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Author: Hernández-Mínguez, Alberto × WGL Institute: PDI ×

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    On the Promotion of Catalytic Reactions by Surface Acoustic Waves
    (Weinheim : Wiley-VCH, 2020) von Boehn, Bernhard; Foerster, Michael; von Boehn, Moritz; Prat, Jordi; Macià, Ferran; Casals, Blai; Khaliq, Muhammad Waqas; Hernández-Mínguez, Alberto; Aballe, Lucia; Imbihl, Ronald
    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. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Polarized recombination of acoustically transported carriers in GaAs nanowires
    (London : BioMed Central, 2012) Möller, Michael; Hernández-Mínguez, Alberto; Breuer, Steffen; Pfüller, Carsten; Brandt, Oliver; de Lima Jr, Mauricio M.; Cantarero, Andrés; Geelhaar, Lutz; Riechert, Henning; Santos, Paulo V.
    The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport.
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    Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves
    (London : Nature Publishing Group, 2017) Foerster, Michael; Macià, Ferran; Statuto, Nahuel; Finizio, Simone; Hernández-Mínguez, Alberto; Lendínez, Sergi; Santos, Paulo V.; Fontcuberta, Josep; Hernàndez, Joan Manel; Kläui, Mathias; Aballe, Lucia
    The magnetoelastic effect—the change of magnetic properties caused by the elastic deformation of a magnetic material—has been proposed as an alternative approach to magnetic fields for the low-power control of magnetization states of nanoelements since it avoids charge currents, which entail ohmic losses. Here, we have studied the effect of dynamic strain accompanying a surface acoustic wave on magnetic nanostructures in thermal equilibrium. We have developed an experimental technique based on stroboscopic X-ray microscopy that provides a pathway to the quantitative study of strain waves and magnetization at the nanoscale. We have simultaneously imaged the evolution of both strain and magnetization dynamics of nanostructures at the picosecond time scale and found that magnetization modes have a delayed response to the strain modes, adjustable by the magnetic domain configuration. Our results provide fundamental insight into magnetoelastic coupling in nanostructures and have implications for the design of strain-controlled magnetostrictive nano-devices.
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    Dynamically tuned non-classical light emission from atomic defects in hexagonal boron nitride
    (London : Springer Nature, 2019) Lazić, Snežana; Espinha, André; Yanguas, Sergio Pinilla; Gibaja, Carlos; Zamora, Félix; Ares, Pablo; Chhowalla, Manish; Paz, Wendel S.; Palacios Burgos, Juan José; Hernández-Mínguez, Alberto; Santos, Paulo V.; van der Meulen, Herko P.
    Luminescent defects in hexagonal boron nitride (h-BN) have recently emerged as a promising platform for non-classical light emission. On-chip solutions, however, require techniques for controllable in-situ manipulation of quantum light. Here, we demonstrate the dynamic spectral and temporal tuning of the optical emission from h-BN via moving acousto-mechanical modulation induced by stimulated phonons. When perturbed by the propagating acoustic phonon, the optically probed radiative h-BN defects are periodically strained and their sharp emission lines are modulated by the deformation potential coupling. This results in an acoustically driven spectral tuning within a 2.5-meV bandwidth. Our findings, supported by first-principles theoretical calculations, reveal exceptionally high elasto-optic coupling in h-BN of ~50 meV/%. Temporal control of the emitted photons is achieved by combining the acoustically mediated fine-spectral tuning with spectral detection filtering. This study opens the door to the use of sound for scalable integration of h-BN emitters in nanophotonic and quantum information technologies. © 2019, The Author(s).