Seznam abstraktů 2023: POSTEROVÁ SEKCE A

Quantum computing is newly emerging information-processing technology which is foreseen to be exponentially faster than classical supercomputers. Current quantum processors are nevertheless very limited in their availability and performance and many important software tools for them do not exist yet. Therefore, various systems are studied by simulating the run of quantum computers. Building upon our previous experience with quantum computing of small molecular systems (see I. Miháliková et al., Molecules 27 (2022) 597, and I. Miháliková et al., Nanomaterials 2022, 12, 243), we have recently focused on computing electronic structure of periodic crystalline materials. Being inspired by the work of Cerasoli et al. (Phys. Chem. Chem. Phys., 2020, 22, 21816), we have used hybride variational quantum eigensolver (VQE) algorithm, which combined classical and quantum information processing. Employing tight-binding type of crystal description, we present our results for crystalline diamond-structure silicon. In particular, we focus on the states along the lowest occupied band within the electronic structure of Si and compare the results with values obtained by classical means. While we demonstrate an excellence agreement between classical and quantum-computed results in most of our calculations, we further critically check the sensitivity of our results with respect to computational set-up in our quantum-computing study. A few results were obtained also using quantum processors provided by the IBM.

Materials with a phase transition represent one of the main directions toward tunable nanophotonic devices. Even though the volatile vanadium dioxide (VO2) has already been proposed and applied to various tunable and memory devices, its dielectric to metallic transition is still not fully understood, especially at the nanoscale. Here, by observing the optical resonances of individual VO2 nanocrystals during the phase transition in transmission electron microscopy (TEM), we better understand the hysteresis behavior of the VO2 phase transition and show its potential for novel multilevel nanoscaled memory.

Organic thermoelectric (TE) materials combine TE conversion with flexibility, and could facilitate development of self-sustainable wearable electronic devices. In these systems, organic TE materials-based flexible TE generators could generate power from the temperature differences between human body and ambient environment for non-stop operation of self-sustainable wearable electronics without the necessity of external recharging. Among various organic TE materials, polyaniline (PANI) and especially the carbon nanotube (CNT)/PANI composites are receiving special interest for such applications due mainly to the excellent p-p stacking between CNTs and PANI that provide simultaneous enhancement of electrical conductivity and Seebeck coefficient. As it is known, chemical oxidative polymerization of aniline in the presence and absence of CNTs is the most common procedure to prepare CNT/PANI and PANI in the TE field, and the most common initiator in aforementioned reaction is ammonium persulfate (APS). However, the structure of APS is actually rather different than PANI. Alternatively, we propose in the present work to use benzoyl peroxide (BPO) as an initiator to prepare PANI and CNT/PANI for TE applications. Because, unlike APS, phenyl rings of BPO might help to realize structural coherency, and hence the resultant samples might exhibit better thermoelectric power factor. To check the validity of this idea, we prepared PANI and CNT/PANI by using BPO as an initiator, and compared their TE properties with the samples that prepared traditionally by using APS as an initiator. For the BPO-synthesized samples, the polymerization reactions were performed by inverted emulsion polymerization since BPO is not soluble in water. The TE properties were determined by Linseis LSR-3/800 Seebeck coefficient and electrical resistance measurement system. Strikingly, we report that BPO-synthesized samples exhibited both higher electrical conductivity and Seebeck coefficient, providing a significant enhancement in power factor as compared to APS-synthesized PANI and CNT/PANI. ACKNOWLEDGEMENTS: This work was supported by The Scientific and Technological Research Council of Türkiye (TUBITAK) under the Grant No. 221M082.

GaN based high electron mobility transistors (HEMTs) are very attractive for high-frequency and high-power applications due to excellent nitride material properties. Contacts with low contact resistivity (typically below 10−5 Ωcm2 for high power devices) are essential for good device performance. For laboratory characterization of GaN based structures, a quick way of the ohmic contact preparation is to solder indium. Nevertheless, such contacts suffer from low reproducibility and degradation. The usage of annealed multi-metal contacts is therefore highly desirable.
In this work we report on the recessing and alloying of three types of the Ti/Al/Ti/Au contacts to 2D electron system: (1) hetero-dimensional (2D-3D), (2) lateral 3D, and (3) planar (above-channel) contacts. AlGaN/GaN HEMT structures are grown on silicon substrates and provided with evaporated contacts. We compare samples cut of the same substrate and formed into mesa structure by reactive ion etching. The etch depth of the mesa structures, where the contact metallization is subsequently applied, is varied from 0 (no etch) to 50 nm. Surface properties of etched AlGaN/GaN HEMT structures are studied using SEM and AFM. Electrical properties of AlGaN/GaN HEMT structures before and after contact annealing are characterized by transfer length method and van der Pauw measurements. Based on the comparison of contact resistivity values and their temperature dependence for samples with different contact types, we discuss underlying transport mechanisms in contacts and suitability of particular contact types for AlGaN/GaN HEMT structure characterization. ACKNOWLEDGEMENTS: This work was supported by grants LM2023051 and LTAIN19163.

Heaters are an indispensable part of gas sensing platforms. It serves to heat the sensor, which increases the sensitivity of the active layer and helps in the desorption of the detected gas. The sensors are also heated to stabilize the parameters against the ambient temperature.
For the fabrication of electronic circuits and devices including sensing platforms and heating structures is becoming increasingly popular to use flexible electronics. In particular, the use of inkjet printing technology allowing localized deposition of ink at low temperatures on a large area. Many kinds of inks such as conductive, semi-conductive, or dielectric can be used.
In this research, we present the design preparation, simulation, fabrication, and characterization of the inkjet printed heaters. The structures are based on silver nanoparticle ink printed on a flexible substrate and are sintered with intense pulsed light. The printed heaters consist of connection pads, interconnection pathways, and heater patterns. Two types of heater patterns were designed (meander and double spiral type). Both of the prepared patterns were simulated in Ansys simulation software to obtain the heat distribution. The microheaters were printed on a PET substrate and characterized with a thermal imaging camera. Based on the results obtained from these measurements, a calibration table was created.

The diamond semiconductor exhibits notable figures of merit within the class of wide band-gap semiconductors, making it particularly suitable for high performance power electronic and quantum optical devices. The present study delves into an investigation of the growth, electrical, and optical properties of epitaxial boron-doped diamond oriented along the {115} crystallographic direction, with varying boron concentrations. Specifically, we employed oxygen addition in the process gas to diminish the boron concentration within the epitaxial layer [1]. Additionally, we successfully manufactured a thick () diamond plate with heavy doping along the {115} orientation, a crucial element in the production of vertical power electronic devices.
The crystalline quality and the concentration of doped diamond exhibiting metallic conductivity were investigated by X-ray tomography, Hall effect measurements, and Raman spectroscopy. Surface morphology and growth rate were examined via atomic force microscopy and scanning electron microscopy in cross-section. Determination of boron concentration within the epitaxial layers was achieved through analysis of the diamond zone-center phonon Raman peak and secondary ion mass spectroscopy [2]. These findings underscore the potential for a more streamlined and feasible approach in the creation of vertical devices, such as high-power Schottky diodes [3], through the growth of high quality, thick {115} oriented epitaxial layers characterized by high boron concentrations (~1020 cm-3), low resistivity, and less boron-doped diamond layers than those utilizing conventional {100} or {111} oriented epitaxial layers. ACKNOWLEDGEMENTS: The financial support from the following source is gratefully acknowledged: the Czech Science Foundation grant ID: 21-03538S, the Czech Academy of Sciences - CNRS mobility plus project CNRS-22-13 and SOLID21 - CZ.02.1.01/0.0/0.0/16_019/ 0000760. REFERENCES: [1] S. A. Bogdanov et al. 74 (2017) 59.; [2] V. Mortet et al. Carbon 168 (2020) 319.; [3] H. Umezawa et al. J. Appl. Phys., 53 (2014) 05FP06.

The paper describes the performance of chemical-mechanical processing of GO, rGO and biochar (grinding in a ball mill in (NH4)2SO4) in order to obtain a nanomaterial for application as a supercapacitor. The paper presents the synthesis of carbon nanomaterials, including their characteristics according to available measurement techniques. The experimental part is devoted to the specification of the ball milling conditions. Subsequently, elemental analysis and TGA analysis were determined for ground samples. This is followed by a discussion of the results and a comparison of the obtained results with results from professional publications.

We demonstrate a league of Valley-Spin Hybrid (VSH) layered architectures assembled from double-decker single-molecule magnets (SMMs) and atomically thin two-dimensional (2D) crystals. A VSH prototype is manifested by the thermal evaporation of terbium bis-phthalocyanine onto CVD-grown monolayers of Molybdenum dioxide which is characterized by atomic force microscopy and Raman spectroscopy. Raman correlation analysis reveals moderate p-type doping in monolayer which is well corroborated by the density functional theory calculations. The intensity of the defect peak (i.e., ‘B’ exciton) is elevated due to the superposition of the excitons while the ‘A’ exciton peak is found to be moderately red-shifted. Further, a temperature and magnetic field-dependent valley contrast in VSH is obtained by helicity-resolved photoluminescence, and strikingly, an off-resonance enhancement of valley polarization is found in ‘A’ exciton-related valley emission at room temperature. This effect is explained by a non-radiative energy drain mechanism in which interaction with the unoccupied electronics states of the SMM plays a crucial role in draining the population of the non-radiative excitons. These fascinating properties, along with feasible production and reliable stability of the VSH prototypes pave a direction for multi-responsive opto-spin/valleytronics devices for information storage and processing.

We present here a comparative study of the magnetic and optical properties of quasi-two-dimensional electrons in artificial graphene-like superlattices composed of circular and elliptical quantum dots. The rich underlying physics of two-dimensional electrons subjected to periodic modulation and transverse magnetic field, as well as new technologies of construction of graphene-like semiconductor nanostructures with tunable properties make artificial graphene an invaluable playground for revealing fundamental physics and for designing novel nanodevices.
We analyze the impact of a transverse magnetic field on the electronic band structure and interminiband absorption coefficient using a complete set of orthogonal basis functions with a specific focus on the symmetries of quantum dots and the lattice. The magnetic field is a key determinant, altering the band structure and the optical characteristics of artificial graphene. We observe qualitative modifications in the electron energy dispersion in reciprocal space and the magneto-optical properties of the considered structure, influenced by the number of magnetic flux quanta through the lattice unit cell due to the interplay between two fundamental length-scales: the lattice period and the magnetic length. Our study reveals significant changes in the miniband structure attributable to the ellipticity of the quantum dots. Even a slight deviation from the spherical geometry of quantum dots leads to topological transformations in the band structure, inducing consequential changes in the interminiband absorption spectrum. In conclusion, this study advances our understanding of the magnetic and optical properties of artificial graphene-like superlattices, with implications for their applications in future magneto-optical devices.

Exotic properties of 2-dimensional (2D) magnetic materials have been leading the hunting of new materials which have outstanding potential to be the building blocks for next-generation electronics, data storage as well as energy storage devices. Nevertheless, their unstable nature ambient environment, expensive and time-consuming process to grow, unfriendly for mechanical exfoliation, and hard to manufacture on a commercial scale are still dragging the possibility of using 2D magnetic materials on full commercial scales. In this study, we first successfully prepared stable, homogenous, and controlled CrCl3 crystals on different substrates using a fast and economical evaporation procedure. Secondly, we have studied and tracked the evolution of structural and magnetic phase transitions using temperature and magnetic field dependence Raman spectroscopy in addition to photoluminescence response using both linear and circularly polarized light. This study highlights the capability of Raman spectroscopy to get vivid information, unfolding the temperature dependence magnetic phase as well as tracking the progression of structural transition locally, which is not quite straightforward using other traditional characterization techniques. Temperature dependence XRD results and Raman spectrum together with magnetometer data further maintain the fact that extensive coexistence of intermediate structural and magnetic phases in a fairly wide temperature range.

The quartz crystal microbalance (QCM) represents an acoustic (mass) analytical platform suitable for detecting gases and biomolecules in air and liquid, respectively. Several studies have shown that the sensing performance, sensitivity, and selectivity of QCMs are further enhanced by using an appropriate functional layer. Among others, diamond is one such attractive material thanks to its extraordinary properties. However, the use of standard CVD diamond growth procedures at 800 °C cannot be applied to the QCM substrate due to its low phase transition temperature (570 °C). An alternative solution here offers a low-temperature (400 °C) linear antenna microwave plasma. In this work, we demonstrate technological progress in diamond growth on QCM substrates in terms of maintaining their functionality and the ability to cover both sides in one deposition cycle due to low pressure (<15 mbar) and placement of the QCM substrate in the so called cold plasma region. Diamond-coated QCM substrates were successfully used to detect gas molecules (NO2, NH¬3) or volatile organic compounds (ethanol), and the technological challenges will be critically discussed. Moreover, we introduce progress in developing an innovative approach for detecting the SARS-CoV-2 coronavirus causing the respiratory disease COVID-19, utilizing aptasensors with great potential for application in clinical practice. ACKNOWLEDGEMENTS: This research was supported by the bilateral project no. SAV-AV ČR-23-11 and 23-04322L, and used the CzechNanoLab infrastructure (no. LM2023051). M. V. acknowledges project no. 19MRP0010 financed from the MoRePro Programme and the Slovak Academy of Sciences funding, A.P. acknowledges project no. VEGA 2/0160/21.

Structuring of polycrystalline diamond is crucial for fabricating active and passive electronic components, microelectromechanical components (MEMS), and other devices. In specific applications, etched depth in tens of micrometers is demanded. This study presents a novel approach to achieve controlled deep etching of diamond using nickel (Ni) as the catalyst in a thermochemical process conducted at different gas compositions and temperatures to 950 °C. Only minimal etching was observed under a Ni mask when the diamond was treated in hydrogen plasma. Introducing CO2 to the gas mixture enhanced the etching by 2-3 times. Unfortunately, the etching was also observed over the entire film area, including unmasked regions. Conversely, the use of water vapor demonstrated excellent etching selectivity, where the unmasked diamond area remained unaffected. This etching process was strongly pressure-dependent. In the low-pressure range (5 ÷ 50 Torr), catalytic etching achieved a maximum depth of 2-3 µm before slowing down due to the formation of a graphitized cap layer on the top surface, which limited the access of -OH to the diamond-Ni interface. Increasing the pressure to atmospheric levels resolved this issue, forming structures with depths up to 10 µm within 30 minutes. Catalytically driven thermochemical etching of diamond proves to be a cost-effective alternative to dry plasma etching processes, especially for the fabrication of deep etches (>50 µm) required for diamond-based 3D dosimeters, electrochemical electrodes, biocompatible neuronal interfaces, energy storage devices, and other applications. This work was supported by the bilateral research project no. LUASK 22 147 (SK no SK-CZ-RD-21-0116).

The silicon vacancy (SiV) color center is a light emitting crystallographic point defect that can be prepared at high densities in diamond thin films using the chemical vapor deposition process. Polycrystalline diamond (PCD) thin films with thickness varying from 100 to 500 nm can be fabricated on a large scale at a reasonable price, which might be applicable in photonics or biosensing. Advantages of PCD include its high chemical inertness, thermal stability, and high durability. However, the practical usage of the diamond films is limited due to their polycrystalline nature and by the inhomogeneous properties of the SiV centers in the PCD. The boundaries between the individual diamond grains cause strain in the material and unwanted background photoluminescence (PL). In this work, we investigated the influence of deposition process parameters on the optical properties of diamond thin films grown on silica substrates in order to suppress the strain and the background PL. We systematically increased the ratio of CH4 to H2 from 1 to 15% and studied how it influences the chemical, structural, and PL properties of the grown films. The steady-state PL spectra showed that with increasing the amount of CH4, the values of the SiV zero phonon line (ZPL) spectral position slowly decrease towards the monocrystalline reference sample, which shows that the quality of the fabricated PCD is improving. The samples with the highest SiV ZPL to PL background ratio were the samples grown with the ratio of CH4 to H2 between 4 and 8%. Lastly, Raman spectroscopy, SEM, and AFM measurements gave us information about the structural changes and their dependence on the amount of CH4 used during the deposition.

Nowadays, radiation detectors can be found in a wide range of different fields (medicine, environmental monitoring, high energy physics, security and safety, photon science, or astronomy). Important parameters for radiation detectors are high charge carrier mobility and good radiation hardness. Here, diamond has been proven as a perspective semiconductor for the fabrication of ionizing radiation detectors. However, due to the high cost and scarcity of monocrystalline diamond, polycrystalline diamond (PCD) becomes a viable alternative. It has already been demonstrated that PCD exhibits comparable behaviour to monocrystalline diamond in terms of dosimetric properties, including good linearity and dose rate dependence. Here, we report the detection of alpha particles using a PCD layer (thickness of 3 um) grown on a boron-doped silicon (100) substrate. The current-voltage characteristics were measured at room temperature from -60 V to 60 V, and the dark current value was below 100 pA at 60 V. The fabricated PCD detector was placed in a vacuum and connected to a spectrometric set-up and exposed to monoenergetic 5.5 MeV alpha particles generated by 241-Am. The detected spectrum of prepared PCD detector shows peak corresponding to alpha paricles. The relative energy resolution defined as the full width at half maximum divided by peak position is about 10%. Further optimization of PCD detectors in term of their thickness and active area is prepared. ACKNOWLEDGEMENTS: This work was supported by the grant No. SK-CZ-RD-21-0116 (CZ no. LU-ASK22147) and APVV-22-0382.

The unique valley-type electronic band structure found in 2D materials has positioned them as excellent candidates for the development of cutting-edge spintronic and valleytronic devices. However, the presence of intricate excitonic energy levels (such as neutral, charge, and localized excitons) and defects bands reduce the electronic and optical efficiency, limiting their potential for practical applications. Consequently, comprehending and controlling the transition of various quasiparticle energy levels between K and K' becomes crucial. In this study, we systematically introduce sulfur isotopes into monolayer WS2 grown via chemical vapor deposition and explored optical response of neutral excitons, neutral and charge biexcitons, trions, and localized excitons under resonance excitation. Given that the optical properties of WS2 are heavily influenced by the external variables, we vary the magnetic fields from 0 to 14 T at fixed temperatures of 4K, 80K, and 300K to gain a deeper understanding of optical transitions at K and K', the formation of quasi-particles (specifically spin qubit coupling), and the intricate interplay between photons and phonons. Our findings thus provide valuable insights for the design and optimization of future devices utilizing 2D materials.

We report the optical and transport properties of a multilayer system constituted by ITO, an square lattice of Ag NPs on the uniaxial LiNbO3, the polymer PMMA and a substrate of SiO2. We investigate the compositional and geometrical parameters dependences on the stacked layers optical absorption. The effective dielectric function of the ensemble aggregates of Ag NPs and uniaxial LiNbO3 crystal are treated through the extended Maxwell-Garnett approximation [1]. The multilayer absorbance A = 1 - R - T, where R and T represent the reflectance and transmittance, respectively, is determined by means of the transfer matrix method [2]. We observe that the conditions for which the filling factor is higher, the system absorbance is greater. In addition, we evaluate the dielectric modulus parameter and the ac-electrical conductivity [3] of the effective medium layer (active layer) in the perpendicular and parallel directions of the Ag NPs plane. For both directions, when the filling factor is high enough, we find the negative epsilon condition, typical issue observed in metamaterials. For the ac-electrical conductivity, we identify different resonances for the perpendicular and parallel directions of the Ag NPs plane, which correspond to different dielectric functions of the effective layer in the perpendicular and parallel directions of the Ag NPs plane. REFERENCES: [1] T. Menegotto and F. Horowitz, Applied Optics 53 (2014) 2853.; [2] M. Born and E. Wolf, Principles of Optics, Cambridge University Press (1999).; [3] N.S. Kumar, R.P. Suvarna and K.C.B. Naidu, Materials Chemistry and Physics 223 (2019) 241.

High-power lasers operating in the infrared range 2 -3 μm represent a key component of advanced devices such as eye-safe laser micromachining apparatus, navigating and tracking systems, chemical sensors, etc. However, the further improvements in lasers and related final devices are facing a shortage of suitable materials. The common silica glasses exhibit limited spectral transparency while chalcogenide glasses with good transparency in infrared exhibit low thermal and chemical stability which limits the laser emitted power. Transparent ceramics can bridge these shortcomings for high thermal stability, high transparency in infrared and low-phonon energy.
In this contribution, we propose a versatile approach to nanocrystalline coatings of Ho-doped La2Zr2O7 phosphors. Transparent coatings with tailored structural and morphological properties were prepared by sol-gel method followed by customized radiation thermal treatment. We studied the effect of the nanocrystal morphology on the optical properties with special scope on the luminescence at 2.1 and 2.9 μm. The nanocrystal size and density of the coatings increased with increased processing temperature and time. The refractive index correlated with the nanocrystal size reaching the value up to 2.28 at 640 nm. Although, the coatings exhibited a strong photoluminescence at 2.1 μm with a decay time of 6.48 ms, the observed intensity of the emission at 2.9 μm was limited.
The demonstrated nanocrystalline materials represent promising alternative to conventional silica or chalcogenide glasses allowing the construction of planar solid-state lasers with enhanced stability.

Recently, Sc-Sb-Te material has been found to enable ultrafast crystal nucleation due to the formation of Sc-stabilized octahedral motifs in the amorphous phase, which makes it suitable for phase change memory applications. In comparison with solid phase memories based e.g. on Ge-Sb-Te nucleation might be faster and more efficient. The properties and structure of the material may be affected by the presence of oxygen present either in the precursors or as a result of oxidation of the material after its preparation.
The layers of various Sc:Sb:Te ratios were prepared either on glass or on silicon wafers by magnetron sputtering using two cathodes (Sc and Sb2Te3). The assumed thickness of the layers was cca 200 nm. Axima Resonance MALDI TOF Mass Spectrometer (Shimadzu), afforded with ion trap and pulsed nitrogen laser (337 nm, 10 ns), was employed to characterize deposited thin films.
Peaks of oxidized species were identified in the mass spectra as a proof of oxidation of the material. In addition, differences in mechanical properties between layers of different composition were observed due to differences in laser energy of ablation treshold. Mass spectrometry, specifically LDI-TOF-MS was thus proved as fast, sensitive and efficient tool for characterization of Sc-Sb-Te thin layers. ACKNOWLEDGEMENTS: This work was supported by projects no. 22-07635S (Czech Science Foundation), no. MUNI/A/1301/2022 and no. MUNI/A1298/2022.

Linking data derived from optical, atomic, and electron microscopes has facilitated genuine correlative multimodal analysis of experimental samples. This comprehensive approach enables the correlated assessment and visualization of a diverse array of encompassing structural, chemical, mechanical, electrical, and magnetic properties ranging from biology to the analysis of semiconductors, nanomaterials, and their interfaces. Self-sensing atomic force microscopy (AFM) cantilevers play a key role, where the choice of tip material is of key importance. This study presents the fabrication method for applying a thin conductive boron-doped diamond (BDD) coating to self-sensing AFM cantilevers. BDD has recently attracted interest in many areas of R&D due to its exceptional properties like hardness, adjustable hydrophobicity, and resistance to biofouling.
In this contribution, motivated by the fabrication of BDD self-sensing AFM cantilevers, we present a comprehensive exploration of the fabrication process and its key parameters. This includes an investigation into the impact of gas composition, the CH4 and N2 concentrations and the growth temperature, on the morphology evolution and growth kinetics of synthesized BDD films. BDD films with a B/C ratio (2 000 and 10 000 ppm) were successfully grown over CH4 concentrations from 0 % to 30 % and growth temperatures from 1000 °C down to 700 °C. Our study examines surface morphology and growth mechanism by scanning electron microscopy. Additionally, we evaluate the quality of the synthesized films employing Raman spectroscopy. We established the bases for further optimization of the deposition process, focusing on refining both the structure and materials employed in self-sensing AFM cantilevers, emphasizing gas composition.

The development of advanced devices, such as fuel cells, electro-active polymer actuators, and supercapacitors, relies on the mechanical reliability of nanoporous carbon film electrodes. However, the inherent fragility of these electrodes has been a significant hindrance to achieving long-term stability. In this study, a dramatic improvement in the robustness of nanoporous carbon film electrodes is demonstrated, overcoming their conventional brittleness. Remarkable enhancements in the mechanical properties of the electrode are achieved by thermal reconfiguration of the nanostructure of electrodes. Compared to previously reported intrinsic properties, the Young's modulus, tensile strength, and elongation are highly improved. The key to this improvement lies in the nanostructural interconnections formed among neighboring carbon agglomerates through the self-alteration of the ionomer binding and filling of small voids during the ionomer's melt flow over the transition temperatures. Additionally, the electrical characteristics of these nanoporous carbon films are investigated. The thermal transitions of the few-nanometer ionomer binder cause the reconfiguration of charge conductors, optimizing continuities in ionic and electronic conductors. As the reconfiguration temperature increases, the nano-networking of these conductors experiences significant self-enhancement. Electrochemical impedance spectroscopy further confirms the enhancements in ionic and electronic resistances due to the higher degree of nano-networking in the conductors.

Magnetic nanoparticles (MNPs), in particular spinel ferrites, have been intensively scrutinized by the scientific community due to their inherent magnetic properties exploitable in various biomedical, environmental, sensing, and information storage applications. The common strategies of tuning their properties count on controlling the size, shape, and rational substitution of the MNPs; recently, smart surface functionalization with magnetic and chiral molecules has been successfully introduced. In this work, spin hybrid MNPs obtained via coupling of the MNPs with magnetic complex molecules will be presented. The synthetic strategies include “tail-head” on-particle synthesis, click chemistry and seed-mediated growth. Two classes of spin hybrid MNPs were obtained: i) three-dimensionally (3D) interconnected networks, each of which associates two different spin components, and ii) core-shell type MNP - spin cross-over (SCO) hybrids. The resulting nanomaterials were characterized by transmission electron microscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, and Fourier-transform infrared spectroscopy, and the proposed morphology and composition were confirmed. Finally, magnetic properties were explored using SQUID magnetometry, and the effect of coupling the MNPs to the magnetic molecules was determined. In the 3D networks and in the core-shell architectures, the experiments revealed an increase in the mean blocking temperature (in the thermodynamic equilibrium limit) and mean magnetic moment per MNP. Also, the SCO temperature was found to be significantly increased compared to the original SCO polymer.

The development of technology in recent years requires cheap high-performance magnets, ideally ones that do not contain rare earth metals or noble metals. Fe-Ni based alloys seem to be promising materials especially the Fe50N50i L10 phase (tetrataenite) has a great perspective for the production of hard magnetic materials. In this study, a promising method of preparation of nanoparticles of this alloy from iron-nickel oxalate precursor was studied. The coprecipitation method was used to prepare oxalate precursors, which were subsequently subjected to controlled thermal decomposition in a reducing hydrogen atmosphere. The morphology and properties of the obtained particles were studied using scanning electron microscopy (SEM) connected to energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Mössbauer spectroscopy (MS), respectively magnetic measurement.
SEM analysis showed that the particles had an approximately cube-shaped unit cell morphology with a size in the range of 1 - 2 m. showed a change in magnetic behaviour. The samples after annealing contain several phases with variable content Fe-Ni. The formation of magnetically suitable Fe-Ni phases in the samples after annealing was confirmed by magnetic measurement. Mössbauer spectroscopy proved to be a very suitable and beneficial method for characterizing individual phases of the Ni-Fe system.

Diamond and transition metal dichalcogenides (TMD) are materials that exhibit distinct chemical, physical, and opto-electronic characteristics. Their combination into diamond-TMD heterostructures (D-TMD) can benefit from the complementary properties of these two components. For this reason, various technological procedures are being studied and optimized to obtain D-TMD heterostructures in various configurations, which will be usable for a wide range of applications (e.g. sensors, photonics).
In this work, we focus on the technological challenges related to the preparation of D-TMD heterostructures (specifically diamond with MoS2 or PtSe2), comparing the difference between the growth mechanism of diamond on TMDs and TMDs on diamond. From an application point of view, we introduce a functional diamond-MoS2 conductivity gas sensor. By combining the two-dimensional subsurface hole gas (2DHG) P-type conductivity of diamond and the inherent N-type conductivity of MoS2, the prepared sensor exhibited improved sensitivity to oxidizing (NO2) and reducing (NH3) gases at room temperature. Furthermore, through theoretical calculations, we demonstrate a method to precisely adjust the spectral position of the leaky modes of the diamond-based photonic crystal structure. This fine-tuning is achieved without post-processing of the diamond itself, involving only the MoS2 (multi) layer(s) on top of the photonic structure. ACKNOWLEDGEMENTS: This work was supported by the MoRePro project No. 19MRP0010 and funding from the Slovak and Czech Academy of Sciences.

Reducing the size of a diamond to the nanoscale leads to the emergence of several unique properties that are not inherent in a bulk diamond. One example is the formation of strongly positive zeta potential in water after hydrogenation of diamond nanoparticles, nanodiamonds (NDs). However, the origin of the highly positive zeta potential of H-NDs and relationships between H-ND, and the formation of the positive zeta potential is unclear.
Here, we present a comprehensive study aimed at maximizing the positive zeta potential of H-ND by understanding the contribution of H-ND parameters to the formation of the positive zeta potential. The strategy is based on the variation of the H-ND parameters and hydrogenation temperature. The monitored ND parameters are: size, microstructure, nitrogen content, level of hydrogenation, and non-diamond carbon content. To achieve this, we use two distinct ND samples; defective and sp2-C rich detonation nanodiamonds (DND) with 3-6 nm in size and 2.3 at.% of the nitrogen content, and high-pressure high-temperature nanodiamond (HPHT ND) with a monocrystalline structure, low sp2-C, and low nitrogen content down to few ppm. Hydrogenation temperature varied between 500-1000°C which covers the partial ND hydrogenation (500-600°C), full hydrogenation (700-800°C), and full hydrogenation + generation of sp2-C surface structures (900-1000°C).
The H-ND zeta potential is then related to the ND parameters and their evolution, which are evaluated using a set of complementary analytical techniques; transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) that together provide a comprehensive picture.

Optically active nanodiamonds (NDs) have gained significant importance as the material of choice for biological, optoelectronic, and quantum applications. However, current production methods lag behind the real needs. In this work, we investigate the photoluminescence (PL) properties of silicon-vacancy (SiV) color centers in nanodiamond particles (NDPs) prepared using a microwave plasma chemical vapor deposition (CVD) system. We show that this approach is a promising alternative method of producing engineered nanodiamonds with active doping. NDPs are obtained by the ultrasonic disintegration of porous diamond films grown by Bottom-Up approach by molten salt thermal etching treatment (ACS AEM 1 (2023) 1446) and Top-Down approach from porous films- ACS Omega 4 (2019) 8441) , then both porous diamond layers were disintegrated, purified and sonicated into diamond nanoparticles/clusters (colloids). The precursor diamond porous films and the obtained NDP were characterized by various complementary analytical techniques (SEM, TEM, DLS) focusing on Raman and PL measurements in dependence on the surface chemistry and the morphology (porous film vs. NDPs). We show that the SiV PL intensity of the NDPs remained the same as that of the initial diamond porous films and the SiV PL sensitivity to hydrogen and oxygen terminations was preserved. In particular, an enhancement of the SiV zero-phonon line (ZPL) emission was observed after the O2 plasma treatment.

Recently, vanadium oxides and other semiconductor substrates have been intensively studied for surface-enhanced Raman scattering (SERS) due to their advantages such as greater uniformity, stability, and spectral reproducibility compared to plasmonic substrates. The main limiting factor is the lower enhancement, which is why new materials and procedures for substrate preparation are still being sought. The combination of vanadium oxide substrates with various noble metals has shown promise for enhancing the signal while retaining the previously mentioned advantages.
The substrates for SERS measurements were prepared using a novel plasma-based gas aggregation technique, where a silicon wafer was coated with a vanadium pentoxide/metal composite. The size, shape, and spatial distribution of the nanostructures can be customized to optimize the SERS enhancement factor. The analyte solution was dropped to the substrate's surface and subsequently air-dried. SERS spectra were acquired using a confocal Raman microscope with a 632.82 nm excitation wavelength.
SERS spectra of methylene blue in an initial concentration of 10^-6 M were measured to determine the optimal parameters for preparing the substrates. We observed significant enhancements compared to vanadium oxide substrates without noble metals (Ag, Au) while maintaining spectral stability. These measurements demonstrate the promising potential of vanadium oxide/metal substrates for achieving higher signal enhancements. We suggest that further research and exploration of alternative material combinations and shapes of nanostructures are promising for advancements in this field. ACKNOWLEDGEMENTS: Support by grant 22-16667S from the Czech Science Foundation.

Tellurium-containing compounds are used in practical applications such as metallurgy as a carbide stabilizer in cast iron, in medical diagnosis, and in molecular imaging (quantum dots). The successes of Te-based compounds suggest highly practical uses for other Te-based compounds. Synthesis of TeC has not been described in the literature. Laser ablation synthesis (LAS) coupled with mass spectrometry was used here for in situ TeC clusters synthesis and identification of the reaction products to better understand TeC formation.
Laser desorption ionization time-of-flight mass spectrometry (LDI-TOF-MS) was used to generate TeC clusters and determine their stoichiometry via computer modeling of isotopic patterns. Various sources of carbon were tested: graphite, graphene, graphene oxide, and nanodiamond.
In this work, via adsorption of carbon nanoparticles (nanodiamonds) from suspension to Te particles composites were prepared. Suspension of fine-powdered Te was mixed with a suspension of nanodiamonds (both in acetonitrile), and the resulting precipitated nanocomposite was suitable for the synthesis of binary tellurium carbide clusters (TemCn+/-) using LDI. Various unary and binary clusters were formed. In addition, hydrogenated clusters TemCnH+/- (n = 1-9) were observed.
The Te-nanodiamond nanocomposite was found to be the most suitable precursor for the generation of binary tellurium carbides clusters. In total, 35 binary TemCn+/- clusters were identified, when several of them were not obtained using commercial TeC material. ACKNOWLEDGEMENTS: Supported by the Grant Agency of Czech Republic: project no. GA22-07635S and Masaryk University: project no. MUNI/A/1298/2022 and MUNI/A/1301/2022.

High-power lasers operating in the infrared range 2 -3 μm represent a key component of advanced devices such as eye-safe laser micromachining apparatus, navigating and tracking systems, chemical sensors, etc. However, the increasing laser power is limited by low thermal stability and high phonon energy of suitable materials. The common silica glasses exhibit limited spectral transparency and high phonon energy. Widely used chalcogenide glasses shows good transparency in infrared and low phonon energy, but exhibit low thermal and chemical stability which limits the laser emitted power. Transparent ceramic can bridge these shortcomings for high thermal stability, high transparency in infrared and low-phonon energy.
In this contribution, we propose a generic approach to Ho3+-doped nanocrystalline luminophores crystallizing in the pyrochlore lattice with the general formula A2Ti2O7 (A=Y, Lu, Yb). Nanocrystalline ceramic with tailored structural and morphological properties was prepared by sol-gel method followed by thermal treatment. We studied the effect of the nanocrystal morphology and chemical composition on the optical properties with special scope on the luminescence at 2.1 and 2.9 μm. The nanocrystal size increased with increased processing temperature and time. The phonon energy slightly decreased with increasing molar mass of the crystal lattice. Although, the studied compounds exhibited a strong photoluminescence at 2.1 μm with a decay time longer than 4.5 ms, the observed intensity of the emission at 2.9 μm was limited for the presence of residual -OH groups. The demonstrated nanocrystalline materials represent promising alternative to conventional silica or chalcogenide glasses allowing the construction of planar solid-state lasers with enhanced stability. ACKNOWLEDGEMENTS: This work was supported by the Czech Science Foundation, contract No 22-14200S.

Single standing (MnO2, WO3, or ZnO) nanowires (NWs) were deposited by means of dielectrophoresis upon two perpendicularly aligned gold electrode transducer and tested electrically. NWs were mainly self-made, either by hydrothermal or AACVD synthesis. They were up to 10 μm long and less than 100 nm in diameter. To envision the semiconductive behavior of those nanowires, impedance spectroscopy and Mott-Schottky capacitance-voltage (CV) analyses were performed in solid state (without an electrolyte) at diverse parameters, e.g., frequency, illumination, etc. Schottky barrier height of the diverse gold/NWs interfaces was estimated by CV or current-voltage measurements. Moreover, charge carrier concentrations, semiconductor type (n-, or p-type) and interface depletion layer thickness were estimated with careful consideration and subtraction of parallel side capacitances, such silicon substrate capacitance. This research is intended for future gas sensing experiments based on single standing NWs. Different gas ambiences, such as NO2, ethanol, H2, etc., will be explored.

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induced the generation of spin separated species including electron/hole (e-/h+) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e-/h+ pairs and triplet species depend on the solvent polarity, featuring a substantial stabilization of the triplet state in non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerged from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties have been dissected theoretically by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakes model systems, revealing the importance of the size-dependence and interlayer effects. The formation of the spin separated states in Asp-CDs enabled the photoproduction of hydrogen peroxide from water and water/2-propanol mixture via water oxidation reaction.

In order to enhance the dielectric properties of the dielectric, carbon-based low-dimensional materials such as carbon nanotubes (CNT) or graphene were mixed or placed at the interfaces within the polymer-based dielectric. Electroluminescence (EL) devices containing such dielectric materials were fabricated, where organic or inorganic materials served as the luminescent layer. When CNT was mixed, the current decreased (turn-on voltage decreased by a minimum of 5 times, and current decreased by 70%), and the brightness improved, leading to an enhancement in the efficiency of the luminescent device. This improvement was achieved by maintaining the CNT concentration below the critical concentration and using short-length CNTs to suppress percolation networking.
The quality of the dielectric layer, composed of a polymer-based composite material, such as cyanoethylated-pullulan (CEP), was also crucial for enhancing the luminescence characteristics of AC-driven inorganic EL devices. When chlorinated CNTs were used, the brightness improved by 50% compared to the control luminescent device, and the current decreased by 30%, demonstrating the best performance. Additionally, by mixing 2D nano-material, reduced graphene oxide (rGO), within the dielectric layer, the chemical reduction time of rGO was adjusted (6, 12, 18, 24 hours). The dielectric film containing rGO with the second-longest reduction time exhibited the highest performance, showing the same trend in inorganic EL devices incorporating it. The balance between the removal of oxygen-related functional groups attached to the rGO surface during the reduction process and the attachment of additional functional groups from the reducing agent was found to be crucial in achieving these results. To obtain high-quality dielectric films from CNTs and graphene, it was evident that the percolation among these nano-materials needed to be suppressed.

Single-crystalline silicon with a porous structure at the micrometer to nanometer level is currently used as a sensor for electrochemical or optical-based detection because of its exceptional optical, surface, and electronic properties. However, further research into this structured nanomaterial is ongoing and points to its potential use in other detection and sensor fields. This work focuses on the careful preparation and application of porous silicon sensor substrates for the detection of perfluorooctanoic acid (PFOA). PFOA is captivating because it is a known contaminant and a substance that the human body cannot naturally excrete, which over time leads to the accumulation of this compound in the blood and organs and can cause health complications. In the first step of the realization of the work, a number of samples with different morphologies and sizes of the porous structure were prepared and the best ones were used in the subsequent step. Then, the porous Si surface was coated with a thin layer of gold by a vacuum sputtering method to increase the surface conductivity and introduce plasmon-active properties. The sample surface was modified with amino-containing organic moieties to ensure high surface affinity towards PFOA molecules (and their selective capture). The successful modification of the surface morphology, chemistry, and properties was verified by SEM, UV-vis, and IR spectroscopy. PFOA detection was subsequently performed in two modes: electrochemical impedance spectroscopy (EIS) and surface-enhanced Raman spectroscopy (SERS). The EIS and SERS experiments showed that a reliable determination of the PFOA is possible at a concentration in water up to nanomoles/liter. In conclusion, the successful experiments in the detection of PFOA give us hope that the developed sensor could be used for the detection of other hazardous substances with similar size, structure, and functional groups.