Investigation of layers’ properties using brush discharge: Mobility of charge carriers in the layer is zero

This work is mainly based on the paper “R. Rinkunas, S. Kuskevicius, A contactless method of resistance measurement, Tech. Phys., 59 (2009) 133–137”. This paper contains a proposed contact less method for measuring resistivity of various materials, as well as various ambient parameters related to resistivity, e.g., humidity, intensity of illumination, sample thickness, etc. The mentioned paper describes experimental applications of the proposed method for measuring resistances in the range from 10⁷ Ω to 10¹³ Ω.In this work, a model of the method proposed previously is presented. On the basis of that model, it has been determined that during charging of an insulating layer of a material (on whose surface the deposited ions are immobile), the charge flux becomes wider as it approaches the surface of the insulator. For example, the diameter of the charge flow region may increase from 0.2 mm (near the needle tip) up to 2 cm near the surface of the insulator. [Those numbers correspond to the distance h = 1 mm between the needle and the substrate, insulating layer thickness 40 μm and needle–substrate voltage of 4000 V. A change of those parameters would cause a change of the size of the spot on the layer surface].It has been determined experimentally that resistance of the air gap between the needle and the substrate is linearly dependent only on h, whereas the electromotive force, which is responsible for the electric current from the needle to the substrate, also depends only on h.The radial coordinate of the points where the gradient of the electric charge density is largest is equal to h/2 (a zero radial coordinate corresponds to the point that is directly below the needle).During transfer of charge carriers from the needle onto the surface of the insulating layer, the largest potential is obtained at the point corresponding to radial coordinate r = 0, but this potential is still smaller than the electromotive force that causes electric current in the circuit (i.e., the difference between the power supply voltage and the voltage on the capacitor formed by the needle and the substrate, when no charge has been deposited yet).The time dependence of charging current and of the potential difference between the needle and the substrate is not monotonic: at first the current increases, then it begins to decrease, and the potential difference at first decreases, then it begins to increase. The initial parts of those dependences can be explained by the “breakdown” of the capacitor formed by the needle and the substrate, and the subsequent time dependence is determined by the increase of the insulating layer potential due to accumulation of charge on it.     

Defect chemistry and electrical properties of La1−xSrxCoO3−δ IV. Electrical properties

This paper considers electrical properties of La_1−xSr_xCoO_3−δ in terms of defect models, such as random defect model and the cluster model. It is shown that the experimental data of the electrical conductivity may be explained in terms of the random defect model rather than the cluster model.     

Defect chemistry and electrical properties of La1-xSrxCoO3-δ

This paper considers defect chemistry models of La_1−xSr_xCoO_3−δ, such as random defect model and the cluster defect model. These models are considered in terms of defect equilibria with respect to (i) the formation of oxygen vacancies, (ii) intrinsic electronic ionisation and (iii) the formation of defect clusters. The defect models are derived using the available data of nonstoichiometry for the LSC materials.     

Defect and electrical properties of nanocrystalline tungsten trioxide

Nanocrystalline tungsten trioxide particles were prepared by a wet-chemical method. Transmission electron microscope (TEM) analysis shows that the average grain size is about 15nm. The oxygen deficiency of nanometre-sized sample is higher than that of ordinary tungsten trioxide. The electric conductivity increases because of high oxygen deficiency. Ironic relaxation polarization and crystallographic shear (CS) planes theory were used to explain the unusual dielectric characteristic of nanocrystalline tungsten trioxide.     

Synthesis,phase formation,and properties of nanomaterials based on the titanium dioxide−iron(III) oxide binary system

The properties of nanomaterials based on the titanium dioxide?iron(III) oxide binary system prepared by low-temperature coprecipitation from aqueous solutions are studied. The effect of thermal treatment conditions and other factors on the process of phase formation and the properties of the synthesized products is examined. It is demonstrated that these materials have a relatively low photocatalytic activity but a high sorption capacity.     

Structural and electronic properties of monolayer hydrogenated honeycomb III–V sheets from first-principles

Using first-principles calculations, we investigate the structural and electronic properties of monolayer hydrogenated honeycomb III–V sheets. The lattice constants and cohesive energies of the hydrogenated III–V (XY H₂, X=B, Al, Ga, and Y =N, P, As) sheets depend on the III–V elements and follow the same trend as the atomic radii of the elements. We find that the short lattice constants correspond to the large cohesive energies of the hydrogenated III–V sheets. Similar to the graphane sheet, the hydrogenated BP and BAs sheets prefer the chair conformation. While for the hydrogenated BN, AlN, AlP, and GaN sheets, the boat conformation is favored. For the hydrogenated AlAs, GaP, and GaAs sheets, the chair and boat conformations are degenerate structures. We obtain that all the hydrogenated III–V sheets are wide-gap semiconductors. With GW corrections, the band gaps of hydrogenated III–V sheets follow the order of nitrogen > phosphorous > arsenic compounds for both the chair and boat conformations.     

Nanostructure and thermal-optical properties of vanadium dioxide thin films

A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis shows that the films have a columnar nanostructure with an average grain of 8 nm. The resistivities as a function of ambient temperatures tested by four-point probes for as-deposited films present that the transition temperature for nanostructure of vanadium dioxide films is near 35 ℃ which lowers about 33 ℃ in comparison with the transition temperature at 68 ℃ in its microstructure.     

Magnetic and electronic properties of hexairon(III) nanocluster with cyclic structure: a Mössbauer study

A molecular cluster containing a coplanar ring of iron(III) ions with spin 5/2 was investigated by Mössbauer spectroscopy. The iron spins are antiferromagnetically coupled so that the ground state has total spin S=0. Spectra in the absence of an applied magnetic field consisted of a quadrupolar doublet, the linewidth of which monotonically increased with the temperature. A quadrupolar splitting of about 0.35 mm/s was found. Calculations of the ironorbital electronic populations were carried out and the quadrupolar splitting was estimated. Its value was in agreement with the experimental one. In addition, the trend of the linewidth was explained in terms of isotropic spin fluctuations. Spectra in the presence of a 4.5 T longitudinal magnetic field were also collected. The hyperfine field was obtained from their fitting. Differences with respect to the hyperfine field obtained from susceptibility data were also interpreted in terms of spin fluctuations.     

Investigation of structural and electronic properties of β- HgS: Molecular dynamics simulations

The pressure induced phase transition of β-HgS is studied using an ab initio molecular dynamics simulation. The structural phase transformation from the zinc-blende structure to the NaCl-type structure (space group $Fm\overline{3}m$) and from this structure to CsCl-type structure ($Pm\overline{3}m$) with the application of hydrostatic pressure is predicted. Additionally, the electronic properties of HgS and various physical properties such as the lattice constants, the bulk modulus and the pressure derivative of the bulk modulus are revealed. Furthermore, these phase transitions are obtained using the total energy and enthalpy calculations. According to these calculations these transformations are occurring at about 20?GPa and 28?GPa for $F\overline{4}3m$ →$Fm\overline{3}m$ and $Fm\overline{3}m$ →$Pm\overline{3}m$, respectively.     

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.     

Structural and electronic properties of BN M?bius stripes

In the present contribution it is applied first-principles calculations to investigate the electronic structure of boron nitride M?bius stripes, with armchair and zigzag configurations, obtained from boron nitride nanoribbons using a ??cut?? and ??glue?? process. The results show that the structural stability strongly depends on the length and width of the stripe. It is also found that the energy gap and work function depends on the structure chirality. Due to the formation of an antiphase boundary, zigzag stripes present tunable electronic properties, with significant potential for technological applications.     

Vacancy induced changes in the electronic structure of titanium carbide—II. Electron densities and chemical bonding

In a recent paper, we presented the band structure and the state densities for an ordered model structure for TiCn_0.75 and discussed the changes which occur in comparison with stoichiometric TiC. Starting from these results, we investigate in the present paper, on the basis of calculated electron densities, how the bonding situation is influenced by the vacancies on the carbon sublattice in TiC_0.75. The results can be summarized as follows: The presence of empty lattice sites leads to the formation of new types of bonds not present in TiC; i.e., weak bonds between second nearest Ti neighbors across the vacancy sites and stronger Ti-Ti bonds in the Ti octahedra around the vacancies caused by the reduction of the number of C-Ti bonds. An analysis of the electron densities also shows a strengthening of the covalent Ti-Ti bonds involving Ti atoms not immediately adjacent to a vacancy as well as an increase of the ionic character of the C-Ti bonds.     

Structural and electronic properties of small bimetallic Ag–Cu clusters

The structural and electronic properties of small gas-phase Ag_mCu_n clusters with m+n=2–5 atoms are investigated using spin-polarized density functional theory. The LANL2DZ effective core potential and the corresponding basis set are employed while the performance of several exchange-correlation functionals is assessed. For a given cluster size all possible compositions are subject to optimization using a variety of initial structures. The geometry, binding energy, relative stability, ionization potential, electron affinity and HOMO-LUMO gap are reported for the lowest energy structure of every cluster size and composition. The results show that planar structures are favored, triangular for trimers, rhombic for tetramers and trapezoidal for pentamers. Moreover, for tetramers and pentamers we found that silver atoms demonstrate a clear tendency to occupy edge positions. The calculation of electronic properties indicates that although all exchange-correlation functionals predict the same trends, the choice of method is crucial concerning the final quantitative results.     

Ab-initio calculation of electronic structure and optical properties of AB-stacked bilayer α-graphyne

Monolayer α-graphyne is a new two-dimensional carbon allotrope with many special features. In this work the electronic properties of AA- and AB-stacked bilayers of this material and then the optical properties are studied, using first principle plane wave method. The electronic spectrum has two Dirac cones for AA stacked bilayer α-graphyne. For AB-stacked bilayer, the interlayer interaction changes the linear bands into parabolic bands. The optical spectra of the most stable AB-stacked bilayer closely resemble to that of the monolayer, except for small shifts of peak positions and increasing of their intensity. For AB-stacked bilayer, a pronounced peak has been found at low energies under the perpendicular polarization. This peak can be clearly ascribed to the transitions at the Dirac point as a result of the small degeneracy lift in the band structure.     

Electronic structure and optical properties of III–VI crystals

The polarized spectra of the full set of optical functions of GaS, GaSe, InSe, GaTe, InS, and TlSe crystals are determined in a wide range of fundamental-absorption energies. The ?₂ and -Im?^?1 spectra are decomposed into elementary components. The main parameters of the components were determined and the main features of the spectra and transition components are established. The results obtained are explained on the basis of the theoretical band calculations.     

Structural and thermodynamic properties of metallic hydrides used for energy storage☆

Nowadays, energetic needs are mainly covered by fossil energies leading to pollutant emissions mostly responsible for global warming. Among the different possible solutions for the greenhouse effect reduction, hydrogen has been proposed for energy transportation. Indeed, H₂ can be seen as a clean and efficient energy carrier. However, beside the difficulties related to hydrogen production, efficient high capacity storage is still to be developed. Hydrogen can be stored as a compressed gas, in liquefied tanks or absorbed in solids. Many metals and alloys are able to store large amounts of hydrogen. This latter solution is of interest in terms of safety, global yield and long time storage. However, to be suitable for applications, such compounds must present high capacity, good reversibility, fast reactivity and sustainability. In this paper, we will review on the structural and thermodynamic properties of metallic hydrides. Their solid–gas hydrogenation behaviour and the related absorption–desorption isotherm curves are examined as a useful criterion for the selection of suitable materials for applications. The storage performances obtained with these alloys are reported and some solutions to common problems such as corrosion, passivation, decrepitation, poor kinetic and short cycle life are discussed.     

Sc doping of MgB2: the structural and electronic properties of Mg1−xScxB2

We have investigated the effect of electron doping on the superconducting properties of MgB₂. For the purpose we have synthesized several samples along the Mg_1−xSc_xB₂ section. The X-ray diffraction measurements reveal small changes in the lattice parameters suggesting that the Sc doping could be considered to simply fill the boron σ bands. Radio frequency surface resistivity measurements has been used to obtain the variation of T_c with Sc doping. Increasing the Sc content, the experimental T_c diverges from the T_c predicted by the BCS single band theory showing the key role of interchannel pairing near a shape resonance.     

Lattice dynamics and electronic structure of cobalt–titanium spinel Co2TiO4

Physics of the Solid State - The results are presented on phonon excitations and the electronic structure of Co2TiO4 inverse spinel in which magnetically ordered cobalt ions Co2+ (3d 7) are in...