We report a comprehensive study of physical properties of the binary superconductor compound SnAs. The electronic band structure of SnAs was investigated using both angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and density functional theory (DFT) within generalized gradient approximation (GGA). The DFT/GGA calculations were done including spin-orbit coupling for both bulk and (111) slab crystal structures. Comparison of the DFT/GGA band dispersions with ARPES data shows that (111) slab much better describes ARPES data than just bulk bands. Superconducting properties of SnAs were studied experimentally by specific heat, magnetic susceptibility, magnetotransport measurements and Andreev reflection spectroscopy. Temperature dependences of the superconducting gap and of the specific heat were found to be well consistent with those expected for the single band BCS superconductors with an isotropic s-wave order parameter. Despite spin-orbit coupling is present in SnAs, our data shows no signatures of a potential unconventional superconductivity, and the characteristic BCS ratio 2/Tc = 3.48 − 3.73 is very close to the BCS value in the weak coupling limit.
In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin–orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn4As3, with non-centrosymmetric unit cell (R3m).We have characterised the normal and superconducting states using a range of methods. Angle-resolved photoemission spectroscopy shows a multiband Fermi surface and the presence of two surface states, confirmed by density-functional theory calculations. Specific heat measurements reveal a superconducting critical temperature of Tc ∼ 1.14 K and an upper critical magnetic field of Hc > 7 mT, which are both confirmed by ultra-low temperature scanning tunneling microscopy and spectroscopy. Scanning tunneling spectroscopy shows a fully formed superconducting gap, consistent with conventional s-wave superconductivity.
In pnictide RbEuFe4As4, superconductivity sets in at 36 K and coexists, below 15−19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-terminated and small Eu-terminated terraces, both manifesting 1 × 2 and \sqrt 2 × \sqrt 2 reconstructions. On \sqrt 2 × \sqrt 2 surfaces, a hidden electronic order with a period ∼5 nm was discovered. A superconducting gap of ∼7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated ∼1.8eV below the Fermi level and thus do not contribute directly to Cooper pair formation.
NaCl is one of the simplest compounds and was thought to be well-understood, and yet, unexpected complexities related to it were uncovered at high pressure and in low-dimensional states. Here, exotic hexagonal NaCl thin films on the (110) diamond surface were crystallized in the experiment following a theoretical prediction based on ab initio evolutionary algorithm USPEX. State-of-the-art calculations and experiments showed the existence of a hexagonal NaCl thin film, which is due to the strong chemical interaction of the NaCl film with the diamond substrate.
A novel triphenylamine derivative-linked ionic liquid unit, 1-(6-((4-(bis(4-(thiophen-2-yl)phenyl)amino)- benzoyl)oxy)hexyl)-3-methyl-imidazolium tetrafluoroborate (TTPAC6IL-BF4), was designed and synthesized successfully, and its corresponding polymer PTTPAC6IL-BF4 was obtained by the electropolymerization method. The highest occupied molecular orbital energy band of TTPAC6IL-BF4 is higher and the onset oxidative potential lower compared with that of 6-bromohexyl 4-(bis(4-(thiophen-2-yl)phenyl)amino) benzoate (TTPAC6Br) without modifying the ionic liquid unit. The results imply that introducing an ionic liquid unit to the side chain is an efficient method to improve the switching time of conjugated polymers and would be inspirational for the design and preparation of novel bifunctional electrochromic polymeric electrolytes.
The aim of the article was to study the hardness of a metal surface modified with ultrafine particles of minerals by two different methods (instrumental indentation and Vickers hardness measurement) and a comparative analysis of the measurement results obtained by these methods.Standard Vickers hardness measurements at loads of 0.025, 0.1, and 0.5 kgf showed a qualitative difference between the hardness values of the two samples modified with different mixtures of ultrafine particles of minerals and a large heterogeneity of the hardness values over the area. By the method of instrumental hardness, standard measurements were performed without preliminary selection of the indentation site (at a load of 1.05 N) and measurements during indentation into even sections (at low loads of 10 mN).It is noted that the high precision of measurements implemented by instrumental indentation, due to the large roughness of the samples, leads to large values of the error in calculating the measurement results. An additional difference in the results of measurements performed by two methods at shallow indentation depths may be due to the fact that the object under study has a complex structure consisting of a metal matrix and particles distributed over the depth of the sample. A possible way out of the situation lies in the transition from the use of hardness measures when calibrating instruments to standard samples of properties for which the constancy of mechanical properties in the measured range of indentation depths will be ensured, but which are not yet available in research practice.
The damage features of the vanadium surface layer under the action of pulsed laser radiation are investigated. Laser irradiation of the samples was carried out in air using the GOS 1001 installation in the modulated q-factor mode with a flux density q equal to 1.2 × 108 W / cm2, pulse duration τ0 = 50 ns, the number of pulses N from 1 to 6. It is shown that the typical surface damage is melting of the material, formation of the grid of microcracks, formation of wave-like relief and drip structures. The central zone is characterized by the highest degree of damage, where along with the above mentioned damage there are individual drops of metal that are crystallized like a spiral. The zone of thermal influence adjacent to the central zone of irradiation is damaged much weaker and the degradation of the surface increases with the increase in the number of laser pulses. As a result of laser processing, along with the change in the topography of the material surface, changes in the diffractograms of samples were also observed: the texture weakens, the peaks become wider, the lattice period increases (3.022 – before irradiation, 3.027 after irradiation). It was found that the preliminary argon ions (dose 1022 m-2, E = 20 keV) irradiation of samples practically does not affect the nature of surface damage in the central zone after laser treatment, whereas in the adjacent zone of thermal influence there is a break of local surface areas.
Single crystals of Pr3+ doped hexa-aluminate Sr0.7La0.3Mg0.3Al12O19 (ASL) were prepared for spectroscopic characterization. We investigated their optical spectroscopic properties in σ and π polarization of light. Absorption spectra were recorded in extended spectral range, 400 nm–5400 nm. Energies of Pr3+ crystal field states were determined. In addition to the major D3h sites, minor sites were found. Judd-Ofelt analysis was performed: the J-O parameters Ωt were determined to be 1.06 x 10^-20 cm-2, 2.31 x 10^-20 cm-2 and 3.43 x 10^-20 cm-2 for t = 2, 4 and 6, respectively. The radiative lifetime was 38 μs for the emitting state 3P0.
Typical configurations of broken dislocation boundaries formed during plastic deformation at faceted grain boundaries have been analyzed. The reasons for their formation have been determined. It has been shown that the shape and sizes of strain-induced broken dislocation boundaries can be determined by the geometry of a faceted boundary and the relevant slip systems of lattice dislocations. The calculations carried out in the framework of the 2D model make it possible to explain the morphology of the observed broken dislocation boundaries.
We report on the first high-resolution optical spectroscopy study of LiYF4:Ho in an external magnetic field. Peculiarities in the hyperfine structure of holmium spectral lines are discussed for the cases H||c and H⊥c (H = 0.53 and 0.87 T). The spectra reveal a strong interaction between crystal-field levels, mediated by Zeeman and hyperfine terms in the Hamiltonian. A study of the magnetic-field-dependent isotope shifts in 7Li0.1 6Li0.9YF4:Ho (0.1 at.%) single crystals delivers an estimate of the difference in magnetic g factors for holmium centers with all 6Li isotopes in the nearest surrounding of Ho3+ (g(0)) and the centers having one 7Li isotope there (g(1)):g(1) − g(0) = 0.01 ± 0.005.
Hybrid membranes were prepared by incorporating silica with propyl-imidazoline groups in polybenzimidazoles (phthalide-containing PBI or PBI based on 2,6- or 2,5-pyridinedicarboxylic acids). The influence effects of the silica precursor hydrolysis conditions on the conductivity of the hybrid membranes are studied. Ionic conductivity, water uptake, phosphoric acid doping, and gas permeability of the obtained materials were found to depend on the preparation method and the silica loading. The materials with 10 wt% of functionalized silica present the highest conductivity. A decrease of hydrogen permeability is observed for low silica loadings.
Recent theoretical studies predict the suppressed ferroelectric instability in orthorhombic Pnma perovskites and experimental evidence is due. We observed significant softening at cooling of the lowest-frequency polar phonon at the Brillouin zone center in the Pnma antiferromagnetic fluoroperovskite NaMnF3 that is the direct proof of the theoretically predicted ferroelectric instability. In contrast to oxides where the hybridization plays the dominant role, the effective ionic charges in fluoroperovskites are close to their nominal valencies that confirms the geometric origin of the observed incipient ferroelectricity. Furthermore, below the Néel temperature, the softening phonon clearly shows a strong coupling with the magnetic subsystem as a result of dynamical modulation of the superexchange interaction. Our findings clarify microscopic mechanisms of the incipient multiferroicity in the Pnma fluoroperovskites and reveal still unexplored opportunities of this class of materials for further research and potential applications.
In the paper we demonstrate that the thermal doping of SiO2 film by phosphorus, causing formation of thin film of phospho-silicate glass on its surface, allows to rise charge stability of gate dielectric of MIS structure. We have ascertained that a presence of the film of phospho-silicate glass has given a possibility to significantly lower local injection currents flowing within defects because of electron capturing by traps located in the film of phospho-silicate glass what results in the rising of energy barrier. As a result, amount of the structures that comes to a state of breakdown at low values of charge injected into the dielectric under high fields noticeably reduces. We show that heating processes of injected electrons lowers in the films of phospho-silicate glass and this results in increasing of charge stability of the gate dielectric under high-field injection.
A novel acceptor–donor–acceptor chromophore IDTT-HC2P with an indacenodithienothiophene core linked with two hydrazinylidenecyclopentadiene terminal acceptor groups was designed and synthesized via the reaction of dilithiated indacenodithienothiophene with the corresponding diazo compound. The frontier orbital energy levels as well as the bandgap which were estimated from both optical and electrochemical properties are very closely related to those of ITIC which in turn is associated with high power conversion efficiencies.
In the paper the content of individual elements (Fe, Co, Zr, Ca and F) contained in nanocomposites FeCoZr ferromagnetic alloy in the CaF2 transparent ceramics dielectric matrix, depending on the content of the metal phase x was determined by the X-ray diffusion microanalysis (EDX) method. The nanocomposites were made by sputtering by argon ions. Investigations of changes in the chemical composition of nanocomposites under the influence of high-temperature treatments were carried out using the thermogravimetry method in the temperature range from 25 °C to 1000 °C with a temperature increase rate of 10 °C/min. On the basis of the research, a model of changes of the structural-phase state of nanogranular layers of ferromagnetic alloy Fe45Co45Zr10 in the transparent ceramics CaF2 matrix occurring under the influence of high-temperature treatments was proposed.
The damage and structural state of the surface layer of Al–Li–Mg samples composed of Al–5% Mg–2% Li (wt %) under pulsed action of power streams of high-temperature deuterium plasma and highenergy deuterium ions in the Plasma Focus (PF) device have been investigated. The radiation power density was q ~ 106 W/cm2; the pulse duration was 50–100 ns. Pulsed thermal heating and rapid cooling is established to lead to the melting and solidification of a thin surface layer of the alloy for several tens of nanoseconds. At the same time, in the superheated surface layer of the alloy, microcavities of a spherical shape are formed which is associated with intense evaporation of lithium into micropores within the heated layer. Thermal stresses caused by abrupt heating, melting, and cooling of a thin surface layer of metal result in formation of microcracks in the near-surface zone of the samples. The evaporation by the power electron beam of the elements of the anode material of the PF device (copper and tungsten) and their subsequent deposition onto the irradiated surface of the investigated samples in the form of droplets of submicron size are noted. It is shown that the thermal and radiationstimulated processes generated in the alloy under the action of pulsed energy fluxes in the implemented irradiation regime lead to the redistribution of elements in the surface layer of the aluminum solution, contributing to an increase in magnesium content and the formation of magnesium oxide on the surface.
The paper presents a study of the processes of electron trapping in metal–insulator–semiconductor (MIS) structures with gate dielectric based on silicone dioxide doped with phosphorus under high-field Fowler–Nordheim tunnel injection of electrons in a range of temperatures from 293 to 373 K. We have ascertained that the negative charge being trapped in phosphosilicate glass (PSG) consisted of two components with a different energy of the thermal ionization ΔEa1 = 0.2–0.3 eV and ΔEa2 = 1.0–1.2 eV. A part of the charge with a low energy of the thermal ionization virtually drain off at annealing temperature of 473 K for a period of time of 20 min and then the dielectric contains only the thermostable part of the negative charge that can be utilized to correct the threshold voltage of MIS transistors. We have ascertained that an implementation of the high-field tunnel injection of electrons for MIS structures with SiO2–PSG gate dielectric has raised not only density of negative charge trapped but also its thermostable component.
A model of the electric field enhanced thermal (thermo-field) emission of electrons from the metal cathode substrate into a thin insulating film on its surface is developed. A system of equations for the cathode surface temperature in the arc discharge and the electric field strength in the film, providing the required discharge current density, is formulated. It is shown that existence of the insulating film can result in a considerable reduction of the cathode temperature in the discharge due to lower potential barrier height at the metal-insulator boundary than at the metal-discharge boundary in case of the cathode without the film. It is found that due to an enhancement of the thermal emission of electrons into the film by the electric field generated in it, an additional decrease in the cathode temperature by about 100 K takes place.
A model of the thermo-field electron emission from the metal cathode with a thin insulating surface film at temperatures of 200–400 K is developed. An expression for the film emission efficiency in the gas discharge is obtained. The efficiency is equal to the fraction of electrons emitted into the film from the metal substrate, which enter the discharge volume and increase the effective secondary-electron emission yield of the cathode. It is shown that the thermo-field mechanism of electron emission influences noticeably the ignition voltage of the low-current discharge with such cathode at rather low temperatures exceeding the room temperature by less than 100 K.
Absorption, emission and excitation spectra of 50 MeV electron beam irradiated and asgrown YAG single crystals were studied and compared in the 10-300 K temperature range using timeresolved luminescence spectroscopy under UV/VUV/XUV excitation by synchrotron radiation and cathodoluminescence. The emission spectra consist of intrinsic (excitonic) and defect related nonelementary bands in the VIS/UV range. It is shown that fast electrons create stable F and F+ color centers with characteristic emission and absorption bands in the visible/UV range. Induced absorption caused from these defects starts at 4.2 eV. Energy transfer from host to color centers is not efficient process.
Mechanical performances of titanium biomedical implants manufactured by superplastic forming are strongly related to the process parameters: the thickness distribution along the formed sheet has a key role in the evaluation of post-forming characteristics of the prosthesis. In this work, a finite element model able to reliably predict the thickness distribution after the superplastic forming operation was developed and validated in a case study. The material model was built for the investigated titanium alloy (Ti6Al4V-ELI) upon results achieved through free inflation tests in different pressure regimes. Thus, a strain and strain rate dependent material behaviour was implemented in the numerical model. It was found that, especially for relatively low strain rates, the strain rate sensitivity index of the investigated titanium alloy significantly decreases during the deformation process. Results on the case study highlighted that the strain rate has a strong influence on the thickness profile, both on its minimum value and on the position in which such a minimum is found.