On the promotion of catalytic reactions by surface acoustic waves

Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis,sensor and nanotechnology.SAWswere shown to cause astrong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However,the promotion mechanism has not been unambiguously identified. Using stroboscopic X-ray photoelectron spectro-microscopy, we were able to evidence asub-nano-second work function change during propagation of 500 MHz SAWs on a9nm thick platinum film. We quantify the work function change to 455 meV.Such asmall variation rules out that electronic effects due to elastic deformation (strain) play amajor role in the SAW-induced promotion of catalysis.In asecond set of experiments,SAW-induced intermixing of afive monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be amajor cause for catalytic promotion

Resonant and Off-Resonant Magnetoacoustic Waves in Epitaxial Fe3Si/GaAs Hybrid Structures

Surface acoustic waves (SAWs) provide an efficient dynamical coupling between strain and magnetization in micro- and nanometric systems. Using a hybrid device composed of a piezoelectric, GaAs, and a ferromagnetic Heusler alloy thin film, Fe3Si, we are able to quantify the amplitude of magnetoacoustic waves generated with SAWs via magnetic imaging in an x-ray photoelectron microscope. The cubic anisotropy of the sample, together with a low damping coefficient, allows for the observation of resonant and nonresonant magnetoelastic coupling. Additionally, via micromagnetic simulation, we verify the experimental behavior and quantify the magnetoelastic shear strain component in Fe3Si, which appears to be large (b2=10±4MJm−3)

Perturbation and numerical solutions of non-Newtonian fluid bounded within in a porous channel: Applications of pseudo-spectral collocation method

In the current study, the effects of fluidic parameters with entropy generation properties on velocity, temperature, and entropy numbers of non-Newtonian fluid flowing through the porous channel are investigated. The complex system of fluid equations is handled with analytically and numerically. The first-order perturbation expansion is employed on both velocity and temperature to obtain the approximate analytical solution. A comparison of the analytical solution is made with numerical results that are obtained by discretizing the system of boundary value problems. The pseudo-spectral collocation method was used for the discretization, and the Newton method was to get the solutions to the complex differential equations. In the Newton method, the finite difference approximation of Jacobian is utilized. The pseudo-spectral solutions are in good agreement with the analytical findings. The order of accuracy in temperature and velocity profiles is of order 10−6 which will be compared in the future with the experimental results of given non-Newtonian fluid

Role of phytohormones in heavy metal tolerance in plants: A review

Heavy metal (HM)-mediated toxic effects on plants have attained considerable attention worldwide as they directly threaten the food supply chain. Although various measures have been taken to mitigate the adverse effects of heavy metal stress in plants, significant research gaps must be proactively addressed. Fascinatingly, the exogenous application of phytohormones has recently attained substantial interest in regulating the negative effects of HM stress. Phytohormones are signaling transductional molecules that mitigate HM toxicity in plants and support their growth and development. Both exogenous treatments and manipulation of the endogenous status of phytohormones through regulating their signaling/biosynthesis-related genes are effective strategies for protecting plants against HM-induced toxic effects. However, to achieve maximum benefits from phytohormone-mediated subcellular mechanisms to mitigate HM toxicity, it is necessary to gain in-depth understanding on their potential pathways. The current review focuses primarily on the major mechanistic phytohormonal-mediated approaches involved in alleviating the toxic effects of HMs in plants. Moreover, the potential roles of major phytohormones in triggering protein molecules, signaling transductions, and gene expressions to avoid, tolerate, or alleviate HM toxicity in plants are also discussed. This information provides systematic understanding on the mechanisms of phytohormones in modulating heavy metal tolerance in plants and could help to guide the development of strategies to improve plant tolerance against HM toxicity

Clocked dynamics in artificial spin ice

Abstract Artificial spin ice (ASI) are nanomagnetic metamaterials with a wide range of emergent properties. Through local interactions, the magnetization of the nanomagnets self-organize into extended magnetic domains. However, controlling when, where and how domains change has proven difficult, yet is crucial for technological applications. Here, we introduce astroid clocking, which offers significant control of ASI dynamics in both time and space. Astroid clocking unlocks a discrete, step-wise and gradual dynamical process within the metamaterial. Notably, our method employs global fields to selectively manipulate local features within the ASI. Sequences of these clock fields drive domain dynamics. We demonstrate, experimentally and in simulations, how astroid clocking of pinwheel ASI enables ferromagnetic domains to be gradually grown or reversed at will. Richer dynamics arise when the clock protocol allows both growth and reversal to occur simultaneously. With astroid clocking, complex spatio-temporal behaviors of magnetic metamaterials become easily controllable with high fidelity

Clocked dynamics in artificial spin ice

Artificial spin ice (ASI) are nanomagnetic metamaterials with a wide range of emergent properties. ASI systems have recently shown promise as substrates for novel computing devices. A precondition for computation is the ability to control how the artificial spins change their state over time. Detailed control of the state evolution in ASI systems has proven difficult. Here, we introduce astroid clocking, a global field protocol that carefully exploits the intrinsic switching astroids of the nanomagnets to selectively address spins within the ASI. The resulting clocked dynamics is characterized by discrete, gradual evolution of spin states. We demonstrate, both experimentally and in simulations, how astroid clocking of pinwheel ASI allows ferromagnetic domains to be gradually grown or reversed at will. More complex dynamics arise when the clock protocol allows both growth and reversal to occur within the same clock cycle. Astroid clocking offers unprecedented control of ASI dynamics in both time and space, and enables new directions in ASI research and beyond

XMCD data and XAS spectra, and simulation data for Clocked Dynamics in Artificial Spin Ice

<p><strong>Experimental data</strong></p><p>Raw data of XMCD images collected at ALBA Synchrotron between 8th to 12th of September 2022. The data are used to create the experimental magnetization curves and magnetic contrast images in the paper <i>Clocked dynamics in artificial spin ice. </i>Additionally, XAS spectra of the Fe L3 edge obtained prior to imaging are included.</p><p>Folder numbers starting at 225 through to 320 contain the data for the unipolar clocking experiment. The folder "001_XAS_Fe" contains the XAS spectrum of the sample taken prior to this series. <br>Folder numbers starting at 166 through to 217 contain the data for the bipolar clocking experiment. The folder "013_XAS_Fe_L3_CN" contains the XAS spectrum of the sample prior to this series.</p><p><strong>Simulation data</strong></p><p>The resulting data from flatspin simulations that are plotted as magnetization curves in the paper <i>Clocked dynamics in artificial spin ice. </i></p><p>The folder "flatspin-unipolar" contains the data for the unipolar clocking experiment.<br>The folder "flatspin-bipolar" contains the data for the bipolar clocking experiment.</p&gt

On the Promotion of Catalytic Reactions by Surface Acoustic Waves

Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis, sensor and nanotechnology. SAWs were shown to cause a strong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However, the promotion mechanism has not been unambiguously identified. Using stroboscopic X‐ray photoelectron spectro‐microscopy, we were able to evidence a sub‐nanosecond work function change during propagation of 500 MHz SAWs on a 9 nm thick platinum film. We quantify the work function change to 455 μeV. Such a small variation rules out that electronic effects due to elastic deformation (strain) play a major role in the SAW‐induced promotion of catalysis. In a second set of experiments, SAW‐induced intermixing of a five monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be a major cause for catalytic promotion.The authors thank Werner Seidel for technical support in the fabrication of the IDTs, Rolf J. Haug, Hannover, for help in preparation of the samples, and Leo Zhigilei for carefully reading the manuscript. The research leading to this result has been supported by the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. LA and MF acknowledge support from Spanish MINECO through Grant No. RTI2018‐095303‐B‐C53. FM and BC acknowledges support from Spanish MINECO through Grants No. RYC‐2014‐16515, No. MAT2015‐69144‐P, No. SEV‐2015‐0496 and No. MAT2017‐85232‐R. Open access funding enabled and organized by Projekt DEAL.Peer reviewe

GHz sample excitation at the ALBA-PEEM

We describe a setup that is used for high-frequency electrical sample excitation in a cathode lens electron microscope with the sample stage at high voltage as used in many synchrotron light sources. Electrical signals are transmitted by dedicated high-frequency components to the printed circuit board supporting the sample. Sub-miniature push-on connectors (SMP) are used to realize the connection in the ultra-high vacuum chamber, bypassing the standard feedthrough. A bandwidth up to 4 GHz with -6 dB attenuation was measured at the sample position, which allows to apply sub-nanosecond pulses. We describe different electronic sample excitation schemes and demonstrate a spatial resolution of 56 nm employing the new setup