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Plasma treatment of porous polymeric materials is a promising method for creating new materials that can be used for different tasks, including in medicine, for the development of new types of biocompatible and biodegradable polymeric materials. This paper is devoted to the study of plasma treatment of porous polylactide to clarify discharge conditions and improve the effectiveness of the treatment process. Experiments were conducted to determine conditions for the ignition of a discharge and its electrical parameters in samples of porous polylactide at different air pressures. An experimental study of the degree of processing (hydrophilization) of the cavities of polylactide samples was carried out depending on processing time, gas pressure, and the corresponding input energy of the discharge. An infrared spectroscopic study of the treated and untreated samples was conducted, and the impact of treatment on the functional groups on the polymer surface is shown. The effect of electret properties of polylactide on the discharge ignition in its cavities is demonstrated.

Plasma treatment of porous polymeric materials is a critical technology for creating new polymer materials that can be used in various applications. Porous polymers can be used in new approaches for creation of safe and compact hydrogen storage systems that can dramatically change existing hydrogen energy utilization. There are other potential applications for the development of new types of biocompatible and biodegradable polymeric materials for general use and for creation of new types of implants and dressing materials in medicine. Clarification of breakdown conditions of narrow discharge gaps in the micrometer region and optimization of the treatment process for different gap dimensions is the goal of this paper. The article is devoted to the experimental study of the breakdown process in the discharge gap by pulsed barrier discharge at different pressures and gaps in the region of the minimum of the Paschen curve. New approximation of the Paschen curve with the variable γ as a function of Pd, which is in good correlation with experimental results, has been proposed. A new approach is proposed for treating the inner surface of dielectric material pores with a barrier discharge, optimizing the pressure inside the pores; treating pores of a micron size requires a pressure significantly higher than atmospheric. The first results were obtained, which demonstrated the possibility of modifying the thickness of the polymer material by treatment with the barrier discharge at the time of gas pressure relief in the discharge chamber.

Reported here are the results of measurements of the resistivity (ρ) up to 300 K and of the thermoelectric power (TEP) up to 400 K of ceramic samples of the title materials. We determined also their room‐temperature lattice parameters and oxygen content as functions of Co concentrations. The metal–nonmetal transition in YBa2Cu3−xCoxOy and in EuBa2Cu3−xCoxOy is marked by the onset of the deviation of the maximum absolute TEP from a value calculated from a simple narrow‐band formula. The results indicate that the effective valency of Pr in PrBa2Cu3−xCoxOy varies from ∼3.5 at x=0 to ∼3 for x=0.5. For x=0 this material is close to the metal–nonmetal transition. In the nonmetallic regime the electrical transport is by activated hopping. In certain ranges of Co content the results are consistent with two‐band hopping conductivity with two branches, a low‐temperature and a high‐temperature branch of variable‐range‐hopping (VRH) conductivity. In the VRH regime there is a remarkable correlation between the two res...

Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

We present an analysis of recombination activity of intrinsic defects (VCd, TeCd, VTe, and Tei) in CdTe based on the multiphonon single-mode carrier-capture model, with vibronic parameters obtained using hybrid density functional theory. This analysis allows us to determine the defects and the corresponding electronic processes that have high trapping rates for electrons, for holes, or for both. The latter, being potentially the most active recombination centers, decreases the carrier lifetime in the absorber layer of a CdTe solar cell. Taking into account the relatively high calculated capture cross-sections of the TeCd antisite defect (σ = 8.7× 10−15 cm2 for electron capture on TeCd+2 defect, σ = 6.8 × 10−14 cm2 for hole capture on TeCd+1 defect at room temperature) and its deep trapping level (0.41 eV for +2/+1 level), we conclude that this defect is the most active recombination center among the intrinsic defects in p-type CdTe. Other processes that do not lead to effective recombination are: (i) fast hole capture on Tei+1 defect (σ = 1.1 × 10−13 cm−2), (ii) electron capture on TeCd+1 defect (σ = 2.9 × 10−15 cm−2), (iii) somewhat slower hole capture on TeCd0 defect (σ = 9.4 × 10−20 cm−2), (iv) hole capture on VCd−1 defect (σ = 7 × 10−19 cm2), and (v) electron capture on Tei+1 defect (σ = 4.4 × 10−19 cm−2). The cross-sections are found to be negligibly small for the remaining capture processes.

We performed fully ab initio calculations of carrier mobility in bulk 4H-SiC and at 4H-SiC/SiO2 interface containing some neutral point defects such as silicon and carbon substitutionals, carbon dimers, and oxygen interstitials using Green's functions technique. Obtained values are ∼10–80 cm2/V·s, which is in reasonable agreement with experiment. It is shown that the presence of such defects with concentrations as low as 1%–3% may give significant contribution to mobility degradation. Concentration dependence of mobility comes to saturation at the maximal considered defects concentration of 3%.

While electromagnetic fields induce structural changes in cell membranes, particularly electroporation, much remains to be understood about membrane level temperature gradients. For instance, microwaves induce cell membrane temperature gradients (∇T) and bioeffects with little bulk temperature change. Recent calculations suggest that nanosecond pulsed electric fields (nsPEFs) may also induce such gradients that may additionally impact the electroporation threshold. Here, we analytically and numerically calculate the induced ∇T as a function of pulse duration and pulse repetition rate. We relate ∇T to the thermally induced cell membrane electric field (Em) by assuming the membrane behaves as a thermoelectric such that Em ∼ ∇T. Focusing initially on applying nsPEFs to a uniform membrane, we show that reducing pulse duration and increasing pulse repetition rate (or using higher frequency for alternating current (AC) fields) maximizes the magnitude and duration of ∇T and, concomitantly, Em. The maximum ∇T ini...

A scheme of the scanning rotational microscope is designed. This scheme is based on using carbon nanotubes simultaneously as a probe tip and as a bolt/nut pair which converts translational displacements of two piezo actuators into pure rotation of the probe tip. First-principles calculations of the interaction energy between movable and rotational parts of the microscope confirms the capability for its operation. The scanning rotational microscope with a chemically functionalized nanotube-based tip can be used to study how the interaction between individual molecules or a molecule and a surface depends on their relative orientation., Comment: 4 pages, 3 figures

The effect of the acceleration of carbon nanotube (CNT) growth from methane via modification of the gas composition with plasma discharge is studied by means of kinetic modeling. A model of CNT growth describing the detailed gas-phase and surface kinetics of hydrocarbons in catalytic chemical vapor deposition is used. It is shown that the effect of plasma is related to the formation of active species in the gas phase that can easily adsorb and dissociate on the catalyst surface. It is also demonstrated that in addition to the adsorption of carbon precursors, the CNT growth rate can be limited by the gas-phase diffusion of carbon species to the catalyst surface. The critical energy input above which the dominant contribution to CNT growth is provided by non-radical neutral species is calculated and confirmed by analytic estimates.

The effect of in-plane lattice strain on the atomic and electronic properties of low-index transition metal (M=Ti, Nb, and Ta) carbide surfaces is studied by first-principles molecular dynamics calculations using a pseudopotential plane-wave technique. The most stable cubic rock-salt phase is considered for carbides. The first-principle study of various [(001), (110), and metal-terminated (111)] carbide surfaces reveals that both compressive and tensile strains strongly affect surface relaxation and electronic properties (work function values and band structures). The most stable (001) carbide surfaces exhibit rumpling between transition metal and carbon atoms in the topmost surface layers, which depends on the applied strain. The work function (WF) for the metal-terminated (111) surfaces varies monotonically, rather strongly depending on the applied strain (the range of variation reaches about 1 eV), while the WF for the (001) surface varies nonmonotonically with a much smaller resulting variation over the wide range of the applied strains. Surface energy calculations show that surface stability is also governed by the applied strain.

The key stages of the dry oxidation of the SiC(0001) surface are analyzed based on first-principles calculations. It is found that an abrupt SiC/SiO2 interface model results in a large activation barrier of oxygen penetration to the silicon carbide, and thus the penetration is probably the rate-limiting step for the entire dry-oxidation process. The subsequent reactions of SiC oxidation after oxygen penetration are investigated, and it is found that CO release is competing with carbon dimer formation. These dimers probably are responsible for near-interface traps in the silica layer generated during SiC oxidation. The possible passivation reactions of a carbon dimer defect by active species, such as O2, NO, and H2 are investigated. It is found that an oxygen molecule can break a Si–C bond via dissociation in the triplet state and finally can produce two CO molecules from the carbon dimer defect. The NO molecule can easily break a Si–C bond of a carbon dimer defect and form cyano groups –CN, which can fina...

We report on transport measurements on polycrystalline samples of A2MnReO6 (A=Ca, Sr, Ba), CMRO, SMRO, and BMRO, in the Ohmic and non-Ohmic regimes. The resistivity follows, over wide ranges of temperatures, the relation derived for variable range hopping of carriers localized in a parabolic gap, ρ=ρo exp(To/T)1/2. The values of To are unusually high for the Efros Shklovskii Coulomb gap interpretation. The thermopower is large and positive for SMRO and BMRO and even larger and negative for CMRO. The magnitude of the thermopower and its temperature dependence indicate that it may be unrelated to the hopping conductivity. The theoretical relations for hopping in the intermediate electric field regime provide reasonable approximations for the measured nonlinear conductivity of most samples (and for one sample also for the high-field regime). However, localization lengths derived from the non-Ohmic regime are much larger than those estimated from To. Clues to settle these inconsistencies are suggested.

We report high-field conductivity measurements of polycrystalline samples of La1.67Sr0.33NiO4 and Nd1.67Sr0.33NiO4 at various temperatures in the stripe ordered state. Since their discovery, an important issue has been the response of the stripes to high electric fields. The main result of this work is that while the pulsed I−V characteristics, using single short current pulses, are ohmic for Nd1.67Sr0.33NiO4 up to fields of ∼550 V/cm and ohmic or only slightly non-ohmic for La1.67Sr0.33NiO4 in fields of the same order of magnitude, the corresponding dc I−V characteristics are strongly nonlinear. The conditions for four-probe pulsed I−V measurements that avoid self-heating were determined experimentally. The low-field resistivity and the thermopower of our samples are in satisfactory agreement with those reported in the literature for polycrystals and for single crystals of these materials.

We report measurements of conductivity under high electric fields of polycrystalline Sr2IrO4 at various temperatures, motivated by an earlier report on negative differential resistivity of a single crystal of this material. While our dc I‐V characteristics are strongly nonlinear, the pulsed characteristics show almost negligible nonlinearity up to fields of ∼500V∕cm. We report also on low-field electronic transport measurements (resistivity and thermopower) as function of temperature, which are in qualitative agreement with recently published results.

Using first-principles calculations we investigated the oxidationproperties of model Pt ∕ HfO 2 interfaces as a function of oxygen partial pressure. A wide range of interfacial oxygen concentrations were explored, varying from an oxygen-free interface to the case of 1 oxygen ML separating the Pt ( 111 ) slab from the first Hf plane in the monoclinic HfO 2 ( 001 ) slab. In all cases the interfaces were optimized using ab initio molecular dynamics. It was found that 1 ML of oxygen at the Pt ∕ HfO 2 interface is only possible for chemical potentials equivalent to an oxygen pressure of tens of bars. With respect to silicon oxidation only the oxygen-free interface is stable. Depending on the anneal conditions, intermediate concentrations of ~ 0.25 or ∼ 0.75 ML of oxygen at the interface are possible, while the concentration of 0.5 ML is only stable over a narrow range of conditions. The band offset and work of separation were calculated for Pt ∕ HfO 2 interfaces as a function of the oxygen concentration at the interface. The valence band offset drops sharply with increasing oxygen chemical potential, from ∼ 3.0 to ∼ 1.0 eV . The same trend is observed for the work of separation, which decreases from ∼ 6 J ∕ m 2 for an oxygen-free interface to ∼ 1 J ∕ m 2 for one oxygen monolayer. These findings may shed new light into recent experimental data reporting exceedingly small values for the effective work function of Pt on HfO 2 and its dependence on the oxygen partial pressure during high temperature annealing.

Using first-principles calculations, we compared the segregation trends at the surface of metal alloys with those at an interface with HfO2. The choice of this oxide was motivated by its significance as a potential replacement for SiO2 in advanced transistors. We considered Mo–Re and Mo–Pt alloys as typical examples of disordered and ordered alloys, respectively. The segregation to the surface/interface was analyzed in terms of metal and oxygen adsorption energies. It is shown that chemical bonding at the metal/oxide interface strongly influences segregation both in Mo–Re and Mo–Pt alloys. In particular, bonding with oxygen atoms at the oxide/Mo–Re alloy interface depletes the Re content of the interfacial layer. In the case of Mo–Pt on HfO2 an oxygen-rich interface promotes the formation of one monolayer (but not two monolayers) of Mo separating PtMox from HfO2, while a stoichiometric interface favors an abrupt PtMox∕HfO2 interface. This study also shows that the presence of Mo in the alloy stabilizes Pt...

The thermodynamic and electronic properties of tungsten carbide surfaces and interfaces with monoclinic hafnia (WC∕m-HfO2) are investigated through first-principles calculations. We show that oxidation of the WC surface and of the WC∕m-HfO2 interface is energetically favorable. An oxygen monolayer on the W-terminated WC(0001) surface gives rise to a larger vacuum work function than that for the C-terminated WC(0001) surface, while the opposite result is obtained for the WC(0001) effective work function on hafnia: a carbon intermediate layer results in larger work function than an oxygen intermediate layer. This result is explained by the atomic structure of the intermediate layers neighboring the interface which differ if the interface is O or C rich.

The electronic properties of molybdenum surfaces and interfaces with monoclinic zirconia (Mo∕m-ZrO2) of different stoichiometries are investigated through first-principles calculations. We show that oxygen adsorption on the Mo(110) surface strongly increases the Mo vacuum work function, and that a similar trend is observed for the Mo(110) work function on zirconia upon oxygenation of the stoichiometric Mo∕m-ZrO2 interface, albeit to a smaller extent. As expected, Mo∕m-ZrO2 interface reduction/oxidation decreases/increases the Mo effective work function. However, interface overoxidation leading to the formation of a thin MoOx layer between Mo and m-ZrO2 (Mo∕MoOx∕m-ZrO2) causes a work-function decrease with respect to the stoichiometric Mo∕m-ZrO2 interface value. This result is especially surprising because calculations indicate that subsurface oxidation of Mo slabs increases the Mo vacuum work function. Moreover, the calculated vacuum work function of rutile MoO2(110) slab is ∼6.0eV, considerably larger th...

The atomic structure, stability and electronic properties of zirconium and hafnium nitrides and oxynitrides (MN, M3N4, and M2N2O; M=Zr, Hf) have been studied using first-principles density functional theory calculations. It is found that the orthorhombic Pnam structure of M3N4, which was observed experimentally for zirconium nitride, is more stable for this stoichiometry than the cubic spinel and rock-salt-type structures. The calculated band structures and electronic densities of states demonstrate that both the MN and M3N4 phases of zirconium and hafnium nitrides in the rock-salt-type structure are characterized by metallic properties, while the orthorhombic structure of the M3N4 phase exhibits an insulating behavior in agreement with experimental observations. The formation of nitrogen vacancies in the insulating M3N4 phase converts it into the metallic MN phase. Calculations of Zr2N2O and Hf2N2O in the cubic Bixbyite-type and hexagonal P3–ml crystal structures predict that these materials are insulato...