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The newly synthesized compound Fe[SeO4]OH belongs to the kieserite-like structure. Using the superspace approach, possible polytypes are predicted for R[MO4]Z, where R = Mg, Fe, Ni, Co, Zn, Mn, Al, V, Sb, Y; M = S, Se, P, As; Z = OH, H2O, F, O.

Ba4Fe4ClO9.5−x compounds are built of a Ba2Fe4O9.5−x framework with open hexagonal channels. (Ba–Cl–Ba) trimers located in the channels and the framework O atoms cause incommensurability, which is tuned under different annealing conditions.

The structure of Ba5(IO6)2 has been redetermined at two different temperatures, namely 298 and 80 K, with a high crystalline single-crystal. In comparison with previous determinations based on powder diffraction patterns, the present redetermination results are of greatly improved precision of the structural parameters. The ambiguity of the space-group assignment was eliminated with three-dimensional patterns from a single-crystal sample., The crystal structure of Ba5(IO6)2, penta­barium bis­(orthoperiodate), has been re-investigated at room temperature based on single-crystal X-ray diffraction data. In comparison with a previous crystal structure determination by the Rietveld method, an improved precision of the structural parameters was achieved. Additionally, low-temperature measurements allowed the crystal structure evolution to be studied down to 80 K. No evidence of structural transition was found even at the lowest temperature. Upon cooling, the lattice contraction is more pronounced along the b axis. This contraction is found to be inhomogeneous along different crystallographic axes. The inter­atomic distances between different Ba atoms reduce drastically with lowering temperature, resulting in a closer packing around the IO6 octa­hedra, which remain largely unaffected.

Quantum spin liquids are exotic states of matter that form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of ${\mathrm{K}}_{2}{\mathrm{Ni}}_{2}({\mathrm{SO}}_{4}{)}_{3}$ forming a three-dimensional network of ${\mathrm{Ni}}^{2+}$ spins. Using density functional theory calculations, we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering, and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field $B\ensuremath{\gtrsim}4\text{ }\text{ }\mathrm{T}$ diminishes the ordered component and drives the system into a pure quantum spin liquid state. This shows that a system of interconnected $S=1$ trillium lattices exhibits a significantly elevated level of geometrical frustration.

We report magnetic properties of a $3{d}^{9}$ $({\mathrm{Cu}}^{2+})$ magnetic insulator ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ measured on both powder and single crystal. The magnetic atoms of this compound form layers whose geometry can be described either as a system of chains coupled through dimers or as a kagome lattice where every third spin is replaced by a dimer. Specific heat and DC susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with an $S=1/2$ degree of freedom per ${\mathrm{Cu}}^{2+}$, and so is the effective moment extracted from DC susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to an $\ensuremath{\sim}{120}^{\ensuremath{\circ}}$ spin structure in which ferromagnetic intradimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ represents a type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.

The discovery of multiple coexisting magnetic phases in the crystallographically homogeneous compound ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ has stimulated ongoing research activity. In recent years the main focus has been on the zero-field-state properties, where exceedingly long timescales have been established. In this study we report a detailed investigation of static and dynamic properties of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ across the magnetic field induced transition around 3.5 T. This region has so far been practically neglected, while we argue that in some aspects it represents a simpler version of the transition across the $B=0$ state. Investigating the frequency dependence of the ac susceptibility, we reveal that on the high-field side ($Bg3.5$ T) the response corresponds to a relatively narrow distribution of magnetic clusters. The distribution appears very weakly dependent on magnetic field, with an associated energy barrier of around 200 K. Below 3.5 T a second contribution arises, with much smaller characteristic frequencies and a strong temperature and magnetic field dependence. We discuss these findings in the context of intrachain and interchain clustering of magnetic moments.

Coupling of spin-waves with electromagnetic cavity field is demonstrated in an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at 0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures were found at crossings of spin-wave resonances with Fabry-Perot cavity modes formed in samples. The obtained spectra are explained in terms of classical electrodynamics and a microscopic model., Comment: 3 pages, 2 figures

In nodal-line semimetals linearly dispersing states form Dirac loops in the reciprocal space, with high degree of electron-hole symmetry and almost-vanishing density of states near the Fermi level. The result is reduced electronic screening and enhanced correlations between Dirac quasiparticles. Here we investigate the electronic structure of ZrSiSe, by combining time- and angle-resolved photoelectron spectroscopy with ab initio density functional theory (DFT) complemented by an extended Hubbard model (DFT +U +V). We show that electronic correlations are reduced on an ultrashort timescale by optical excitation of high-energy electrons-hole pairs, which transiently screen the Coulomb interaction. Our findings demonstrate an all-optical method for engineering the band structure of a quantum material., Comment: 6 pages, 3 figures

While in 3D materials melting is a single, first-order phase transition, in 2D systems, it can also proceed via an intermediate phase. For a skyrmion lattice in Cu2OSeO3, magnetic field variations can tune this quasiparticle 2D solid into a skyrmion liquid via an intermediate hexatic phase with short-range translational and quasi-long-range orientational order. The phase transition most commonly observed is probably melting, a transition from ordered crystalline solids to disordered isotropic liquids. In three dimensions, melting is a single, first-order phase transition. In two-dimensional systems, however, theory predicts a general scenario of two continuous phase transitions separated by an intermediate, oriented liquid state, the so-called hexatic phase with short-range translational and quasi-long-range orientational orders. Such hexatic phases occur in colloidal systems, Wigner solids and liquid crystals, all composed of real-matter particles. In contrast, skyrmions are countable soliton configurations with non-trivial topology and these quasi-particles can form two-dimensional lattices. Here we show, by direct imaging with cryo-Lorentz transmission electron microscopy, that magnetic field variations can tune the phase of the skyrmion ensembles in Cu(2)OSeO(3)from a two-dimensional solid through the long-speculated skyrmion hexatic phase to a liquid. The local spin order persists throughout the process. Remarkably, our quantitative analysis demonstrates that the aforementioned topological-defect-induced crystal melting scenario well describes the observed phase transitions.

The crystal structure of [ZnCl2(NH3)2], diamminedichloridozinc, was re-investigated at low temperature, revealing the positions of the hydrogen atoms and thus a deeper insight into the hydrogen-bonding scheme in the crystal packing. In comparison with previous crystal structure determinations [MacGillavry & Bijvoet (1936).Z. Kristallogr.94, 249–255; Yamaguchi & Lindqvist (1981).Acta Chem. Scand.35, 727–728], an improved precision of the structural parameters was achieved. In the crystal, tetrahedral [Zn(NH3)2Cl2] units (point-group symmetrymm2) are linked through N—H...Cl hydrogen bonds into a three-dimensional network.

Topological quantum materials have stimulated growing attention because they reveal novel aspects of condensed matter physics and point to new opportunities in materials science, in particular for thermoelectrics. Here, we experimentally study thermoelectric effects in ${\mathrm{HfTe}}_{5}$, which was predicted to be at the boundary between strong and weak topological insulators. The magnetic field dependence of ${\mathrm{HfTe}}_{5}$ thermoelectric properties attests to the anomalous character of this material, supported by our angle-resolved photoemission spectroscopy (ARPES) measurements. At 36 K, the thermopower of $\ensuremath{-}277\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ is reached when a field of 0.4 Tesla is applied, while it is $\ensuremath{-}157\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ at zero field and a large Nernst coefficient up to $600\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ is observed at 100 K with magnetic field of 4 T. A possible topologically nontrivial band structure is proposed to account for our observations. Our results constitute a highly constraining set of data for any model of transport based on ${\mathrm{HfTe}}_{5}$ band structure. Furthermore, the extraordinary thermoelectric properties suggest a new paradigm for the development of thermoelectric applications based on layered transition-metal chalcogenides.

Coupling of magnons with cavity photons at THz frequencies is reported in an antiferromagnet dysprosium ferrite (DyFeO 3 ).

We report electrical conductivity measurements of Polymethyl-methacrylate filled by onion-like carbon particles with primary particle size of $\approx 5$ nm. We shown that the conductivity $\sigma$ is exceptionally high even at very low loadings, and that its low-temperature dependence follows a Coulomb gap regime at atmospheric pressure and an activated behavior at a pressure of $2$ GPa. We interpret this finding in terms of the enhancement under the applied pressure of the effective dielectric permittivity within the aggregates of onion-like carbons, which improves the screening of the Coulomb interaction and reduces the optimal hopping distance of the electrons., Comment: 4 pages, 3 figures, 1 page of supplementary material

Author(s): Jovic, V; Koch, RJ; Panda, SK; Berger, H; Bugnon, P; Magrez, A; Smith, KE; Biermann, S; Jozwiak, C; Bostwick, A; Rotenberg, E; Moser, S | Abstract: The efficiency and stability of RuO2 in electrocatalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties, determined by a complex interplay of lattice-, spin-rotational, and time-reversal symmetries, as well as the competition between Coulomb and kinetic energies. This interplay was predicted to produce a network of Dirac nodal lines (DNLs), where the valence and conduction bands touch along continuous lines in momentum space. Here we uncover direct evidence for three DNLs in RuO2 by angle-resolved photoemission spectroscopy. These DNLs give rise to a flat-band surface state that is readily tuned by the electrostatic environment, and that presents an intriguing platform for exotic correlation phenomena. Our findings support high spin-Hall conductivities and bulk magnetism in RuO2, and are likely related to its catalytic properties.

Using soft x-ray angle-resolved photoemission spectroscopy we probed the bulk electronic structure of T_{d}-MoTe_{2}. We found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations. Unveiling the importance of Coulomb interaction opens up a new route to comprehend the unique properties of MoTe_{2}, and is significant for understanding the interplay between correlation effects, strong spin-orbit coupling and superconductivity in this van der Waals material.

Magnetic skyrmions are topologically protected spin-whirls currently considered as promising for use in ultra-dense memory devices. Towards achieving this goal, exploration of the skyrmion phase response and under external stimuli is urgently required. Here we show experimentally, and explain theoretically, that in the magnetoelectric insulator Cu2OSeO3 the skyrmion phase can expand and shrink significantly depending on the polarity of a moderate applied electric field (few V/μm). The theory we develop incorporates fluctuations around the mean-field that clarifies precisely how the electric field provides direct control over the free energy difference between the skyrmion and the surrounding conical phase. The quantitative agreement between theory and experiment provides a solid foundation for the development of skyrmionic applications based on magnetoelectric coupling.

Here we report on experiments performed by linear-dichroism angle resolved photoelectron spectroscopy (LD-ARPES) on septuple layers (SL) topological insulator GeBi2Te4. The linear dichroic signals, both for the valence band states and in the topologically protected surface state are interpreted as a probe of the symmetry of the states. The observation of a change in the LD-ARPES spectrum at the top of VB is attributed to the band parity inversion which is predicted by theory for all materials entering the topologically protected phase. Finally, the opening of a gap in the surface state dispersion along the non-high symmetry direction is reported. This is proposed to originated from the interaction between the surface state and the VB, leading to the formation of surface resonances.

The reaction center protein is the unit in the photosynthetic organisms in which the primary events of the photoelectric energy conversion take place during photosynthesis. When the photochemistry following the excitation of the reaction center by light is oversaturated there is a large probability to form reactive oxygen species (ROS, e.g., singlet oxygen (O-1(2))). Because the ROS components decrease the overall yield of the photochemical energy conversion there is a considerable effort in many laboratories to find conditions to reduce these harmful compounds. The aim of our work is to create a system by using carbon nanotubes (CNTs) and RCs for efficient light-energy conversion. The role of the O-1(2) that destroys the RC structure is discussed. 1,3-Diphenylisobenzofuran was used to detect the concentration of the O-1(2). Although, O-1(2) can be sensitized by CNTs in certain conditions, in our experiments the main sources of the O-1(2) are the RCs. The concentration of the O-1(2) in the equilibrium is determined by the forward sensitization and the backward deactivation processes of the components and functions of the CNT/RC composite. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Magnetic skyrmions are promising candidates as information carriers in logic or storage devices thanks to their robustness, guaranteed by the topological protection, and their nanometric size. Currently, little is known about the influence of parameters such as disorder, defects or external stimuli, on the long-range spatial distribution and temporal evolution of the skyrmion lattice. Here, using a large (7.3x7.3{\mu}m$^{2}$) single crystal nano-slice of Cu$_{2}$OSeO$_{3}$, we image up to 70,000 skyrmions, by means of cryo-Lorentz Transmission Electron Microscopy as a function of the applied magnetic field. The emergence of the skyrmion lattice from the helimagnetic phase is monitored, revealing the existence of a glassy skyrmion phase at the phase transition field, where patches of an octagonally distorted skyrmion lattice are also discovered. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations and the temporal fluctuations of these domains is filmed. These results demonstrate the importance of direct-space and real-time imaging of skyrmion domains for addressing both their long-range topology and stability., Comment: 31 pages (16 + 15 supplementary material),17 figures (4 + 13 supplementary material)

Since their discovery, carbon nanotubes (CNTs) have attracted intense attention to broad range of potential applications. In contrast to the 1D isolated single-walled carbon nanotubes (SWCNT), 2D films or bundles made of thousands of tubes have been introduced as more advantageous building blocks for new types of applications in mechanically flexible and stretchable, optically transparent electronic systems. In our experiments, we combined photosynthetic reaction centre proteins, the light energy converter units in living cells, purified from purple bacteria, with multiwalled carbon nanotube (MWCNT) bundles. The change in the conductivity of the bare MWCNT bundles and the RC/MWCNT composite after light excitation was measured and compared. We found that the electrical conductivity under light excitation depends on the intrinsic conductivity of individual tubes within the bundles and on structural characteristics, like geometry (diameter, length, spatial arrangement, interconnects, etc.) and the electronic coupling with the RCs. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report magnetic and thermodynamic properties of a 4d1 (Mo5+) magnetic insulator MoOPO4 single crystal, which realizes a J1−J2 Heisenberg spin-1/2 model on a stacked square lattice. The specific-heat measurements show a magnetic transition at 16 K which is also confirmed by magnetic susceptibility, ESR, and neutron diffraction measurements. Magnetic entropy deduced from the specific heat corresponds to a two-level degree of freedom per Mo5+ ion, and the effective moment from the susceptibility corresponds to the spin-only value. Using ab initio quantum chemistry calculations, we demonstrate that the Mo5+ ion hosts a purely spin-1/2 magnetic moment, indicating negligible effects of spin-orbit interaction. The quenched orbital moments originate from the large displacement of Mo ions inside the MoO6 octahedra along the apical direction. The ground state is shown by neutron diffraction to support a collinear Neel-type magnetic order, and a spin-flop transition is observed around an applied magnetic field of 3.5 T. The magnetic phase diagram is reproduced by a mean-field calculation assuming a small easy-axis anisotropy in the exchange interactions. Our results suggest 4d molybdates as an alternative playground to search for model quantum magnets.

The prediction of Weyl fermions in the low-temperature noncentrosymmetric $1{T}^{\ensuremath{'}}$ phase of ${\mathrm{MoTe}}_{2}$ still awaits clear experimental confirmation. Here, we report angle-resolved photoemission (ARPES) data and ab initio calculations that reveal a surface state arc dispersing between the valence and the conduction band, as expected for a Weyl semimetal. However, we find that the arc survives in the high-temperature centrosymmetric $1{T}^{\ensuremath{'}\ensuremath{'}}$ phase. Therefore, a surface Fermi arc is not an unambiguous fingerprint of a topologically nontrivial phase. We have also investigated the surface state spin texture of the $1{T}^{\ensuremath{'}}$ phase by spin-resolved ARPES, and identified additional topologically trivial spin-split states within the projected band gap at higher binding energies.

Magnetic skyrmions are localized nanometric spin textures with quantized winding numbers as the topological invariant. Rapidly increasing attention has been paid to the investigations of skyrmions since their experimental discovery in 2009, due both to the fundamental properties and the promising potential in spintronics based applications. However, controlled creation of skyrmions remains a pivotal challenge towards technological applications. Here, we report that skyrmions can be created locally by electric field in the magnetoelectric helimagnet Cu$\mathsf{_2}$OSeO$\mathsf{_3}$. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical spin background. Our discovery is highly coveted since it implies that skyrmionics can be integrated into contemporary field effect transistor based electronic technology, where very low energy dissipation can be achieved, and hence realizes a large step forward to its practical applications.

Physical review / B 96(24), 241408 (2017). doi:10.1103/PhysRevB.96.241408, $MoTe_2$ has recently been shown to realize in its low-temperature phase the type-II Weyl semimetal (WSM). We investigated by time- and angle- resolved photoelectron spectroscopy (tr-ARPES) the possible influence of the Weyl points on the electron dynamics above the Fermi level $E_F$, by comparing the ultrafast response of $MoTe_2$in the trivial and topological phases. In the low-temperature WSM phase, we report an enhanced relaxation rate of electrons optically excited to the conduction band, which we interpret as a fingerprint of the local gap closure when Weyl points form. By contrast, we find that the electron dynamics of the related compound $WTe_2$is slower and temperature independent, consistent with a topologically trivial nature of this material. Our results shows that tr-ARPES is sensitive to the small modifications of the unoccupied band structure accompanying the structural and topological phase transition of $MoTe_2$., Published by Inst., Woodbury, NY

We here report a detailed high-pressure infrared transmission study of BiTeCl and BiTeBr. We follow the evolution of two band transitions: the optical excitation $\beta$ between two Rashba-split conduction bands, and the absorption $\gamma$ across the band gap. In the low pressure range, $p< 4$~GPa, for both compounds $\beta$ is approximately constant with pressure and $\gamma$ decreases, in agreement with band structure calculations. In BiTeCl, a clear pressure-induced phase transition at 6~GPa leads to a different ground state. For BiTeBr, the pressure evolution is more subtle, and we discuss the possibility of closing and reopening of the band gap. Our data is consistent with a Weyl phase in BiTeBr at 5$-$6~GPa, followed by the onset of a structural phase transition at 7~GPa., Comment: are welcome

Multiwalled carbon nanotubes (MWCNTs) were successfully covered with metal oxides - such as TiO2, ZnO, Al2O3, SnO2, and In2O3 nanoparticles - with different preparation methods under solvent conditions. The applied synthesis techniques were impregnation, a hydrothermal process and a ball-milling method. As-prepared inorganic coverage layers were characterized by TEM, HRTEM, SEM, SEM-EDX, and X-ray diffraction techniques. Results revealed that the choice of synthesis technique affects the quality and the layer structure of the deposited inorganic particles on the surface of carbon nanotubes. These materials might be suitable for nanotechnology applications. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Since materials science is of great importance, the application of composite materials based on carbon nanotubes (CNTs) is widely investigated. Current work is aimed at preparing nanocomposites of TiO2/MWCNT using an impregnation method combined with slow hydrolysis. Different titanium alkoxide compounds as Ti(OEt)(4), Ti(OiPr)(4), and Ti(OBu)(4), respectively, were used as precursor materials to cover the surface of CNTs in ethanolic medium. In our samples themass ratiowas 10:1 (TiO2:MWCNT). The produced composite materials were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman microscopy, transmission (TEM) and scanning electron microscopy (SEM) techniques; moreover, thermal analysis and the determination of the specific surface area (BET) were also carried out. These as-prepared TiO2/MWCNT composites were also tested as photocatalysts in degradation reaction of the model compound salicylic acid. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Photosensitizers may convert molecular oxygen into reactive oxygen species (ROS) including, e.g., singlet oxygen (O-1(2)), superoxide anion (O-2(-center dot)), and hydroxyl radicals ((OH)-O-center dot), chemicals with extremely high cyto- and potential genotoxicity. Photodynamic ROS reactions are determinative in medical photodynamic therapy (cancer treatment with externally added photosensitizers) and in reactions damaging the photosynthetic apparatus of plants (via internal pigments). The primary events of photosynthesis take place in the chlorophyll containing reaction center protein complex (RC), where the energy of light is converted into chemical potential. O-1(2) is formed by both bacterial bacteriochlorophylls and plant RC triplet chlorophylls in high light and if the quenching of O-1(2) is impaired. In plant physiology, reducing the formation of the ROS and thus lessening photooxidative membrane damage (including the RC protein) and increasing the efficiency of the photochemical energy conversion is of special interest. Carbon nanotubes, in artificial systems, are also known to react with singlet oxygen. To investigate the possibility of O-1(2) quenching by carbon nanotubes in a biological system, we studied the effect of carbon nanotubes on O-1(2) photogenerated by photosynthetic RCs purified from purple bacteria. 1,3-Diphenylisobenzofuran (DPBF), a dye responding to oxidation by O-1(2) with absorption decrease at 420nm was used to measure O-1(2) concentrations. O-1(2) was produced either from a photosensitizer (methylene blue) or from triplet photosynthetic RCs and the antioxidant capacity of carbon nanotubes was assessed. Less O-1(2) was detected by DPBF in the presence of carbon nanotubes, suggesting that these are potential quenchers of this ROS. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

H2O2 is a product of reactions catalysed by several oxidase enzymes and it is essential in environmental and pharmaceutical analyses. The most commonly used enzyme in understanding the biological behaviour of catalysed oxidation of H2O2 is horseradish peroxidase (HRP). In our experiments HRP was bound to carboxyl-functionalized multiwalled carbon nanotubes (MWNT-COOH) by N-hydroxysuccinimide (NHS) and 1-[3-dimethylaminopropyl]-3-ethyl-carbodiimide (EDC) crosslinkers. The activity of this bio-nanocomposite and the limit of detection (LOD) for H2O2 were determined by measuring the fluorescence of tetraguaiacol (which chemical is the product of guaiacol oxidation after addition of H2O2 to the reaction mixture) as a function of time. The hydrogen peroxide biosensor we developed exhibited a detection limit of 1.2 mu MH(2)O(2)s(-1) which resolution was better than the one measured in solution by about a factor of eight (it was 10 mu MH(2)O(2)s(-1) in solution). An attempt has been made to measure the concentration of H2O2 in an electrochemical cell with HRP immobilized on the surface of an electrode made of indium tin oxide (ITO, a transparent conductive oxide) and MWNT. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Carbon nanotubes (CNTs) are grown on PAN-based carbon fibers by means of catalytic chemical vapor deposition technique. By using catalytic thermal decomposition of hydrocarbon, CNTs can be grown in the temperature range of 650750 degrees C. However, carbon fibers suffer significant damages resulting in decrease of initial tensile strength. By applying the oxidative dehydrogenation reaction of C2H2 with CO2, we found an alternative way to grow CNTs on carbon fibers at low temperatures, such as 500 degrees C. Scanning electron microscope results combined with single fiber tests indicate that this low temperature growth enables homogeneous grafting of CNTs onto carbon fibers without degradation of tensile strength.

Electrons in low-dimensional materials sometimes reorganize themselves with a new translational symmetry, which gives rise to an energetically more favorable ground state. This phenomenon, called a charge density wave (CDW) phase, is often the result of the coupling of electrons to phonons. In the quasi-two-dimensional material TiSe${}_{2}$, the CDW occurring at low temperature is unusual, since it appears to be driven by strong electron-hole correlations, which in turn couple to phonons. In this work, the authors use time- and angle-resolved photoemission spectroscopy to investigate the peculiar nature of the CDW phase in TiSe${}_{2}$.Depending on the temperature at which measurements are performed, they observe that the response of the material is either strongly coupled to the lattice or dominated by its electronic degrees of freedom. This selective response is enhanced by tuning the pump pulse wavelength to specific optical resonances. They conclude that their measurements do indeed confirm a combined scenario, for which both the electron-hole correlations and the coupling to phonons are essential to the origin of the CDW phase in TiSe${}_{2}$.

The complex electronic properties of ${\mathrm{ZrTe}}_{5}$ have recently stimulated in-depth investigations that assigned this material to either a topological insulator or a 3D Dirac semimetal phase. Here we report a comprehensive experimental and theoretical study of both electronic and structural properties of ${\mathrm{ZrTe}}_{5}$, revealing that the bulk material is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we identify at the top of the valence band both a surface and a bulk state. The dispersion of these bands is well captured by ab initio calculations for the STI case, for the specific interlayer distance measured in our x-ray diffraction study. Furthermore, these findings are supported by scanning tunneling spectroscopy revealing the metallic character of the sample surface, thus confirming the strong topological nature of ${\mathrm{ZrTe}}_{5}$.

Detection of sub-THz spin cycloid resonances (SCRs) of stoichiometric BiFeO3 (BFO) was demonstrated using a vector network analyzer. Continuous wave absorption spectroscopy is possible, thanks to heterodyning and electronic sweep control using frequency extenders for frequencies from 480 to 760 GHz. High frequency resolution reveals SCR absorption peaks with a frequency precision in the ppm regime. Three distinct SCR features of BFO were observed and identified as Psi(1) and Phi(2) modes, which are out-of-plane and in-plane modes of the spin cycloid, respectively. A spin reorientation transition at 200 K is evident in the frequency vs temperature study. The global minimum in linewidth for both Psi modes at 140 K is ascribed to the critical slowing down of spin fluctuations. (C) 2016 Author(s).

Nanocomposite SnO2/multiwall-carbon-nanotubes were prepared by the sol-gel method. The morphology of prepared nanocomposite powder was investigated by scanning electron microscopy. Energy-dispersive X-ray and X-ray diffraction analyses were carried out, the element structure of a nanocomposite has been determined. Ceramic and thick film gas sensors made of the nanocomposite multiwall-carbon-nanotube/SnO2/Pd structure were manufactured and investigated. After the sensitization in the Ru(OH)Cl-3 water solution, these sensors have rather high response to isobutane already at 120 degrees C. The response of prepared sensors was measured at different gas concentrations and at different temperatures of the work body. (C) 2012 Elsevier B.V. All rights reserved.

The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Hall-effect and a spin-transfer torque at ultra-low current densities. In the insulating compound Cu2OSeO3, magneto-electric coupling enables control of the skyrmion lattice via electric fields, promising a dissipation-less route towards novel spintronic devices. One of the outstanding fundamental issues is related to the thermodynamic stability of the skyrmion lattice. To date, the skyrmion lattice in bulk materials has been found only in a narrow temperature region just below the order-disorder transition. If this narrow stability is unavoidable, it would severely limit applications. Here we present the discovery that applying just moderate pressure on Cu2OSeO3 substantially increases the absolute size of the skyrmion pocket. This insight demonstrates directly that tuning the electronic structure can lead to a significant enhancement of the skyrmion lattice stability. We interpret the discovery by extending the previously employed Ginzburg-Landau approach and conclude that change in the anisotropy is the main driver for control of the size of the skyrmion pocket. This realization provides an important guide for tuning the properties of future skyrmion hosting materials., submitted to Scientific Reports

The long term stability and the redox interaction between single walled carbon nanotubes (SWNTs) and photosynthetic reaction center proteins (RCs) purified from purple bacterium Rhodobacter sphaeroides R-26 in the SWNT/RC complex has been investigated. The binding of SWNT to RC results in an accumulation of positive (the oxidized primary electron donor, P+) and negative (semiquinone forms, Q(A)(-) and Q(B)(-), the reduced primary and secondary quinones, respectively) charges followed by slow reorganization of the protein structure after excitation. The photochemical activity of the SWNT/RC complexes remains stable for several weeks even in dried form. In the absence of SWNT the secondary quinone activity decays quickly as a function of time after drying the RC onto a glass surface. Polarography measurements substantiate the idea that there is an electronic interaction between the RCs and SWNTs after light excitation, which was suggested earlier by optical measurements. The special electronic properties of the SWNT/protein complexes open the possibility for several applications, e. g., in microelectronics, analytics, or energy conversion and storage. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Photosynthetic reaction center (RC) is one of the most important proteins, because it is Nature's solar battery converting light energy into chemical potential in the photosynthetic membrane assuring conditions for carbon reduction in cells. Although it is developed in nanometer scale, and is working in nanoscopic power, this is the protein that assures the energy input practically for the whole biosphere on Earth. The extremely large quantum yield of the primary charge separation (close to 100%) in the RC offers a big challenge to use it in nanodevices. Results of structural (AFM, EM), optical, and electro chemical investigations on RC bio-nanocomposite materials based on different carrier matrices (e.g., CNTs, ITO) will be presented.

Cubic ZnMnO3 powder in the form of well-crystalline nanoflakes have been synthesized at low temperatures from a nitrate precursor. The electrical properties of cubic ZuMnO(3) samples have been established by DC resistivity (rho) and thermo-electric power (Seebeck coefficient) measurements on a pressed pellet. The material exhibits insulator behavior with 0.7 eV acceptor ionization energy in the measured temperature range of 170-300 K. The thermo-electric power indicates a positive sign of the charge carriers. The obtained material exhibits a superparamagnetic signature with a blocking temperature of 9 K and the ZFC-FC splitting temperature of 15 K. (C) 2010 Elsevier Ltd. All rights reserved.

Recent advances in nanotechnology led to the development of various nanostructures especially that of carbon-based nanomaterials (CBNs) for industrial and biomedical uses. As a result, the production as well as the human exposure to these materials will increase in the future. Thus, it is primordial to also know the associated health hazards. We performed in vitro cell viability studies on different types of cultured cells exposed to multiwalled carbon nanotubes and carbon nanoparticles. Our work indicates that the tested materials are toxic and that the effects of materials are cell type dependent. Light microscopic observations of the cells when exposed to the highest dose of nanomaterials showed morphological alterations, which are characteristic for cell death, and were most pronounced in the case of macrophage cells. Further experiments are aimed at elucidating the mechanisms of toxicity of CBNs. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Transition-metal-doped ZnO is considered a promising candidate for applications in spintronics. Here, we developed it novel and versatile synthetic route for obtaining impurity-free Mn-doped zinc oxide (Zn1-xMnxO) materials witha well-controlled content of Mn, with x up to 1.8 atomic %. Zn1-xMnxO is produced by thermal decomposition in reducing atmosphere of an inorganic precursor. Mn-doped hydrozincite. The materials are of high purity, as shown by detailed characterization. The obtained systems exhibit a spin-glass phase below 40 K together with a weak ferromagnetic ordering of the Mn dopants within the ZnO matrix.

We prepared a Mg-2 mass % multiwall carbon nanotubes composite employing a powder metallurgy technique. The kinetics of hydrogen absorption/desorption of the as-synthesized composite was much faster than that of reference samples of pure Mg. The pressure-composition isotherm (measured at 300 °C) of the as-synthesized composite exhibited no measurable pressure hysteresis, with the equilibrium hydrogen pressures in the plateau region being higher than those of pure Mg by a factor of up to 1.8. Equal channel angular pressing of the as-synthesized composite led to a slow down of the absorption/desorption processes at the initial stages of the processes, and to their acceleration at the later stages. We suggested that the mechanism responsible for the good kinetic performance of the as-synthesized composite was fast diffusion of hydrogen through the cores of carbon nanotubes. We put forward a hypothesis relating the increase in equilibrium hydrogen pressure in the as-synthesized composite to the elastic constraints imposed by carbon nanotubes on the Mg matrix.

We present a compact nuclear magnetic resonance (NMR) probe which is compatible with a magnet of a commercial superconducting quantum interference device magnetometer and demonstrate its application to the study of a quantum magnet. We employ trimmer chip capacitors to construct an NMR tank circuit for low temperature measurements. Using a magnetic insulator MoOPO4 with S = 1/2 (Mo5+) as an example, we show that the T-dependence of the circuit is weak enough to allow the ligand-ion NMR study of magnetic systems. Our 31P NMR results are compatible with previous bulk susceptibility and neutron scattering experiments and furthermore reveal unconventional spin dynamics.

In this article, we report on the mass production of carbon nanotubes using a continuous production system based on a rotary tube furnace. At first, we have optimized the composition of the metallic nanoparticles. Bimetallic Fe2Ni and Fe2Co alloys exhibit higher catalytic activity than pure Fe, Co or Ni. Then, catalyst production process has been modified for the preparation of large quantity of catalyst with low aggregation suitable for large scale synthesis of CNTs. A production rate of about 1.2 kg per day has been achieved. This is yielding to a cost production of less than $1 per gram. Finally, we show that the CNTs growth can also be obtained on naturally occurring calcite support for further cost reduction of the synthesis. Quality of the CNTs produced has been established by measuring their mechanical properties using AFM. Young's modulus of the CNTs can be as high as the ideal value of 1 TPa. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report resistivity and thermo-electric power measurements of the anatase phase of TiO2 under pressure up to 2.3 GPa. Despite its transparent appearance, the single crystal of anatase exhibits a metallic-like resistivity above 60 K, at all pressures. The rather high value of the thermo-electric power at room temperature points to complex transport mechanism in this phase.

SU8-carbon nanotube composites have been produced to enhance the mechanical, electrical, and thermal properties of SU8 photoresists. Homogeneous composites materials have been obtained when multiwalled carbon nanotubes (MWCNTs) functionalized with COOH groups were used. Indeed, COOH groups can react with the epoxy ring of the SU8 molecule yielding an improved interaction between carbon nanotubes (CNTs) and the polymer matrix. Impedance spectroscopy was used to study the conducting percolation path in the composites, that is the quality of the nanotube dispersion in the epoxy matrix. It turns out that propylene glycol methyl ether acetate (PGMEA) as well as gamma-butyrolacton (GBL) are very suitable solvent to prepare SU8-MWCNTs composites of good homogeneity. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We have attempted to prepare graphene samples by mechanical exfoliation of HOPG (highly oriented pyrolytic graphite) using scotch tape. Random testing of the flakes by AFM has shown in majority single layer graphene. Nevertheless, the presence of ultrathine graphite cannot be excluded in the large assembly of flakes needed for electron spin resonance (ESR) measurements. Graphene flakes sitting on ESR-silent scotch tapes were stacked parallel to form a multilayer sandwich. The ESR measurements performed in the 4-300 K range yielded narrow Lorentzian line. The spin susceptibility was decreasing linearly with decreasing temperature as expected for the conical band dispersion of graphene. Below 70 K the spin susceptibility started to deviate from the linear temperature dependence and a Curie-like behavior was observed. This contribution to the susceptibility is due to the existence of defects or impurities, which are in strong exchange coupling limit with conduction electrons. The temperature dependence of the linewidth suggests Elliott's mechanism for spin relaxation in graphene flakes. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim