arXiv subjects

Jakub Zlámal

Publications and source records attributed to Jakub Zlámal.

6 recordsLinked to original sources

arXiv2025

Casimir-like effect driven self-assembly of graphene on molten metals

Casimir effect, explained by Hendrik Casimir in 1948, is a macroscopic manifestation of quantum electrodynamics. Symmetry breaking due to space confinement of vacuum fluctuations in between two planar mirrors results in an attractive force acting between the two mirrors. Here, we show that spontaneous self-assembly of two-dimensional (2D) layered materials grown on molten metals (rheotaxy) is driven by the mechanical forces exerted by the liquid on the graphene domain and that these forces are subject to a Casimir-like effect. We present in situ environmental and ultrahigh vacuum scanning electron microscopy observations of chemical vapor deposition of graphene on both solid and molten gold and copper, which reveal that the self-assembly occurs via translational and rotational motions of graphene domains during growth on molten metals. Using high-temperature (~ 1300 K) atomic force microscopy measurements of graphene/molten-metal interfaces, coupled with density functional theory and continuum modelling of 2D layers floating on a liquid surface, we attribute the observed phenomena to Casimir-like effect of surface undulations and give further guidance for achieving seamless stitching of 2D layer domains into large scale monolayers.

cond-mat.mes-hall↗

arXiv2024

Accelerating the laser-induced phase transition in nanostructured FeRh via plasmonic absorption

By ultrafast x-ray diffraction we show that the laser-induced magnetostructural phase transition in FeRh nanoislands proceeds faster and more complete than in continuous films. We observe an intrinsic 8 ps timescale for nucleation of ferromagnetic (FM) domains in both types of samples. For the continuous film, the substrate-near regions, which are not directly exposed to light, are only slowly transformed to the FM state by domain wall motion following heat transport. In contrast, numerical modeling of the plasmonic absorption in the investigated nanostructure reveals a strong contribution near the FeRh/MgO interface. On average, the absorption is larger and more homogeneous in the nanoislands, enabling the phase transition throughout the entire volume at the intrinsic nucleation timescale.

cond-mat.mtrl-sci↗

arXiv2022

Observing high-k magnons with Mie-resonance-enhanced Brillouin light scattering

Magnonics is a prospective beyond CMOS technology which uses magnons, the quanta of spin waves, for low-power information processing. Many magnonic concepts and devices were recently demonstrated at macro- and microscale, and now these concepts need to be realized at nanoscale. Brillouin light scattering spectroscopy and microscopy (BLS) has become a standard technique for spin wave visualization and characterization, and enabled many pioneering magnonic experiments. However, due to its fundamental limit in maximum detectable magnon momentum, the conventional BLS cannot be used to detect nanoscale spin waves. Here we show that optically induced Mie resonances in dielectric nanoparticles can be used to extend the range of accessible spin wave wavevectors beyond the BLS fundamental limit. The method is universal and can be used in many magnonic experiments dealing with thermally excited as well as coherently excited high-momentum, short-wavelength spin waves. This discovery significantly extends the usability and relevance of the BLS technique for nanoscale magnonic research.

cond-mat.mes-hall↗

arXiv2022

Geant4 simulation of the residual background in the ATHENA Wide Field Imager from protons deflected by the Charged Particle Diverter

X-ray telescopes opened up a new window into the high-energy universe. However, the last generation of these telescopes encountered an unexpected problem: their optics focused not only X-rays but low-energy (so called soft) protons as well. These protons are very hard to model and can not be distinguished from X-rays. For example, 40\% of XMM-Newton observations is significantly contaminated by soft proton induced background flares. In order to minimize the background from such low-energy protons the Advanced Telescope for High ENergy Astrophysics (ATHENA) satellite introduced a novel concept, the so called Charged Particle Diverter (CPD). It is an array of magnets in a Hallbach design, which deflects protons below 76 keV before they would hit the Wide Field Imager (WFI) detector. In this work, we investigate the effect of scattering of the deflected protons with the CPD walls and the inner surfaces of the WFI detector assembly. Such scattered protons can loose energy, change direction and still hit the WFI. In order to adopt the most realistic instrument model, we imported the CAD model of both the CPD and the WFI focal plane assembly. Soft protons corresponding to $\approx$2.5 hours of exposure to the L1 solar wind are simulated in this work. The inhomogeneous magnetic field of the CPD is included in the simulation. We present a preliminary estimate of the WFI residual background induced by soft proton secondary scattering, in the case of the optical blocking filter present in the field of view. A first investigation of the volumes responsible for scattering the protons back into the field of view is reported.

astro-ph.IM↗

arXiv2022

Athena charged particle diverter simulations: effects of micro-roughness on proton scattering using Geant4

The last generation of X-ray focusing telescopes operating outside the Earth's radiation belt discovered that optics were able to focus not only astrophysical X-ray photons, but also low-energy heliophysical protons entering the Field of View (FOV). This "soft proton" contamination affects around 40\% of the observation time of XMM-Newton. The ATHENA Charged Particle Diverter (CPD) was designed to use magnetic fields to move these soft protons away from the FOV of the detectors, separating the background-contributing ions in the focused beam from the photons of interest. These magnetically deflected protons can hit other parts of the payload and scatter back to the focal plane instruments. Evaluating the impact of this secondary scattering with accurate simulations is essential for the CPD scientific assessment. However, while Geant4 simulations of grazing soft proton scattering on X-ray mirrors have been recently validated, the scattering on the unpolished surfaces of the payload (e.g. the baffle or the diverter itself) is still to be verified with experimental results. Moreover, the roughness structure can affect the energy and angle of the scattered protons, with a scattering efficiency depending on the specific target volume. Using Atomic Force Microscopy to take nanometer-scale surface roughness measurements from different materials and coating samples, we use Geant4 together with the CADMesh library to shoot protons at these very detailed surface roughness models to understand the effects of different material surface roughnesses, coatings, and compositions on proton energy deposition and scattering angles. We compare and validate the simulation results with laboratory experiments, and propose a framework for future proton scattering experiments.

astro-ph.IM↗

arXiv2021

Strong coupling in a Au plasmonic antenna-SiO$_{2}$ layer system: a hybrid mode analysis

A detailed analysis of the optical response of a system accommodating several coupled modes is needed for the complete understanding of the strong coupling effect. In this paper, we report on the analysis of scattering cross section spectra of Au antennas on a SiO$_{2}$ layer on a Si substrate in the IR region. A classical model of coupled oscillators is used for determining the resonant energies, damping rates and coupling strengths of four phonon polariton modes in the SiO$_{2}$ layer coupled to a localized surface plasmon mode in a Au antenna. The calculated Hopfield mixing coefficients then show the contribution of the individual uncoupled modes to the hybrid modes of the coupled system.

cond-mat.mes-hall↗