SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

Carbon quantum dots (CQDs) are quasi-spherical nanoparticles with crystalline graphitic core, and nitrogen and oxygen-containing functional gorups. They have fascinating fluorescent properties associated to their band gap tuned by varied nanometer size sp2-core and defects controlled by edge configuration and functional groups. However, the optical properties of solvothermally-synthesized dots could also be affected by the presence of unreacted species or small organic molecules. The intense excitation-independent photoluminescence (PL) was indeed attributed to molecular fluorophores, which may be surface-bound or embedded in the carbon matrix. In this work, I will discuss the origin of the optical properties of nitrogen-doped CQDs obtained by three methods. Two of them use the chemical reaction of glucose and ethylenediamine and, therefore, the structure of N-CQDs could in principle contain molecular fluorophores, especially in the case of spontaneous reaction that, after 5 months, resulted in N-CQDs exhibiting similar structural properties, optical absorption in the UV-VIS range, and PL emission [1] as those synthesized in the microwave reactor [2]. The third method is a recently discovered unique extraction of N-CQDs from plasma-deposited amorphous organic thin films with amino groups. Thanks to films' partial water solubility, the presence of fluorescent nanoparticles was detected in water extracts. High-resolution TEM proved that the nanoparticles are graphitic, and their PL spectra have similarities to N-CQDs from glucose and ethylenediamine.
REFERENCES: [1] J. Gómez, M. Sulleiro, N. Pizúrová et al., Appl. Surf. Sci. 610 (2023) 155536; [2] J. Gómez, M. Sulleiro, A. Dolečková et al., J. Phys. Chem. C 125 (2021) 21044.

Carbon nanodots (CDs) are promising fluorescent nanomaterials for photonic and optoelectronic applications, although their implementation in solid-state devices is often hindered by aggregation-induced quenching. Here, we demonstrate the fabrication of carbon nanodot superparticles (SPs) through an emulsion-templated self-assembly strategy and investigate the effect of polyethylene glycol (PEG) functionalization on their structural organization and optical properties. Bare CDs together with PEG400- and PEG3000-functionalized CDs were assembled into compact spherical superstructures with diameters ranging from hundreds of nanometers to a few micrometers, as confirmed by electron microscopy.
Optical characterization revealed that PEG functionalization induces a reproducible blueshift of the emission together with an increase in photoluminescence quantum yield and excited-state lifetime, both before and after assembly. Remarkably, these optical improvements are preserved in the superparticles, demonstrating that controlled hierarchical assembly effectively suppresses the aggregation-induced quenching typically observed in carbon-based nanomaterials. The results indicate that PEG acts as an efficient spacer, modulating interparticle interactions while maintaining the emissive properties of the individual nanodots.
The environmental stability of the superparticles was also investigated. Photobleaching measurements performed under controlled atmospheres show that water vapor strongly accelerates emission quenching, whereas the optical response remains significantly more stable under nitrogen. These findings suggest that humidity penetrates the superparticle architecture, disrupting interparticle interactions and partially degrading the assembled structure.
Overall, this work demonstrates that emulsion-templated assembly provides an effective route toward luminescent carbon-based optical metamaterials with tunable photophysical properties, while highlighting the importance of encapsulation strategies to ensure long-term environmental stability for practical applications.

Atomically precise graphene quantum dots, also known as nanographenes, are an emerging family of light emitting nanomaterials which behave as highly efficient solution-processable emitters, thanks to their tunable optical transitions with narrow bandwidth and near-unity photoluminescence quantum yields [1].
Despite these outstanding photophysical properties, optical gain from nanographenes remains scarcely reported in the literature. Here, we demonstrate amplified spontaneous emission and lasing from solutions of rod-shaped nanographenes composed of exactly 114 sp² carbon atoms (C114) [2], explored in different optical cavity geometries. By tuning nanographene concentration, we achieve lasing emission from two distinct spectral peaks, and we fully characterize the lasing dynamics and properties of the emitted laser beam. Furthermore, with an appropriate choice of the experimental conditions, we were able to observe a stochastic interplay and competition between the relative intensities of the two lasing modes.
This tunable dual-peak lasing behavior establishes nanographenes as a versatile platform for multi-wavelength lasing applications, paving the way for nanographene-based coherent light sources in next-generation organic photonic devices.
REFERENCES: [1] M. Reale et al. Carbon 206, 45 (2023); [2] Medina-Lopez et al., Nat. Commun. 14, 4728 (2023).

Random lasers (RLs) have emerged as an attractive class of laser sources offering unique advantages over conventional lasers in selected photonic applications. Carbon dots (CDs) are a well-established family of sustainable and versatile fluorescent nanomaterials for applications ranging from sensing and bioimaging to optoelectronics. Despite their promise as gain media for RLs, achieving stable, controllable and unambiguous random lasing from CDs remains challenging, and systematic studies of the statistical properties of their emission are still scarce.
Here, we demonstrate random laser (RL) emission from CDs dispersed together with TiO₂ nanoparticles acting as scattering centers [2]. The lasing behavior is systematically investigated under different excitation conditions using established statistical methods to analyze the emission spectra. The CD-based RL exhibits ultranarrow coherent lasing peaks (~0.7 nm) superimposed on a broader incoherent RL background (~10 nm), with the relative contribution of the two regimes tunable by the experimental conditions. We further exploit the emitted light for speckle-free imaging of biological tissues and microparticles, highlighting the practical potential of these sources.
These results establish CDs as environmentally friendly, low-cost gain media for random lasers with tunable emission characteristics, paving the way for sustainable photonic light sources for imaging and optoelectronic applications.
REFERENCES: [1] A. Sciortino et al. Chem. Mater. 30, 1695 (2018); [2] A. Pramanik et al. ACS Photonics 11, 3055 (2024).

Plastic waste contributes significantly to environmental challenges due to its persistent nature and low global recycling rates. In this context, upcycling plastic polymers into carbon-based nanomaterials offers a sustainable alternative, as most plastics are composed of carbon. In this study, polystyrene (PS) waste is used as a rich aromatic carbon precursor for the synthesis of solid-state fluorescent carbon dots (SS-CDs) via a simple thermal approach. The proposed method leverages a spontaneous separation process, in which the SS-CDs isolate during the solvothermal reaction in ethanol, preventing non-radiative recombination and enabling robust solid-state emission. This phase separation is driven by the developing immiscibility of the hydrophobic units of SS-CDs as they nucleate from the initially soluble PS precursor, eliminating the need for complex post-synthesis separation. The resulting SS-CDs exhibit excitation-independent photoluminescence with a broad emission spanning 400-650 nm, an average lifetime of 4.5 ns, and a moderate photoluminescence quantum yield (PLQY) of 19 % in toluene. Structural characterization indicates a low degree of surface oxidation of the SS-CDs, contributing to stable solid-state optical behavior. This ability to generate solid-state emissive carbon dots directly from plastic waste highlights a sustainable route toward value-added nanomaterials with potential applications in solid-state lighting and optical sensing, while providing a platform for further optimization of structure-property relationships.

Ferromagnets have long been the foundation of spintronics applications. However, materials with compensated magnetic order, such as antiferromagnets, offer distinct advantages, including faster dynamics and a wider range of available materials. This has spurred significant research into antiferromagnetic spintronics, leading to many exciting discoveries [1]. Despite these advancements, antiferromagnets are often not considered robust sources of coherent spin currents. Recently, a new class of compensated magnets, altermagnets, has been identified, combining key advantages of both ferromagnets and antiferromagnets and offering promising potential for spintronics applications [2,3].
In this talk, I will briefly introduce the concept of altermagnetism and present several materials that can host altermagnetic order and that we have studied experimentally. I will focus on some of the experimental verifications of altermagnetic materials [4-6]. I will then discuss our studies of electronic spin transport in these systems, including the observation of the anomalous Hall effect in a single layer of an altermagnetic material and its thermoelectric counterpart, the anomalous Nernst effect [7]. Next, I will focus on heterostructures containing altermagnets and show that they can behave similarly to ferromagnets in generating robust spin currents [7]. Finally, I will discuss the implications of altermagnetism for magnon-mediated spin currents [8].
REFERENCES: [1] T. Jungwirth et al., Nature Nanotechnology 11, 231-241 (2016); [2] L. Šmejkal et al., Physical Review X 12, 040501 (2022); [3] C. Song, HR et al., Nature Reviews Materials, 1-13 (2025); [4] R. D. Gonzalez Betancourt, HR et al., Physical Review Letters 130, 036702 (2023); [5] H. Reichlová et al., Nature Communications 15, 4961 (2024); [6] A. Badura, HR et al., Nature Communications 16, 7111 (2025); [7] J. Mencos, HR et al., arXiv:2512.17427; [8] M. Leiviskä, HR et al., Physical Review Materials 9, 084403 (2025)

Alpha-phase gallium oxide (α-Ga2O3) is a promising ultra-wide bandgap semiconductor with a critical electric field of approximately 5.2 MV/cm for high-power electronics. This study presents a planar MOSFET comparison between α-Ga2O3 and silicon (Si) using Silvaco Atlas simulations. To isolate the intrinsic material advantage, both devices were simulated with an identical planar structure (1 µm channel/drift region, equal doping and gate dielectric thickness), representing a material-limited rather than a technologically fair comparison, since neither device was optimized for its material. The Si device exhibited a threshold voltage of 0.62 V, a drain current of 0.75 A at a gate overdrive of 3.4 V and drain voltage of 9 V, an on-resistance of 0.464 Ω·cm2, and an avalanche breakdown voltage of 9.13 V (Selberherr model). For α-Ga2O3, due to unstable impact ionization convergence, breakdown was instead estimated using an electric-field criterion, identifying the drain voltage at which the peak field reaches the material's critical field. α-Ga2O3 exhibited a threshold voltage of 2.78 V, a drain current of 0.88 A at a comparable overdrive, an on-resistance of 0.869 Ω·cm2, and an estimated breakdown voltage of 48 V, roughly 5.3 times higher than Si. Despite the higher on-resistance, the Baliga power figure of merit shows a 14.8 times improvement for α-Ga2O3 over Si, confirming its strong intrinsic potential even under identical, non-optimized structural constraints. This advantage was found to increase with temperature, reaching approximately 17 times at 500 K.

Multifunctional nanomaterials increasingly rely not only on chemical composition, but also on the spatial organization of active units at the nanoscale. In this contribution, I will discuss strategies for designing silica-based nanostructured materials in which molecular or atomic centers are distributed on surfaces or inside ordered mesopores. A key element is the two-dimensional solid-solvent strategy, enabling controlled deposition and separation of active species while preserving accessibility and inter-site communication.
The first class of materials involves nanostructured silicas modified with molecular magnetic units. Their controlled distribution on silica surfaces provides a route toward engineering magnetic interactions, signal amplification, and collective responses relevant to neuromorphic concepts and physical neural networks. The second class is based on SBA-15 mesoporous silica functionalized with separated copper centers. In this architecture, Cu-O-P units anchored through propyl-phosphonate ligands act as atomically dispersed catalytic sites. Such materials operate as single-atom catalysts and nanozyme-like systems capable of trigger-free generation of reactive oxygen species, with potential applications in antimicrobial coatings, self-disinfecting filters, and synthetic enzyme platforms.
The same principle of spatially controlled active centers can also be extended to photonics. Recent results on single-molecule inorganic chromophores confined in SBA-15 show that SHG and THG responses are governed not only by local coordination chemistry, but also by synthesis-controlled inter-unit spacing. This opens a route to tunable nonlinear optical materials for photonics and optical neural networks.
Together, these examples illustrate a general design concept: one nanostructured silica platform can be transformed into materials with magnetic, catalytic, biomedical, and photonic functions by controlling the distribution and interactions of active centers.

This work presents the development of a direct ink writing (DIW) printhead for four-dimensional (4D) printing and the formulation of a magnetically active hydrogel ink. 4D printing extends conventional 3D printing by enabling printed structures to change their properties over time in response to external stimuli. Magnetically active hydrogels are materials able to deform when subjected to external magnetic field. Their potential uses include biomedical applications, such as surgical grippers and soft robotic systems for targeted drug delivery. A DIW printhead for a Prusa 3D printer was designed using a heated syringe filled with hydrogel ink, extruded through a conical needle by a powered piston. At the nozzle tip, magnetic particles are oriented by magnetic field generated by four perpendicular magnetic poles allowing omnidirectional orientation of the magnetic particles. The ink consists of an agarose matrix filled with carbonyl iron microparticles (CIP). Samples containing 10-60 wt% CIP were prepared and their rheology was characterised. All formulations exhibited pseudoplastic behaviour, and their viscoelastic moduli increased linearly with CIP concentration. The effective elastic modulus in compression was determined, revealing a pronounced stiffness increase under applied magnetic field. In higher concentrations particle debonding and extraction by magnetic field occurred. The main drawbacks of the current ink are sedimentation, oxidation and debonding of the CIP.

The present research reports a nanostructured MoTe2-MoS2 n-n heterojunction-based gas sensor developed on a Silicon (Si) substrate, demonstrating room-temperature (RT, 30 °C) nitrogen dioxide (NO2) sensing. A controlled and one-step magnetron co-sputtering approach is utilized to deposit MoTe2-MoS2 nanocomposite thin film on a Si substrate, producing a uniform, dense, and porous nanoscale morphology. Herein, surface analysis and structural characterization of the MoTe2-MoS2/Si sensor reveal a rough and defect-rich morphology with abundant exposed edge sites, which significantly enhances the availability of active adsorption sites for effective gas sensing. The developed MoTe2-MoS2/Si heterostructured sensor delivers an exceptional sensor response of 74.4% with an ultrafast response/recovery time of 7.5/2 s towards 25 ppm NO2 at RT. Additionally, the present sensor showcases highly reproducible and consistent behaviour over a wide range of NO2 concentrations (1-60 ppm), along with remarkable selectivity against common potential interfering gases (NO2, H2S, NH3, CO, H2) and a low detection limit of 700 ppb. This study provides critical insights into NO2 sensing induced by heterointerface band modulation and defect-assisted adsorption at the sensor’s surface, thereby providing a strong foundation for a reliable platform for high-performance NO2 gas sensors based on the MoTe2-MoS2 heterostructure.

Hydrogen-terminated high-pressure high-temperature nanodiamonds (HPHT H-NDs) combine nanoscale dimensions and high crystallinity with an unusual surface electronic structure that enables interfacial charge transfer, charge-carrier accumulation, and the generation of highly reducing solvated electrons under illumination. A distinctive spectroscopic signature of this charge-responsive interface is a narrow infrared transmission window near 1330 cm-1, attributed to Fano-type destructive interference between the zone-center diamond phonon and a continuum of near-surface charge carriers [1].
Here, we show that the spectral profile of this feature is sensitive to the interfacial molecular environment of HPHT H-NDs. The response was first observed during interactions with polymers such as methylcellulose, chitosan, and polyvinylidene fluoride [2,3], and was subsequently investigated more systematically using ionic surfactants, where the integrated area of the transmission window was found to correlate with electrical conductivity. Most recently, the approach was extended to per- and polyfluoroalkyl substances (PFAS), comparing C4 and C8 compounds with carboxylate and sulfonate headgroups. Comparative FTIR analysis reveals that PFAS adsorption depends strongly on nanodiamond type and molecular structure: hydrogenated detonation nanodiamonds retain both sulfonate- and carboxylate-terminated PFAS, whereas HPHT H-NDs show the strongest adsorption for the long-chain sulfonate PFOS. Remarkably, however, all investigated PFAS induce a pronounced 1330 cm⁻¹ transmission window in HPHT H-NDs, indicating that even weakly adsorbed species can measurably perturb the near-surface electronic structure. Such molecularly induced electronic changes may be directly relevant to reported photocatalytic PFAS degradation, in which solvated electrons play a key role [4,5].
The results establish the 1330 cm⁻¹ transmission feature as a promising infrared spectroscopic probe of molecularly induced charge transfer and carrier redistribution at H-ND interfaces, with the potential to support mechanistic understanding and the rational design of nanodiamond-based photocatalytic systems.
REFERENCES: [1] O.S. Kudryavtsev et al., Nano Lett. 22 (2022) 2589-2594; [2] K. Kolarova et al., Diam. Relat. Mater. 134 (2023) 109754; [3] A. Sokeng Djoumessi et al. Sol. RRL 10 (2026) e202500508; [4] W.A. Maza et al., Appl. Catal. B Environ. 325 (2023) 122306; [5] R. Jimenez et al., https://doi.org/10.26434/chemrxiv-2025-zp563-v2

Understanding how chiral π-conjugated molecules interact with different crystallographic facets of magnetic oxide surfaces is essential for the design of hybrid materials for spintronic and magnetoelectronic applications. We reveal, by scanning electron microscopy, a pronounced facet dependence in the morphology of CoO deposited on four crystallographically distinct ZnO surfaces; the polar (0001) Zn-face and ("000" "1" ̅) O-face, and the nonpolar ("10" "1" ̅"0" ) and ("11" "2" ̅"0" ) faces, ranging from sparse, fine particulate clusters on the two polar faces, through coarse fiber- and rod-like features on ("10" "1" ̅"0" ), to dense, interleaved nanoflake (“rose-like”) aggregates on ("11" "2" ̅"0" ). This facet-selective organization motivates a computational investigation of Co and [7]-helicene adsorption on the same facets using density-functional tight-binding (DFTB) and machine-learning interatomic potentials. Spin-polarized DFTB, enabled by newly identified Co-Zn Slater-Koster parameters, gives Co adsorption energies in the range -4.52 to -5.81 eV across the four facets, binding most strongly on the nonpolar ("11" "2" ̅"0" ) facet. We used this DFTB reference to benchmark five pretrained universal machine-learning potentials; M3GNet-MP-PES and M3GNet-MP-DIRECT-PES (2021), and three successive generations of MACE-MP-0 (L0 and L1, 2023; L2, 2024), by their agreement with the relaxed DFTB geometry across all four facets. MACE-MP-0 L2 (2024) reproduces the DFTB geometry and energetics most closely, while M3GNet-MP-PES (2021) achieves comparable agreement at roughly one-quarter of the computational cost: M3GNet-MP-DIRECT-PES (2021) diverges from both, which dedicated pair-potential energy scans trace to a spurious long-range (2-4 Å) repulsive artifact absent from the other four potentials. The adsorption of helical π-conjugated molecules on transition-metal-doped polar oxide surfaces poses a stringent test for machine-learning interatomic potentials, combining mixed ionic-covalent bonding, localized dopant d-states, and dispersion-dominated molecule-surface coupling; MACE-MP-0 L2's higher-order equivariant message passing captures this combination better than the other models tested, while remaining transferable across all four ZnO terminations. These combined experimental and computational results establish MACE-MP-0 L2 as a reliable, DFTB-validated foundation model for subsequent studies of magnetism in this chiral-molecule/magnetic-oxide system.

ZnO is among the most widely used electron-transport oxides owing to its high carrier mobility and strongly facet-dependent surface properties, while CsPbBr₃ (CPB) is a chemically simple, defect-tolerant model perovskite. Interfaces between such halide perovskites and charge-selective metal-oxide layers are crucial for controlling carrier injection, band alignment, energy conversion, photoluminescence, scintillation, and long-term device stability. Yet the atomistic mechanisms linking oxide surface polarity and vacancy chemistry to interfacial bond formation and opto-electronic properties remain largely unresolved.
Here we combine theoretical simulations with machine-learning force-field optimization and dielectric-dependent hybrid DFT with experimental facet-resolved PL, XPS, SEM, and Kelvin-probe measurements across all four low-index ZnO orientations with deposited CPB (nano)crystals. We identify three nanoscale bonding regimes (Zn-Br bridging, Pb substitution at Zn vacancies, and dangling bond mediated adsorption) that jointly control interfacial coupling. Cooperative Pb substitution at Zn vacancy with Zn-Br bridging on Zn-terminated ZnO yields the highest binding energy for PbBr₂-terminated CPB, more than twice that of CsBr-terminated CPB (−4.47 eV), and drives the strongest band edge re-hybridization observed. XPS confirms the predicted Pb-O/Zn-Br bridges. Kelvin probe shows the largest work function shift on the lowest coverage Zn-terminated ZnO surface. A few strongly bonded nanoscale crystals rather than high density coverage can thus control the interfacial dipole. On the other hand, the O-terminated ZnO surface uniquely drives oxygen-mediated bromide extraction that etches CPB crystallites into quantum-dot-like domains, giving a 3 times larger PL blue shift.
These results establish ZnO facet polarity and vacancy coordination as atomic scale design parameters governing opto-electronic properties and offering practical concepts for scintillators and photodetector engineering. The authors acknowledge financial support from the Czech Science Foundation project No. 24-12872S and the program “Strategy AV 21” of the Czech Academy of Sciences.

Nano-diamonds (NDs) have attracted attention for various potential applications, such as catalysis and electronics. NDs are also known to exhibit photoluminescent properties as a result of various impurity embedding during synthesis. Moreover, the conduction band minimum (CBM) of diamond is located close to the vacuum level, and its energy position can be modulated by surface termination. In particular, hydrogen-terminated diamond is known to exhibit a negative electron affinity, in which the CBM lies above the vacuum level. As a result, photoexcited electrons generated by band-gap excitation are expected to possess exceptionally strong reducing power. However, surface sp²-bonded carbon components can act as recombination sites for photogenerated charge carriers, thereby significantly deteriorating the photocatalytic efficiency. Therefore, in this work, the surface sp² components of NDs were systematically analyzed using Transmission electron microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS), and the potential implications for photocatalytic and electronic applications of NDs are also discussed.

CNTs-nZVI nanocomposites produced by plasma-catalytic pyrolysis were evaluated as supercapacitor electrode materials. The material was synthesized in a single-step process from methane and Fe2O3 using a water/argon-stabilized plasma torch, enabling simultaneous methane conversion, iron oxide reduction, and CNT growth. As-synthesized, acid-treated, and thermally/acid-treated materials were fabricated into symmetric supercapacitor electrodes. The thermally/acid-treated sample exhibited the best electrochemical performance, achieving an areal capacitance of 9.7 mF cm-2 and a specific capacitance of 12.1 F g-1 at scan rate of 0.1 V s-1. It also retained approximately 90% of its capacitance after 10,000 cycles, indicating good cycling stability. These results demonstrate the potential of plasma-derived CNTs-nZVI nanocomposites for energy-storage applications.