Influence Of Surface Acoustic Wave Research Articles

Influence of surface acoustic wave (SAW) on nanoscale in-plane magnetic tunnel junctions

The use of voltage induced strain to switch magnetic tunnel junctions (MTJs) is a promising solution for reducing the switching energy in MRAM technologies. The MTJ is integrated with a piezoelectric layer to generate the strain. A very thin layer is needed to switch with small voltages and small energy dissipation. It is challenging to synthesize ultrathin piezoelectric layers that retain a high degree of piezoelectricity. An alternate approach is to use time-varying strain generated by a surface acoustic wave (SAW). This approach does not require a thin piezoelectric layer since the SAW is confined to the surface of the layer. In this study, we fabricated in-plane MTJs on piezoelectric LiNbO3 substrates and used IDTs to generate the SAW signal within the substrate. Our results showed that the SAW signal had a significant influence on the resistance and the tunneling magnetoresistance (TMR) ratio of the MTJs. The influence was much less significant in nanometer size MTJs than in micrometer sized ones. Most surprisingly, the SAW signal caused the tunneling magnetoresistance ratio (TMR) to drop below zero for the micrometer size MTJ, meaning that the antiparallel resistance RAP is temporarily less than the parallel resistance RP under SAW excitation. Our results provide insight into the dynamic behavior of MTJs under periodic strain and the dependence of this behavior on the device dimensions as they are scaled down to nanometer sizes.

Significant Suppression of Dark Current in a Surface Acoustic Wave Assisted MoS2 Photodetector

Abstract2D materials are considered as potential candidates for the next generation of optoelectronic materials. However, their optical absorption is typically weak due to thickness limitations, greatly restricting the photodetection capabilities of devices. To enhance the photoelectric gain of 2D materials or devices and improve detection sensitivity, various modulation methods such as strain, electric field, and magnetic field are commonly introduced. Among them, surface acoustic wave (SAW) represents a unique and effective modulation approach. In this study, photodetectors are fabricated based on few‐layer MoS2 on a SAW delay line on a LiTaO3 substrate. The interaction between SAW and MoS2 successfully manipulates the optoelectronic performance of the MoS2‐based devices. Under the influence of SAW, the dark current of the devices is significantly reduced by more than two orders of magnitude, while the photocurrent remains almost unchanged, resulting in excellent photoresponse performance. The devices provide a promising pathway for high‐performance optoelectronic applications and reveal a new possibility for acoustic devices in optoelectronics.

Research on Temperature Monitoring Method and System Design for Key High Voltage Equipment of Wind Farm

This paper focuses on the temperature detection of high-voltage equipment in wind power plant, puts forward the surface acoustic wave measurement method, and deeply studies the design process of surface acoustic wave sensor device and the design scheme of monitoring system. In different process materials of piezoelectric substrate and antenna design mode, there will be great differences in the transmission efficiency and anti-interference ability of surface acoustic wave. Therefore, the influence of surface acoustic wave on the performance of surface acoustic wave sensor device is possible Testing and setting the surface measurement parameters can improve the measurement performance. In the aspect of detection system, the typical key temperature monitoring equipment of high voltage switch cabinet in wind farm is selected to form a practical deployment scheme, which realizes the integrated functions of automatic temperature measurement, parameter optimization and adjustment, alarm and so on. The research and design method in this paper has great practical application value in the operation and control of new energy system.

Water droplet motion under the influence of Surface Acoustic Waves (SAW)

The water droplet motion processes actuated by applying surface acoustic waves at various RF powers and frequencies were investigated by numerically modelling and compared with experiment. A three-dimensional computational model of a free water droplet streaming on the surface of the substrate have been developed using Finite Element Method (FEM) with Laminar Two-Phase Flow Moving Mesh approach for Navier–Stokes equations which were coupled with Convection Wave equation (CWE) module of the COMSOL Multiphysics. Water droplet motion speeds were experimentally measured and confirmed for water droplets with the volumes of 2 and 5 μl, at SAW frequencies 34 and 58 MHz, and power range 0.1–1.23 W. The effect of frequency on microfluidic performance such as streaming flows and droplet motion has been studied both numerically and experimentally toward developing MEMS devices for future energy sources, e.g., for direct methanol fuel cells, hydrogen energy, as well as for use in a wide variety of chemical, water desalination and purification of other fluids from salts, germs, bacteria, and viruses based on perspective multiphysical effects.

Effects of Hall current and permeability on the stability of peristaltic flow

Pumping molecules and atoms near or along surfaces under the perturbing influence of surface acoustic wave is important in micro-flow systems. These micro-flow systems can circulate heat-transfer fluids over silicon chips, reconstitute dried drugs and possibly synthesize chemicals from liquid to solid constituents. The stability of acoustic streaming flow induced by a small-amplitude surface acoustic wave propagating along the walls of a confined parallel-plane channel with a magneto incompressible fluid through a porous medium is considered. The stability related to the flow initiated by the peristaltic waves propagating along the deformable walls is explored numerically. The neutral stability boundary is gotten by understanding the significant Orr–Sommerfeld condition. The Chebyshev collocation method is employed to solve the resulting generalized eigenvalue problem. The critical Reynolds number and the corresponding wave number are obtained for different values of $$K_{0}=c/u_{\max }$$ (ratio of the wave speed to the maximum speed of the basic flow), magnetic field M, Hall current $$\beta _{1}$$ and permeability parameter k. Different values of the critical Reynolds number are obtained when $$K_{0}=c/u_{\max }$$ =1 (rigid wall) and $$\ne 1$$ for deformable walls. It is found that the critical Reynolds number (when the wall is deformable; $$K_{0}=10$$ ) becomes 577.22 which is much less than conventional rigid-wall case [5772, obtained by Orszag using the spectral method (Orszag in J Fluid Mech 50:689–703. https://doi.org/10.1017/S0022112071002842 , 1971)]. The effect of incrementing of $$K_{0}$$ and k shows destabilizing effect on the fluid flow while increasing in the values of M and $$\beta _{1}$$ exhibits a stabilizing influence on the fluid flow. So, various kinds of noises like Hall current, permeability and peristaltic waves propagating along the walls will premature any instability mechanism considering the temporal growth of the disturbances. Also, the range of wave numbers relevant to the peristaltic wave or the Reynolds number of this basic flow must be carefully selected for the optimal flow control usage in bio-MEMS.

Effect of surfactants on thin film spreading under influence of surface acoustic wave

For the spreading of thin and free film of a partially wetting liquid with insoluble surfactant under the influence of surface acoustic wave, the dimensionless evolution equations governing the spreading dynamics are derived. The evolution equations contain the film thickness and the surface concentration of insoluble surfactant. Assuming that the thickness of the thin film is much smaller than the wavelength of sound in the liquid, the sound leaking off the surface acoustic wave cannot be sustained in the liquid film, and the acoustic radiation pressure and attenuation of the acoustic wave in the solid are both weak. Then the films spreading under different physical mechanisms are observed by numerical simulation. The results show that the surface acoustic wave drives the liquid film to spread and move. When the capillary stress is weak and the liquid film spreading is mainly controlled by the drift induced by surface acoustic wave, the spreading process consists of rapid spreading stage and balancing stage, and the Marangoni effect caused by uneven distribution of surfactant makes the liquid film spread faster in the first stage. When the capillary stress and the drift jointly dominate film spreading, the spreading process contains three stages, i.e. spreading stage, contracting stage and balancing stage. The effect of surfactant accelerates the spreading process, but the existence of contracting stage makes it take longer for the film to reach equilibrium. In addition, the disjoining pressure used in this paper promotes the liquid film spreading, as well as the Marangoni effect. As the correlation coefficient between disjoining pressure and surfactant concentration, <i>α</i>, and the Marangoni number, <i>M</i>, increase, the maximum thickness and the spreading radius of liquid film change faster.

Simulation of mass transfer of liquids through microchannels under the influence of surface acoustic waves

Parametric research of the mass transfer of liquids through flat microchannels under the influence of surface acoustic waves was performed using numeric simulation.

Investigation of the Surface Condition of an Electrode after Electropolishing under the Influence of Surface Acoustic Waves

The observation of acoustic enhancement ofthe anodiccurrentin an electropolishing experiment promises to be useful in acceleration of industrial electrochemical processes. Besides the process, however, the surface condition after the electropolishing is of importance as well. This investigation is focused onthe surface condition of the electropolished surface after an acoustic wave treatment. At the anode surface acoustic waves, especially Scholte waves, will be generated. Theevanescentpartof the wave will propagate in the electrolyte and cause Schlichting streaming in the boundary layer. For different frequencies and different intensities of the surface acoustic wave the surface roughness of the anode is analyzed by a laser scanning microscope.The results of the investigation will allow to find the best parameters for polishing and to avoid cavitation damage.

Acoustomagnetic pulse experiments in LiNbO3∕Mn12 hybrids

We report here on the influence of surface acoustic waves (SAWs) on the magnetization of a Mn12-acetate single crystal. The crystal was mounted on the surface of a piezoelectric LiNbO3 substrate containing an interdigital transducer for the excitation of SAWs. The magnetization of the crystal was measured using a rf superconducting quantum interference device with a time resolution of 1μs. The piezoelectric material was excited by SAW pulses of different frequencies produced by applying microwave pulses to the transducer. Our data show that molecular magnets onto the LiNbO3 surface can be used as very sensitive detectors of the SAW frequency and intensity.

Photoluminescence of GaAs(110) quantum wells modulated by surface acoustic waves

We studied the low temperature (15K) photoluminescence properties of un-doped GaAs(110) quantum wells modulated by surface acoustic waves (SAW) by photoluminescence (PL) spectroscopy technique. Under the influence of the SAW, the decreasing of PL intensity and the splitting of the PL lines were observed. The magnitude of the splitting can be up to 10meV when the power applied to the transducers is 20dBm. Furthermore, the spin injection in GaAs(110) quantum wells generated by circular polarization light under the influence of SAW was also discussed.

Photoluminescence kinetics in GaAs under the influence of surface acoustic waves

The kinetics of the low-temperature photoluminescence (PL) of GaAs under the influence of the electric field of a surface acoustic wave (SAW) is investigated experimentally. When a SAW pulse (delayed by 20–30 µs with respect to the laser pulse) with a field strength of up to ∼50 V/cm is applied, the rate of the conduction band-to-acceptor transitions increases considerably (by a factor of up to 10–20), while the rate of the donor-acceptor pair transitions does not vary significantly nor is the excitonic PL enhanced. The data obtained provide evidence of shallow-level donor ionization by the SAW electric field and corroborate the recombination model proposed previously, which explains the slow nonexponential decay of the free-electron PL in pure GaAs by the effect of multiply repeated capture of free conduction-band electrons by shallow-level donors.

Influence of surface acoustic waves on lateral forces in scanning force microscopies

We present a detailed study of the influence of ultrasonic surface acoustic waves (SAWs) on point-contact friction. Lateral force microscopy (LFM) and multimode scanning acoustic force microscopy (SAFM) were used to measure and to distinguish between the influence of in-plane and vertical surface oscillation components on the cantilever’s torsion and bending. The experiments show that friction can locally be suppressed by Rayleigh-type SAWs. Through the mapping of crossed standing wave fields, the wave amplitude dependence of the friction is visualized within microscopic areas without changing other experimental conditions. Above a certain wave amplitude threshold, friction vanishes completely. We found that the friction reduction effect is caused by the vertical oscillation components of the SAW. Purely in-plane polarized Love waves do not give rise to a significant friction reduction effect. Thus, we conclude that the mechanical diode effect, i.e., the effective shift of the cantilever off of the oscillating surface, is responsible for the SAW-induced lubrication. This explanation is supported by vertical and lateral SAFM measurements: in areas with completely vanishing friction, low frequency vertical cantilever oscillations are still observable, whereas lateral (torsional) cantilever oscillations are no longer excited. Additionally, at very high Rayleigh wave amplitudes an effect of lateral force rectification was observed. It results in a scan direction-independent appearance of the LFM traces.

A photoemission electron microscopy (PEEM) study of the effect of surface acoustic waves on catalytic CO oxidation over Pt{110}

A photoemission electron microscope (PEEM) was used to study the influence of surface acoustic waves (SAWs) on the reactive behaviour of adsorbate structures during CO oxidation over Pt{110} at temperatures around 485 K and CO and O 2 pressures around 10 −5 and 10 −4 mbar, respectively. It was found that surface acoustic wave excitation can suppress and reverse the process of CO poisoning of the catalyst, and thus bring the system back into the highly reactive regime. From work function measurements of the CO-covered surface during acoustic excitation it is concluded that the observed effect is due to acoustically induced CO desorption.

X-Ray diffraction under surface acoustic wave excitation

The influence of surface acoustic waves (SAW) on grazing incidence diffraction (GID) and high resolution X-ray diffraction in Bragg-geometry (HRXD) was investigated on high-quality YZ-cut LiNbO 3 single crystals. α f-resolved GID-profiles of the (00.6) and the (00.12) reflection as a function of the SAW excitation voltages show both substantial increase of the diffracted intensity (up to 100%) and a simultaneous sharpening of the profiles. Profiles for different incident angles were measured and simulated by model calculations in the framework of dynamical diffraction theory. The lattice displacements induced by the SAW were taken into account by varying the structure factors by an additional Debye–Waller factor. The model calculations agree well with experimental results and serve as an estimate for the amplitude of the longitudinal component of the SAW reaching 0.04 nm for the highest excitation voltage. It is shown that under SAW excitation, the α f-profile of the weaker (00.12)-reflection can also be calculated using the distorted-wave-Born-approximation, which implies a kinematic description of the scattering process. Under SAW-excitation, the integrated intensity of HRXD profiles of the (30.0) Bragg-reflection increases up to 360% of its original value. This also shows the gain of diffracted intensity caused by reduced extinction.

Grazing-incidence diffraction on LiNbO3 under surface acoustic wave excitation

X-ray diffraction under grazing incidence and exit angles,α i andα f (GII) was used for the first time to study longitudinal displacements in surface acoustic waves (SAW) propagating on LiNbO3 single crystals. Theα f-resolved (006)-diffraction spectra have been investigated as a function of the applied voltage for SAW excitation. Substantial increase of diffraction intensity (up to 100%), accompanied by a sharpening of the diffraction profile was found in these measurements. The most pronounced influence of SAW on GID was observed for both theα i andα f near the critical angleα c. The diffraction rods were successfully simulated in the framework of dynamical diffraction theory, using only one SAW-related parameter, namely an additional Debye-Waller factor responsible for reduction of the scattering amplitude. This heuristic approach allowed to explain all experimental effects and served to estimate the amplitudes of the longitudinal component of the SAW in the near-surface layer of LiNbO3.

Locking of the tunneling distance in STM-type junctions: The influence of surface acoustic waves.

We numerically investigate the influence of surface acoustic waves on single-electron tunneling in STM-type tunnel junctions. Surface acoustic waves (SAW's) propagate along a solid surface and periodically change the distance between STM tips and substrates. Since tunneling rates have an exponential dependence on tunneling distance, SAW strongly affects tunneling phenomena. It is found that the regularity of the SET oscillations is associated with a locking phenomenon of the tunneling distance, where the tunneling distance behaves like the Brownian motion of a particle in the tilted-washboard potential. \textcopyright{} 1996 The American Physical Society.