation between the two noises can induce a net transport. The efficiency shows many interesting features as a function of the applied force, the noise intensity, the external load, etc. The efficiency can be maximized as a function of noise intensity (or temperature), which shows that the thermal fluctuation can facilitate the efficiency of energy transformation. [ABSTRACT FROM AUTHOR]

It is known that acoustic nonlinear effects in thermoacoustic refrigerators are unfavorable to the performance because they transfer the acoustic energy of the fundamental wave to harmonic waves, while only the former is useful for refrigeration. To study the nonlinear effects in loudspeaker-drive thermoacoustic refrigerators, we measure the acoustic performance in a coupling system composed of a resonant pipe driven by an electrodynamic loudspeaker via an inverse horn. It is found that the nonlinear effects increase both the acoustic pressure of fundamental wave in the resonant pipe and the electroacoustic transfer efficiency of the system. Then, a theoretical model is established to study the nonlinear effects in the coupling system, in which the nonlinearities arising from the loudspeaker, inverse horn, and resonant pipe are taken into account, and the simulated results are used to explain the experimental phenomena. [ABSTRACT FROM AUTHOR]

In an ultrasonic sensor, the electromechanical coupling coefficient, sensitivities related to the mass load and conductivity variation, insert loss and minimum detectable mass are important parameters determining the performance of the sensor, while it is challenging to optimize the abovementioned five parameters simultaneously. In this paper, we show that the multi-mode characteristic of Lamb wave provides possibilities to improve the performance of ultrasonic sensors by simultaneously considering the five parameters. According to the simulated results, piezoelectric films, relative thicknesses of films and substrates, structures of interdigital transducers, operating wavelengths and frequencies are optimized based on properly selected operating modes of Lamb wave. Then, high performance of Lamb wave sensors can be realized, in which high electromechanical coupling coefficients, mass sensitivities and conductivity sensitivities in addition to low insert losses and minimum detectable masses are simultaneously achieved. [ABSTRACT FROM AUTHOR]

A relative permeability model for transient two-phase flow in fractal porous media is derived based on the fractal characteristics of pore size distribution and the assumption that porous media consists of capillary bundles. The functions in this model are tortuosity fractal dimension, pore fractal dimension, and maximum and minimum pore diameters. Every parameter has clear physical meaning without the use of empirical constants. Good agreement between model predictions and experimental data is obtained, the sensitive parameters that influence the relative permeability are specified and their effects on relative permeability are discussed. [ABSTRACT FROM AUTHOR]

The phase velocities, electromechanical coupling coefficients, conductivity sensitivities, insert losses, and minimum detectable masses of Rayleigh and Lamb waves sensors based on silicon carbide (SiC) substrates are theoretically studied. The results are compared with the performances of the sensors based on conventional silicon substrates. It is found that the sensors using SiC substrates have higher electromechanical coupling coefficients and conductivity sensitivities than the conventional silicon-based sensors in virtue of piezoelectricity of the SiC. Moreover, higher phase velocities in SiC substrates can reduce the insert losses and minimum detectable masses of the sensors. In this case, in the detection of the gas with the tiny mass as the hydrogen, in which the conductivity sensitivity is more important than the mass sensitivity, the sensor based on the SiC substrate has a higher sensitivity and exhibits the potential to detect the gas with the concentration below the ppm level. According to the results, the performances of the sensors based on the Rayleigh and Lamb waves using the SiC substrates can be optimized by properly selecting piezoelectric films, structural parameters, and operating wavelengths. [ABSTRACT FROM AUTHOR]