One-phonon Raman spectra of carbon in composite films prepared by modification of amorphous hydrogenated carbon by copper and cobalt

One-phonon visible-range Raman spectra of a-C: H〈Cu〉 and a-C: H〈Co〉 composite films with comparable metal and carbon contents were studied in the frequency region 1200–1700 cm^?1 including the carbon sp²-bond vibrations. Broad bands G and D characteristic of unmodified a-C: H films, as well as some additional features, are observed experimentally in the spectra. By unfolding the spectra into Gaussian components, it was possible to follow the variation of Raman shifts and of contributions of individual components to the spectrum as a function of metal content and thermal annealing. The data obtained, complemented by available information on carbon sp²-coordinated systems, show that incorporation of Cu or Co favors growth and ordering of graphite-like nanoclusters in a-C: H, the effect being substantially stronger in the case of Co. It is shown that the process of metal-stimulated graphitization includes carbon bond breaking with the formation of short chainlike fragments and their linkage with the formation of aromatic-ring nanoclusters. A qualitatively similar sp²-structure rearrangement takes place under thermal annealing. For the Cu and Co concentrations studied, the linear dimensions L _a of graphite-like clusters are estimated to vary from ～0.8 nm in unannealed a-C: H to ～1.0 and ～1.2 nm in annealed a-C: H〈Cu〉 and a-C: H〈Co〉, respectively. The number of aromatic rings in these clusters is approximately estimated to increase from 12 to 16 (for Cu) and 20 (for Co).     

EPR and photoluminescence spectra of smooth CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films from T-10 tokamak: The effect of iron impurity

The electron and spin structure of thick smooth hydrocarbon CD _x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD _x films. A certain similarity of the CD _x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD _x samples, contributing to the conversion of sp ³ → sp ² in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.     

Influence of surface properties on the structure of granular silver films and excitation of localized plasmons

Granular silver films deposited on a thin insulating film of amorphous hydrogenated carbon (a-C:H) and transparent conducting electrode (polycrystalline indium tin oxide (ITO) layer) have been investigated by spectroscopy and microscopy methods. The extinction spectra of silver films on the surface of these materials are found to be significantly different. An annealing of silver films causes a blue shift of the peak of plasmon resonance band in the spectrum of silver nanoparticles: by 16 nm on the a-C:H surface and by 94 nm on the ITO surface. Silver films on the surface of a-C:H films are characterized by a narrower band in the extinction spectrum, which is peaked at 446 nm. The changes observed in the optical density of Ag films are related to the change in size and area of nanoparticles. The results of spectral studies of Ag films are in agreement with the data on the nanostructure obtained by scanning electron microscopy and statistical image processing. The spectra of granular silver films are shown to correlate well with the nanoparticle distribution function over the film area.     

Deposition of silicon–carbon coatings from the plasma of a non-self-sustained arc discharge with a heated cathode

Amorphous hydrogenated carbon doped with silicon oxide (a-C:H:Si:O), which is referred to as silicon–carbon coatings in this work, consists of thin amorphous films, which are used as commercial solid lubricants due to their higher stability under extreme environmental conditions as compared to amorphous hydrogenated carbon. The deposition of silicon–carbon coatings from the plasma of a non-self-sustained arc discharge with a heated cathode is considered. Silicon–carbon coatings are deposited using polyphenul methylsiloxane as a precursor at a flow rate of 0.05 mL/min in an argon atmosphere at a pressure of 0.1 Pa. A high-frequency power supply is used to apply a high-frequency bias voltage to a substrate during deposition. After deposition, the mechanical properties of the coatings are studied. The maximum hardness of the coating is 20 GPa at a minimum friction coefficient of 0.16 and a wear rate of 1.3 × 10^–5 mm³ N^–1 m^–1. Energy dispersive analysis shows that the coatings contain a significant content of carbon and oxygen (about 80 and 15%, respectively) and a low content of silicon (about 5%).     

Effect of Doping on the Properties of Hydrogenated Amorphous Silicon Irradiated with Femtosecond Laser Pulses

A comparative analysis of the effect of femtosecond laser irradiation on the structure and conductivity of undoped and boron-doped hydrogenated amorphous silicon (a-Si: H) is performed. It is demonstrated that the process of nanocrystal formation in the amorphous matrix under femtosecond laser irradiation is initiated at lower laser energy densities in undoped a-Si: H samples. The differences in conductivity between undoped and doped a-Si: H samples vanish almost completely after irradiation with an energy density of 150–160 mJ/cm².     

Properties of nanogranular metal-dielectric composites in strong electric fields and the cluster electronic states

The electrical resistance of granular structures with ferromagnetic and nonferromagnetic metal nanoparticles embedded in concentrations below the percolation threshold was studied in strong electric fields. More specifically, amorphous silicon dioxide containing nanoparticles of a Co₄₁Fe₃₉B₂₀ alloy [(a-SiO₂)_{100? x}(Co₄₁Fe₃₉B₂₀)_x structure] and amorphous hydrogenated carbon with embedded copper nanoparticles, a-C: H(Cu), were investigated. The (a-SiO₂)_100?x(Co₄₁Fe₃₉B₂₀)_x structures revealed changes in the electrical resistance and magnetoresistance after being subjected to a strong electric field. The changes could have reversible or irreversible character and depended on the electrical prehistory of the sample. A strong electric field caused not only a decrease in the electrical resistance but also a decrease in the magnetoresistance, although the magnetization of the sample remained unchanged. The temperature dependences of the current in a-C: H(Cu) films exhibited conductivity peaks under a decrease in temperature in strong electric fields and transitions from the insulating to conducting state; after the field was removed, there occurred reverse transitions and conductivity relaxation, as well as pronounced changes in the dielectric permittivity and an increase in dielectric losses with increasing temperature. A model of cluster electronic states (CESs) is proposed to account for the experimental findings. These states are created by electrons of the metal grains and matrix defects near the Fermi surface. The observed features find explanation in a change in the CES structure. A strong electric field does not bring about d-electron delocalization, and the fraction of d electron wave functions in a CES is small.     

Edge electroluminescence of silicon: An amorphous-silicon-crystalline-silicon heterostructure

Silicon edge electroluminescence (EL) was observed on an amorphous-silicon-crystalline-silicon heterostructure (a-Si: H(n)/c-Si(p)) in the temperature range from 77 to 300 K. The room-temperature EL internal quantum efficiency of the heterostructure under study was found to be about 0.1%. A theoretical analysis of the emissive properties of the a-Si: H(n)/c-Si(p) heterostructure was made in terms of the model of an abrupt planar p-n junction and showed that, for optimal doping, the internal quantum efficiency of the EL may be as high as a few percent at a modulation frequency of about 50 kHz.     

Diamondlike nanocomposite a-C:H:Cr Coatings: Structure,mechanical, and tribological properties

The results from a comprehensive investigation of the structure, phase and chemical composition, microhardness, and nanomechanical and tribological properties of chromium-doped coatings of hydrogenised amorphous carbon a-C:H:Cr are presented. The coatings are deposited via reactive magnetron sputtering in an Ar + C₂H₂ + N₂ gas mixture at various volume concentrations of nitrogen and acetylene. It is found that the carbon in the coatings is formed as disordered mixtures of domains with tetrahedral (sp ³) and hexagonal (sp ²) carbon coordinations. In addition, the doping metal in the coating consists of nanosized inclusions of metallic chromium and its carbide and nitride phases. Additional nitrogen doping resulting in the formation of chromium nitride is shown to improve the micromechanical and tribological properties of the obtained coatings.     

Structure of the 1<Emphasis Type="Italic">d</Emphasis>2<Emphasis Type="Italic">s</Emphasis> Shell from the Data on Single-Nucleon-Transfer Reactions

For the stable silicon isotopes ²⁸Si and ³⁰Si, the energies and occupancies of single-particle states of the 1d2s shell are determined by analyzing the combined data for the nucleon stripping and pickup reactions. From the results of analysis and the available experimental data, the variation of the 1d2s proton-shell structure with increasing neutron number for the silicon isotopes with A = 26–34 is discussed.     

Effect of high doses on the Si <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> x-ray emission spectra of silicon implanted with iron ions under steady-state conditions

The effect of high doses on p-and n-type silicon samples implanted with Fe⁺ ions under steady-state conditions (implantation energy, 100 keV; ion current density, 0.6–0.8 μA/cm²; irradiation dose, 10¹⁴–10¹⁶ ions/cm²) is investigated using Si L _{2, 3} x-ray emission spectroscopy (the 3d3s → 2p electronic transition). An analysis of the Si L x-ray emission spectra of the silicon samples is performed by comparison with the spectra of reference materials and the spectra of silicon samples implanted with Fe⁺ ions in a pulsed mode. The Si L x-ray emission spectra are simulated by the molecular dynamics and full-potential linearized augmented-plane-wave (FLAPW) methods. It is revealed that the effect of high doses under steady-state conditions of Fe⁺ ion implantation into the semiconductor crystal matrix exhibits specific features: the disordering of the structure and partial amorphization of the sample from the surface deep into the bulk are more pronounced than those observed under conditions of pulsed ion implantation, although virtually no recrystallization of the sample at the threshold dose occurs. The most probable origins and mechanisms of the effect of high doses on the samples under investigation are discussed.     

Probing the sign-changeable interaction between dark energy and dark matter with current observations

We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b(a) = b_0 a + b_e(1-a), where at the earlytime the coupling is given by a constant b_e and today the coupling is described by another constant b_0. We explore six specific models with(i) Q = b(a)H_0ρ_0,(ii) Q = b(a)H_0ρ_(de),(iii) Q = b(a)H_0ρ_c,(iv) Q = b(a)Hρ_0,(v) Q = b(a)Hρ_(de), and(vi) Q = b(a)Hρ_c.The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements,and the Hubble constant direct measurement. We find that, for all the models, we have b_0 0 and b_e 0 at around the 1σ level,and b_0 and b_e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.     

Quantifying Correlations via the Wigner-Yanase-Dyson Skew Information

In this paper, based on a discussion about the Wigner-Yanase-Dyson (WYD) skew information, the measure F_a,α(ρ_ab) for correlations in terms of the WYD skew information is introduced and discussed. The following conclusions are obtained. For a classical-quantum state ρ_ab, F_a,α(ρ_ab)=0 if and only if ρ_ab is a product state; F_a,α(ρ_ab) is locally unitary invariant and convex on the set of states with the fixed marginal ρ_a; F_a,α(ρ_ab) decreases under local random unitary operation on H_b; For a quantum-classical state ρ_ab, F_a,α(ρ_ab) decreases under local operation on H_b; Lastly, F_a,α(ρ_ab) is computed for the pure states and the Bell-diagonal states, respectively.     

Single-particle properties of <Emphasis Type="Italic">N</Emphasis> = 12 to <Emphasis Type="Italic">N</Emphasis> = 20 silicon isotopes within the dispersive optical model

Experimental neutron and proton single-particle energies in N = 12 to N = 20 silicon isotopes and data on neutron and proton scattering by nuclei of the isotope ²⁸Si are analyzed on the basis of the dispersive optical model. Good agreement with available experimental data was attained. The occupation probabilities calculated for the single-particle states in question suggest a parallel-type filling of the 1d and 2s _1/2 neutron states in the isotopes ^{26,28,30,32,34}Si. The single-particle spectra being considered are indicative of the closure of the Z = 14 proton subshell in the isotopes ^30,32,34Si and the N = 20 neutron shell.     

Sodium–cesium molybdenum-oxide bronzes

The region of the electrolytic deposition of bialkaline sodium–cesium molybdenum-oxide bronzes is established. A correlation between the nonstoichiometry of bronzes and Mo_nO_3n–x oxides with respect to molybdenum charge density, crystal structure, and type of electrical conduction is found. The importance of the Mo_nO_3n–x homologous series in the formation of the nonstoichiometry of bronzes and their physical properties is shown. The electrophoretic deposition of coatings with binary bronzes for the anticorrosion protection of metals is investigated.     

Röntgenspektroskopische Untersuchung der Struktur des Valenzbandes von Silicium,Siliciumcarbid und Siliciumdioxid

With a photon-counting concave grating spectrograph the SiL _2,3 emission bands of pure Si, SiC and SiO₂ (quartz) were investigated. The observed bands are in good agreement with recent measurements using photon-counting devices but differ markedly from those obtained with photographic registration. The comparison of these SiL _2,3 bands with the corresponding SiKβ bands observed by other authors shows that the intensity distributions are more or less complementary. For Si and SiC the experimental results are compared with recent calculations of the electronic band structure. The agreement between the measuredK andL emission bands of silicon and the calculated density of states curve of silicon is satisfactory.     

On rational functions of first-class complexity

It is proved that, for every rational function of two variables P(x, y) of analytic complexity one, there is either a representation of the form f(a(x) + b(y)) or a representation of the form f(a(x)b(y)), where f(x), a(x), b(x) are nonconstant rational functions of a single variable. Here, if P(x, y) is a polynomial, then f(x), a(x), and b(x) are nonconstant polynomials of a single variable.     

Enhancement of Fluorescence and Raman Scattering in Cyanine-Dye Molecules on the Surface of Silicon-Coated Silver Nanoparticles

A method of formation of a composite structure based on silver nanoparticles and a thin protective silicon film (AgNPs/Si) is developed. Enhancement of the fluorescence and Raman scattering in cyaninedye molecules deposited onto the formed nanostructure is observed. The optical properties and morphology stability of particles that are in contact with cyanine-dye solutions in organic solvents are studied. It is shown that the AgNPs/Si composite structure can be multiply used as an SERS-active surface.     

Berechnung des Magnetisierungs-„Ripple“ in ferromagnetischen dünnen Schichten

By means of straight forward analysis a complete calculation is given of magnetization ripple in polycrystalline ferromagnetic films. Wavelenghts and practical relations for ripple amplitude, length of coherence, and angle fluctuation are derived (which were so far only rather incompletely available from a very rough model of the ripple, given previously by the author). The dependence of ripple wavelength (λ ₀) on average crystallite sizea reaches a plateau at a definite critical valuea=a _g ∶λ ₀≈4a fora<a _g ,λ ₀ independent ofa fora>a _g , as has been found most recently byBaltz andDoyle.     

Bound states of three and four resonantly interacting particles

We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonance bound state of two fermions in a spin-singlet state, with corresponding scattering length a _F . Applying this approach to the calculation of the dimmer-dimer scattering length a _B , we recover exactly the already known result a _B = 0.6 a _F . We use the developed approach to obtain new results in 2D for fermions and bosons. Namely, we calculate bound state energies for three bbb and four bbbb resonantly interacting bosons in 2D. For the case of resonance interaction between fermions and bosons, we exactly calculate bound state energies of the following complexes: two bosons plus one fermion bbf, two bosons plus two fermions bf↑bf↓, and three bosons plus one fermion bbbf.     

Interface bonding of NiCrAlY coating on laser modified H13 tool steel surface

Bonding strength of thermal spray coatings depends on the interfacial adhesion between bond coat and substrate material. In this paper, NiCrAlY (Ni-164/211 Ni22 %Cr10 %Al1.0 %Y) coatings were developed on laser modified H13 tool steel surface using atmospheric plasma spray (APS). Different laser peak power, P _p, and duty cycle, DC, were investigated in order to improve the mechanical properties of H13 tool steel surface. The APS spraying parameters setting for coatings were set constant. The coating microstructure near the interface was analyzed using IM7000 inverted optical microscope. Interface bonding of NiCrAlY was investigated by interfacial indentation test (IIT) method using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers indenter. Diffusion of atoms along NiCrAlY coating, laser modified and substrate layers was investigated by energy-dispersive X-ray spectroscopy (EDXS) using Hitachi Tabletop Microscope TM3030 Plus. Based on IIT method results, average interfacial toughness, K _avg, for reference sample was 2.15 MPa m^1/2 compared to sample L1 range of K _avg from 6.02 to 6.96 MPa m^1/2 and sample L2 range of K _avg from 2.47 to 3.46 MPa m^1/2. Hence, according to K _avg, sample L1 has the highest interface bonding and is being laser modified at lower laser peak power, P _p, and higher duty cycle, DC, prior to coating. The EDXS analysis indicated the presence of Fe in the NiCrAlY coating layer and increased Ni and Cr composition in the laser modified layer. Atomic diffusion occurred in both coating and laser modified layers involved in Fe, Ni and Cr elements. These findings introduce enhancement of coating system by substrate surface modification to allow atomic diffusion.