Seznam abstraktů 2021: POSTEROVÁ SEKCE A

Despite the many advantages over conventional semiconductor quantum dots, the application potential of photoluminescent gold nanoclusters is limited by their relatively low quantum yield. Plasmonic enhancement is a common strategy for improving the performance of weak fluorophores, yet in the case of gold nanoclusters this method is still poorly explored. Here we present a detailed study of combining gold nanoclusters with plasmonic gold nanorods in a compact core-shell nanostructure with significantly enhanced photoluminescence. The extraordinary degree of control over the structural parameters of the hybrid nanoparticles allows us to study the effect of several parameters such as excitation wavelength, nanocluster-nanorod distance, and relative loading of nanoclusters per single nanorod. The highest photoluminescence intensity enhancement (4.4x) was obtained when excitation wavelength matched the strong longitudinal plasmonic band of gold nanorods and when the separation distance between nanoclusters and nanorods was decreased to 5 nm. The presented results are relevant not only for application of AuNCs in optoelectronic devices, but also in photosensitization and catalysis.

In this contribution the ceramic nanoparticles, BaTiO3 (BT), were successfully and controllably coated with two monomers, poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) using SI-ATRP approach. The presence of the polymers on the surface was investigated using FTIR and TGA techniques. The molecular weight and polydispersity index were calculated from the gel permeation chromatography, while monomer conversion was confirmed using nuclear magnetic resonance. Both methods provide clear statement that controlled radical polymerization was successful. The surface of the neat BT, BT-PBA and BT-PMMA nanoparticles was investigated using BET analysis and using contact angle. The nanoparticles were mixed with poly(vinylidene fluoride) (PVDF) using micro compounder. The compatibility of the nanoparticles and PVDF matrix was evaluated investigation of the viscoelastic properties using dynamic mechanical analyzer. The contribution of the enhanced compatibility between the nanofiller and matrix was elucidated by electrical response to vibration testing. Finally, it will be presented how the SI-ATRP modification of BT nanoparticles with PBA and PMMA influence the capability for vibration sensing applications.
ACKNOWLEDGMENTS: The authors gratefully acknowledge the Czech Science Foundation grant no. 19-17457S for the financial support. This work was supported by the Ministry of Education, Youth and Sports of the Czech republic - DKRVO (RP/CPS/2020/003).

The low resistance of ohmic contacts on diamond is important for the fabrication of diamond power electronic devices with fast switching capabilities for future high voltage applications. The low barrier height between the metal and diamond, high doping and elevated temperature are the most critical parameters to reach the low contact resistivity.
In this work, we characterize titanium/gold ohmic contacts on the heavily boron-doped (113) epitaxial diamond layers. Titanium (Ti) is one of the most commonly used metals to fabricate ohmic contacts on boron-doped diamond. Ti ohmic contacts covered by gold cap layer have a good thermal stability. Epitaxial boron doped diamond layers were grown using a 1.5 kW resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition system (AX5010) from Seki Diamond Systems. The nanostructure of the (113) diamond surface was characterized by the atomic force microscopy and scanning electron microscopy. The circular contacts were patterned by lift-off method. The metal layers were evaporated using Angstrom Covap and annealed at temperature up to 700 °C. The electrical measurement was done using precision semiconductor parameter analyzer - Agilent 4156C with the probe station Cascade Mictotech M150 .
The contact resistance has been analyzed by the Circular Transmission Line Model (C-TLM). We used the analytical model of thermoemission, field enhanced emission and the image force influence including Fermi level position dependence on the boron concentration. We used the Silvaco TCAD 2D simulation to estimate the measurement error connected to the nonzero metal resistance. The resulting simulation values are consistent with the experimental results.

In recent years, there has been a clear shift from conventional fossil fuels to systems based on renewable energy and the production of clean energy from hydrogen. The lack of active and stable electrocatalysts for the oxygen reduction reaction (ORR) generally limits feasibility of hydrogen utilization as a fuel and requires the development of new advanced materials. In this work, we present an effective plasmon-enhanced catalysts for ORR based on carbonized iron-doped polypyrrole nanotubes (PPyNTs). PPyNTs were annealed at different conditions to obtain Fe-4N type catalysts. The morphology of the prepared nanostructures was analysed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After the optimization of the preparation conditions, particular attention was given to introducing of plasmon-active component, for which metal nanoparticles (MeNPs) were chosen. The successful introducing of MeNPs into the catalyst and preservation of its nanostructure was again confirmed by SEM, TEM and the chemical composition was analysed by X-ray photoelectron spectroscopy. The ability of the polypyrrole to retain its morphology upon to graphitisation is of outmost importance, for the construction of such applications such as photoactive electrodes and high-area catalysts. We showed that the introducing of MeNPs as a plasmon component, resulting in enhanced catalytic activity for ORR compared to non-photosensibilized structures. Overall, high surface area, porous structure, catalytic activity make the annealed polypyrrole structure with plasmon component an attractive for practical applications in fuel cell.

Using density functional theory (DFT), time-dependent density functional theory (TD-DFT), and Green-function-based many-body theory (GW+BSE) we investigated the electronic structures and the optical properties of a set of 2D materials (group III-V structures, graphene derivatives, TMDs). We provided the basic properties with the generalized gradient approximations (GGA) density functional (namely PBE) and hybrid functional (namely HSE06). Further, we obtained the optical gaps and absorption spectra for these 2D semiconductors by time-dependent density functional theory based on scissor-corrected PBE and HSE06 density functionals. The optical gaps provided by the TD-HSE06 method for these materials range between 1 and 6 eV and agree well with the same from reference many-body GW+BSE calculations. Thus, the time-dependent HSE06 approach has been shown as a promising and effective first principle approach for excitonic effect in 2D semiconductors.

In recent years, many efforts have been made for the development of graphene/metal nanocomposites that would demonstrate, excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties, so they could be utilized in various scientific and technological fields. Especially, the incorporation of silver nanowires (AgNWs) in graphene derivatives, have attracted particular attention, because, due to their morphological characteristics (e.g. shape, size), they can build an efficient conductive network and, notably, improve the electrical properties of the composite. Therefore, in this work, hybrids of simultaneously reduced and functionalized graphene oxide (rGO) and AgNWs - in different ratios - were effectively developed and characterized by various methods (including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal analysis (TGA/DSC) and electrical measurements). A sulfonated aromatic diamine was used as reducing agent for the efficient reduction and functionalization of GO in the presence of preformed AgNWs made by a facile polyvinylpyrrolidone (PVP)-mediated polyol method. The as prepared rGO/AgNWs composites exhibited high conductivity and dispersibility in water, due to the synergistic effect of their components, so they are considered as very promising materials to be used in a broad range of applications such as conductive inks for flexible electronics and sensors.

Recently, binary metal sulphides such as CoS, FeS and NiS have been used in many fields due to their abundance in nature, high electrocatalytic activity and electrical conductivity. Many strategies have been developed to synthesize metal sulphide structures, including direct elemental reaction in a high-temperature quartz tube, ball mill solid-state metathesis reaction, chemical vapor deposition, thermal decomposition, hydrothermal, solvothermal, sonochemical, and electrochemical. However, most of these synthesis strategies have disadvantages such as long time at high temperature or high-pressure conditions, complex processes and requiring advanced equipment or technical skill to prepare precursor materials. The microwave method attracts attention because it is very fast, very efficient, and environmentally friendly in the synthesis of nanomaterials. Among photovoltaic devices, dye-sensitized solar cells (DSSCs) have been studied intensively due to their advantages such as short repayment time, low cost-performance ratio, and simple fabrication processes. In this study, a simple, cost-effective, and ultrafast microwave method for preparing ternary Fe-Co sulphides (FeCo2S4) is reported for the first time. The obtained FeCo2S4 nanoparticles were successfully produced and their usability as counter electrodes in DSSC was investigated. The nanoparticles films produced were characterized by SEM, XRD, XPS, Raman, TEM, TGA, CV, and electrochemical impedance (EIS) measurements. In photovoltaic analysis, the conversion efficiency of nanoparticles DSSCs increased compared to binary FeS counter electrode cells. As a result, it has been determined that produced nanocomposites can be used in DSSCs instead of Pt, which is expensive and has limited stock in terms of both cost and durability and photovoltaic performance.





Acknowledgement: Authors would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK Grant Number 120M101) for the financial support of this research.

Colloidal semiconductor quantum dots (QDs) are known to show optical and electrical properties which depend on their size, shape, and composition. When large numbers of interacting QDs are combined in assemblies, they can create “artificial solids,” which are expected to yield novel properties. In such assemblies, QDs are coupled via long-range dipolar interactions, which allows for exciton diffusion as a result of the energy transfer (ET) process. In turn, such new materials have many potential technological applications in the areas of photovoltaics, sensing, or information processing. However, strong ET in QDs assemblies can also negatively impact the performance of some devices, such as QD-based light-emitting diodes (QLEDs). In theory, the negative impact of ET process can be limited by growing QDs of thicker shells, which results in better spatial separation between centers of QDs. Here, we examine homo-ET between monodisperse core/gradient-shell CdSe/CdZnS QDs emitting at 1.928 eV (close to “deep-red”) that display a narrow emission spectrum and have about 90% of luminescence quantum yield. The investigated QDs are characterized by relatively thick shell, which allows to limit ET process between QDs contained in a densely packed film. The impact of ET on optical properties of such film is investigated experimentally by means of time-resolved spectroscopy. It is shown that for such QDs, ET occurs predominantly between QDs of very different sizes, from high to low energy tails of the emission spectrum, and for this reason its negative impact on the emission properties of the film is limited.

The success of graphene opened a door for a new class of semiconducting 2D transition metal chalcogenide materials (TMDs) displaying unique properties [1]. ALD MoS2, as TMDs benchmark, has been widely studied for several applications. In parallel, 2D selenide and telluride analogues, i.e. MoSe2 and MoTe2, have also attracted important interest due to intriguing properties, such as a higher electrical conductivity than that of MoS2 among others [2, 3].
Recently, we have demonstrated the ALD synthesis of both 2D MoSe2 [4-7] and 2D MoTe2 [8] (using an in-house synthesized precursors), as well as their outstanding performances in different applications. XPS turned a key tool to provide detailed chemical composition analysis of as-deposited 2D Mo TMDs family on different nature substrates. Besides, the post-performance XPS characterization was appealing since the applications of the aforementioned 2D materials involved chemical and/or electronic processes on the surface and it enabled to identify potential chemical composition changes and physico-chemical photo-electro stability of the 2D TMDs. This presentation will thus focus on the XPS as key tool for assessment of chemical composition of both as-deposited and post-performance 2D Mo TMDs family, recent experimental results as well as the description of some inherent drawbacks that XPS must face during the analysis of the 2D materials.
REFERENCES: [1] A. V. Kolobov, J. Tominaga, Two-Dimensional Transition-Metal, Dichalcogenides. Springer Series in Materials Science, Springer International Publishing AG, Switzerland 2016.; [2] D. Kong, H. Wang, J. J. Cha, M. Pasta, K. J. Koski, J. Yao, Y. Cui, Nano Lett. 2013, 13, 1341.; [3] A. Eftekhari, Appl. Mater. Today 2017, 8.; [4] R. Zazpe et al, FlatChem 2020 21 100166.; [5] J. Charvot et al, Chempluschem 2020 85 576.; [6] J. Rodriguez-Pereira et al, Surf. Sci. Spectra 2020 27 024006.; [7] R. Zazpe et al, ACS Appl. Nano Mater. 2021, 3, 12, 12034.; [8] R. Zazpe et al, Appl. Mater. Today 2021, 23, 101017.

There are many processes and modifications for the production of graphene oxide (GO) that are based on the original synthesis by W.S.Hummers and R.E.Offeman (1957), B.C.Brodie (1859) or L.Staudenmaier (1898). Not all modifications produce high-quality material. The GO production process we use is a modified production according to Mr. W.S.Hummers and Mr. R.E.Offeman. Because the synthesis itself consists of several individual steps each step must be controlled in order to achieve the best result. Quality control at every step helps us to reduce the content of impurities and increase the yield of the final product. Impurities can be toxic or electrochemically active and thus have a direct effect on the application of the produced material. The ideal result is that the final product will contain only GO with individual large sheets and will not contain any other impurities and byproducts from synthesis such as potassium, chlorine, sulfur, manganese salts, or non-exfoliated graphite oxide. At the same time, we must reach sufficient production and small losses. We use Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM-EDX), X-ray Fluorescence (XRF), elemental analysis, Atomic Force Microscopy (AFM), UltraViolet-Visible Spectroscopy (UV-VIS), conductometer and pH meter to control the individual steps. The result of our production is single layer GO with large area sheets.

The preparation methods of three-dimensional (3D) heterostructures from individual sheets of two-dimensional (2D) nanomaterials remain a highly-interesting issue in materials science research. Thanks to the presence of synergistic effects related to physical or chemical bonding between different low-dimensional sheets, the prepared composite structures often exhibit unique properties, which are absent in the pristine parental materials. One of the most extensively investigated 3D systems are macroscopic aerogel structures based on transition metal carbides called MXenes with graphene derivatives. Typically, the preparation procedures are based on the reducing agent-assisted hydrothermal process which induces covalent bonding between the MXene and GO sheets. However, the process conditions such as the water environment and elevated temperature promotes the decomposition of environmentally unstable MXenes toward transition metal oxides. Herein, we present a novel approach of the preparation of aerogel heterostructures based on Ti3C2Tx (MXenes) and graphene oxide (GO) sheets. The colloidal solutions of both types of sheets underwent silane-grafting processes. The inter-sheet crosslinks between the amine groups of the aminosilanized sheets of both counterparts were induced using glutaraldehyde homo-crosslinker. The reacted solution was shock-frozen with liquid nitrogen and freeze-dried. The as-obtained MXene-GO aerogel, as well as similarly-prepared MXene and GO reference aerogels were investigated via scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared absorption spectroscopy (FT-IR), Raman spectroscopy and powder X-ray diffraction (XRD). Thanks to the capping of the MXene’s external Ti-atoms with Ti-O-Si bond, the MXenes in aerogel structure are protected from the environmental oxidation, thus can be potentially applied in environmental remediation.

Lightweight and flexible material with enhanced electromagnetic interference shielding effectiveness is highly in demand in the electronics and communication industry. Herein, we synthesized CoFe2O4 and ZnFe2O4 nanoparticles using the sonochemical method, and further, these nanoparticles embedded inside thermoplastic polyurethane (TPU) along with reduced graphene oxide (rGO) by melt-mixing approach using microcompounder. CoFe2O4 or ZnFe2O4 nanocomposites in the TPU matrix with rGO showed outstanding electromagnetic shielding performance having a constant thickness of 0.80 mm, only. The maximum shielding effectiveness, SET was found to be 48.3 dB for ZnFe2O4 nanocomposite and 50.76 dB for CoFe2O4 nanocomposite. These results indicate that the developed nanocomposite can be potentially utilized for electromagnetic shielding application.

The chemical vapor deposited (CVD) graphene with large monolayer coverage is preferred for applications over the mechanical cleavage of graphite. Large-area graphene has a lot of potential in electrochemical applications, e.g., as electrodes for supercapacitors, smart windows etc. Therefore, it is important to study the electrochemical doping of graphene with such a lateral resolution that enables the assessment of the influence of the local structure on the electrochemical performance. The recently developed micro-droplet in situ Raman spectroelectrochemical technique was used to provide insights into localized structural changes as a function of electrochemical doping as well as other parasitic redox reactions at small area (few hundreds μm2) of the 1L CVD graphene. The Raman frequency of the G peak was shifted by up to ⁓ 30 cm-1 for hole doping with all cl- based monovalent (3M, 6M LiCl) and multivalent (1.6M, 2.5M AlCl3) electrolyte salts. On the other hand, extensive shift in G peak frequency (ΔωG) 36 and 39 cm-1 was observed for ClO4- based 2.4M Zn ClO4 and 2.4M Al (ClO4)2. The larger doping level for ClO4- based salt illustrates the effect of ionic radii rather than ionic strength

Despite recent advances in the field of growth and development of applications of chemical vapor deposition (CVD) graphene, epitaxial graphene on silicon carbide remains highly attractive for several applications requiring high degree of crystallographic ordering, constant orientation of graphene in space, continuity of the layer over large areas and resistance to harsh external conditions. Electronics, especially devices working in difficult environment, are one of the biggest such applications. The main practical factor hindering its widespread adoption, is very high production cost.
Here, we present the design of a high vacuum reactor dedicated to the growth of graphene using partly reversible graphitization under Si flux [1] in the scale of 2” wafers. Process flows allowing for the synthesis and processing of material are described and the resulting graphene wafers are characterized using X-ray photoelectron spectroscopy, Raman Spectroscopy and Atomic Force Microscopy. Our results confirm a high degree of uniformity and continuity of obtained graphene layers, as well as lack of high steps created in the step-bunching mechanism.
Our results form the basis for the strong upscaling of the production of graphene on silicon carbide, especially after introducing processes at the 4” wafer scale, leading to decreased manufacturing costs and fostering its adoption into several key industry sectors.
ACKNOWLEDGEMENTS: We would like to acknowledge the financial support of the National Centre for Research and Development (grant no. TANGO-IV-A/0026/2019-00). REFERENCE: [1] P.Ciochoń, M. Marzec, N. Olszowska, J. Kołodziej, Appl. Surf. Sci. 528 (2020), 146917, DOI: 10.1016/j.apsusc.2020.146917.

Despite their great significance to the global industrial and technological sectors [1], [2], volatile organic compounds (VOCs) also contribute to the emission of greenhouse gases, thereby impacting adversely to the environment and humanity at large. As such, development of novel sensing materials has recently gained great prominence for implementation in portable VOCs sensing devices. Amongst such materials, graphene-based materials have been extensively used owing to their fascinating properties. Furthermore, easy modulation of their intrinsic properties via the intentional doping with boron (B) and/or nitrogen (N) atoms can bestow graphene with a variety of new or improved catalytic and structural properties required for VOCs sensing. Therefore, herein, the influence of the B/N domains on the electrochemical properties of variously co-doped reduced graphene oxide nanostructures was investigated. The BN-rGO materials were synthesized through microwave-assisted simultaneous reduction and co-doping technique using ammonia borane (AB) and tetramethylammonium borohydride (TMABH) as B and N sources. With 0.5 ratio for B/N domain, AB-based BN-rGO sensors were sensitive selective to both ethanol methanol, whilst the 0.3 B/N domain ratio limited TMABH-based BN-rGO sensors to detection of methanol. In hindsight, the study highlighted the significance of the B/N domains on the surface chemistry of co-doped graphene towards selective recognition of VOCs

The costs and production equipment complexity associated with the reduced graphene oxide (rGO) reduction process still limit its large-scale production from starting graphene oxide (GO) precursors. We demonstrate fast, low-cost, scalable, chemical-free, and low-temperature fabrication of rGO sheets using an electrical plasma-triggered reduction-exfoliation of GO sheets. The reduction-exfoliation realized using the atmospheric Diffuse Coplanar Surface Dielectric Barrier Discharge (DCSBD) plasma source in atmospheric-pressure N2 resulted in an approximately 105 fold decrease of the rGO sheet resistivity compared to unmodified GO sheet. The properties of the rGO sheets were examined using XPS, SEM, and Raman spectroscopy. It is believed that the method presented opens new opportunities for low-cost industrial-scale production of rGO sheets, rGO-based paper and rGO composites for various modern industrial applications.

Metal-graphene hybrids have gained considerable attention in many applications, due to the unique characteristics and the great advantages rising from the combination of the parent materials. In this work, the development of reduced graphene oxide-silver nanoparticles (rGO/AgNPs) was presented, and the effect of the metal loading on specific properties, such as hydrophilicity and electrical conductivity of these composites, was also studied. The post synthetic route followed involved the reduction of silver ions on the surface of preformed rGO. The reduced and at the same time functionalized GO (rGO) was developed using a sulfonated aromatic diamine. Sodium borohydride (NaBH4) was used as the reducing agent of the metal precursor (i.e. AgNO3). Four different silver loadings (5, 10, 15, and 50 wt%) were studied and used to prepare the nanocomposites. All the samples were fully characterized through X-ray diffraction (XRD) measurements, Scanning and Transmission Electron microscopy (SEM and TEM respectively), Thermogravimetric Analysis (TGA), while their electrical and dispersibility properties in various solvents were also evaluated. It was shown that the hybrids’ sheet resistance decreased with increasing AgNPs loading, improving the conductivity of the pristine rGO when the silver content became at least 10 wt%. The composites displayed excellent features to be utilized in a variety of electrical applications.

The self-organized 1D TiO2 nanotubular layers have attracted considerable scientific and technological interest over the past two decades, all motivated by a great performance in the range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses. The synthesis of these nanotubular layers has been carried out by a conventional electrochemical anodization of Ti sheet. Except the 1D character, these nanotubes possess unique features such as tunable dimensionality, structural flexibility, unidirectional electron transport through nanotube walls, chemical and mechanical stability and biocompatibility.
One of the major application targets of TiO2 nanotubes has been their utilization as scaffolds or templates for deposition of secondary materials towards new applications. In particular, for the photoelectrochemical applications (e.g. photovoltaics) TiO2 nanotubes offer the advantage of directed charge transport and controlled phase separation between the donor and acceptor materials, unlike within randomly ordered mesoporous TiO2 supports.
Numerous techniques were utilized for this purpose, such as for example hydrothermal routes, electrodeposition or Atomic Layer Deposition (ALD) techniques. Electrodeposition is very powerful technique to deposit metals, oxides or other rather complex materials (such as CuInSe2) within the nanotubes various by means of complete filling or decoration with. On the other hand, ALD can deposit the widest range of secondary materials within TiO2 nanotubes by means of homogenous coatings.
The presentation will be focused on various morphologies of TiO2 nanotube layers (including double- wall, single-wall ones) that are filled, decorated or coated by various materials using electrodeposition. Experimental details and some very recent photo-electrochemical and structural characterizations of a new type of heterostructured photo-chemical cell will be presented and discussed.

Diamond is seen as the best wide-bandgap semiconductor for the fabrication of high-performance high power and/or high-frequency electronic devices due to its outstanding properties. Recent studies have demonstrated the interest in (113) epitaxial diamond layers in the fabrication of diamond electronic devices thanks to the high growth rate, the high boron incorporation efficiency, the smooth and almost defect-free surface of diamond layers grown on this vicinal surface. After the control of defect and dopant concentration, the growth of multilayer with different dopant concentrations is the second necessary step in the fabrication of diamond electronic devices like Schottky diodes. The fabrication of a semi vertical Schottky diode requires the growth of bilayer which consists of a low boron doped diamond layer (p-) upon an heavily boron doped diamond layer (p++). The fabrication of this p++/p- bilayer is not straightforward due to the large lattice mismatch between low and highly boron-doped diamond layers which lead to the formation of cracks.
In this work, we present the study of the formation of cracks in diamond p++/p- epitaxial bilayer. Epitaxial diamond layers were grown on (113) substrates using a 1.5 kW resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system AX5010, Seki Diamond Systems in two steps. A five micrometer thick heavily boron-doped ([B]=1021 cm-3) diamond layer is grown first on the (113) substrate before the deposition of a none intentionally doped layer. Undoped diamond layers have been grown with different thicknesses and methane concentrations. Boron concentration in the layers has been determined by both Raman spectroscopy and secondary ion mass spectroscopy. Film thickness is determined by cross-section scanning electron microscopy after edge polishing. Cracks in the diamond layers have been observed by optical and electronic microscopies. Experimental results show there is a critical thickness of ca. 4 um above which all undoped layers are cracked. The formation of these cracks is attributed to the relaxation of elastic energy stored in the epitaxial undoped layer due to the large lattice mismatch (ca. 0.8 %) between the undoped and the heavily boron-doped diamond layers.
ACKNOWLEDGEMENTS: This work was financially supported by the project 20-11140S of Czech Science Foundation and the Operational Program Research, Development, and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. SOLID21 - CZ.02.1.01/0.0/0.0/16_019/0000760)

This research aims at synthesizing multilayer oxide thin films made of Al2O3 and Ta2O5 for dielectric applications. Multilayer thin films made of two, four, or eight oxide layers are synthesized by physical vapor deposition (PVD), specifically the mid-frequency pulsed direct current magnetron sputtering. The thin films are made of stoichiometric Al2O3 and Ta2O5 layers having a specific morphology observed from cross-section images obtained by scanning electron microscopy (SEM). The Al2O3 layers have a columnar structure whereas the Ta2O5 layers are uniformly dense. X-ray diffraction (XRD) characterizations show that these oxide layers have very limited crystallinity due to the experimental conditions used during the magnetron sputtering process, particularly the low temperature of the substrate.
The dielectric behavior of the multilayer oxide thin films is assessed by measuring their dielectric breakdown potential. The two layers and the four layers systems have intermediate values in comparison with the dielectric breakdown potentials measured for a monolayer of Al2O3 and a monolayer of Ta2O5 produced in the same experimental conditions. In the case of the eight layers system, the dielectric breakdown potential value is the highest one, even higher than that measured for a monolayer of Ta2O5.

A poor extraction of light from thin layers of materials with high refractive index often limits the efficiency of devices based on the photoluminescence or electroluminescence processes. One approach to improve the light extraction consists in a periodic patterning of the layer, i.e. fabrication of photonic crystal (PhC) slabs. Subsequently, the modes initially guided in the planar layer becomes leaky due to the Bragg diffraction of light on the PhC slab.
Light extraction from diamond is of particular importance because of the presence of color centers that have many promising applications in many fields ranging from sensors and medicine to quantum information processing. However, required accurate structuring of diamond is generally complicated due to its hardness and chemical inertness.
In this work, we will present a new method for spectral tuning of the leaky modes that is based on the overgrown of the existing nanoscale photonic structures with a thin layer of diamond. This method allows us to achieve optimal dimensions for the extraction of light emitted by silicon vacancy (SiV) centers. Furthermore, the SiV centers are created only in the top layer, which improves the sensitivity of the SiV centers on the effects in the surface vicinity. We will discuss rich background of diamond photonic structures and show how our method may improve practical performance of devices based on the photoluminescence of diamond color centers such as biosensors or sources of non-classical states of light.

Among the most important and actively used classes of materials one may point out scintillators. Scintillator transforms high energy ionizing radiation of X-, -rays, charged and neutral particles into visible or UV/VUV photons. One of the most important application is in detectors of incredibly sensitive time-of-flight positron emission tomography requiring very fast scintillators. At present, zinc oxide (ZnO) nanostructures have exhibited excellent timing properties. Corresponding photoluminescence (PL) spectrum is composed of a narrow UV exciton band demonstrating fast decay and a very broad defect-related band with slow decay within almost the whole visible spectral range. Growth conditions, doping and/or post growth treatment make influence on both signals. It is possible to tune the material properties to use either of these bands separately. The influence of Mo on the ZnO crystalline structure is not known yet. Therefore, the aim of this work is to study heavy Mo-doped hydrothermally grown ZnO structures (various doping levels from 2 to 25%) to discover the changes occurring to the ZnO and creation of new material phases. It has been found that, the increased Mo doping level resulted in the smaller amount of the ZnO and creation of zinc molybdates instead. The samples were additionally annealed in air at elevated temperatures. The creation of the paramagnetic Mo5+ and ZnO phase (due to the presence of the g = 1.96 shallow donor signal typical for ZnO structures) were detected by electron paramagnetic resonance (EPR). The EPR results were correlated to the data obtained by PL spectroscopy.

An understanding of the structures and shapes of metallic nanoparticles (NPs) is important because their mechanical, chemical, electronic, and optical properties can very different from those of bulk single crystals [1]. Although the thermodynamically stable shape of a larger particle should correspond to the Wulff construction, NPs with a small number of atoms need not have a fixed shape at the given temperature but maybe fluctuating dynamically between different shapes [2]. The mechanism of shape changes could be affected by preexisting internal interfaces belongs to the common twin boundaries which have relatively low energies. Such interfaces can nucleate during the growth of NPs. However, other types of special interfaces can also occur in consequences of faults during the growth. These interfaces result in bicrystal NPs whose equilibrium shapes depends on the boundary type [3].
In the present work we predict the shape of Mg NPs with different types of internal interfaces by using Wulff construction as well as using atomistic simulation. Atomistic simulation is used to study stability of NPs and possible evolution of internal interfaces inside NPs as well as for study of the kinetics associated with interface motion. ACKNOWLEDGMENTS: This research was funded by Brno University of Technology, specific research project grant number CEITEC-J-21-7507. REFERENCES: [1] Qian Yu et.al., Appl. Phys. Lett. 2015, 106, 261903.; [2] Emilie Ringe et. al., J. Phys. Chem. C 2013, 117, 15859−15870.; [3] Emilie Ringe J. Phys. Chem. C 2020, 124, 15665−15679.

Since the beginning of the 20th century, nitrides of the IV group transitional metals have gathered significant attention from the scientific and industrial sectors. To date, hafnium nitride (HfN) has been recognized as a promising material for plasmonic, hot solar cells, biosensing, decorative, and architectural glass applications. We report on a gas-phase synthesis of Hf and HfN nanoparticles (NPs) by reactive DC magnetron sputtering. To our best knowledge, Hf/HfN NPs have never been produced in such a way. For sputtering in Ar, metal Hf NPs are produced and characterized by a mean size of 19 nm, dodecahedron shape, and hexagonal crystal structure (194). The addition of nitrogen to argon renders NPs having a cubic crystal structure (255), irregular morphology, yet of a similar 19 nm mean size. With increasing an N2 flow rate, a transition from irregular towards close-to-spherical shape and increased crystal/amorphous phase ratio are observed. From the chemical viewpoint, nitridation leads to the formation of HfN NPs. XPS measurements were performed without breaking the vacuum to confirm an N/Hf ratio of 0.91 and 1.05 for the lower and higher N2 flows used. However, the NP exposure to the ambient atmosphere triggers the oxidation of their surface. The STEM-EDS elemental mapping shows the formation of a 2 nm oxidized layer but confirms a homogeneous distribution of nitrogen within the NP volume. The method aims to provide a roadmap to engineer NPs with tailor-made morphologies, composition and optoelectronic properties.
ACKNOWLEDGEMENTS: The work was supported via the grant GACR 21-12828S from the Czech Science Foundation, M.P., K.B. and T.K. also appreciate the support from the Charles University via a student grant SVV 260 579-2021.

Polyvinylidene fluoride (PVDF) polymeric nanofibers deposited by roller electrospinning on polypropylene non-woven fabric were treated with atmospheric pressure plasma to hydrophilize its surface. Diffuse coplanar surface barrier discharge (DCSBD) was employed to generate low-temperature atmospheric plasma in ambient air and nitrogen. Changes in wettability were determined by evaluating water contact angles before and after plasma treatment for various treatment times. The effect of aging of plasma-treated surfaces stored in laboratory conditions was studied in the course of storage time. The chemical composition of the surfaces was determined by X-ray photoelectron spectroscopy (XPS) which showed a decrease in carbon and an increase in oxygen atomic concentrations. Subsequently, significant differences in loading of iron oxide nanoparticles between treated and untreated PVDF samples were observed by scanning electron microscopy.

Silver and copper nanofluids are of high scientific interest due to the plasmonic performance of nanoparticles (NPs). The scientific potential of such systems can be enhanced by mixing Ag and Cu NPs in one liquid matrix. Herein, we developed a solution-free, vacuum-based technique for the preparation of optically active bimetallic nanofluids. For this aim, a unique configuration of the experimental setup was employed that utilized two individual magnetron-based gas aggregation cluster sources to co-deposit Ag and Cu NPs into vacuum compatible liquid polyethylene glycol (PEG, 400 g/ml). The concentration of NPs was tuned by the deposition time or rate. The mean diameter of Ag and Cu NPs was 55 ± 9 nm and 25 ± 5 nm, respectively, as determined by SEM. The UV-Vis spectra of as-prepared single-metal nanofluids demonstrated Localized Surface Plasmon Resonance (LSPR) at 425 nm for Ag and 716 nm for Cu. Nevertheless, the nanofluids were opaque grey because of larger NP aggregates present in the solution. After 15 minutes of ultrasonication, the LSPR maxima blue-shifted and intensified, pointing to the destruction of the aggregates with the formation of a larger amount of constituent NPs. Consequently, the nanofluids became homogeneously colorized, yielding the Ag nanofluid yellow and the Cu nanofluid green. Simultaneous deposition of Ag and Cu NPs produced bimetallic nanofluids, which demonstrated a double LSPR and a similar post-sonication blue shift of the absorption maxima. This approach opens a simple route towards the synthesis of bimetallic nanofluids with tunable composition for optical applications.
ACKNOWLEDGEMENTS: The work was supported via the grant GACR 21-12828S from the Czech Science Foundation. K.B. and M.P. also appreciate the support from Charles University via a student grant SVV 260 579-2021.