arXiv subjects

Jiří Liška

Publications and source records attributed to Jiří Liška.

10 recordsLinked to original sources

arXiv2026

Durable Enhancement of $\mathbf{MoS_2}$ Single-Layer Photoluminescence by Ultraviolet Laser Treatment Under Ambient Conditions

Single-layer molybdenum disulfide ($MoS_2$) possesses significant potential for nanoscale optoelectronics, but achieving high-intensity, long-term-stable photoluminescence (PL) emission remains a challenge. In this work, we demonstrate a remarkably robust, more than 8-fold maximum enhancement in the PL intensity of exfoliated and CVD-grown single-layer $MoS_2$ via a non-destructive ultraviolet (UV) laser treatment method. This substantial increase in radiative efficiency is accompanied by a trion-to-neutral exciton transition in the PL signal and a corresponding blue shift of the Raman $E_{2g}^1$ and $A_{1g}$ vibrational modes, signaling successful electron depletion (p-doping) and formation of Mo-O bonds, respectively. Furthermore, we demonstrate precise spatial control over PL properties by confining PL treatment exclusively to the UV laser-treated area. Crucially, the enhanced PL performance shows exceptional longevity; the CVD sample and the exfoliated sample remained stable for the entire monitoring period (72 and 32 days, respectively) under ambient conditions. We further investigated UV laser treatment in a controlled-environment chamber under argon, nitrogen, and oxygen atmospheres, distinguishing the influence of oxygen as the PL treatment agent. These findings establish a reliable pathway for the permanent treatment of single-layer $MoS_2$ PL properties, an essential step toward practical, high-performance nanophotonic devices.

cond-mat.mes-hall↗

arXiv2026

Dilute Zn alloying in biodegradable Mg wires: microstructure, mechanical performance, and degradation behavior

Dilute Mg-Zn wires are of great interest for biodegradable small-bone fixation, as magnesium degradation can support bone-related processes, while low zinc additions may provide biological benefits without compromising biocompatibility. In this work, the influence of Zn content below the room-temperature solubility limit was assessed in Mg-Zn wires intended for resorbable implant applications. Mg-0.4Zn, Mg-0.6Zn, Mg-0.8Zn, and Mg-1.5Zn alloys were processed by single-step direct hot extrusion into thin wires and characterized by correlative microstructural analysis, tensile testing, bending experiments, and in vitro degradation. All compositions achieved a recrystallized fine equiaxed grain size of 5.0-5.9 um and exhibited ultimate tensile strengths of 246-256 MPa with elongations of 23-28 %. In these thin wires, Zn content had only a limited effect on grain size, tensile properties, and bending behavior, although lower-Zn alloys showed a pronounced sharp yield point. Bending was governed mainly by extrusion texture and preserved reversible plasticity through twinning and detwinning. Simulated body fluid caused rapid localized degradation and loss of mechanical integrity within 7 days, while the biologically more relevant DMEM-based medium better reflected the expected in vivo response. Together, these findings support dilute Mg-Zn wires as a simple material platform for the development of future resorbable bone fixation devices.

cond-mat.mtrl-sci↗

arXiv2023

Structural color filters with compensated angle-dependent shifts

Structural color filters use nano-sized elements to selectively transmit incident light, offering a scalable, economical and environmentally friendly alternative to traditional pigment- and dye-based color filters. However, their structural nature makes their optical response prone to spectral shifts whenever the angle of incidence varies. We address this issue by introducing a conformal VO2 layer onto bare aluminum structural color filters. The insulator-metal transition of VO2 compensated the spectral shift of the filter's transmission at a 15° tilt with 80% efficiency. Unlike solutions that require adjustment of the filter's geometry, this method is versatile and suitable also for existing structural filters. Our findings also establish tunable materials in general as a possible solution for angle-dependent spectral shifts.

physics.optics↗

arXiv2022

Fabrication and micro-Raman spectroscopy of arrays of copper phthalocyanine molecular-magnet microdisks

Phthalocyanines as organic semiconductors and molecular magnets provide plenty of industrial or high-tech applications from dyes and pigments up to gas sensors, molecular electronics, spintronics and quantum computing. Copper phthalocyanine (CuPc) belongs among the most used phthalocyanines, typically in the form of powder or films but self-grown nanowires are also known. Here we describe an opposite, i.e., top-down approach based on fabrication of ordered arrays of CuPc microstructures (microdisks) using electron beam lithography and other steps. Among critical points of this approach belongs a choice of a proper resist and a solvent. Fabricated CuPc microdisks have a diameter of 5 $μ$m and heights from 7 up to 70 nm. Micro-Raman spectroscopy of the films and microdisks reveals a crystalline $β$ phase associated with a paramagnetic form. Additional measurements with an increasing laser power show a significant shift ($Δω$ ~ 7.1 cm$^{-1}$ ) and broadening of a peak at 1532 rel$\cdot$cm$^{-1}$ corresponding to the phonon B1g mode. The observed smooth changes exclude a phase transition and confirm the thermally stable polymorph. Our versatile fabrication technique using the common lithographic resist brings new possibilities for the fabrication of various micro/nanostructures such as micromagnets, heterostructures or organic electronic devices.

physics.app-ph↗

arXiv2021

Correlative electron and light spectroscopy of strongly-coupled mid-infrared plasmon and phonon polaritons

The ability to control and modify infrared excitations in condensed matter is of both fundamental and application interests. Here we explore a system supporting low-energy excitations, in particular, mid-infrared localized plasmon modes and phonon polaritons that are tuned to be strongly coupled. We study the coupled modes by using far-field infrared spectroscopy, state-of-the-art monochromated electron energy-loss spectroscopy, numerical simulations and analytical modeling. We demonstrate that the electron probe facilitates a precise characterization of polaritons constituting the coupled system, and enables an active control over the coupling and the resulting sample response both in frequency and space. Our work establishes a rigorous description of the spectral features observed in light- and localized electron-based spectroscopies, which can be extended to analogous optical systems with applications in heat management, and electromagnetic field concentration or nanofocusing.

physics.optics↗

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↗

arXiv2017

CzeV - The Czech Variable Star Catalogue

We present the first release of the Czech Variable star catalogue that currently contains 1228 stars whose variability was discovered by 60 Czech observers. The catalogue contains confirmed variable stars of various types, but also candidates. We give precise coordinates, cross identification with other catalogues, information about constellation, variability type, brightness, light elements, name of the discoverer and year of discovery. In eighty-eight percent of stars the variability type is estimated, for more than 60 % of the stars the light ephemerides are given.

astro-ph.SR↗

arXiv2016

The SERMON project: 48 new field Blazhko stars and an investigation of modulation-period distribution

We investigated 1234 fundamental mode RR Lyrae stars observed by the All Sky Automated Survey (ASAS) to identify the Blazhko (BL) effect. A sample of 1547 BL stars from the literature was collected to compare the modulation-period distribution with stars newly identified in our sample. A classical frequency spectra analysis was performed using Period04 software. Data points from each star from the ASAS database were analysed individually to avoid confusion with artificial peaks and aliases. Statistical methods were used in the investigation of the modulation-period distribution. Altogether we identified 87 BL stars (48 new detections), 7 candidate stars, and 22 stars showing long-term period variations. The distribution of modulation periods of newly identified BL stars corresponds well to the distribution of modulation periods of stars located in the Galactic field, Galactic bulge, Large Magellanic Cloud, and globular cluster M5 collected from the literature. As a very important by-product of this comparison, we found that pulsation periods of BL stars follow Gaussian distribution with the mean period of $0.54\pm0.07$ d, while the modulation periods show log-normal distribution with centre at $\log(P_{\rm m}~{\rm [d]})=1.78\pm0.30$ dex. This means that 99.7 % of all known modulated stars have BL periods between 7.6 and 478 days. We discuss the identification of long modulation periods and show, that a significant percentage of stars showing long-term period variations could be classified as BL stars.

astro-ph.SR↗

arXiv2016

Review of candidates of binary systems with an RR Lyrae component

We present an overview and current status of research on RR Lyrae stars in binary systems. In present days the number of binary candidates has steeply increased and suggested that multiple stellar systems with an RR Lyrae component is much higher than previously thought. We discuss the probability of their detection using various observing methods, compare recent results regarding selection effects, period distribution, proposed orbital parameters and the Blazhko effect.

astro-ph.SR↗

arXiv2012

Visual minima timings of eclipsing binaries: To use or not to use?

Plenty of mid-eclipse timings of short-periodic eclipsing binaries derived from series of visual observations appear to be an acceptable source of information for orbital period analyses, namely if they were done in time-intervals not covered by other types of observations. However, our thorough period analysis of the nearly contact eclipsing binary BS Vulpeculae proves that visually determined timings done in 1979--2003 were undoubtedly biased to accommodate the existing linear ephemeris. The heavily subjective character of visual observations disqualifies them as a source of true phase information apt for fine eclipsing binary period analyses. Consequently we warn against the use of visual timings without a preceding careful verification.

astro-ph.SR↗