Lidé

prof. RNDr. Bohuslav Rezek, Ph.D.

Všechny publikace

Correlative atomic force microscopy and scanning electron microscopy of bacteria-diamond-metal nanocomposites

  • DOI: 10.1016/j.ultramic.2023.113909
  • Odkaz: https://doi.org/10.1016/j.ultramic.2023.113909
  • Pracoviště: Katedra fyziky
  • Anotace:
    Research investigating the interface between biological organisms and nanomaterials nowadays requires multi-faceted microscopic methods to elucidate the interaction mechanisms and effects. Here we describe a novel approach and methodology correlating data from an atomic force microscope inside a scanning electron microscope (AFM-in-SEM). This approach is demonstrated on bacteria-diamond-metal nanocomposite samples relevant in current life science research. We describe a procedure for preparing such multi-component test samples containing E. coli bacteria and chitosan-coated hydrogenated nanodiamonds decorated with silver nanoparticles on a carbon-coated gold grid. Microscopic topography information (AFM) is combined with chemical, material, and morphological information (SEM using SE and BSE at varied acceleration voltages) from the same region of interest and processed to create 3D correlative probe-electron microscopy (CPEM) images. We also establish a novel 3D RGB color image algorithm for merging multiple SE/BSE data from SEM with the AFM surface topography data which provides additional information about microscopic interaction of the diamond-metal nanocomposite with bacteria, not achievable by individual analyses. The methodology of CPEM data interpretation is independently corroborated by further in-situ (EDS) and ex-situ (micro-Raman) chemical characterization as well as by force volume AFM analysis. We also discuss the broader applicability and benefits of the methodology for life science research.

Enhanced antimicrobial and photocatalytic effects of plasma-treated gallium-doped zinc oxide

  • DOI: 10.1016/j.apsusc.2024.159567
  • Odkaz: https://doi.org/10.1016/j.apsusc.2024.159567
  • Pracoviště: Katedra fyziky
  • Anotace:
    We characterize gallium-doped zinc oxide (ZnO:Ga) after exposure to hydrogen or oxygen plasma for potential use as a novel antibacterial and photocatalytic material. ZnO:Ga were composed of smooth rods with a thick central portion and tapered nanometre-sized ends alongside clusters of thin disk particles. Plasma treatment removed material from the rod surface and introduced features such as small holes or pits that increased the surface roughness and reduced the zinc ion concentration measured from colloidal suspensions. The surface charge of ZnO:Ga was influenced by plasma treatment: hydrogen plasma induced a positive surface charge whereas oxygen plasma resulted in a negative surface charge. However, electrostatic interactions with negatively charged bacteria were not the predominant mechanism underlying the antibacterial effect of ZnO:Ga. Treatment with oxygen or hydrogen plasma enhanced the antibacterial effect of ZnO:Ga against gram-positive bacteria, yet only oxygen plasma caused an enhancement against gram-negative bacteria. The photocatalytic effect of ZnO:Ga was enhanced after oxygen plasma treatment but supressed by hydrogen plasma treatment. The results indicate that plasma treatment of ZnO:Ga can successfully alter material properties to provide enhancement of the antibacterial and photocatalytic effects, however the type of feed gas used should be carefully chosen based upon the desired application.

Absolute energy levels in nanodiamonds of different origins and surface chemistries

  • DOI: 10.1039/d3na00205e
  • Odkaz: https://doi.org/10.1039/d3na00205e
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanodiamonds (NDs) are versatile, broadly available nanomaterials with a set of features highly attractive for applications from biology over energy harvesting to quantum technologies. Via synthesis and surface chemistry, NDs can be tuned from the sub-micron to the single-digit size, from conductive to insulating, from hydrophobic to hydrophilic, and from positively to negatively charged surface by simple annealing processes. Such ND diversity makes it difficult to understand and take advantage of their electronic properties. Here we present a systematic correlated study of structural and electronic properties of NDs with different origins and surface terminations. The absolute energy level diagrams are obtained by the combination of optical (UV-vis) and photoelectron (UPS) spectroscopies, Kelvin probe measurements, and energy-resolved electrochemical impedance spectroscopy (ER-EIS). The energy levels and density of states in the bandgap of NDs are correlated with the surface chemistry and structure characterized by FTIR and Raman spectroscopy. We show profound differences in energy band shifts (by up to 3 eV), Fermi level position (from p-type to n-type), electron affinity (from +0.5 eV to -2.2 eV), optical band gap (5.2 eV to 5.5 eV), band gap states (tail or mid-gap), and electrical conductivity depending on the high-pressure, high-temperature and detonation origin of NDs as well as on the effects of NDs' oxidation, hydrogenation, sp(2)/sp(3) carbon phases and surface adsorbates. These data are fundamental for understanding and designing NDs' optoelectrochemical functional mechanisms in diverse application areas.

Creation and Plasmon-Assisted Photosensitization of Annealed Z-Schemes for Sunlight-Only Water Splitting

  • DOI: 10.1021/acsami.3c02884
  • Odkaz: https://doi.org/10.1021/acsami.3c02884
  • Pracoviště: Katedra fyziky
  • Anotace:
    Solely light-induced water splitting represents a promisingavenuefor a carbon-free energy future, based on reliable energy sources.Such processes can be performed using coupled semiconductor materials(the so-called direct Z-scheme design) that facilitate spatial separationof (photo)excited electrons and holes, prevent their recombination,and allow water-splitting half-reactions proceeding at each correspondingsemiconductor side. In this work, we proposed and prepared a specificstructure, based on WO3g-x /CdWO4/CdS coupled semiconductors, created by annealing of a commonWO(3)/CdS direct Z-scheme. WO3-x /CdWO4/CdS flakes were further combined with a plasmon-activegrating for the creation of the so-called artificial leaf design,making possible complete utilization of the sunlight spectrum. Theproposed structure enables water splitting with high production ofstoichiometric amounts of oxygen and hydrogen without undesirablecatalyst photodegradation. Several control experiments confirm thecreation of electrons and holes participating in the water splittinghalf-reaction in a spatially selective manner.

Electrical properties of MXene thin films prepared from non-aqueous polar aprotic solvents

  • DOI: 10.1557/s43578-023-01033-6
  • Odkaz: https://doi.org/10.1557/s43578-023-01033-6
  • Pracoviště: Katedra fyziky, Katedra elektrotechnologie
  • Anotace:
    For sustainable energy technologies, MXenes offer unique properties such as high electrical conductivity, hydrophilicity, excellent thermal stability, large interlayer spacing, easily tunable structure, high surface area, and microporous structure that facilitate faster ion transfer. To address limitations of aqueous MXene suspension, Ti3C2-type MXene thin films are prepared from non-aqueous suspensions in N,N-dimethyl formamide (DMF) and N-methyl-2-pyrrolidone (NMP) using solvent exchange method followed by spin coating or drop casting on gold interdigitated electrodes (IDE) and ceramic substrates and their electrical properties are compared. Electrical properties investigated by impedance spectroscopy (4 Hz to 8 MHz) and four-point probe (FPP) measurements show that DMF-MXene layers exhibit higher electrical conductivity than MXene deposited from NMP. The material technology and electrical properties of MXene thin films prepared from non-aqueous solvents may thus be promising for possible use of MXenes in hybrid photovoltaic devices as charge-transporting layers.

Energy transfer between Si nanocrystals and protoporphyrin molecules as a function of distance, orientation and size

  • DOI: 10.1002/jcc.27071
  • Odkaz: https://doi.org/10.1002/jcc.27071
  • Pracoviště: Katedra fyziky, Katedra řídicí techniky
  • Anotace:
    The interaction between protoporphyrin molecules (donor) and Si nanocrystals (acceptor) up to 2.5 nm for varying distances and orientations is studied by DFT, semi-empirical and TDDFT methods. Simulations show an effect on electronic structure, indicative of electron charge transfer in parallel orientation and small distances and nonelectron energy transfer for different orientations and larger distances. An absorption-emission spectral overlap is observed. The calculations of coupling and energy transfer rates show a distance dependence typical of fluorescence resonance energy transfer (FRET) in the long range, while in the short and ultra-short range the distance dependence indicates electron transfer in addition to FRET. The Si NCs with the smallest size yield larger couplings than the larger nanocrystals. The PPIX/Si NC coupling was enhanced by adding a plasmon nanoparticle as a bridge in the donor-acceptor system. Results using Au nanoparticles show increased energy transfer rates up to 10(4) and lower distance dependence.

Helicene-based π-conjugated macrocycles: their synthesis, properties, chirality and self-assembly into molecular stripes on a graphite surface

  • DOI: 10.1039/d2nr04209f
  • Odkaz: https://doi.org/10.1039/d2nr04209f
  • Pracoviště: Katedra fyziky
  • Anotace:
    Fully aromatic helicenes are attractive building blocks for the construction of inherently chiral pi-conjugated macrocyclic nanocarbons. These hitherto rare molecular architectures are envisaged to exhibit remarkable (chir)optical properties, self-assembly, charge/spin transport, induced ring current or a fascinating Mobius topology. Here the synthesis of helically chiral macrocycles that combine angular dibenzo[5]helicene units as corners and linear trans-stilbene-4,4 '-diyl linkers as edges is reported. By subjecting a racemic or enantiopure divinyl derivative of dibenzo[5]helicene to olefin metathesis, which was catalysed by a 2nd generation Piers catalyst under kinetic control, a pi-conjugated helicene cyclic trimer (33%) and a tetramer (22%) were obtained, which were separated by GPC. Combining racemic/asymmetric synthesis with the resolution of enantiomers/diastereomers by SFC/HPLC on a chiral column, both homochiral (+)-(M,M,M)/(-)-(P,P,P) and heterochiral (+)-(M,M,P)/(-)-(M,P,P) stereoisomers of the helicene cyclic trimer could be obtained in an enantio- and diastereomerically enriched form. The complete energy profile of their interconversion was compiled on the basis of kinetic measurements and numerical solution of the proposed kinetic model. In equilibrium, the heterochiral diastereomer predominates over the homochiral one (ca. 75 : 25 at 76 degrees C). pi-Conjugation along a large, twisted circuit in the helicene cyclic trimer is rather disrupted, stabilising this formally antiaromatic molecule. Using an optimised PeakForce mode of ambient AFM, the self-assembly of otherwise highly mobile stereoisomers of the helicene cyclic trimer on the HOPG surface could be studied. Irrespective of the stereochemistry, strong preferences for the edge-to-edge interaction of these macrocycles were found to form very long parallel 1D molecular stripes in ordered 2D nanocrystals, a result also supported by molecular dynamics simulations. Six trityl groups, initially intr

Hydrogenation of HPHT nanodiamonds and their nanoscale interaction with chitosan

  • DOI: 10.1016/j.diamond.2023.109754
  • Odkaz: https://doi.org/10.1016/j.diamond.2023.109754
  • Pracoviště: Katedra fyziky
  • Anotace:
    Hydrogenation of the surface can provide specific and unique properties to nanodiamonds. In this study, a series of high-pressure high-temperature nanodiamonds (HPHT NDs) with varying levels of hydrogenation and sp2 carbon content is prepared and characterized in terms of optical properties, structure, surface chemistry, particle size distribution, and zeta potential. The higher the surface sp2-C content and level of hydrogenation the better dispersibility in acidic to neutral pH and higher isoelectric points are achieved. We further evaluated the interaction of hydrogenated HPHT NDs with chitosan by infrared spectroscopy and atomic force microscopy. We have found that chitosan is electrostatically attracted to the hydrogenated HPHT NDs, it improves the dispersibility of the HPHT NDs with a lower level of hydrogenation, and it provides colloidal stability in the broad pH range 2–11 to all hydrogenated HPHT NDs. Finally, we demonstrate that chitosan coating enables the decoration of hydrogenated HPHT NDs by silver nanoparticles.

Nanodiamonds as Charge Extraction Layer in Organic Solar Cells: The Impact of the Nanodiamond Surface Chemistry

  • DOI: 10.1002/solr.202201061
  • Odkaz: https://doi.org/10.1002/solr.202201061
  • Pracoviště: Katedra fyziky
  • Anotace:
    Diamond nanoparticles so-called nanodiamonds (NDs) have recently experienced raising scientific interest due to interesting optical and electronic properties, nontoxicity, biocompatibility, and large surface area. Another significant feature of NDs is the versatility of the surface chemistry, where various functional groups can be attached. This provides an excellent platform for adjusting NDs properties and functions for many applications including in photovoltaic devices. Herein, high-pressure high-temperature (HPHT) NDs are tested as charge extraction material in organic solar cells using various surface chemistries: as-received (HPHT ND-ar), oxidized (HPHT ND-O), and hydrogenated (HPHT ND-O-H) NDs. Despite the high work function values (approximate to 5.3 eV) of HPHT ND-ar and HPHT ND-O, which make these materials normally suitable for hole extraction, devices made with them failed. In contrast, the work function decreases upon hydrogenation (approximate to 4.5 eV) of the beforehand oxidized NDs, making them interesting for electron extraction. By employing such HPHT ND-O-H for electron extraction layers, PBDB-T:ITIC-based devices reach 77%, while PM6:Y6-based devices reach even 85% of the performance when process on standard ZnO electron transport layers. Improvement of the film-forming qualities of this new electron extraction material is expected to further improve the performance.

Non-contact non-resonant atomic force microscopy method for measurements of highly mobile molecules and nanoparticles

  • DOI: 10.1016/j.ultramic.2023.113816
  • Odkaz: https://doi.org/10.1016/j.ultramic.2023.113816
  • Pracoviště: Katedra fyziky
  • Anotace:
    Atomic force microscopy (AFM) is nowadays indispensable versatile scanning probe method widely employed for fundamental and applied research in physics, chemistry, biology as well as industrial metrology. Conventional AFM systems can operate in various environments such as ultra-high vacuum, electrolyte solutions, or controlled gas atmosphere. Measurements in ambient air are prevalent due to their technical simplicity; however, there are drawbacks such as formation of water meniscus that greatly increases attractive interaction (adhesion) between the tip and the sample, reduced spatial resolution, and too strong interactions leading to tip and/or sample modifications. Here we show how the attractive forces in AFM under ambient conditions can be used with advantage to probe surface properties in a very sensitive way even on highly mobile molecules and nanoparticles. We introduce a stable non-contact non-resonant (NCNR) AFM method which enables to reliably perform measurements in the attractive force regime even in air by controlling the tip position in the intimate surface vicinity without touching it. We demonstrate proof-of-concept results on helicene-based macrocycles, DNA on mica, and nanodiamonds on SiO2. We compare the results with other conventional AFM regimes, showing NCNR advantages such as higher spatial resolution, reduced tip contamination, and negligible sample modification. We analyze principle physical and chemical mechanisms influencing the measurements, discuss issues of stability and various possible method implementations. We explain how the NCNR method can be applied in any AFM system by a mere software modification. The method thus opens a new research field for measurements of highly sensitive and mobile nanoscale objects under air and other environments.

Peculiarities Related to Er Doping of ZnO Nanorods Simultaneously Grown as Particles and Vertically Arranged Arrays

  • DOI: 10.1021/acs.jpcc.3c05471
  • Odkaz: https://doi.org/10.1021/acs.jpcc.3c05471
  • Pracoviště: Katedra fyziky, Katedra elektrotechnologie
  • Anotace:
    A unique set of undoped and Er doped ZnO nanorods that are grown by a hydrothermal method under the exactly same conditions in the form of 2D nanoarrays on SiO2/ZnO substrate or in a free-standing form on random nucleation seeds in solution were investigated. Their optoelectronic properties are characterized by a photo-, radio-, and cathodoluminescence in correlation with scanning electron microscopy, energy dispersive X-ray spectroscopy, electron paramagnetic resonance spectroscopy, resonance Raman spectroscopy and theoretical computing by using density functional theory. We demonstrate that erbium is incorporated at regular zinc site in the 2D arrays and as additional nucleation seeds in the free-standing nanorods. The deposited nanorods contain larger number of shallow donors (by about two orders of magnitude) and larger number of free carriers (by about one order of magnitude) as compared to the free-standing ones. It is related to the fact that the nanorods grow about one order of magnitude larger and in polycrystalline bunches on the random seeds in solution compared to the deposited arrays. Doping by Er slows down the excitonic emission further from 465 to 522 ps.

Polarization Controlled Assembly of Ultrathin Thiorphan Nanostructures on ZnO Surface Facets

  • DOI: 10.1021/acs.langmuir.2c02393
  • Odkaz: https://doi.org/10.1021/acs.langmuir.2c02393
  • Pracoviště: Katedra fyziky
  • Anotace:
    Despite the importance of thiorphan as a small molecule with vital biological roles, its interactions with zinc oxide (ZnO) nanomaterials that are prospective in drug delivery and theranostic applications have not yet been sufficiently explored. Here the impact of surface polarity of different ZnO facets on thiorphan adsorption is studied both experimentally by atomic force microscopy (AFM) and angle resolved X-ray photoelectron spectroscopy (XPS) and theoretically by force field molecular dynamics (FFMD) and density functional tight binding simulations (DFTB). Polar ZnO surfaces cause the formation of thiorphan nanodots, where the size of the nanodots depends on the direction of dipoles: small (4 nm) nanodots are formed on Zn-face ZnO, while large (25 nm) nanodots are formed on O-face ZnO. Nonpolar ZnO surfaces cause self-assembly into layered nanoislands with characteristic 4 nm layer thickness, which subsequently merge into rigid nanolayers. The self-assembly is shown to be controlled solely by the effect of surface dipole electric field orientation and magnitude, whereas effects of surface chemistry or solution are negligible. The results thus also show a way for controlling the assembly of thiorphan and other molecular nanomaterials for diverse applications.

Racemic dimers as models of chiral macrocycles self-assembled on pyrolytic graphite

  • DOI: 10.1016/j.cartre.2023.100284
  • Odkaz: https://doi.org/10.1016/j.cartre.2023.100284
  • Pracoviště: Katedra fyziky
  • Anotace:
    Fully aromatic helicenes are fascinating building blocks for the construction of inherently chiral macrocyclic nanocarbons. Such helicene-based non-planar macrocycles interact with each other and underlying substrate and form various 2D crystals. However, the role of their chirality remains unknown. In Atomic Force Microscopy (AFM) the macrocycles show stripes with six-fold symmetry but only faintly visible internal structure that is not sufficient to see individual adsorbed molecules and identify their chirality. Here, AFM data of self-assembled helicene-based 2D molecular crystals are analyzed by a new computational method that combines various information from AFM image and expected molecular shape taken from molecular dynamic simulations. Possible molecule arrangements are thereby computed and four basic structural elements (dimers) with the smallest deviation from AFM topography image are found. Validation procedure using larger AFM image with many 2D crystal domains improves the resolution in AFM data and allows reliable and reproducible reconstruction of molecular sub-structure, precise molecules position within the 2D crystal as well as their chirality. The presented results and developed mathematical method are generally applicable to study ensembles of molecules with known atom coordinates and to any image with periodic pattern.

Changes of Morphological, Optical, and Electrical Properties Induced by Hydrogen Plasma on (0001) ZnO Surface

  • DOI: 10.1002/pssa.202100427
  • Odkaz: https://doi.org/10.1002/pssa.202100427
  • Pracoviště: Katedra fyziky
  • Anotace:
    Plasma provides specific adjustment of solid-state surface properties offering an alternative to high temperature treatment. Herein, hydrogen plasma treatment of monocrystalline (0001) ZnO surface is studied in an inductively coupled plasma reactor with reduced capacitively coupled plasma mode. The crucial role of electrical grounding of the sample holder for plasma etching and related changes in the morphology, optical, and electrical properties of surfaces exposed to electron and ion bombardment are explained. The effects on the chemical composition of the surface are analyzed by X-ray photoelectron spectroscopy (XPS), optical properties by photoluminescence spectroscopy, topography, roughness, and surface measurements by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). All methods show altered ZnO surface properties before and after plasma treatment strongly depending on the electrical potential of the holder.

Coating Ti6Al4V implants with nanocrystalline diamond functionalized with BMP-7 promotes extracellular matrix mineralization in vitro and faster osseointegration in vivo

  • DOI: 10.1038/s41598-022-09183-z
  • Odkaz: https://doi.org/10.1038/s41598-022-09183-z
  • Pracoviště: Katedra fyziky
  • Anotace:
    The present study investigates the effect of an oxidized nanocrystalline diamond (O-NCD) coating functionalized with bone morphogenetic protein 7 (BMP-7) on human osteoblast maturation and extracellular matrix mineralization in vitro and on new bone formation in vivo. The chemical structure and the morphology of the NCD coating and the adhesion, thickness and morphology of the superimposed BMP-7 layer have also been assessed. The material analysis proved synthesis of a conformal diamond coating with a fine nanostructured morphology on the Ti6Al4V samples. The homogeneous nanostructured layer of BMP-7 on the NCD coating created by a physisorption method was confirmed by AFM. The osteogenic maturation of hFOB 1.19 cells in vitro was only slightly enhanced by the O-NCD coating alone without any increase in the mineralization of the matrix. Functionalization of the coating with BMP-7 resulted in more pronounced cell osteogenic maturation and increased extracellular matrix mineralization. Similar results were obtained in vivo from micro-CT and histological analyses of rabbit distal femurs with screws implanted for 4 or 12 weeks. While the O-NCD-coated implants alone promoted greater thickness of newly-formed bone in direct contact with the implant surface than the bare material, a further increase was induced by BMP-7. It can be therefore concluded that O-NCD coating functionalized with BMP-7 is a promising surface modification of metallic bone implants in order to improve their osseointegration.

Effect of electron irradiation on polypropylene and polystyrene foils studied by pattern recognition methods on electron spectroscopy data

  • Autoři: Lesiak, B., Zemek, J., Jiricek, P., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Polymer-Plastics Technology and Materials. 2022, 61(3), 251-262. ISSN 2574-0881.
  • Rok: 2022
  • DOI: 10.1080/25740881.2021.1978487
  • Odkaz: https://doi.org/10.1080/25740881.2021.1978487
  • Pracoviště: Katedra fyziky
  • Anotace:
    Degradation of polypropylene (PP) and polystyrene (PS) surfaces under electron beam in ultra-high vacuum is studied by electron spectroscopy, pattern recognition, and atomic force microscopy. Effects on hydrogen, carbon sp(2)/sp(3) content, and microstructure are quantified and correlated. Electron irradiation at 1500 eV causes hydrogen and C sp(3) content decrease and surface morphology modification. Roughness changes from 29 to 15 nm on PP, whereas it remains 5 nm on PS. Decreasing C sp(3) content in PP, contrary to PS, indicates C-H, C-C bonds scission and carbonization. Cross-linking predominates over carbonization in PS, confirming its better stability, in agreement with surface morphology data.

Effect of oligothiophene spacer length on photogenerated charge transfer from perylene diimide to boron-doped diamond electrodes

  • DOI: 10.1016/j.solmat.2022.111984
  • Odkaz: https://doi.org/10.1016/j.solmat.2022.111984
  • Pracoviště: Katedra fyziky
  • Anotace:
    Organic-based photovoltaic devices emerged as a complementary technology to silicon solar cells with specific advantages in terms of cost, ease of deployment, semi-transparency, and performance under low and diffuse light conditions. In this work, thin-film boron-doped diamond (B:NCD) electrodes are employed for their useful op-tical, electronic, and chemical properties, as well as stability and environmental safety. A set of oligothiophene perylene diimide (nT-PDI) donor-acceptor chromophores is designed and synthesized in order to investigate the influence of the oligothiophene spacer length when the nT-PDI molecule is attached to a B:NCD electrode. The chromophores are anchored to the diamond surface via diazonium grafting followed by Sonogashira cross -coupling. X-ray photoelectron spectroscopy shows that the surface coverage decreases with increasing oligo-thiophene length. Density functional theory (DFT/TDDFT) calculations reveal the upright nT-PDI orientation and the most efficient photogenerated charge separation and injection to diamond for elongated oligothiophene chains (8T-PDI). Yet, the maximum photovoltage is obtained for an intermediate oligothiophene length (3T-PDI), providing an optimum between decreasing transport efficiency and increasing efficiency of charge separation and reduced recombination with increasing oligothiophene length. Holes transferred from nT-PDI to diamond persist there even after the illumination is switched off. Such features may be beneficial for application in solar cells.

Photophysical Properties of CdSe/CdTe Bilayer Solar Cells: A Confocal Raman and Photoluminescence Microscopy Study

  • Autoři: Abudulimu, A., Ing. Jaroslav Kuliček, Ph.D., Bastola, E., Phillips, A.B., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: IEEE 49th Photovoltaics Specialists Conference (PVSC). Institute of Electrical and Electronics Engineers, Inc., 2022. p. 1088-1090. Conference Record of the IEEE Photovoltaic Specialists Conferenc. ISBN 978-1-7281-6117-4.
  • Rok: 2022
  • DOI: 10.1109/PVSC48317.2022.9938717
  • Odkaz: https://doi.org/10.1109/PVSC48317.2022.9938717
  • Pracoviště: Katedra fyziky
  • Anotace:
    Understanding and controlling the optical and electrical properties of the solar cells, from the absorber layer to the complete devices, is one of the key elements for engineering high-efficiency devices. Such an understanding, especially the correlation between device performance and optical-structural-morphological properties of film stack, is still lacking in the field of cadmium selenide/telluride alloy-based solar cells. Here, we report confocal Raman and photoluminescence microscopy study results obtained through exciting both film and glass sides of cadmium selenide and cadmium telluride bilayer device stacks treated with cadmium chloride. We show that the device stack, especially the glass side, losses significant charge carries to the recombination arising from uniformity issues related to material composition, energetics, and defects. Furthermore, there is a high energy tail emission peak originating from CdTe, and CdSe can suppress it significantly under CdCl-2 treatment.

Small angle symmetry splitting of helicene-based molecular wires on pyrolytic graphite

  • DOI: 10.1016/j.carbon.2022.03.013
  • Odkaz: https://doi.org/10.1016/j.carbon.2022.03.013
  • Pracoviště: Katedra fyziky
  • Anotace:
    Synthesis of inherently chiral materials and investigation of their self-assembly into molecular wires or 2D crystals belongs to hot topics in nanotechnology. Here we report an inherent splitting of orientational symmetry of 10e500 nm long molecular wires assembled from 3 nm chiral helicene-based macrocycles on atomically flat HOPG surface. The symmetry splitting of molecular wire orientation by a small angle of (6.5 ± 0.5) is attributed to interaction of individual helicene-based macrocycle with HOPG. There is a good correlation between experimental AFM data and theoretical simulations using ReaxFF force field and Lennard-Jones (L-J) potential. In particular the new 1000 times faster computational method based on L-J potential and sequential addition of molecules is able to simulate formation of molecular wires and emergence of their symmetry splitting, which was not possible to do by conventional molecular dynamics. The method is also sensitive to chirality of the studied molecules; enantiomers and racemates placed on HOPG form different arrangements. This opens new possibilities for simulations of large molecular systems.

Strong Structural and Electronic Binding of Bovine Serum Albumin to ZnO via Specific Amino Acid Residues and Zinc Atoms

  • DOI: 10.1002/cphc.202100639
  • Odkaz: https://doi.org/10.1002/cphc.202100639
  • Pracoviště: Katedra fyziky
  • Anotace:
    ZnO biointerfaces with serum albumin have attracted noticeable attention due to the increasing interest in developing ZnO-based materials for biomedical applications. ZnO surface morphology and chemistry are expected to play a critical role on the structural, optical, and electronic properties of albumin-ZnO complexes. Yet there are still large gaps in the understanding of these biological interfaces. Herein we comprehensively elucidate the interactions at such interfaces by using atomic force microscopy and nanoshaving experiments to determine roughness, thickness, and adhesion properties of BSA layers adsorbed on the most typical polar and non-polar ZnO single-crystal facets. These experiments are corroborated by force field (FF) and density-functional tight-binding (DFTB) calculations on ZnO-BSA interfaces. We show that BSA adsorbs on all the studied ZnO surfaces while interactions of BSA with ZnO are found to be considerably affected by the atomic surface structure of ZnO. BSA layers on the (0001?) surface have the highest roughness and thickness, hinting at a specific upright BSA arrangement. BSA layers on (101?0) surface have the strongest binding, which is well correlated with DFTB simulations showing atomic rearrangement and bonding between specific amino acids (AAs) and ZnO. Besides the structural properties, the ZnO interaction with these AAs also controls the charge transfer and HOMO-LUMO energy positions in the BSA-ZnO complexes. This ZnO facet-specific protein binding and related structural and electronic effects can be useful for improving the design and functionality of ZnO-based materials and devices.

Bactericidal effect of zinc oxide nanoparticles on Gram-positive and Gram-negative strains in reverse spin bioreactor

  • DOI: 10.1088/1757-899X/1050/1/012013
  • Odkaz: https://doi.org/10.1088/1757-899X/1050/1/012013
  • Pracoviště: Katedra fyziky
  • Anotace:
    We present an experimental study investigating the efficacy of zinc oxide nanoparticle use for bacterial decontamination of water using reverse spin technology. The number of viable bacteria reduced with treatment time and the rate of inactivation was dependent on zinc oxide concentration. Gram-positive S. aureus bacteria were more resistant to zinc oxide nanoparticles compared to Gram-negative E. coli, however both strains were completely eradicated after 4 hours using a concentration of 10 μg/mL. Nanoparticles did not inhibit growth of bacteria when added to an agar surface, neither when in liquid before bacteria inoculation nor when loaded onto filter paper disks after bacteria inoculation. These results emphasise the importance of efficient reactor mixing to enhance interaction capability for ZnO use in water decontamination.

Effect of ZnO nanoparticle sizes and illumination on growth inhibition of Escherichia coli and Staphylococcus aureus bacteria in cultivation medium

  • DOI: 10.1088/1757-899X/1050/1/012007
  • Odkaz: https://doi.org/10.1088/1757-899X/1050/1/012007
  • Pracoviště: Katedra fyziky
  • Anotace:
    We study antibacterial effects of the zinc oxide nanoparticles (ZnO NPs) in cultivation medium (Mueller-Hinton broth) on Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria models. We compare synthesized ZnO hedgehog NPs and commercial ZnO NPs (50 nm and 20 μm nominal size) in different concentrations (1 mg/mL and 0.1 mg/mL). Results show that E. coli are more sensitive to the ZnO presence in the cultivation media than S. aureus. We also characterize influence of visible and UV light on the ZnO NP effects.

Electron emission from H-terminated diamond enhanced by polypyrrole grafting

  • DOI: 10.1016/j.carbon.2020.12.043
  • Odkaz: https://doi.org/10.1016/j.carbon.2020.12.043
  • Pracoviště: Katedra fyziky
  • Anotace:
    Electron emission plays an important role in diverse applications, from cold cathodes to chemical processes (solvated electrons, water purification), energy generation (thermionic or dye-sensitized solar cells), and even cancer treatment. Here we show that by surface treatment using electrochemically grown polypyrrole the secondary-electron emission and photoelectron emission from boron-doped diamond is enhanced even above the intensity of electron emission from the hydrogen-terminated surface with negative electron affinity. This enhancement is stable in air for at least one month and it persists also in vacuum after thermal annealing. Scanning electron microscopy, Kelvin probe force microscopy, total photoelectron yield spectroscopy as well as surface mapping by Auger and secondary ion mass spectroscopies are used to characterize and correlate the surface electronic and chemical properties. A model of the electron emission enhancement is provided.

Gamma radiation effects on diamond field-effect biosensors with fibroblasts and extracellular matrix

  • Autoři: Krátká, M., Čermák, J., Vachelová, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Colloids and Surfaces B: Biointerfaces. 2021, 204 ISSN 0927-7765.
  • Rok: 2021
  • DOI: 10.1016/j.colsurfb.2021.111689
  • Odkaz: https://doi.org/10.1016/j.colsurfb.2021.111689
  • Pracoviště: Katedra fyziky
  • Anotace:
    Due to high biocompatibility, miniaturization, optical transparency and low production cost together with high radiation hardness the diamond-based sensors are considered promising for radiation medicine and biomedicine in general. Here we present detection of fibroblast cell culture properties by nanocrystalline diamond solution-gated field-effect transistors (SG-FET), including effects of gamma irradiation. We show that blank nanocrystalline diamond field-effect biosensors are stable at least up to 300 Gy of γ irradiation. On the other hand, gate current of the diamond SG-FET biosensors with fibroblastic cells increases exponentially over an order of magnitude with increasing radiation dose. Extracellular matrix (ECM) formation is also detected and analyzed by correlation of electronic sensor data with optical, atomic force, fluorescence, and scanning electron microscopies.

Growth and properties of diamond films prepared on 4-inch substrates by cavity plasma systems

  • Autoři: Babčenko, O., Ing. Štěpán Potocký, Ph.D., Aubrechtová Dragounová, K., Szabó, O., Bergonzo, P., prof. RNDr. Bohuslav Rezek, Ph.D., Kromka, A.
  • Publikace: NANOCON Conference Proceedings - International Conference on Nanomaterials. Ostrava: TANGER, 2021. p. 86-92. ISSN 2694-930X. ISBN 978-80-87294-98-7.
  • Rok: 2021
  • DOI: 10.37904/nanocon.2020.3701
  • Odkaz: https://doi.org/10.37904/nanocon.2020.3701
  • Pracoviště: Katedra fyziky
  • Anotace:
    Two microwave (2.45 GHz) plasma systems with ellipsoidal and multimode clamshell cavity for diamond synthesis by chemical vapor deposition were compared. Both systems are capable of high pressure (up to 20 kPa) operation and high growth rates (several µm/h). It was shown that by using the multimode operation of the clamshell cavity system and specially design sample holder, it is possible to sustain a plasma in a cavity and reach good enough process reproducibility and diamond film quality over 4-inch substrates.

Growth Inhibition of Gram-Positive and Gram-Negative Bacteria by Zinc Oxide Hedgehog Particles

  • DOI: 10.2147/IJN.S300428
  • Odkaz: https://doi.org/10.2147/IJN.S300428
  • Pracoviště: Katedra fyziky
  • Anotace:
    Purpose: Nanomaterials for antimicrobial applications have gained interest in recent years due to the increasing bacteria resistance to conventional antibiotics. Wound sterilization, water treatment and surface decontamination all avail from multifunctional materials that also possess excellent antibacterial properties, eg zinc oxide (ZnO). Here, we assess and compare the effects of synthesized hedgehog-like ZnO structures and commercial ZnO particles with and without mixing on the inactivation of bacteria on surfaces and in liquid environments.

Microscopic Study of Bovine Serum Albumin Adsorption on Zinc Oxide (0001) Surface

  • DOI: 10.1002/pssa.202000558
  • Odkaz: https://doi.org/10.1002/pssa.202000558
  • Pracoviště: Katedra fyziky
  • Anotace:
    Properties and functions of various ZnO materials are intensively investigated in biological systems for diagnostics, therapy, health risks assessment as well as bactericidal and decontamination purposes. Herein, the interface between ZnO and biological environment is studied by characterizing adsorption of bovine serum albumin (BSA) and fetal bovine serum (FBS) using atomic force microscopy with CF4-treated tips. Similar molecular morphologies (thickness around 2 nm) yet different binding forces to ZnO (10–25 nN) are observed. These observations are corroborated by atomic scale simulations of BSA on (0001) ZnO surface using force-field method and showing rearrangements of Zn surface atoms. Such binding may have an impact also on other properties of ZnO–BSA complex.

MICROSTRUCTURE AND OPTO-ELECTRONIC EFFECTS IN MXENES SPINCOATED FROM POLAR APROTIC SOLVENTS ON ITO

  • Autoři: Sasitharan, K., Ing. Jaroslav Kuliček, Ph.D., Soyka, Y., Prochazka, M., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Conference Proceedings - NANOCON 2021, 13th International Conference on Nanomaterials - Research & Application. Ostrava: Tanger Ltd., 2021. p. 23-28. ISSN 2694-930X. ISBN 978-80-88365-00-6.
  • Rok: 2021
  • DOI: 10.37904/nanocon.2021.4307
  • Odkaz: https://doi.org/10.37904/nanocon.2021.4307
  • Pracoviště: Katedra fyziky
  • Anotace:
    MXenes have drawn considerable attention in the past decade, thanks to their attractive properties such as metallic conductivity and surface hydrophilicity. While MXenes form highly stable dispersions in water, it can act as a limitation for certain applications such as photoactive layer in photovoltaic devices. In this work, delaminated MXenes of aqueous solution type Ti3C2 were prepared first, and then we have used a solvent-exchange technique to prepare suspensions of MXenes in three polar aprotic solvents namely, DMSO, DMF and NMP. Upon spin-coating under the same conditions, each solvent variation yields a different thin film morphology – in terms of particle size and surface coverage, as evidenced from AFM investigations. While the MXenes in DMSO yielded large aggregated particles with µm-sized islands in the film, MXenes in DMF and NMP were found to form films with well-dispersed MXene sheets in the size range 250 nm-50 nm and 80 nm-10 nm, respectively. This study also provides additional insights into the microstructure and opto-electronic properties of the MXene thin films using correlative Raman microscopy and photoluminescence spectroscopy. The information provided by this study on the variation in the properties depending on the solvent used to process and spin-cast the films are important for evaluating MXenes in thin film device applications.

Nanodiamond surface chemistry controls assembly of polypyrrole and generation of photovoltage

  • Autoři: Miliaieva, D., Matunová, P., Cermak, J., Stehlik, S., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Scientific Reports. 2021, 11(1), ISSN 2045-2322.
  • Rok: 2021
  • DOI: 10.1038/s41598-020-80438-3
  • Odkaz: https://doi.org/10.1038/s41598-020-80438-3
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanoscale composite of detonation nanodiamond (DND) and polypyrrole (PPy) as a representative of organic light-harvesting polymers is explored for energy generation, using nanodiamond as an inorganic electron acceptor. We present a technology for the composite layer-by-layer synthesis that is suitable for solar cell fabrication. The formation, pronounced material interaction, and photovoltaic properties of DND-PPy composites are characterized down to nanoscale by atomic force microscopy, infrared spectroscopy, Kelvin probe, and electronic transport measurements. The data show that DNDs with different surface terminations (hydrogenated, oxidized, poly-functional) assemble PPy oligomers in different ways. This leads to composites with different optoelectronic properties. Tight material interaction results in significantly enhanced photovoltage and broadband (1-3.5 eV) optical absorption in DND/PPy composites compared to pristine materials. Combination of both oxygen and hydrogen functional groups on the nanodiamond surface appears to be the most favorable for the optoelectronic effects. Theoretical DFT calculations corroborate the experimental data. Test solar cells demonstrate the functionality of the concept.

Optical emission spectroscopy of radio frequency inductively coupled plasma for cold hydrogenation of nanoparticles

  • Autoři: Remeš, Z., Kromka, A., Micova, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: IOP Conference Series: Materials Science and Engineering, Volume 1050, Development of Materials Science in Research and Education (DMSRE30 2020) 7th-11th September 2020, Pavlov, Czech Republic. Bristol: IOP Publishing Ltd, 2021. ISSN 1757-899X.
  • Rok: 2021
  • DOI: 10.1088/1757-899X/1050/1/012012
  • Odkaz: https://doi.org/10.1088/1757-899X/1050/1/012012
  • Pracoviště: Katedra fyziky
  • Anotace:
    The radio frequency inductively coupled plasma (ICP) offers an alternative "cold" way to affect the size, composition, structure, and surface functionality of nanoparticles (NPs), such as metal oxide NPs, providing further adjustment of their physical and chemical properties. The ICP was monitored in-situ by optical emission spectroscopy (OES). In particular, hydrogen, oxygen, argon, and nitrogen plasma was studied. OES data show that despite the decrease of the optical emission intensity with increasing gas pressure, the concentration of atomic hydrogen increases with pressure and radio frequency power.

PLASMA-SYNTHESISED ZINC OXIDE NANOPARTICLE BEHAVIOR IN LIQUIDS

  • DOI: 10.37904/nanocon.2021.4318
  • Odkaz: https://doi.org/10.37904/nanocon.2021.4318
  • Pracoviště: Katedra fyziky
  • Anotace:
    Zinc oxide nanoparticles have been synthesized using non-thermal atmospheric pressure plasma (ZnO-NTP). We investigated the behavior of these ligand-free as a colloid suspension using different solvents, from deionized water to physiological saline and microbial culture broth. We found that the zeta potential of ZnO-NTP became more negative after exposure to microbial culture broth relative to water, which suggests increased colloid stability. Photoluminescence spectra of ZnO-NTP were similar regardless of liquid type, yet optical and fluorescent images of samples showed different agglomeration behavior depending on liquid type. Scanning electron microscopy images revealed large agglomerates of ZnO-NTP interacting with the surface of bacteria cells, ranging in size from 200 nm up to 2 µm. We also studied effect of sub-lethal concentrations of ZnO-NTP on bacteria under illumination. There was no significant difference in viable bacteria concentration after 24h exposure to 10 µg/mL ZnO-NTP relative to untreated control irrespective of sample illumination.

Size and nitrogen inhomogeneity in detonation and laser synthesized primary nanodiamond particles revealed via salt-assisted deaggregation

  • DOI: 10.1016/j.carbon.2020.09.026
  • Odkaz: https://doi.org/10.1016/j.carbon.2020.09.026
  • Pracoviště: Katedra fyziky
  • Anotace:
    Detonation nanodiamonds (DND), their properties and deaggregation remain an active field of research. Here we innovated the salt-assisted ultrasonic deaggregation (SAUD) by employing NaHCO3 (a milling agent with relatively low solubility) followed by dialysis (a purification step) and processed two DND and one laser-synthesized (LND) commercial powders. The obtained ND colloids were separated to single-digit supernatant with the yield of 57-65% and sediment fractions by centrifugation and analyzed separately. By thermal analysis we evidenced chemical sensitization of the SAUD-processed DNDs manifested by significantly lower combustion temperatures. By correlation of spectroscopic, microscopic, and thermal analysis techniques we revealed a size and shape inhomogeneity of primary DND particles, also affecting strength of aggregation. By elemental analysis of the fractions we also show that nitrogen content is systematically higher in the smaller primary DND particles. Those features are inherent to all the three ND samples. The provided analyses highlight the need for better understanding of relations between detonation synthesis parameters and properties of the synthesized DNDs in terms of DND primary particle size, aggregation and nitrogen incorporation. (C) 2020 Elsevier Ltd. All rights reserved.

Size Effects on Surface Chemistry and Raman Spectra of Sub-5 nm Oxidized High-Pressure High-Temperature and Detonation Nanodiamonds

  • Autoři: Stehlik, S., Mermoux, M., Schummer, B., Vanek, O., Vlk, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Journal of Physical Chemistry C. 2021, 125(10), 5647-5669. ISSN 1932-7447.
  • Rok: 2021
  • DOI: 10.1021/acs.jpcc.0c09190
  • Odkaz: https://doi.org/10.1021/acs.jpcc.0c09190
  • Pracoviště: Katedra fyziky
  • Anotace:
    Understanding materials with dimensions down to a few nanometers is of major importance for fundamental science as well as prospective applications. Structural transformation and phonon-confinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm in size. Here, we investigate the effect of size on the surface chemistry, microscopic structure, and Raman scattering of high-pressure high-temperature (HPHT) and detonation nanodiamonds (DNDs) down to 2-3 nm. The surface and size of NDs are controlled by annealing in air and ultracentrifugation resulting in three ND fractions. Particle size distribution (PSD) of the fractions is analyzed by combining dynamic light scattering, analytical ultracentrifugation, small-angle X-ray scattering, X-ray diffraction, and transmission electron microscopy as complementary techniques. Based on the obtained PSD, we identify size-dependent and synthesis-dependent differences of ND properties. In particular, interpretation of Raman scattering on NDs is revisited. Comprehensive comparison of detonation and pure monocrystalline HPHT NDs reveals effects of diamond core size and defects, chemical and temperature (in)stability, and limitations of current phonon confinement models. In addition, low-frequency Raman scattering in the 20-200 cm(-1) range is experimentally observed. The size dependence of this signal for both HPHT NDs and DNDs suggests that it may correspond to confined acoustic vibrational, "breathing-like" modes of NDs.

Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers

  • Autoři: Fait, J., Varga, M., Hruška, K., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Nanophotonics. 2021, 10(15), 3895-3905. ISSN 2192-8614.
  • Rok: 2021
  • DOI: 10.1515/nanoph-2021-0369
  • Odkaz: https://doi.org/10.1515/nanoph-2021-0369
  • Pracoviště: Katedra fyziky
  • Anotace:
    The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.

Study of bovine serum albumin interaction with zinc oxide surfaces by force field simulations

  • Autoři: Hematian, H., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: IOP Conference Series: Materials Science and Engineering, Volume 1050, Development of Materials Science in Research and Education (DMSRE30 2020) 7th-11th September 2020, Pavlov, Czech Republic. Bristol: IOP Publishing Ltd, 2021. ISSN 1757-899X.
  • Rok: 2021
  • DOI: 10.1088/1757-899X/1050/1/012006
  • Odkaz: https://doi.org/10.1088/1757-899X/1050/1/012006
  • Pracoviště: Katedra fyziky
  • Anotace:
    We studied the interactions of bovine serum albumin (BSA) molecule with ZnO surfaces by force field simulations. The different orientations of BSA over the two main nonpolar wurtzite ZnO surfaces (10$$\overline 1$$0) and (11$$\overline 1$$0) have been investigated. These surfaces contain both Zn and O atoms. We compare the results also with polar Zn-face (0001) surface. The results demonstrate tendency of BSA molecule for being adsorbed on the ZnO surface in specific orientations. This happens either by bonding between a hydrogen atom of BSA molecule to an oxygen atom of the ZnO surface or by physical attraction inducing ZnO atoms displacement in some cases.

COMPARISON OF MICROBIAL INTERACTIONS OF ZINC OXIDE NANOMATERIALS IN VARIOUS SIZE AND SHAPE

  • DOI: 10.37904/nanocon.2019.8666
  • Odkaz: https://doi.org/10.37904/nanocon.2019.8666
  • Pracoviště: Katedra fyziky
  • Anotace:
    Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria inactivation by ZnO NP with novel hedgehog-like morphology using model gram-negative (E. coli) and gram-positive (S. aureus) bacteria. E. coli exposed to the novel ZnO hedgehog NP during growth resulted in 4 orders of magnitude reduction in viable cell concentration after 24 h, which is more than 2 orders higher reduction compared to commercially available ZnO NPs with nominal sizes from 50 nm to 20 um. There was a positive correlation between hedgehog NP concentration and bacteria cell concentration reduction within the range tested 0.1 – 1.0 mg/mL. S. aureus was less sensitive to ZnO NP exposure and inactivation effect of various ZnO NP was comparable. The effect can be thus atrributed to direct mechanical damage of the bacterial mebrane that is the most effective for the novel hedgehog ZnO NP. This conclusion was corroborated also by disk diffusion assays

Crucial role of charge transporting layers on ion migration in perovskite solar cells

  • Autoři: Abudulimu, A., Lang, L., Guilin, L., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Journal of Energy Chemistry. 2020, 47 132-137. ISSN 2095-4956.
  • Rok: 2020
  • DOI: 10.1016/j.jechem.2019.12.002
  • Odkaz: https://doi.org/10.1016/j.jechem.2019.12.002
  • Pracoviště: Katedra fyziky
  • Anotace:
    The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovskite with large contribution from grain boundaries are the most common interpretations for the hysteresis. Yet, the high performing devices often include intermediate hole and electron transporting layers, which can further complicate the dynamical process in the device. Here, by using Kelvin Probe Force Microscopy and Confocal Photoluminescence Microscopy, we elucidate the impact of charge-transporting layers and excess MAI on the spatial and temporal variations of the photovoltage on the MAPbI3-based solar cells. By studying the devices layer by layer, we found that the light-induced ion migration occurs predominantly in the presence of an imbalanced charge extraction in the solar cells, and the charge transporting layers play crucial role in suppressing it. Careful selection and processing of the electron and hole-transporting materials are thus essential for making perovskite solar cells free from the ion migration effect.

Immuno-probed graphene nanoplatelets on electrolyte-gated field-effect transistor for stable cortisol quantification in serum

  • Autoři: Nur Nasyifa, M.M., Ruslinda, A.R., Abdul Halim, N.H., Zainol Abidin, A.S., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Journal of the Taiwan Institute of Chemical Engineers. 2020, 117 10-18. ISSN 1876-1070.
  • Rok: 2020
  • DOI: 10.1016/j.jtice.2020.12.008
  • Odkaz: https://doi.org/10.1016/j.jtice.2020.12.008
  • Pracoviště: Katedra fyziky
  • Anotace:
    Physiological and emotional stress affects the regulation of cortisol secretion, a routine process in circadian rhythm. Regular monitoring of cortisol level as a biomarker in the blood stream becomes vital to determine cortisol-related diseases. This study reports immuno-probed graphene nanoplatelets on electrolyte-gated field-effect transistor (EGFET) biosensor for cortisol determination in human serum. Solution-processed graphene nanoplatelets were evidenced on the surface by Raman spectroscopy analysis and utilized as the transducing element on the field-effect transistor. Further, confirmed the binding events of the antibody on graphene nanoplatelets using X-Ray Photoelectron Spectroscopy and characterized the electrostatic gating effect of cortisol and intermediate functionalization on graphene nanoplatelets-EGFET. The biosensor exhibited good sensitivity of 72.30 µA.(g/mL)−1 in a linear range between 1.00 pg/mL to 10.00 ng/mL, with a limit of detection (LOD) of 0.85 pg/mL. Confirmation with binding events on the biosensor was done using the relevant molecules, progesterone, cortisone, and corticosterone, and found to be selective towards cortisol. Cortisol was also successfully detected with interference by the human serum, suggesting the capability of graphene nanoplatelets-EGFET sensor for determining cortisol in a complex matrix.

Mathematical method for submolecular resolution of helicene-based macrocycles by atomic force microscopy in air

  • Autoři: Egor Ukraintsev, Ph.D., Houska, V., Vacek, J., Stary, I., Stara, I.G., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Proceedings 11th International Conference on Nanomaterials - Research & Application. Ostrava: Tanger, 2020. p. 561-567. ISSN 2694-930X. ISBN 978-80-87294-95-6.
  • Rok: 2020
  • DOI: 10.37904/nanocon.2019.8492
  • Odkaz: https://doi.org/10.37904/nanocon.2019.8492
  • Pracoviště: Katedra fyziky
  • Anotace:
    We introduce a straightforward mathematical method for improving the AFM image resolution, applied to image analysis of helicene-based macrocycles adsorbed on HOPG. The method reveals structural details from insufficiently resolved AFM images and attributes them to internal structure and ordering of the macrocycles. Our findings are also corroborated by molecular mechanics simulations, validating that the structure provided by the method has lower potential energy compared to other tested macrocycle arrangements.

Microscopic and Kelvin Probe study of charge transporting layers role in MAPI perovskites with varied composition

  • DOI: 10.37904/nanocon.2019.8662
  • Odkaz: https://doi.org/10.37904/nanocon.2019.8662
  • Pracoviště: Katedra fyziky
  • Anotace:
    Perovskites are one of the most intensively studied photovoltaic materials nowadays. Microscopic studies can provide useful information about material roughness, conductivity, structure, mechanical and opto-electronic properties as well as about kinetic effects from short to long time scale for understanding and improving the photovoltaic performance. Here, time-resolved photovoltage was measured by Kelvin probe in the dark and under white light illumination. Morphology was characterized by optical and atomic force microscopy. We identify the impact of charge transporting layers (CTLs) on structural and opto-electronic properties of MAPbI3 perovskite with different ratio of MAI and PbI2.

Nanocrystalline Diamond Electrolyte-Gates in Field Effect Transistor for a Prolific Aptasensing HIV-1 Tat on Hydrogen-terminated Surface

  • Autoři: Ahmad, N., Rahim, Ruslinda A., prof. RNDr. Bohuslav Rezek, Ph.D., Kromka, A., Procházka, V.
  • Publikace: International Journal of Nanoelectronics and Materials. 2020, 13(2), 295-306. ISSN 1985-5761.
  • Rok: 2020
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanocrystalline diamonds have recently gained great attention to circumvent the current hurdles, with their appealing properties such as high-surface-area to volume ratio, low-background current, wide potential window, biocompatibility, and chemical stability. The nanocrystalline diamonds electrolyte-gated field-effect transistor (NCD-EGFET) can operate directly in solution without involving gate oxides in bringing the hydrogen-tethered moieties and facilitates the p-type surface conductivity. This research investigated on Trans-activator of transcription ( Tat) protein; a powerful viral gene activator that plays a pivotal role in the primary stage of the human immunodeficiency virus type 1 (HIV-1) replication. Dose-dependent interactions of HIV-1 Tat on NCD-EGFET-based RNA aptamer sensing surface were monitored and attained the detection down to 10 fM. The linear regression curve with 3 sigma estimation professed the sensitivity range to be 31.213 mV/log(10) [Tat Concentration]M and the limit of detection of 6.18 fM. The selectivity analysis of NCD-EGFET was conducted with different proteins from HIV (Nef and p24) and Bovine Serum Albumin. Furthermore, to practice in the clinical application, HIV-1 Tat was spiked into the human blood serum and it displayed the genuine non-fouling interaction with the aptamer. The attained high-performance signal enhancement with nanocrystalline diamond-biosensing aids to circumvent the issues in the current diagnosis.

Ni-mediated reactions in nanocrystalline diamond on Si substrates: the role of the oxide barrier

  • Autoři: Tulic, S., Waitz, T., Romanyuk, O., Varga, M., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: RSC Advances. 2020, 10(14), 8224-8232. ISSN 2046-2069.
  • Rok: 2020
  • DOI: 10.1039/d0ra00809e
  • Odkaz: https://doi.org/10.1039/d0ra00809e
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanocrystalline diamond (NCD) films grown on Si substrates by microwave plasma enhanced chemical vapor deposition (MWPECVD) were subjected to Ni-mediated graphitization to cover them with a conductive layer. Results of transmission electron microscopy including electron energy-loss spectroscopy of cross-sectional samples demonstrate that the oxide layer on Si substrates (similar to 5 nm native SiO2) has been damaged by microwave plasma during the early stage of NCD growth. During the heat treatment for graphitizing the NCD layer, the permeability or absence of the oxide barrier allow Ni nanoparticles to diffuse into the Si substrate and cause additional solid-state reactions producing pyramidal crystals of NiSi2 and SiC nanocrystals. The latter are found impinged into the NiSi2 pyramids but only when the interfacial oxide layer is absent, replaced by amorphous SiC. The complex phase morphology of the samples is also reflected in the temperature dependence of electrical conductivity, where multiple pathways of the electronic transport dominate in different temperature regions. We present models explaining the observed cascade of solid-state reactions and resulting electronic transport properties of such heterostructures.

Photogenerated charge collection on diamond electrodes with covalently linked chromophore monolayers

  • Autoři: Raymakers, J., Artemenko, A., Verstraeten, F., Krysova, H., López Carballeira, D., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Electrochimica Acta. 2020, 337 ISSN 0013-4686.
  • Rok: 2020
  • DOI: 10.1016/j.electacta.2020.135762
  • Odkaz: https://doi.org/10.1016/j.electacta.2020.135762
  • Pracoviště: Katedra fyziky
  • Anotace:
    Encouraged by its rich surface chemistry and excellent electrochemical properties, boron-doped nanocrystalline diamond (B:NCD) is a promising p-type photoelectrode in dye-sensitized solar cells. One method of diamond surface functionalization using stable carbon-carbon bonds involves the electrochemical grafting of diazonium salts. However, this method typically leads to multilayers that may complicate the transport of photogenerated charges. Here, we establish functionalization of B:NCD electrodes by a monolayer of ethynylphenyl molecules using sterically hindered 4-(trimethylsilyl)ethynylbenzenediazonium tetrafluoroborate. Both the density and structural orientation of the grafted layer are investigated by angular resolved X-ray photoelectron spectroscopy, confirming the presence of covalently grafted monolayers. After removal of the trimethylsilyl protective groups, the resulting ethynyl functionalities are employed to immobilize organic donor-acceptor chromophores via Sonogashira cross-coupling reactions. Homogenous surface coverage is achieved even on the B:NCD electrode. Atomic scale DFT computing reveals that for the chromophore with the strongest acceptor unit, efficient charge separation of 20 angstrom is obtained where photogenerated holes move directly into diamond. Yet, photocurrent and photovoltage measurements suggest competitive electron recombination to the diamond electrode via the redox electrolyte. Correlation between the density of the molecular layer and photocurrents/photovoltage provides better understanding of the charge generation and recombination pathways in diamond-organic photoelectrochemical cells. (C) 2020 Elsevier Ltd. All rights reserved.

Reactive adsorption and photodegradation of soman and dimethyl methylphosphonate on TiO2/nanodiamond composites (vol 259, 118097, 2019)

  • Autoři: Henych, J., Stehlik, S., Mazanec, K., Tolasz, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Applied Catalysis B: Environmental. 2020, 261 ISSN 0926-3373.
  • Rok: 2020
  • DOI: 10.1016/j.apcatb.2019.118263
  • Odkaz: https://doi.org/10.1016/j.apcatb.2019.118263
  • Pracoviště: Katedra fyziky
  • Anotace:
    Corrigendum to “Reactive adsorption and photodegradation of soman and dimethyl methylphosphonate on TiO2/nanodiamond composites” [Appl. Catal. B: Environ. 259 (2019) 118097].

The bio-chemically selective interaction of hydrogenated and oxidized ultra-small nanodiamonds with proteins and cells

  • DOI: 10.1016/j.carbon.2020.02.061
  • Odkaz: https://doi.org/10.1016/j.carbon.2020.02.061
  • Pracoviště: Katedra fyziky
  • Anotace:
    Ultra-small nanoparticles of a size smaller than or comparable to cell membrane pores (1-5 nm) offer significant potential in the field of biomedicine. This study presents a systematic in vitro investigation of fundamental bio-chemical interactions of such ultra-small hydrogenated and oxidized detonation nanodiamonds (DNDs) with biomolecules and human cells. We apply mass spectrometry methods (LC-MS/MS) for the qualitative and quantitative analysis of the protein corona as a function of the surface chemistry and size of DNDs. We observe that protein interactions with DNDs are more related to their surface chemistry (H/O-termination) rather than size. Bioinformatics characterization of the identified proteins points to the strong influence of electrostatic interaction between proteins and DNDs depending on their termination. Such specific interaction leads to formation of different protein corona on 2 nm DNDs, which influences also interaction with cells including different level of cytotoxicity. (C) 2020 Elsevier Ltd. All rights reserved.

Coherent phonon dynamics in diamond detected via multiphoton absorption

  • Autoři: Zukerstein, M., Trojánek, F., prof. RNDr. Bohuslav Rezek, Ph.D., Šobáň, Z.
  • Publikace: Applied Physics Letters. 2019, 115(16), ISSN 0003-6951.
  • Rok: 2019
  • DOI: 10.1063/1.5119056
  • Odkaz: https://doi.org/10.1063/1.5119056
  • Pracoviště: Katedra fyziky
  • Anotace:
    Coupling between ultrafast lattice dynamics and electronic polarization becomes increasingly important for generating terahertz frequency combs, monitor atomic potential landscapes, or high-speed information processing. Here, we show that the carrier population excited by multiphoton (5-photon) absorption in diamond crystal can be controlled at terahertz frequencies by coherent lattice vibrations-phonons. We introduce and compare two independent methods for direct monitoring of coherent phonon dynamics in diamond by using photoluminescence or photocurrent measurements on femtosecond time scale. We observe a strong signal enhancement compared to standard techniques due to transmission geometry and high-order nonlinearity of optical carrier generation.

Covalent Diamond-Graphite Bonding: Mechanism of Catalytic Transformation

  • Autoři: Tulic, S., Waitz, T., Caplovicova, M., Habler, G., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: ACS NANO. 2019, 13(4), 4621-4630. ISSN 1936-0851.
  • Rok: 2019
  • DOI: 10.1021/acsnano.9b00692
  • Odkaz: https://doi.org/10.1021/acsnano.9b00692
  • Pracoviště: Katedra fyziky
  • Anotace:
    Aberration-corrected transmission electron microscopy of the atomic structure of diamond graphite interface after Ni-induced catalytic transformation reveals graphitic planes bound covalently to the diamond in the upright orientation. The covalent attachment, together with a significant volume expansion of graphite transformed from diamond, gives rise to uniaxial stress that is released through plastic deformation. We propose a comprehensive model explaining the Ni-mediated transformation of diamond to graphite and covalent bonding at the interface as well as the mechanism of relaxation of uniaxial stress. We also explain the mechanism of electrical transport through the graphitized surface of diamond. The result may thus provide a foundation for the catalytically driven formation of graphene-diamond nanodevices.

DFT calculations reveal pronounced HOMO-LUMO spatial separation in polypyrrole-nanodiamond systems

  • Autoři: Matunová, P., Jirasek, V., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Physical Chemistry Chemical Physics. 2019, 21(21), 11033-11042. ISSN 1463-9076.
  • Rok: 2019
  • DOI: 10.1039/c8cp07622g
  • Odkaz: https://doi.org/10.1039/c8cp07622g
  • Pracoviště: Katedra fyziky
  • Anotace:
    The low-cost efficient generation of renewable energy and its blending with societal lifestyle is becoming increasingly pervasive. Diamond-based inorganic-organic hybrid systems may have an immense, yet still mostly unexplored, potential in photovoltaic solar cells applications. In this work, we study the interactions of polypyrrole (PPy) with diamond nanoparticles (so-called nanodiamonds, NDs) by computational density functional theory (DFT) methods. We compute the structural and electronic properties of such hybrid organic-inorganic systems. During modeling, PPy is chemisorbed and physisorbed on (111) and (100) ND edge-like surface slabs terminated with oxygen, hydroxyl, carboxyl, and anhydride functional groups, i. e., in the arrangements most commonly found in real NDs. Moreover, NDs terminated with an amorphous surface layer (a-C: H, a-C: O) are considered to approach realistic conditions even further. In a predominant number of cases, we obtain the spatial separation of HOMO and LUMO at the interface, facilitating exciton dissociation. Further, there is a favorable energy level alignment for charge transport. The theoretical results, therefore, show the promising potential of PPy-ND composites in photovoltaic applications.

Infrared Absorption Spectroscopy of Albumin Binding with Amine-Containing Plasma Polymer Coatings on Nanoporous Diamond Surfaces

  • DOI: 10.1021/acs.langmuir.9b02327
  • Odkaz: https://doi.org/10.1021/acs.langmuir.9b02327
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanocrystalline diamond (NCD) layers functionalized with amine-containing functional groups have generated considerable interest as biocompatible substrates for attachment of biomolecules and cells with a view to biosensor and tissue engineering applications. Here we prepare nanoporous diamond layers with the surfaces modified by hydrogen plasma, oxygen plasma, and conformal 7 nm amine-containing plasma polymer (PP). Immobilization of bovine serum albumin (BSA) molecules is characterized on such surfaces. Grazing angle reflectance infrared spectroscopy as well as X-ray photoelectron spectroscopy show that concentration of amine-containing bonds after BSA exposure depends on the type of NCD surface modification. AFM measurements reveal that BSA proteins are physisorbed on H- and O-terminated diamond surfaces in different thicknesses and morphology. When the diamond layers are coated with the amine-containing PP, BSA molecules assume similar thickness and morphology, and their adhesion is significantly increased on both types of the diamond surfaces.

Maximized vertical photoluminescence from optical material with losses employing resonant excitation and extraction of photonic crystal modes

  • Autoři: Fait, J., Varga, M., Hruška, K., Remeš, Z., Jurka, V., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D., Ondič, L.
  • Publikace: Nanophotonics. 2019, 8(6), 1041-1050. ISSN 2192-8606.
  • Rok: 2019
  • DOI: 10.1515/nanoph-2019-0042
  • Odkaz: https://doi.org/10.1515/nanoph-2019-0042
  • Pracoviště: Katedra fyziky
  • Anotace:
    Optical losses of a host material together with the total internal reflection phenomenon can significantly reduce photoluminescence external quantum efficiency of embedded light-emitters. This is the case for light-emitting color centers in thin layers of nanocrystalline diamond, for silicon nanocrystals in silica dioxide matrices but also for some types of perovskite materials, etc. Here, we show that a significant boost (more than 100-fold en-hancement) of the directional light emission efficiency from light-emitters in diamond can be achieved by using two-dimensional photonic crystal slabs to extract the light emission into vertical direction (resonant extraction) and in the same time to couple the excitation beam into the structure (resonant excitation). We further show that this so-called resonant extraction and excitation scheme provides the highest enhancement when the overlap between the electric field distribution of extraction leaky mode and the region of excited light-emitters is max-imized. This can be achieved by using the same type of the photonic mode for both extraction and excitation, and by optimizing the thickness of a diamond layer. The usage of the same type of modes appears to be more significant than tuning of the Q-factors of the excitation and extraction leaky modes individually. The results of our measurements are supported by the outputs of computer simulations. Our findings may be helpful in design-ing future PhCs for extraction of luminescence originating from various optoelectronic and sensor devices mak-ing use of diamond unique properties. Moreover, our concept can be easily extended to other light-emitting materials with optical losses.

Microscopic study of multifunctional drug molecule adhesion to electronic biosensors coated with diamond and gold nanoparticles

  • Pracoviště: Katedra fyziky, Katedra elektrotechnologie
  • Anotace:
    The easy and fast detection of drug content and concentration levels is demanded in biological research as well as in clinical practice. Here we study on microscopic level how nanodiamonds and gold nanoparticles interact with a multifunctional drug molecule directly on a biosensor surface. The sensors are made of interdigitated Au electrodes coated by 5 nm hydrogenated or oxidized nanodiamonds and further combined with Au colloidal nanoparticles (size 20 nm) providing nanoscale composite (spacing 100 nm). Atomic force microscopy is employed to measure local tip-surface adhesion forces and surface topography. AFM adhesion maps show that the drug binds to all types of nanoparticles and the adhesion is also significantly influenced by the substrates on which the nanoparticles are deposited. Role of local AFM tip interaction with nanostructured surface is also discussed.

Nanoscale frictional properties of ordered and disordered MoS2

  • DOI: 10.1016/j.triboint.2019.03.004
  • Odkaz: https://doi.org/10.1016/j.triboint.2019.03.004
  • Pracoviště: Katedra fyziky, Katedra řídicí techniky
  • Anotace:
    The present work aims to understand the sliding of ordered/disordered molybdenum disulfide against itself by combination of nanoscale sliding experiments and atomistic simulations. Tribological experiments were performed using lateral force microscopy with tips covered by a thin sputtered MoS2film. Nanoscale contact area between the MoS2-coated tips and MoS2 samples opened up the possibility for close comparison with classical molecular dynamics simulations. Our simulations replicated well the coefficient of friction obtained by experiments for various contact conditions and shed light on nanoscale sliding of both crystalline and amorphous MoS2. Experimental sliding at humid environment demonstrated detrimental effect of water molecules on friction. However, such effect was much less pronounced when compared to that observed in macroscopic sliding experiments.

Nucleation of diamond micro-patterns with photoluminescent SiV centers controlled by amorphous silicon thin films

  • Autoři: Fait, J., Potocký, Š., Stehlík, Š., Stuchlík, J., Artemenko, A., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Applied Surface Science. 2019, 480 1008-1013. ISSN 0169-4332.
  • Rok: 2019
  • DOI: 10.1016/j.apsusc.2019.03.064
  • Odkaz: https://doi.org/10.1016/j.apsusc.2019.03.064
  • Pracoviště: Katedra fyziky
  • Anotace:
    Selective deposition of diamond allows bottom-up growth of diamond nanostructures and nanoscale devices. However, it remains challenging to reduce the size of the patterns and to suppress parasitic spontaneous nucleation. We show here that thin layers of hydrogenated amorphous silicon (down to 40 nm) efficiently suppress spontaneous nucleation of diamond. The suppression of diamond nucleation does not depend on the substrate materials below hydrogenated amorphous silicon (Si, SiO2, Pt, Ni). We attribute the suppressed diamond nucleation to surface disorder on atomic scale. By using a structured layer of hydrogenated amorphous silicon, highly selective growth of diamond micro-patterns with optically active SiV centers by low-temperature microwave plasma chemical vapor deposition is achieved.

Reactive adsorption and photodegradation of soman and dimethyl methylphosphonate on TiO2/nanodiamond composites

  • Autoři: Henych, J., Stehlik, S., Mazanec, K., Tolasz, J., Cermak, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Applied Catalysis B: Environmental. 2019, 259 ISSN 0926-3373.
  • Rok: 2019
  • DOI: 10.1016/j.apcatb.2019.118097
  • Odkaz: https://doi.org/10.1016/j.apcatb.2019.118097
  • Pracoviště: Katedra fyziky
  • Anotace:
    We report on the synthesis and characterization of TiO2/Nanodiamond (ND) nanocomposites for rapid decontamination of chemical warfare agents (CWA) and toxic industrial compounds prepared by a simple water-based, low-temperature method using urea as a homogeneous precipitating agent. The excellent water-compatibility of NDs promoted their good dispersion within the TiO2 matrix resulting in intergrown TiO2/ND nanostructures. NDs with an abundance of oxygen-containing surface moieties increased the porosity of the composites resulting in their three times more efficient spontaneous degradation of the CWA soman in solution compared to pure TiO2. In situ DRIFT spectroscopy revealed the enhanced reactive adsorption and solar light photodecomposition of dimethyl methyl phosphonate vapor on TiO2/ND. The charge transfer across TiO2/ND interfaces that hinder recombination of photo-excited electron-hole pairs was inferred from surface potential measurements. The results indicate that well-dispersed NDs forming heterojunctions together with their high porosity contribute to the reactive properties of the nanocomposites.

Structural and Electronic Properties of Oxidized and Amorphous Nanodiamond Surfaces with Covalently Grafted Polypyrrole

  • DOI: 10.1002/pssb.201900176
  • Odkaz: https://doi.org/10.1002/pssb.201900176
  • Pracoviště: Katedra fyziky
  • Anotace:
    Diamond nanoparticles denoted as nanodiamonds (NDs) possess numerous beneficial material properties and are envisioned for a wide range of applications. In this work, complexes of polypyrrole (PPy) organic dye covalently grafted to ND surfaces are investigated by atomic scale density functional theory (DFT) computations with a view to their structural and electronic properties. NDs terminated with oxygen, hydroxyl, carboxyl, anhydride, as well as amorphous carbon (a‐C:H, a‐C:O) have been considered. Thereby the theoretical model is brought close to real nanodiamonds. Spatially separated highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) and a favorable energetic level alignment at the ND–PPy interface are observed for the majority of the oxidized NDs. This feature is also retained for NDs with amorphous surface layer. Excited states are computed by time‐dependent DFT to analyze how the electronic configuration can promote dissociation of excitons, for instance in photovoltaic applications.

Study of photovoltage stability on nano diamond-polypyrrole composites by Kelvin probe method

  • Autoři: Chang, Y., Miliaieva, D., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: 10TH ANNIVERSARY INTERNATIONAL CONFERENCE ON NANOMATERIALS - RESEARCH & APPLICATION (NANOCON 2018). Ostrava: TANGER, 2019. p. 164-168. ISBN 978-80-87294-89-5.
  • Rok: 2019
  • Pracoviště: Katedra fyziky
  • Anotace:
    Diamond thin films and nanodiamond particles are considered promising for addressing the long-term challenge of organic photovoltaics: efficiency and stability. In this work, we characterize stability of surface potential and photovoltage on polyfunctional detonation nanodiamonds merged with polypyrrole oligomers. The polyfunctional-detonation nanodiamond (poly-DND), polypyrrole (PPy), and poly-DND/PPy composites were prepared on p-type silicon wafer substrates. In order to investigate illumination induced effects, surface potential and photovoltage of the samples were characterized by macroscopic Kelvin Probe method as a function of time. The poly-DND/PPy composite exhibits better stability of surface potential and surface photovoltage in short-term as well as in long-term (up to 8 weeks) compared to individual materials. The nanodiamond composites thus appear advantageous for use in organic photovoltaics.

Complex nano-patterning of structural, optical, electrical and electron emission properties of amorphous silicon thin films by scanning probe

  • Autoři: Fait, J., Čermák, J., Stuchlík, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Applied Surface Science. 2018, 428 1159-1165. ISSN 0169-4332.
  • Rok: 2018
  • DOI: 10.1016/j.apsusc.2017.09.228
  • Odkaz: https://doi.org/10.1016/j.apsusc.2017.09.228
  • Pracoviště: Katedra fyziky
  • Anotace:
    Preparation of nanoscale templates represents an important step for synthesis and assembly of diverse nanostructures and nanoscale devices. We show that complex nano-structural templates in a thin (40 nm) layer of hydrogenated amorphous silicon (a‐Si:H) can be prepared by using locally applied electric field in an atomic force microscope (AFM). Depth of the resulting structures (1–40 nm) can be controlled by the process parameters (magnitude of electric field, exposure time, or nano-sweeping of the tip). We demonstrate that complex patterns can be scribed into the a‐Si:H layer in that way. The prepared patterns exhibit different structural, optical, electrical, and electron emission properties, compared to the surroundings as detected by Raman micro-spectroscopy, scanning electron microscopy (SEM), and conductive AFM. The silicon thin films with locally modified properties can be useful in themselves or can serve as templates for further nanoscale growth or assembly.

Functionalization of boron-doped diamond with a push-pull chromophore via Sonogashira and CuAAC chemistry

  • Autoři: Raymakers, J., Krysova, H., Artemenko, A., Cermak, J., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: RSC Advances. 2018, 8(58), 33276-33290. ISSN 2046-2069.
  • Rok: 2018
  • DOI: 10.1039/c8ra07545j
  • Odkaz: https://doi.org/10.1039/c8ra07545j
  • Pracoviště: Katedra fyziky
  • Anotace:
    Improving the performance of p-type photoelectrodes represents a key challenge toward significant advancement in the field of tandem dye-sensitized solar cells. Herein, we demonstrate the application of boron-doped nanocrystalline diamond (B:NCD) thin films, covalently functionalized with a dithienopyrrole-benzothiadiazole push-pull chromophore, as alternative photocathodes. First, a primary functional handle is introduced on H-terminated diamond via electrochemical diazonium grafting. Afterwards, Sonogashira cross-coupling and Cu(i) catalyzed azide-alkyne cycloaddition (CuAAC) reactions are employed to attach the chromophore, enabling the comparison of the degree of surface functionalization and the importance of the employed linker at the diamond-dye interface. X-ray photoelectron spectroscopy shows that surface functionalization via CuAAC results in a slightly higher chromophore coverage compared to the Sonogashira cross-coupling. However, photocurrents and photovoltages, obtained by photoelectrochemical and Kelvin probe measurements, are approximately three times larger on photocathodes functionalized via Sonogashira cross-coupling. Surface functionalization via Sonogashira cross-coupling is thus considered the preferential method for the development of diamond-based hybrid photovoltaics.

Growth of Primary Human Osteoblasts on Plasma-Treated and Nanodiamond-Coated PTFE Polymer Foils

  • DOI: 10.1002/pssb.201700595
  • Odkaz: https://doi.org/10.1002/pssb.201700595
  • Pracoviště: Katedra fyziky
  • Anotace:
    Polytetrafluoroethylene (PTFE) is widely used for constructing tissue replacements, particularly clinically used vascular prostheses, and is also applied in dental and orthopedic surgery, thanks to its non-toxicity, high chemical resistance, low surface energy and excellent thermal stability. We report here on a comparative study in which PTFE is modified with the use of DC argon plasma (8W, 240s) and is coated with hydrogenated or oxidized nanodiamonds (mean size 5nm), with a view to achieving improved body acceptance of the bio-inert pristine material. The surface morphology characterized by scanning electron microscopy reveals a microscale and nanoscale structuring of the PTFE foils with comparable roughness among all samples (analyzed by atomic force microscopy). The water contact angle remains in the highly hydrophobic range (above 100 degrees). However, the proliferation and metabolic activity of primary human hFOB 1.19 osteoblasts (studied for up to 7 days) are significantly enhanced by the plasma and/or by hydrogenated nanodiamond treatment (rather than by oxidized nanodiamond treatment) of the PTFE foil.

Histology and Micro-CT Study of Diamond-Coated Metal Bone Implants in Rabbit femurs

  • Autoři: Potocký, Š., Ižák, T., Dragounová, K., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D., Mandys, V., Bartoš, M., Bačáková, L., Sedmera, D.
  • Publikace: NANOCON 2017 Conference Proceedings. Ostrava: Tanger Ltd., 2018. p. 573-577. ISBN 978-80-87294-81-9.
  • Rok: 2018
  • Pracoviště: Katedra fyziky
  • Anotace:
    A conformal coating of a thin diamond layer on three-dimensional metal bone implants was shown directly on stainless steel and TiAl6V4 cortical screw implant using ultrasonic and composite polymer pretreatment method. The best conformation coverage was achieved in the case of the WO3 interlayer for both stainless steel and TiAl6V4 screws. The process of osteointegration of the screw implants into rabbit femurs is evidenced by the formation of a bone edge via desmogenous ossification around the screws in less than six months after implantation. A detailed evaluation of the tissue reaction around the implanted screws shows good biocompatibility of diamond-coated metal bone implants.

Hydroxylation and self-assembly of colloidal hydrogenated nanodiamonds by aqueous oxygen radicals from atmospheric pressure plasma jet

  • Autoři: Jirasek, V., Stehlik, S., Stenclova, P., Artemenko, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: RSC Advances. 2018, 8(66), 37681-37692. ISSN 2046-2069.
  • Rok: 2018
  • DOI: 10.1039/c8ra07873d
  • Odkaz: https://doi.org/10.1039/c8ra07873d
  • Pracoviště: Katedra fyziky
  • Anotace:
    Plasma chemical surface modification of nanoparticles in gas-liquid type reactors enables a controllable, specific, low-cost, and environmentally friendly alternative to wet chemistry methods or thermal and dry plasma treatments. Here the atmospheric pressure radio-frequency microplasma jet (mu-APPJ) operating with 0.6% O-2 in He is used to deliver aqueous oxygen radicals (AOR) to the surface of similar to 3 nm hydrogenated detonation nanodiamonds (H-DNDs) suspended in water. The AOR-treated H-DND samples are characterized by FTIR and XPS spectroscopies and by AFM and SEM imaging. The main chemical reaction mechanism is identified as the abstraction of surface hydrogen atoms by O or OH radicals and a consequent attachment of the OH group, thereby increasing concentration of alcohols, carboxyls, and aldehydes on the DND's surface. FTIR spectra reveal also a structural re-arrangement of the surface water on the AOR-treated H-DNDs. Yet zeta-potential of AOR-treated H-DNDs still remains positive (decreases from +45 mV to +30 mV). The chemical modification gives rise to formation of nanoscale chain-like aggregates when AOR-treated H-DNDs are deposited on Si substrate.

Inhibition of E. coli Growth by Nanodiamond and Graphene Oxide Enhanced by Luria-Bertani Medium

  • DOI: 10.3390/nano8030140
  • Odkaz: https://doi.org/10.3390/nano8030140
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanodiamonds (NDs) and graphene oxide (GO) are modern carbon-based nanomaterials with promising features for the inhibition of microorganism growth ability. Here we compare the effects of nanodiamond and graphene oxide in both annealed (oxidized) and reduced (hydrogenated) forms in two types of cultivation media—Luria-Bertani (LB) and Mueller-Hinton (MH) broths. The comparison shows that the number of colony forming unit (CFU) of Escherichia coli is significantly lowered (45%) by all the nanomaterials in LB medium for at least 24 h against control. On the contrary, a significant long-term inhibition of E. coli growth (by 45%) in the MH medium is provided only by hydrogenated NDs terminated with C-HX groups. The use of salty agars did not enhance the inhibition effects of nanomaterials used, i.e. disruption of bacterial membrane or differences in ionic concentrations do not play any role in bactericidal effects of nanomaterials used. The specific role of the ND and GO on the enhancement of the oxidative stress of bacteria or possible wrapping bacteria by GO nanosheets, therefore isolating them from both the environment and nutrition was suggested. Analyses by infrared spectroscopy, photoelectron spectroscopy, scanning electron microscopy and dynamic light scattering corroborate these conclusions.

Proton irradiation induced changes in glass and polyethylene terephthalate substrates for photovoltaic solar cells

  • Autoři: Čermák, J., Mihai, L., Sporea, D., Galagan, Y., Fait, J., Artemenko, A., Štenclová, P., prof. RNDr. Bohuslav Rezek, Ph.D., Straticiuc, M., Burducea, I.
  • Publikace: Solar Energy Materials and Solar Cells. 2018, 186 284-290. ISSN 0927-0248.
  • Rok: 2018
  • DOI: 10.1016/j.solmat.2018.06.046
  • Odkaz: https://doi.org/10.1016/j.solmat.2018.06.046
  • Pracoviště: Katedra fyziky
  • Anotace:
    An alkaline earth boro-aluminosilicate glass (Eagle XG), a soda-lime glass, and a light-weight polyethylene-terephthalate (PET) foil, used as typical substrates for photovoltaics, were treated by an energetic proton beam (3 MeV, dose 106–107 Gy) corresponding to approx. 30 years of operation at low Earth orbit. Properties of the irradiated substrates were characterized by atomic force microscopy, optical absorption, optical diffuse reflectance, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and terahertz (THz) spectroscopy. Minimal changes of optical and morphological properties are detected on the bare Eagle XG glass, whereas the bare PET foil exhibits pronounced increase in optical absorption, generation of photoluminescence, as well as mechanical bending. On the other hand, the identical substrates coated with Indium-tin-oxide (ITO), which is a typical material for transparent electrodes in photovoltaics, exhibit significantly higher resistance to the modifications by protons while ITO structural and electronic properties remain unchanged. The experimental results are discussed considering a potential application of these materials for missions in space.

Silicon-Vacancy Centers in Ultra-Thin Nanocrystalline Diamond Films

  • Autoři: Stehlík, Š., Ondič, L., Varga, M., Fait, J., Artemenko, A., Glatzel, T., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Micromachines. 2018, 9(6), ISSN 2072-666X.
  • Rok: 2018
  • DOI: 10.3390/mi9060281
  • Odkaz: https://doi.org/10.3390/mi9060281
  • Pracoviště: Katedra fyziky
  • Anotace:
    Color centers in diamond have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report the optoelectronic investigation of shallow silicon vacancy (SiV) color centers in ultra-thin (7-40 nm) nanocrystalline diamond (NCD) films with variable surface chemistry. We show that hydrogenated ultra-thin NCD films exhibit no or lowered SiV photoluminescence (PL) and relatively high negative surface photovoltage (SPV) which is ascribed to non-radiative electron transitions from SiV to surface-related traps. Higher SiV PL and low positive SPV of oxidized ultra-thin NCD films indicate an efficient excitationemission PL process without significant electron escape, yet with some hole trapping in diamond surface states. Decreasing SPV magnitude and increasing SiV PL intensity with thickness, in both cases, is attributed to resonant energy transfer between shallow and bulk SiV. We also demonstrate that thermal treatments (annealing in air or in hydrogen gas), commonly applied to modify the surface chemistry of nanodiamonds, are also applicable to ultra-thin NCD films in terms of tuning their SiV PL and surface chemistry.

Study of Ni-Catalyzed Graphitization Process of Diamond by in Situ X-ray Photoelectron Spectroscopy

  • Autoři: Romanyuk, O., Varga, M., Tulic, S., Izak, T., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Journal of Physical Chemistry C. 2018, 122(12), 6629-6636. ISSN 1932-7447.
  • Rok: 2018
  • DOI: 10.1021/acs.jpcc.7b12334
  • Odkaz: https://doi.org/10.1021/acs.jpcc.7b12334
  • Pracoviště: Katedra fyziky
  • Anotace:
    Graphene on diamond has been attracting considerable attention due to the unique and highly beneficial features of this heterostructure for a range of electronic applications. Here, ultrahigh-vacuum X-ray photoelectron spectroscopy is used for in situ analysis of the temperature dependence of the Ni-assisted thermally induced graphitization process of intrinsic nanocrystalline diamond thin films (65 nm thickness, 50-80 nm grain size) on silicon wafer substrates. Three major stages of diamond film transformation are determined from XPS during the thermal annealing in the temperature range from 300 degrees C to 800 degrees C. Heating from 300 degrees C causes removal of oxygen; formation of the disordered carbon phase is observed at 400 degrees C; the disordered carbon progressively transforms to graphitic phase whereas the diamond phase disappears from the surface from 500 degrees C. In the well-controllable temperature regime between 600 degrees C and 700 degrees C, the nanocrystalline diamond thin film is mainly preserved, while graphitic layers form on the surface as the predominant carbon phase. Moreover, the graphitization is facilitated by a disordered carbon interlayer that inherently forms between diamond and graphitic layers by Ni catalyst. Thus, the process results in formation of a multilayer heterostructure on silicon substrate.

BACK ELECTRODE INFLUENCE ON OPTO-ELECTRONIC PROPERTIES OF ORGANIC PHOTOVOLTAIC BLEND CHARACTERIZED BY KELVIN PROBE FORCE MICROSCOPY

  • Autoři: Cermak, J., Miliaieva, D., Hoppe, H., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: NANOCON 2016 Conference Proceedings. Ostrava: TANGER, 2017. p. 291-295. ISBN 978-80-87294-71-0.
  • Rok: 2017
  • Pracoviště: Katedra fyziky
  • Anotace:
    Organic photovoltaic (PV) system consisting of P3HT:PCBM blend layer was prepared with an aluminum (Al) back electrode. After the final thermal annealing the Al layer was partially removed. Kelvin Probe Force Microscopy (KPFM) was used to measure photovoltage response to illumination by a solar spectrum light as a function of time (up to 3 weeks). Comparison of the same KPFM measurement on the areas with and without Al revealed differences in both morphology and photovoltage response to illumination. The data are discussed with view to reducing degradation of organic PV devices.

CORRELATED MICROSCOPY OF ELECTRONIC AND MATERIAL PROPERTIES OF GRAPHENE GROWN ON DIAMOND THIN FILMS

  • Autoři: prof. RNDr. Bohuslav Rezek, Ph.D., Cermak, J., Varga, M., Tulic, S., Kromka, A.
  • Publikace: NANOCON 2016 Conference Proceedings. Ostrava: TANGER, 2017. p. 48-53. ISBN 978-80-87294-71-0.
  • Rok: 2017
  • Pracoviště: Katedra fyziky
  • Anotace:
    We study formation and properties of graphene grown on diamond films with a prospect for large area deposition and devices of graphene. Nanocrystalline diamond thin films (grain size similar to 200 nm) are coated with a thin Ni layer (nominal thickness similar to 20 nm) and heated to 900 degrees C in a forming gas atmosphere (H-2/Ar) to initiate a thermally driven catalytic transformation of the diamond surface into graphene by a reaction of Ni with carbon. The samples are cleaned from residual Ni after the catalytic transformation. We employ scanning electron microscopy, Raman micro-spectroscopy, and Kelvin probe force microscopy showing how diamond and grain boundaries influence the graphene growth as well as graphene material, structural, and electronic properties.

Expanding the Scope of Diamond Surface Chemistry: Stille and Sonogashira Cross-Coupling Reactions

  • Autoři: Raymakers, J., Artemenko, A., Nicley, Shannon S., Stenclova, P., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Journal of Physical Chemistry C. 2017, 121(42), 23446-23454. ISSN 1932-7447.
  • Rok: 2017
  • DOI: 10.1021/acs.jpcc.7b06426
  • Odkaz: https://doi.org/10.1021/acs.jpcc.7b06426
  • Pracoviště: Katedra fyziky
  • Anotace:
    Well-defined covalent surface functionalization of diamond is a crucial, yet nontrivial, matter because of diamond's intrinsic chemical inertness and stability. Herein, we demonstrate a two-step functionalization approach for H-terminated boron doped diamond thin films, which can lead to significant advances in the field of diamond hybrid photovoltaics. Primary diamond surface functionalization is performed via electrochemical diazonium grafting of in situ diazotized 4-iodoaniline. The freshly grafted iodophenyl functional moieties are then employed to couple a layer of thiophene molecules to the diamond surface via two well-established Pd-catalyzed cross-coupling reactions, i.e., Stile and Sonogashira. X-ray photoelectron spectroscopy analysis indicates a dense coverage and successful cross-coupling in both cases. However, we find that the Stille reaction is generally accompanied by severe surface contamination, in spite of process optimization and thorough rinsing. Sonogashira cross-coupling on the other hand provides a clean, high quality functionalization over a broad range of reaction conditions. The protocols employing Sonogashira reactions thus appear to be the method of choice toward future fabrication of high-performance dye-functionalized diamond electrodes for photovoltaic applications.

Influence of non-adherent yeast cells on electrical characteristics of diamond-based field-effect transistors

  • DOI: 10.1016/j.apsusc.2016.05.003
  • Odkaz: https://doi.org/10.1016/j.apsusc.2016.05.003
  • Pracoviště: Katedra fyziky, Katedra mikroelektroniky
  • Anotace:
    Diamond thin films provide unique features as substrates for cell cultures and as bio-electronic sensors. Here we employ solution-gated field effect transistors (SGFET) based on nanocrystalline diamond thin films with H-terminated surface which exhibits the sub-surface p-type conductive channel. We study an influence of yeast cells (Saccharomyces cerevisiae) on electrical characteristics of the diamond SGFETs. Two different cell culture solutions (sucrose and yeast peptone dextrose–YPD) are used, with and without the cells. We have found that transfer characteristics of the SGFETs exhibit a negative shift of the gate voltage by −26 mV and −42 mV for sucrose and YPD with cells in comparison to blank solutions without the cells. This effect is attributed to a local pH change in close vicinity of the H-terminated diamond surface due to metabolic processes of the yeast cells. The pH sensitivity of the diamond-based SGFETs, the role of cell and protein adhesion on the gate surface and the role of negative surface charge of yeast cells on the SGFETs electrical characteristics are discussed as well.

Osteoblast adhesion, migration, and proliferation variations on chemically patterned nanocrystalline diamond films evaluated by live-cell imaging

  • DOI: 10.1002/jbm.a.35969
  • Odkaz: https://doi.org/10.1002/jbm.a.35969
  • Pracoviště: Katedra fyziky
  • Anotace:
    Cell fate modulation by adapting the surface of a biocompatible material is nowadays a challenge in implantology, tissue engineering as well as in construction of biosensors. Nanocrystalline diamond (NCD) thin films are considered promising in these fields due to their extraordinary physical and chemical properties and diverse ways in which they can be modified structurally and chemically. The initial cell distribution, the rate of cell adhesion, distance of cell migration and also the cell proliferation are influenced by the NCD surface termination. Here, we use real-time live-cell imaging to investigate the above-mentioned processes on oxidized NCD (NCD-O) and hydrogenated NCD (NCD-H) to elucidate cell preference to the NCD-O especially on surfaces with microscopic surface termination patterns. Cells adhere more slowly and migrate farther on NCD-H than on NCD-O. Cells seeded with a fetal bovine serum (FBS) supplement in the medium move across the surface prior to adhesion. In the absence of FBS, the cells adhere immediately, but still exhibit different migration and proliferation on NCD-O/H regions. We discuss the impact of these effects on the formation of cell arrays on micropatterned NCD. (C) 2017 Wiley Periodicals, Inc.

SPATIALLY SEPARATED HOMO/LUMO AT INTERFACE OF POLYPYRROLE PHYSISORBED ON OXIDIZED NANODIAMOND FACETS

  • Autoři: Matunová, P., Jirasek, V., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: NANOCON 2016 Conference Proceedings. Ostrava: TANGER, 2017. p. 15-19. ISBN 978-80-87294-71-0.
  • Rok: 2017
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanodiamond particles (NDs) have recently risen in popularity owing to their unique and perspective properties. Merging NDs with organic molecules, such as polypyrrole (PPy), into hybrid organic-semiconductor functional systems gives rise to potential applications in photovoltaics, which is supported by prior experimentally observed charge transfer between bulk diamond and PPy. This work focuses on the most relevant (111) and (100) O-terminated ND facets with different coverage of surface terminating oxygens in ether, epoxide, ketone, and peroxide positions. We use density functional theory computations employing B3LYP functional and 6-31G(d) basis set. Energetically the most favorable oxidized ND facets were further optimized with PPy in physisorbed configurations. Analysis of geometry, binding energy, HOMO-LUMO gap, and charge transfer was done on the relaxed PPy-ND structures. Multiple hydrogen bonds are formed between PPy amino groups and O atoms on ND surface. PPy on 1 x 1 reconstructions is energetically favorable with exothermic binding energy (2.7 eV) and high charge transfer (up to 0.26 e(-)) in the dark. The HOMO-LUMO at the PPy-ND interface becomes spatially separated and significantly closer in energy (down to about 1 eV). These features may be beneficial for photovoltaic applications of nanodiamond.

Surface chemistry of water-dispersed detonation nanodiamonds modified by atmospheric DC plasma afterglow

  • DOI: 10.1039/c7ra04167e
  • Odkaz: https://doi.org/10.1039/c7ra04167e
  • Pracoviště: Katedra fyziky
  • Anotace:
    Surface modification of detonation nanodiamonds (DNDs) is a key factor for their application in diverse fields of science and technology. In this work we report on an easy and low-cost method for modifying water-dispersed DNDs by atmospheric DC plasma afterglow. DNDs were used in either as-received form (asrec-DND) or were oxidized by air-annealing at 450 °C for 30 minutes (O-DND). The influence of applied voltage and thus the type of discharge (corona discharge at 10 kV or transient spark discharge at 15 kV) and treatment duration (5 and 10 minutes) on the surface chemistry of DNDs was evaluated by Fourier Transform Infrared (FTIR) spectroscopy supported by X-ray photoelectron spectroscopy (XPS) and dynamic light scattering (DLS). Treated asrec-DNDs revealed stable positive ζ-potential (30 mV) during rearrangement of oxygen-containing moieties (changes in area below 1250 cm−1) as well as CHx groups, reflected in the enormous enhancement of the band at 1328 cm−1 and disappearance of the C[double bond, length as m-dash]C band at 1589 cm−1. On the other hand, the DC discharge afterglow had only minor impact on the surface chemistry of O-DND particles, as detected by FTIR and XPS, while a negative change of ζ-potential by up to 22 mV occurred. O-DND particles dried in vacuum also exhibited a noticeable catalytic effect towards hydrocarbons.

Surface potential of nanodiamonds investigated by KPFM

  • Autoři: prof. RNDr. Bohuslav Rezek, Ph.D., Stehlik, S.
  • Publikace: Nanodiamonds: Advanced Material Analysis, Properties and Applications. Kidlington Oxford OX GB: Elsevier, 2017. p. 273-300. Micro and Nano Technologies. ISBN 978-0-323-43029-6.
  • Rok: 2017
  • DOI: 10.1016/B978-0-32-343029-6.00011-8
  • Odkaz: https://doi.org/10.1016/B978-0-32-343029-6.00011-8
  • Pracoviště: Katedra fyziky
  • Anotace:
    This chapter introduces complex opto-electronic behavior of nanodiamonds when they are in contact with surrounding materials. Kelvin probe force microscopy (KPFM) is used to show that surface potential of nanodiamonds is not uniform but depends on many factors such as substrate and probe material, nanodiamond surface termination, charge trapping, illumination, and adsorbed water. Special attention is devoted to practical aspects and methodology of the KPFM measurements of nanodiamonds and other nanoscale objects, in general. KPFM serves here also as a nanoscale tool for investigation of local charge exchange between the nanodiamonds and surroundings, which is shown to influence also their other physical properties such as photoluminescence, secondary electron emission, and photovoltage.

Ultrathin Nanocrystalline Diamond Films with Silicon Vacancy Color Centers via Seeding by 2 nm Detonation Nanodiamonds

  • Autoři: Stehlik, S., Varga, M., Stenclova, P., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: ACS Applied Materials & Interfaces. 2017, 9(44), 38842-38853. ISSN 1944-8244.
  • Rok: 2017
  • DOI: 10.1021/acsami.7b14436
  • Odkaz: https://doi.org/10.1021/acsami.7b14436
  • Pracoviště: Katedra fyziky
  • Anotace:
    Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5–6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4–6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 1013 cm–2), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiOx substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

Back Electrode Influence on Opto-electronic Properties of Organic Photovoltaic Blend Characterized by Kelvin Probe Force Microscopy

  • Autoři: Čermák, J., Miliaieva, D., Hoppe, H, prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: NANOCON 2016 LIST OF ABSTRACTS. Ostrava: TANGER, 2016. ISBN 978-80-87294-68-0.
  • Rok: 2016
  • Pracoviště: Katedra fyziky
  • Anotace:
    Organic photovoltaic (PV) system consisting of P3HT:PCBM blend layer was prepared with an aluminum (Al) back electrode. After the final thermal annealing the Al layer was partially removed. Kelvin Probe Force Microscopy (KPFM) was used to measure photovoltage response to illumination by a solar spectrum light as a function of time (up to 3 weeks). Comparison of the same KPFM measurement on the areas with and without Al revealed differences in both morphology and photovoltage response to illumination. The data are discussed with view to reducing degradation of organic PV devices.

Bacterial response to nanodiamonds and graphene oxide sheets

  • DOI: 10.1002/pssb.201600237
  • Odkaz: https://doi.org/10.1002/pssb.201600237
  • Pracoviště: Katedra fyziky
  • Anotace:
    Carbon nanomaterials such as nanodiamond (ND) and graphene oxide (GO) attract increasing attention for biomedical applications due their unique and adjustable properties. Here we report on antibacterial activity of NDs and GO as evaluated by bacterial colony counting. ND and GO were used in oxidized (O-ND, GO) or reduced (H-ND, rGO) forms. ND or GO are mixed in Mueller–Hinton (MH) broth with Escherichia coli at the concentration of 1 mg ml−1. The resulting suspensions were cultivated for 5 and 24 h at 37 °C in a shaker. After each period, a sample of the suspension was spread on the MH agar and cultivated for 24 h at 37° C. The effect of nanomaterials on colony forming ability (CFA) of E. coli was evaluated and compared with the negative control sample. The most noticeable effect was that after 5 h H-ND decreased the CFA of E. coli in the MH broth by 60% and GO by 50%. After 24 h, H-ND decreased CFA by 50%. Other nanomaterials had no statistically significant antibacterial effect. Factors influencing ND and GO antibacterial activity against the E. coli and possibly against other bacteria are discussed.

Computational study of physisorption and chemisorption of polypyrrole on H-terminated (111) and (100) nanodiamond facets

  • DOI: 10.1002/pssa.201600228
  • Odkaz: https://doi.org/10.1002/pssa.201600228
  • Pracoviště: Katedra fyziky
  • Anotace:
    Interaction of diamond with molecules is important for various applications. For instance, experimentally ob-served charge transfer between bulk diamond and polypyrrole (PPy) is promising for photovoltaics. Here we explore the interactions of PPy with surfaces of nanodiamonds (NDs) by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of theory. The most probable H-terminated 1 × 1 (111) and 2 × 1 (100) diamond surface facets are considered. Geometrical ar-rangement, binding energy (Eb), interaction energy (Eint), charge transfer (Δq) and HOMO-LUMO gap are calcu-lated on geometrically relaxed structures of PPy on the ND facets in physisorbed or chemisorbed configuration. Energetically the most favourable is physisorption of PPy on NDs. For chemisorption, one-bond contact is more fa-vourable than two-bond contact, with the most probable binding on (100) facet. Charge transfer of electrons (up to Δq = -0.11 e-) from PPy to diamond is observed for all the configurations in the dark. In some cases, the calculations reveal spatial separation of the HOMO and LUMO, which may be useful for photovoltaic applications.

Doping Effects and Grain Boundaries in Thermal CVD Graphene on Recrystallized Cu Foil

  • Autoři: Cermak, J., Yamada, T., Ganzerova, K., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Advanced Materials Interfaces. 2016, 3(16), ISSN 2196-7350.
  • Rok: 2016
  • DOI: 10.1002/admi.201600166
  • Odkaz: https://doi.org/10.1002/admi.201600166
  • Pracoviště: Katedra fyziky
  • Anotace:
    Thermal chemical vapor deposition (CVD) of graphene on a copper (Cu) foil is strongly affected by Cu foil recrystallization and grain formation resulting in a heterogeneous graphene layer. Correlated microscopic scanning probe techniques show different chemical and structural properties (Raman microspectroscopy), electrical conductivity (conductive atomic force microscopy), and electronic structure (Kelvin probe force microscopy) across various types of grains. Graphene on clean Cu grains exhibits work function (WF) higher by 300 meV. This is attributed to the contact doping effect. Graphene of higher quality is formed on Cu grains with a surface cuprous oxide (Cu2O) which forms during the thermal CVD process. The graphene WF is higher by 430 meV there. The WF difference is attributed to the contact doping effect and additional strain-induced doping due to the highly corrugated Cu2O surface. Local electrical conductivity measured by atomic force microscopy and a pair of conductive microprobes corroborates different graphene quality on various Cu grains and reveals that graphene is electrically interrupted at the Cu grain boundaries. Corresponding structural and electronic model of thermal CVD graphene on the Cu foil is presented. The correlation of grain boundaries in Cu foil and graphene is discussed.

Filamentation of diamond nanoparticles treated in underwater corona discharge

  • Autoři: Jirasek, V., Lukes, P., Kozak, H., Artemenko, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: RSC Advances. 2016, 6(3), 2352-2360. ISSN 2046-2069.
  • Rok: 2016
  • DOI: 10.1039/c5ra23292a
  • Odkaz: https://doi.org/10.1039/c5ra23292a
  • Pracoviště: Katedra fyziky
  • Anotace:
    Diamond nanoparticles (DNPs), also known as nanodiamonds, have attracted significant interest in recent years due to a number of potential applications. Their particular usage requires proper surface engineering. In this work, DNPs with a nominal diameter of 5 nm were treated using underwater pulsed streamer corona discharge. A reactor with a needle-to-plate electrode system was employed. The electrolytic conductivity of aqueous DNPs suspensions (0.37 g l(-1)) was adjusted by NaCl to 100 and 500 mu S cm(-1). The discharge-treated particles predominantly formed several mm long filaments consisting of agglomerates with submicron diameter, independent of the solution conductivity and the treatment time. The treatment of DNPs decreased the sp(2)-bonded carbon atoms, as evaluated by XPS for more conductive solution. For both solutions, oxidation of the DNP surface was observed. FTIR measurements showed evolution of new bands at 800-950 cm(-1) and 1261 cm(-1), which were attributed to the formation of epoxides via the attack of HO2 center dot radicals on surface C=C double bonds.

Gamma radiation effects on hydrogen-terminated nanocrystalline diamond bio-transistors

  • DOI: 10.1016/j.diamond.2015.10.015
  • Odkaz: https://doi.org/10.1016/j.diamond.2015.10.015
  • Pracoviště: Katedra fyziky
  • Anotace:
    Diamond is considered as a promising tissue equivalent material in radiation therapies as well as for bio-electronic sensors due to its unique set of properties. These features are combined in this work where effects of gamma irradiation (Co-60, up to 300 Gy) on function and stability of microscopic (60 x 20 mu m(2)) hydrogen-terminated diamond (H-diamond) solution-gated field effect transistors (SG-FET5) are studied. The H-diamond SG-FETs were prepared using 300 nm thin diamond films deposited on glass from methane and hydrogen gas mixture by microwave plasma. Prior to gamma irradiation they were interfaced to proteins (fetal bovine serum) and cells (human sarcoma osteogenic cell line - SAOS2) in cell growth medium. Blank H-diamond SG-FETs did not degrade after the irradiation. With adsorbed proteins and cells they showed specific changes in gate current characteristics (about 100% increase) after the irradiation. These current changes are attributed to modified protein layer and cell morphology on the diamond surface. The presented results establish a first step towards real-time electronic monitoring of cell growth during the irradiation by therapeutically relevant doses. (C) 2015 Elsevier B.V. All rights reserved.

High-yield fabrication and properties of 1.4 nm nanodiamonds with narrow size distribution

  • Autoři: Stehlik, S., Varga, M., Ledinský, M., Miliaieva, D., Kozak, H., Skákalová, V., Mangler, C., Pennycook, T. J., Meyer, J. C., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Scientific Reports. 2016, 6 ISSN 2045-2322.
  • Rok: 2016
  • DOI: 10.1038/srep38419
  • Odkaz: https://doi.org/10.1038/srep38419
  • Pracoviště: Katedra fyziky
  • Anotace:
    Detonation nanodiamonds (DNDs) with a typical size of 5 nm have attracted broad interest in science and technology. Further size reduction of DNDs would bring these nanoparticles to the molecular-size level and open new prospects for research and applications in various fields, ranging from quantum physics to biomedicine. Here we show a controllable size reduction of the DND mean size down to 1.4 nm without significant particle loss and with additional disintegration of DND core agglutinates by air annealing, leading to a significantly narrowed size distribution (±0.7 nm). This process is scalable to large quantities. Such molecular-sized DNDs keep their diamond structure and characteristic DND features as shown by Raman spectroscopy, infrared spectroscopy, STEM and EELS. The size of 1 nm is identified as a limit, below which the DNDs become amorphous.

Influence of air annealing on the luminescence dynamics of HPHT nanodiamonds

  • Autoři: Salava, J., Trojanek, F., Stehlik, S., Varga, M., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Diamond and Related Materials. 2016, 68 62-65. ISSN 0925-9635.
  • Rok: 2016
  • DOI: 10.1016/j.diamond.2016.06.001
  • Odkaz: https://doi.org/10.1016/j.diamond.2016.06.001
  • Pracoviště: Katedra fyziky
  • Anotace:
    We present a study of the influence of air-annealing on the photoexcited charge carriers dynamics on the surface of nanodiamonds of sub-10 nm size. Samples were produced by high temperature annealing of high-pressure, high-temperature nanodiamonds. Measured photoluminescence spectra of annealed nanodiamonds show distinct blue shift and spectral narrowing compared to non-annealed reference. Time-resolved measurements revealed a change in relaxation process in the nanodiamond surface layer due to removal of non-diamond carbon phase on the surface. Spectro-temporal evolution takes place during the first 50 ps after photoexcitation suggesting that non-radiative states play a major role in the charge carrier relaxation. The acceleration of high energy states depopulation, observed for the annealed nanodiamonds, suggests gradual inhibition of non-radiative recombination channels (originally present in large numbers in non-annealed sample), which is in a good agreement with the picture of reduction of non-diamond carbon phase. (C) 2016 Elsevier B.V. All rights reserved.

Microcrystalline Diamond Membrane for Electronic Monitoring of Cells in Microfluidic Perfusion Systems

  • Autoři: prof. RNDr. Bohuslav Rezek, Ph.D., Varga, M., Pedrosa, C., Chu, V.
  • Publikace: Proceedings of the 30th anniversary Eurosensors Conference – Eurosensors 2016. Oxford: Elsevier Ltd, 2016. pp. 1442-1445. ISSN 1877-7058.
  • Rok: 2016
  • DOI: 10.1016/j.proeng.2016.11.412
  • Odkaz: https://doi.org/10.1016/j.proeng.2016.11.412
  • Pracoviště: Katedra fyziky
  • Anotace:
    Self-standing microcrystalline diamond membranes were produced and embedded in three-dimensional microfluidic in-vivo-like perfusion cell culture system. Perfusion of molecules is confirmed by time-resolved fluorescent microscopy. Impedance measurements show that the diamond membranes exhibit a pronounced response to cells compared to a reference microfluidic chip without the membrane. The diamond membranes can thus be applicable as novel sensor elements in microfluidic cell reactors.

Microscopic electrical conductivity of nanodiamonds after thermal and plasma treatments

  • DOI: 10.1557/adv.2016.112
  • Odkaz: https://doi.org/10.1557/adv.2016.112
  • Pracoviště: Katedra fyziky
  • Anotace:
    Atomic force microscopy (AFM) is used to measure local electrical conductivity of HPHT nanodiamonds (NDs) dispersed on Au substrate in the as-received state and after thermal or plasma treatments. Oxygen-treated NDs are highly electrically resistive, whereas on hydrogen-treated NDs electric current around -200 pA at -2 V is detected. The as-received NDs as well as NDs after an underwater radio-frequency (RF) plasma or laser irradiation (LI) treatments contain both electrically conductive (two types: highly and weakly conductive) and highly resistive particles. The higher conductivity is attributed to H-terminated (RF) or graphitized (LI) NDs. The lower conductivity is attributed to NDs with hydrogenated amorphous carbon shell.

Nanocarbon Allotropes-Graphene and Nanocrystalline Diamond-Promote Cell Proliferation

  • DOI: 10.1002/smll.201503749
  • Odkaz: https://doi.org/10.1002/smll.201503749
  • Pracoviště: Katedra fyziky
  • Anotace:
    Two profoundly different carbon allotropes - nanocrystalline diamond and graphene - are of considerable interest from the viewpoint of a wide range of biomedical applications including implant coating, drug and gene delivery, cancer therapy, and biosensing. Osteoblast adhesion and proliferation on nanocrystalline diamond and graphene are compared under various conditions such as differences in wettability, topography, and the presence or absence of protein interlayers between cells and the substrate. The materials are characterized in detail by means of scanning electron microscopy, atomic force microscopy, photoelectron spectroscopy, Raman spectroscopy, and contact angle measurements. In vitro experiments have revealed a significantly higher degree of cell proliferation on graphene than on nanocrystalline diamond and a tissue culture polystyrene control material. Proliferation is promoted, in particular, by hydrophobic graphene with a large number of nanoscale wrinkles independent of the presence of a protein interlayer, i.e., substrate fouling is not a problematic issue in this respect. Nanowrinkled hydrophobic graphene, thus, exhibits superior characteristics for those biomedical applications where high cell proliferation is required under differing conditions.

Nanocrystalline diamond films for electronic monitoring of gas and organic molecules

  • Autoři: Kromka, A., Izak, T., Davydova, M., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: ASDAM 2016 Conference Proceedings - The 11th International Conference on Advanced Semiconductor and Microsystems. Bratislava: Slovenská akademie věd, 2016. pp. 193-198. Proceedings. ISSN 2475-2916. ISBN 978-1-5090-3083-5.
  • Rok: 2016
  • DOI: 10.1109/ASDAM.2016.7805928
  • Odkaz: https://doi.org/10.1109/ASDAM.2016.7805928
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nowadays, implementation of specific materials for (bio) sensors is one of the most rapidly developing micro-electronic field. Synthetic diamond thin films exhibit an extraordinary combination of intrinsic properties which make it an attractive material for investigation of solid state interaction with (bio) molecules or complex biological systems. Hydrogen terminated intrinsic diamond films reveal a phenomenological property - induced p-type surface conductivity which has been found as suitable for fabrication of various electronic devices, mainly impedance elements and field effect transistors. This study draws on research conducted by employing hydrogen terminated nanocrystalline diamond as the functional layer for (bio) sensoric uses and point out recent models for the detection principles.

Oxidation and reduction of nanodiamond particles in colloidal solutions by laser irradiation or radio-frequency plasma treatment

  • Autoři: Kozak, H., Artemenko, A., Cermak, J., Svrcek, V., Kromka, A, prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Vibrational Spectroscopy. 2016, 83 108-114. ISSN 0924-2031.
  • Rok: 2016
  • DOI: 10.1016/j.vibspec.2016.01.010
  • Odkaz: https://doi.org/10.1016/j.vibspec.2016.01.010
  • Pracoviště: Katedra fyziky
  • Anotace:
    Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and C-O-C groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp(2) shell and additional oxidation of the surface to C-O-C groups. On HPHT NDs the RF treatment leads to reduction of C-O-C groups that are transformed into C-OH and C-H moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible. (C) 2016 Elsevier B.V. All rights reserved.

Photoluminescence of nanodiamonds influenced by charge transfer from silicon and metal substrates

  • Autoři: Stehlik, S., Ondic, L., Berhane, Amanuel M., Aharonovich, I., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Diamond and Related Materials. 2016, 63 91-96. ISSN 0925-9635.
  • Rok: 2016
  • DOI: 10.1016/j.diamond.2015.08.009
  • Odkaz: https://doi.org/10.1016/j.diamond.2015.08.009
  • Pracoviště: Katedra fyziky
  • Anotace:
    Photoluminescence of 5 nm detonation nanodiamonds (DNDs) is studied as a function of their surface treatment (hydrogenation/oxidation) and underlying substrate materials (silicon, gold, platinum, and nickel). The substrates affect DND photoluminescence emission spectrum and lifetime in the spectral range of 600-800 nm. The dependence is different for hydrogenated and oxidized DNDs. We attribute these effects to different electrostatic charging of DNDs on the substrates with different work functions (4.4 to 5.5 eV). We discuss the data based on naturally present NV centers, their phonon sideband, and surface-related non-radiative transitions. (C) 2015 Elsevier B.V. All rights reserved.

Real-time Monitoring of Cell Activities by Diamond Solution-gated Field Effect Transistors

  • Autoři: Ižák, T., Procházka, V., Sakata, T., prof. RNDr. Bohuslav Rezek, Ph.D., Kromka, A.
  • Publikace: Proceedings of the 30th anniversary Eurosensors Conference – Eurosensors 2016. Oxford: Elsevier Ltd, 2016. p. 469-472. ISSN 1877-7058.
  • Rok: 2016
  • DOI: 10.1016/j.proeng.2016.11.130
  • Odkaz: https://doi.org/10.1016/j.proeng.2016.11.130
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this study, we present basic aspects for real-time monitoring of cell growth of human cell lines. We successfully fabricated fully optically transparent diamond-based solution-gated field effect transistor (SG-FET) on glass substrates. The diamond transistor functionalities are demonstrated by the sensitivity of electrical characteristics to solutions with different Na+ and K+ ion concentrations, and pH. Moreover, the diamond SG-FETs exhibited sensitivities to the adhesion of proteins and cells, to the cell delamination, or even to the cell death.

Size decrease of detonation nanodiamonds by air annealing investigated by AFM

  • Autoři: Stehlik, S., Miliaieva, D., Varga, M., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: MRS Advances. 2016, 1(16), 1067-1073. ISSN 2059-8521.
  • Rok: 2016
  • DOI: 10.1557/adv.2016.36
  • Odkaz: https://doi.org/10.1557/adv.2016.36
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanodiamonds (NDs) represent a novel nanomaterial applicable from biomedicine to spintronics. Here we study ability of air annealing to further decrease the typical 5 nm NDs produced by detonation synthesis. We use atomic force microscopy (AFM) with sub-nm resolution to directly measure individual detonation nanodiamonds (DNDs) on a flat Si substrate. By means of particle analysis we obtain their accurate and statistically relevant size distributions. Using this approach, we characterize evolution of the size distribution as a function of time and annealing temperature: i) at constant time (25 min) with changing temperature (480, 490, 500°C) and ii) at constant temperature (490°C) with changing time (10, 25, 50 min). We show that the mean size of DNDs can be controllably reduced from 4.5 nm to 1.8 nm without noticeable particle loss and down to 1.3 nm with 36% yield. By air annealing the size distribution changes from Gaussian to lognormal with a steep edge around 1 nm, indicating instability of DNDs below 1 nm.

Spatially separated HOMO/LUMO at interface of polypyrrole physisorbed on oxidized nanodiamond facets

  • Autoři: Matunová, P., Jirásek, V, prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: NANOCON 2016 LIST OF ABSTRACTS. Ostrava: TANGER, 2016. ISBN 978-80-87294-68-0.
  • Rok: 2016
  • Pracoviště: Katedra fyziky
  • Anotace:
    Nanodiamond particles (NDs) have recently risen in popularity owing to their unique and perspective properties. Merging NDs with organic molecules, such as polypyrrole (PPy), into hybrid organicsemiconductor functional systems gives rise to potential applications in photovoltaics, which is supported by prior experimentally observed charge transfer between bulk diamond and PPy. This work focuses on the most relevant (111) and (100) O-terminated ND facets with different coverage of surface terminating oxygens in ether, epoxide, ketone, and peroxide positions. We use density functional theory computations employing B3LYP functional and 6-31G(d) basis set. Energetically the most favorable oxidized ND facets were further optimized with PPy in physisorbed configurations. Analysis of geometry, binding energy, HOMO-LUMO gap, and charge transfer was done on the relaxed PPy-ND structures. Multiple hydrogen bonds are formed between PPy amino groups and O atoms on ND surface. PPy on 1 × 1 reconstructions is energetically favorable with exothermic binding energy (2.7 eV) and high charge transfer (up to 0.26 e-) in the dark. The HOMO-LUMO at the PPy-ND interface becomes spatially separated and significantly closer in energy (down to about 1 eV). These features may be beneficial for photovoltaic applications of nanodiamond.

Special Section Chemical Vapor Deposition Graphene Deposition: Doping Effects and Grain Boundaries in Thermal CVD Graphene on Recrystallized Cu Foil (Adv. Mater. Interfaces 16/2016)

  • Autoři: Čermák, J., Yamada, T., Ganzerová, K., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Advanced Materials Interfaces. 2016, 3(16), ISSN 2196-7350.
  • Rok: 2016
  • DOI: 10.1002/admi.201670077
  • Odkaz: https://doi.org/10.1002/admi.201670077
  • Pracoviště: Katedra fyziky
  • Anotace:
    Complementary to the article 1600166, where Jan Čermák and co‐workers describe doping effects in graphene. this special section cover page illustrates a conductivity landscape of thermal chemical vapor deposition (CVD) graphene on polycrystalline copper foil. The morphology of Cu foil substrate (bottom layer) is modulated by cuprous oxide on some grains. Thermal CVD graphene (middle layer) follows well the substrate morphology. Graphene quality, its electronic and mechanical interaction with Cu grains and boundaries control local electrical current as illustrated by the atomic force microscopy conductivity map (top layer).

Synthesis of polypyrrole on nanodiamonds with hydrogenated and oxidized surfaces

  • Autoři: Miliaieva, D., Stehlik, S., Stenclova, P., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Physica Status Solidi A. 2016, 213(10), 2687-2692. ISSN 1862-6300.
  • Rok: 2016
  • DOI: 10.1002/pssa.201600278
  • Odkaz: https://doi.org/10.1002/pssa.201600278
  • Pracoviště: Katedra fyziky
  • Anotace:
    Composite nanoparticles of detonation nanodiamond (DND) and polypyrrole (PPy) were produced in colloidal solution and on surfaces by wet chemical process. Changes of vibrational bands (in particular>CO and C–H) in Fourier-transform infrared spectroscopy revealed the DND/PPy composite formation and tight interaction of PPy with hydrogenated DND (H-DND) and oxidized DND (O-DND). Atomic force microscopy showed uniform PPy coating but different PPy thickness on H-DND (7.0 nm) and O-DND (3.5 nm). These results suggest different bonding nature and arrangement of PPy on H-DND and O-DND surfaces.

Visible light photodiodes and photovoltages from detonation nanodiamonds

  • DOI: 10.1557/adv.2016.115
  • Odkaz: https://doi.org/10.1557/adv.2016.115
  • Pracoviště: Katedra fyziky
  • Anotace:
    Macroscopic and microscopic photovoltage characteristics of detonation nanodiamonds (DNDs) with distinct surface terminations are presented. Organic photodiodes are fabricated based on P3HT+DNDs mixture (50 wt%). We compare effect of hydrogen and oxygen termination of DNDs. Compared to photodiodes without DNDs the current-voltage characteristics of photodiodes with O-DNDs in dark and under AM 1.5 illumination show reduced dark current, and higher photocurrent and open circuit voltage. H-DNDs shunt the photodiodes, which is attributed to their surface conductivity. Kelvin probe force microscopy detects a reproducible photovoltage of around 5 mV generated by a green laser (532 nm) on both types of pristine DNDs. Thus although conductivity of H-DNDs may represent a problem for photodiodes, both types of DNDs alone can function as miniature energy conversion devices.

Water interaction with hydrogenated and oxidized detonation nanodiamonds - Microscopic and spectroscopic analyses

  • Autoři: Stehlik, S., Glatzel, T., Pichot, V., Pawlak, R., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Diamond and Related Materials. 2016, 63 97-102. ISSN 0925-9635.
  • Rok: 2016
  • DOI: 10.1016/j.diamond.2015.08.016
  • Odkaz: https://doi.org/10.1016/j.diamond.2015.08.016
  • Pracoviště: Katedra fyziky
  • Anotace:
    Water interaction with surface modified nanodiamonds (NDs) is critical for many possible applications of NDs e.g. in biomedicine. Here we report on investigation of water interaction with hydrogenated and oxidized detonation nanodiamonds (H-DNDs, O-DNDs) by means of Fourier transform infrared spectroscopy (FTIR), thermal analysis, and Kelvin probe force microscopy (KPFM). Higher water content (4.4%) as well as weaker interaction of water with H-DNDs are identified by thermal analysis. It is explained by hydrophobicity of the H-DND surface, as revealed by the analysis of bending and stretching vibrations of surface water in FTIR spectra. On the other hand, hydrophilic nature of O-DNDs leads to lower water content (3.1%) but stronger interaction with the O-DND surface. This is evidenced by as high as 300 degrees C desorption temperature of the surface water from O-DNDs. KPFM analysis shows that the surface-bound water can have significant screening effect on contact potential difference (CPD) of nanodiamonds (up to 510 mV) as well as on the CPD difference between H-DNDs and O-DNDs (from 50 mV to 210 mV). Nevertheless, H-DNDs exhibit always lower work function. (C) 2015 Elsevier B.V. All rights reserved.

Diamond-coated field-effect sensor for DNA recognition — Influence of material and morphology

  • Autoři: Izak, T., Sakata, T., Miyazawa, Y., Kajisa, T., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: Diamond and Related Materials. 2015, 60 87-93. ISSN 0925-9635.
  • Rok: 2015
  • DOI: 10.1016/j.diamond.2015.10.020
  • Odkaz: https://doi.org/10.1016/j.diamond.2015.10.020
  • Pracoviště: Katedra fyziky
  • Anotace:
    The influence of nanocrystalline (< 20 nm grains) and microcrystalline (around 100 nm grains) diamond thin film morphology on the capacitance–voltage (C–V) characteristics of diamond-coated field-effect SiN sensors was characterized with respect to DNA recognition. DNA was grafted via –OH surface termination. The sensor materials and surfaces were characterized by scanning electron microscopy, Raman Spectroscopy, fluorescence microscopy, XPS, and contact angle measurements. The C–V characteristics exhibited generally an order of magnitude higher flat band voltage shifts (∆ VF) after complementary DNA hybridization for both types of diamond-coated sensors (160 ÷ 300 mV) compared to reference SiN sensor without diamond layer (11 mV), even if incomplete DNA denaturation and ∆ VF fluctuations (60 mV) were accounted for. While microcrystalline diamond provides the highest response, nanocrystalline diamond provides the highest sensitivity. An explanation based on interfacial charges is proposed.

Size and Purity Control of HPHT Nanodiamonds down to 1 nm

  • Autoři: Stehlik, S., Varga, M., Ledinsky, M., Jirasek, V., Artemenko, A., Kozak, H., Ondic, L., Skakalova, V., Argentero, G., Pennycook, T., C. Meyer, J., Fejfar, A., Kromka, A., prof. RNDr. Bohuslav Rezek, Ph.D.,
  • Publikace: The Journal of Physical Chemistry C. 2015, 119(49), ISSN 1932-7447.
  • Rok: 2015
  • DOI: 10.1021/acs.jpcc.5b05259
  • Odkaz: https://doi.org/10.1021/acs.jpcc.5b05259
  • Pracoviště: Katedra fyziky
  • Anotace:
    High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterized. Moreover we provide experimental evidence of diamond stability down to 1 nm. Controlled annealing at 450 °C in air leads to efficient purification from the nondiamond carbon (shells and dots), as evidenced by X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and scanning transmission electron microscopy. Annealing at 500 °C promotes, besides of purification, also size reduction of nanodiamonds down to ∼1 nm. Comparably short (1 h) centrifugation of the nanodiamonds aqueous colloidal solution ensures separation of the sub-10 nm fraction. Calculations show that an asymmetry of Raman diamond peak of sub-10 nm HPHT nanodiamonds can be well explained by modified phonon confinement model when the actual particle size distribution is taken into account. In contrast, larger Raman peak asymmetry commonly observed in Raman spectra of detonation nanodiamonds is mainly attributed to defects rather than to the phonon confinement. Thus, the obtained characteristics reflect high material quality including nanoscale effects in sub-10 nm HPHT nanodiamonds prepared by the presented method.

Stochastic model explains formation of cell arrays on H/O-diamond patterns

  • DOI: 10.1116/1.4934794
  • Odkaz: https://doi.org/10.1116/1.4934794
  • Pracoviště: Katedra fyziky
  • Anotace:
    Cell migration plays an important role in many biological systems. A relatively simple stochastic model is developed and used to describe cell behavior on chemically patterned substrates. The model is based on three parameters: the speed of cell movement (own and external), the probability of cell adhesion, and the probability of cell division on the substrate. The model is calibrated and validated by experimental data obtained on hydrogen- and oxygen-terminated patterns on diamond. Thereby, the simulations reveal that: (1) the difference in the cell movement speed on these surfaces (about 1.5×) is the key factor behind the formation of cell arrays on the patterns, (2) this difference is provided by the presence of fetal bovine serum (validated by experiments), and (3) the directional cell flow promotes the array formation. The model also predicts that the array formation requires mean distance of cell travel at least 10% of intended stripe width. The model is generally applicable for biosensors using diverse cells, materials, and structures.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk