Structure and phase composition of thin a-C:H films modified by Ag and Ti

The structure and phase composition of thin a-C:H and a-C:H〈M〉 films (M = Ag, Ti, or Ag + Ti) have been studied by Raman and X-ray photoelectron spectroscopy. The a-C:H〈M〉 films were prepared by ion-plasma magnetron sputtering of a combined target of graphite and metal in an Ar–CH₄ gas mixture. The Raman spectra of these films indicate that their structure is amorphous. The a-C:H〈Ag + Ti〉 films have a more graphitized structure in comparison with pure a-C:H films and films containing only one metal. It is established that carbon in the a-C:H〈Ag + Ti〉 films is in the sp ², sp ³, and C=O states, which are characteristic of the a-C:H, a-C:H〈Ag〉, and a-C:H〈Ti〉 films. In addition, there are also ether (–C–O–C–) or epoxy (?C?O–) carbon groups in the a-C:H〈Ag + Ti〉 films. It has been revealed that silver atoms in the a-C:H〈Ag〉 and a-C:H〈Ag + Ti〉 films form no chemical bonds with carbon, oxygen, and titanium. Titanium in the a-C:H〈Ti〉 and a-C:H〈Ag + Ti〉 films exists in the form of titanium IV oxide (TiO₂).     

X-ray photoelectron study of the sample structure upon introduction of carbon additives into an iron matrix

It is shown that both sp ² and sp ³ hybridized structures are formed on the surface of the samples modified with fullerene and alloyed; these structures indicate the formation of carbon nanostructures. On the surface of the samples modified by graphite and alloyed, only graphite-like structures are formed.     

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.     

The effect of alloying on the structure and peculiarities of tribological behavior of vacuum-deposited diamond-like coatings

In this work, we report the results of a study of the atomic and crystalline structures, phase and chemical compositions and tribological properties of DLC coatings deposited by plasma-assisted (PA) CVD (a-C:H:Si and a-C:H:Si:Mo) and magnetron reactive sputtering (a-C:H:Cr). The a-C:H:Si:Mo coatings revealed the formation of ultra-dispersed inclusions of either molybdenum carbides or silicides, whereas no such inclusions were found in the a-C:H:Si compound. The a-C:H:Cr coatings that were deposited in an acetylene–nitrogen gas mixture exhibited a nanocomposite structure composed of chromium, its carbide and nitride phases. The tribological tests showed that the DLC coatings with silicon and silicon–molybdenum have a high friction coefficient and a low working performance, while the chromium-containing coatings have high levels of their mechanical and tribological characteristics, making them promising materials for operation under high contact pressures.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

Effect of concurrent electron irradiation on the structure of deposited carbon films

Carbon films 110–180 nm thick are fabricated on nickel substrates by the ion sputtering of graphite with simultaneous electron irradiation and subsequent ion irradiation. Irradiation leads to the formation of bonds in the films in various proportions due to the sp and sp ³ hybridization of orbitals (sp-and sp ³-bonds). Ion irradiation induces, to a greater extent, the formation of sp bonds, while concurrent electron irradiation increases the portion of sp ³ bonds. Electron and ion irradiation increases the film microhardness which reaches a value of 12 GPa. A model of the kinetics of creating carbon allotropes in a deposited film is proposed, which is based on the competition between the formation and breakage of carbon bonds during hybridization of different types. Electron and ion irradiation influence the probabilities of the formation and breakage of carbon bonds in the deposited film. The model provides a qualitative interpretation of the observed content ratios of carbon phases in the deposited film.     

Partial virial theorems for atomic-molecular systems

New virial relations for three-and four-particle atomic-molecular systems are proposed. Using operators of extension or squeezing of interparticle distances, it is shown that, for all pairs of j and k particles in S states of these systems, the following partial virial relations are valid: 〈2T _jk 〉+〈 V _jk 〉=0, where 〈V _jk 〉 is the average Coulomb interaction energy for a pair of particles and 〈T _jk 〉 is a part of the average kinetic energy of the system. There are three and six such relations for three-and four-particle systems, respectively. The conventional virial theorem (〈 2T〉+〈V〉=0) for the average total kinetic and potential energies of the system (〈 T〉 and 〈V〉, respectively) corresponds to the summation of partial virial relations over all pairs of particles. It is shown by an example of variational calculations of the helium atom ⁴He²⁺ e ^? e ^? and the helium muon-electron mesoatom ⁴He²⁺μ^? e ^? that partial virial relations are a highly sensitive indicator of the accuracy of wave functions.     

Study on LiFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript>/C used as cathode materials for lithium-ion batteries with low Sm component

LiFe_1???x Sm _x PO₄/C cathode materials were synthesized though a facile hydrothermal method. Compared with high-temperature solid-phase sintering, the method can allow for the fabrication of low Sm content (2 %), a scarce and expensive rare earth element, while the presence of an optimized carbon coating with large amount of sp²-type carbon sharply increases the material’s electrochemical performance. The high-rate dischargeability at 5 C, as well as the exchange current density, can be increased by 21 and 86 %, respectively, which were attributed to the fine size and the large cell parameter a/c as much. It should be pointed out that the a/c value will be increased for the LiFePO₄ Sm-doped papered by both of the two methods, while the mechanism is different: The value c is increased for the front and the value a is decreased for the latter, respectively.     

Structural features of carbon materials synthesized by different methods

This paper presents the results of investigations of three types of carbon structures synthesized by different methods, such as arc discharge plasma enhanced chemical vapor deposition of carbon in a magnetic field, chemical dehydrohalogenation of the poly(vinyl chloride)/poly(vinylidene chloride) precursor, and pulsed plasma ion assisted deposition. It has been found that the samples prepared by different methods have a common feature, i.e., the presence of three-dimensional clusters based on sp²- or sp³-bonds surrounded by quasi-one-dimensional carbon chains. It has been shown that the structure of carbon materials changes depending on the synthesis conditions.     

Lattice instability induced by 3<Emphasis Type="Italic">d</Emphasis> impurities in II–VI compound semiconductors

Nickel-impurity-induced transverse displacements of ions in a Zn_1?xNi_xSe lattice (x = 0.0025) were detected. This type of displacement correlates with macroscopic distortions of a crystal associated with transverse ultrasonic waves that are propagated along the 〈110〉 direction. The shear instability is assumed to be due to the hybridization of the sp³ bonds with the 3d states of the impurity centers.     

Percolative transition in carbon-ion implanted type II<Emphasis Type="Italic">a</Emphasis> diamond

Experimental data for the conductivity of type IIa diamond specimens implanted at low temperatures with carbon ions, followed by high temperature annealing, have been analyzed using hopping and percolation theories in the vicinity of the insulator-metal transition. Near the transition it appears that conductivity occurs viasp ²-bonded graphitic clusters which are randomly distributed in thesp ³-bonded diamond matrix. A conductivity crossover between the Mott and Efros-Shklovskii VRH laws has been observed on the insulating side of the transition.     

Fluctuations of charged-particle multiplicities over narrow rapidity intervals in <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">A</Emphasis> collisions at 40 GeV/<Emphasis Type="Italic">c</Emphasis>

Maximum fluctuations of charged-particle multiplicities over narrow rapidity intervals are investigated for high-P_⊥ processes in π^?A collisions (where A=H, D, C, Cu, Pb) at 40 GeV/c. The observed fluctuations are studied by the method of factorial moments. The results show that the factorial moments 〈F _i 〉 vary in proportion to a power of the rapidity gap δy. This suggests that there are dynamical fluctuations in the processes under study. The experimental data are compared with theoretical results obtained on the basis of the model of quark-gluon strings by using the FRITIOF-7.02 package.     

Erzeugung und Ausheilung von Gitterstörungen und ihr Einfluß auf die Supraleitung von Indium und Thallium

The Variation of the transition temperature with residual resistance of coldworked In and Tl shows a similar behaviour as in dilute alloy experiments. Subsequent annealing removes lattice defects in distinct steps and restores the properties of pure samples at temperatures below 250 °K. Some of the results can be interpreted in accordance with the model developed byMarkowitz andKadanoff on alloy experiments. Values for the anisotropy parameter 〈a ²〉_In=0.02 and 〈a ²〉_Tl=0.04 were obtained. The interpretation of the “valence” effect and the influence of stress is discussed.     

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.     

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.     

Scaling of semi-inclusive events in <Emphasis Type="Italic">pp</Emphasis> interactions

The normalized single-particle semi-inclusive double-differential spectrum of π^t- mesons from pp interactions at 6.6–400 GeV/c and the relative concentration of π⁰ and K _S ⁰ mesons in such events of fixed multiplicity of π^? mesons are completely determined by specifying any feature of this spectrum—for example, 〈y²〉 _n or 〈E〉 _n . Therefore, a two-parameter sample of semi-inclusive events that depends on the energy and the multiplicity reduces to a one-parameter sample.     

Dependence of the Daily <Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>F2 Values over Mid-Latitude Stations on the Solar and Geomagnetic Activity

The results of studies of the dependence of the daily electron concentration at maximum of the F2 ionospheric layer in January 2008–2015 on the solar and geomagnetic activity are presented. The solar radio emission flux density indices F_10.7 and geomagnetic activity indices A _p were averaged over 27 days, and 〈F_10.7〉₂₇ and 〈A _p 〉₂₇, respectively, were obtained. Based on the data of three stations, 27-day median (with the middle of January 15) daily N _m F2 variations were obtained for 2008–2015. Based on these data, the following paradox was discovered: in January 2014, when the values of the solar activity index F_10.7 were larger than in 2015, the dailyN _m F2 values were smaller. Averaging over four hours of local daytime (10:00–14:00 LT) gave the daily average January 〈N _m F2〉 values for each selected station for each year. To solve this paradox, a double linear regression of 〈N _m F2〉 on 〈F_10.7〉₂₇ and 〈A _p 〉₂₇ was constructed. Due to this, it was concluded that the contribution of geomagnetic activity to daily January 〈N _m F2〉 values is positive. A comparison of the mean square errors of the linear and double linear regressions for 〈F_10.7〉₂₇ and 〈F_10.7〉₈₁ showed that the use of 〈F_10.7〉₂₇ led to smaller errors than the use of 〈F_10.7〉₈₁.     

Non-extensivity of the chemical potential of polymer melts

Following Flory’s ideality hypothesis, the chemical potential of a test chain of length n immersed into a dense solution of chemically identical polymers of length distribution P(N) is extensive in n . We argue that an additional contribution \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) ～ +1/\( \rho\) \( \sqrt{{n}}\) arises (\( \rho\) being the monomer density) for all P(N) if n ? 〈N〉 which can be traced back to the overall incompressibility of the solution leading to a long-range repulsion between monomers. Focusing on Flory-distributed melts, we obtain \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) (1 - 2n/〈N〉)/\( \rho\) \( \sqrt{{n}}\) for n ? 〈N〉² , hence, \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) -1/\( \rho\) \( \sqrt{{n}}\) if n is similar to the typical length of the bath 〈N〉 . Similar results are obtained for monodisperse solutions. Our perturbation calculations are checked numerically by analyzing the annealed length distribution P(N) of linear equilibrium polymers generated by Monte Carlo simulation of the bond fluctuation model. As predicted we find, e.g., the non-exponentiality parameter K _p \( \equiv\) 1 - 〈N ^p〉/p!〈N〉^p to decay as K _p \( \approx\) 1/\( \sqrt{{\langle N \rangle }}\) for all moments p of the distribution.     

Bestimmung der Kernmomente des Ho165 aus der Hyperfeinstruktur des Grundzustandes im Ho I-Spektrum

In an atomic beam magnetic resonance experiment, the hyperfine interaction constantsA andB of the⁴ I _2/15-groundstate of Ho¹⁶⁵ were found to beA=800,58389 (50) MHz,B=?1667,997 (50) MHz. Using an effective value for 〈r ^?3〉, the magnetic moment of the Ho¹⁶⁵ nucleus was calculated to beμ=4·1(4)μ _n . The quadrupolement was determined by use of the 〈r ^?3〉 given byWatson andFreeman. The result isQ=2·4·10^?24 cm².     

Low-temperature plasticity and lattice dynamics of solid parahydrogen with an isotopic impurity

The low-temperature plasticity of solid polycrystalline parahydrogen doped with an isotopic impurity (deuterium) is studied. The dependences of the rate of steady-state creep in p-H₂ on the impurity concentration and stress are obtained. The deformation of p-H₂ is described with inclusion of the zero-point mean-square displacements 〈x²〉 of particles making up a crystal. The calculated and experimental values of 〈x²〉 are compared for two possible isotope molecules (HD and D₂) at three stress levels. A correlation between the 〈x²〉 values and an increase in the force constants of a p-H₂ crystal doped with the isotopic impurity is established. An increase in the mean-square displacements of p-H₂ with the tensile load is discussed. Deformation-induced purification of a p-H₂ crystal from the isotopic impurity is suggested to occur.