On the structural properties of B–C–N nanotubes

We apply a first-principles method, based on the density functional theory, to calculate the structural stability of B–C–N armchair nanotubes, comparing such results with the ones obtained for zigzag configuration. Analysis of the corresponding strain energies confirm that the stability of BC₂N nanotubes is independent of their chirality and demonstrate that such nanostructures have lower strain than BCN and carbon nanotubes. The results show that the formation energy decreases with the tube diameter and indicate that the most stable nanotubes have the maximum number of B–N and C–C bonds. Therefore, from the experimental point of view, larger diameter BC₂N model-I nanotubes should be more probable to be synthesized.     

Positron annihilation study of ageing precipitation in deformed Fe–Cu–B–N–C

The role of deformation-induced defects and carbon addition on copper precipitation during ageing at 550?°C is investigated in high-purity Fe–Cu–B–N–C alloy samples by positron annihilation spectroscopy. Complementary small-angle neutron scattering (SANS) and hardness tests are utilized to characterize the size distribution of the Cu precipitates formed and their influence on the mechanical properties. Samples with 0 and 8% cold pre-strain are utilized to study the influence of prior tensile deformation on the precipitation kinetics of copper. The time evolution of the coincidence Doppler-broadening spectra indicates that deformation-induced defects enhance the Cu precipitation kinetics, which is confirmed by the SANS results. In the S–W plot, a clear reduction in open volume defects is accompanied by a strong increase of Cu signature during the initial stage of ageing, implying that the open volume defects (mainly dislocations) act as nucleation sites for Cu precipitation. A comparison between the precipitation behaviour of Fe–Cu, Fe–Cu–B–N and Fe–Cu–B–N–C indicates that the addition of carbon does not alter the Cu precipitation mechanism but decelerates the kinetics. Hardness results confirm that carbon counteracts the acceleration of Cu precipitation caused by the addition of B and N.     

Transport properties of H–N2 mixtures

Transport coefficients (shear viscosity, volume viscosity, thermal conductivity, and mass and thermal diffusion coefficients) of H–N₂ mixtures in the dilute-gas limit have been calculated from the intermolecular potential in the temperature range 300–2000K using the classical trajectory method. The intermediate results pertaining to H–N₂ binary interactions are reported, mainly in terms of cross-section ratios. Cross-sections evaluated with the Mason–Monchick approximation yield very good results for this system, the largest deviations, about 2.5%, being observed for the thermal diffusion coefficient. The accuracy here of this approximation can primarily be attributed to a light H atom and a weakly non-spherical potential resulting in a high rotational collision number. Furthermore, we investigate to which H–N₂ cross-sections and their ratios the values of the mixture transport coefficients are most sensitive. Our results indicate that, for some cross-section ratios, reliance on universal correlations at high temperatures, often used in flame codes, can induce sizeable errors in the thermal conductivity coefficient and especially in the thermal diffusion coefficients. We also observed that the volume viscosity is particularly sensitive to the value of the cross-section for internal energy relaxation in H–N₂ collisions.     

Improved O2 sensing performance by modifying P–P ligand in [Cu(N–N)(P–P)] complex

In this paper, a diamine ligand of 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine (OP) and its corresponding Cu(I) complex of [Cu(OP)(POP)]BF₄ with bis(2-(diphenylphosphanyl)phenyl) ether (POP) as the phosphorous ligand are synthesized. Full characterization on [Cu(OP)(POP)]BF₄, including NMR, elemental analysis and single crystal analysis, confirms its molecular identity. Upon photon excitation, the emission of [Cu(OP)(POP)]BF₄ owns a long excited state lifetime of 42.92 μs and shows a maximum at 570 nm, under pure N₂ atmosphere. Theoretical calculation on [Cu(OP)(POP)]BF₄ single crystal suggests that the excited state has a triplet metal-to-ligand-charge-transfer character. By embedding [Cu(OP)(POP)]BF₄ into a optical silica supporting matrix of MCM-41, the emission signal is found to be sensitive towards various oxygen concentrations, with a maximum sensitivity of 7.31 (sensitivity=luminescence intensity in O₂ medium/luminescence intensity in N₂ medium). This improved sensitivity value compared with literature values is attributed to the introduction of POP ligand, which can suppress the intermolecular aggravation between [Cu(OP)(POP)]BF₄ molecules and favor the oxygen attack on [Cu(OP)(POP)]BF₄ excited state. Due to the same reason, a short response time is also observed with stable quenching signal.     

Generalized symmetries of an N=1 supersymmetric Boiti–Leon–Manna–Pempinelli system

The formal series symmetry approach(FSSA), a quite powerful and straightforward method to establish infinitely many generalized symmetries of classical integrable systems, has been successfully extended in the supersymmetric framework to explore series of infinitely many generalized symmetries for supersymmetric systems. Taking the N= 1 supersymmetric Boiti–Leon–Manna–Pempinelli system as a concrete example, it is shown that the application of the extended FSSA to this supersymmetric system leads to a set of infinitely many generalized symmetries with an arbitrary function f(t). Some interesting special cases of symmetry algebras are presented, including a limit case f(t) = 1 related to the commutativity of higher order generalized symmetries.     

Modification of the Structure of Ti–Al–Si–Cu–N Gradient Coatings by Mechanical Tests

Technical Physics - The structural state in the zones of indentation and scratch testing of Ti–Al–Si–Cu–N gradient coatings has been studied using dark-field electron...     

Investigating Thin Ti–O–N Films Deposited via Reactive Magnetron Sputtering

Infrared spectroscopy and atomic emission analysis help establish the corrosion resistance of Ti?O–N films deposited on steel substrates via reactive magnetron sputtering, along with potential biological activity by detecting nitric oxide in model solutions after contact with Ti–O–N coatings. Differential thermal analysis and scanning electron microscopy allow the thermal stability of the films to be judged at temperatures of up to 1300°C.     

Structure of Ti N (N = 6–15) titanium cluster isomers

The atomic structures of various isomers of free Ti _N (N = 6–15) titanium clusters have been studied by molecular dynamics using the many-body interaction potential in the tight binding model. The following parameters of the cluster structure have been calculated: average bond length and energy, coordination number, and frequencies (probabilities) of their appearance. An increase in the cluster size N is accompanied by increased values of these parameters. It is established that the frequency of appearance of an isomer with a given N value increases with the bond energy. The most probable structures of clusters with N = 10–15 correspond to maximum values of the atomic structure parameters among all isomers of a given size.     

Effect of helium ion irradiation on the structure and electrical resistivity of nanocrystalline Cr–N and V–N coatings

The structural stability and electrical resistivity of nanocrystalline Cr–N and V–N coatings prepared by ion beam-assisted deposition were studied. The results showed that under helium ion irradiation up to doses of 1.0^.10¹⁷ ion/cm² the fine-crystalline objects successively increase their resistance without apparent structural changes. The subsequent dose increase leads to gas-vacancy void formation and chromium nitride structure destruction. The presence of the initial closed porosity in vanadium nitride favors its structural stability at investigated maximum damage doses.     

Academician A.N. Sissakian 14.10.1944–01.05.2010

Chronicle

Academician A.N. Sissakian 14.10.1944–01.05.2010     

Detailed modeling of planar transcritical H2–O2–N2 flames

We first investigate a detailed high pressure flame model. Our model is based on the thermodynamics of irreversible processes, statistical mechanics, statistical thermodynamics, and the kinetic theory of dense gases. We study thermodynamic properties, chemical production rates, transport fluxes, and establish that entropy production is non-negative. We next investigate the structure of planar transcritical H₂–O₂–N₂ flames and perform a sensitivity analysis with respect to the model. Non-idealities in the equation of state and in the transport fluxes have a dramatic influence on the cold zone of the flame. Non-idealities in the chemical production rates – consistent with thermodynamics and important to insure positivity of entropy production – may also strongly influence flame structures at very high pressures. At sufficiently low temperatures, fresh mixtures of H₂–O₂–N₂ flames are found to be thermodynamically unstable, in agreement with experimental results. We finally study the influence of various parameters associated with the initial reactants on the structure of transcritical planar H₂–O₂–N₂ flames as well as lean and rich extinction limits.     

Phase composition and magnetic structure in nanocrystalline ferromagnetic Fe–N–O films

The chemical and phase compositions and structure of the Fe–N–O films produced by reactive dc magnetron sputtering (in Ar or Ar + N₂ gas mixture atmospheres) under different conditions (energy parameters of magnetron, residual pressure in the magnetron chamber after preliminary pumping, operating pressure in gas mixture) have been investigated by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and vibrating sample magnetometry. Impurity of nitrogen and oxygen, which are present in the sputtered films, participate in the formation of their phase composition and determine its features. Some phenomena inherent in the nanocrystalline films in the metastable state were found. These are the formation of supersaturated bcc interstitial αFe-based solid solution and precipitation of α’ nitrous martensite with bct crystal lattice. The magnetic structure of the Fe–N–O films, which is characterized by the existence of stochastic domains discovered by correlation magnetometry method, is discussed in terms of the random anisotropy model. It was found that two modes of the magnetic anisotropy field of stochastic domains are formed, which determine the existence of two modes of the coercive field found in the magnetic hysteresis loops.     

Damping and ferromagnetic resonance linewidth broadening in nanocrystalline soft ferromagnetic Fe–Co–Hf–N films

In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe₃₆Co₄₄Hf₉N₁₁ films were deposited by reactive r.f. magnetron sputtering on oxidised 5×5 mm²×380 μm (1 0 0)-silicon substrates with a 6-in. Fe₃₈Co₄₇Hf₁₅ target, as well as magnetic field annealing between 300 and 600 °C. An in-plane uniaxial anisotropy of around 4.5 mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4 T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4 GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 °C to more than 10 nm at 600 °C where the FWHM Δf_eff and the Landau–Lifschitz–Gilbert equation damping parameter α_eff increases with d_nm² and d_nm (e.g. d_nm is the grain diameter of the nonmagnetic Hf–N phase), respectively.     

The high frequency magnetic properties of self assembled Fe–Co–Si–N nanogranular thin films

The effect of a variation in Si and N concentration on the microstructure, crystal structure and high-frequency magnetic properties of Fe–Co–Si–N nanogranular thin films was investigated. The films, prepared by rf magnetron sputtering, consisted of nanosized grains of FeCo as well as a Si and N rich intergranular amorphous phase. The Si concentration had a significant effect on the crystal structure of the FeCo phase. The resistivities of the Fe–Co–Si–N films were significantly enhanced by an increase in Si concentration. The resonant frequency of the Fe–Co–Si–N films could be tuned from 0.45 GHz to 2.1 GHz by controlling Si concentration. The N concentration greatly influenced magnetic properties and the variation in resonant frequency is in agreement with Kittel’s equation.     

Influence of the Si–O–C interplayer on the flexural behaviors of C/Si–C–N composites

Carbon fiber reinforced Si–C–N matrix composite(C/Si–C–N) with a Si–O–C interlayer (C/Si–O–C/Si–C–N) was fabricated via CVI and PIP process. The flexural behaviors of C/Si–O–C/Si–C–N were investigated using the three-point-bending method and the SEM technique. The results indicated that the flexural strengh of the C/Si–O–C/Si–C–N increases with increasing temperature and the modulus of the composite is essentially unchanged. The strength of C/Si–O–C/Si–C–N is comparable to that of C/PyC/Si–C–N, and the role of Si–O–C interlayer in C/Si–C–N can rival that of the PyC interlayer. The weaker interfacial bonding and the larger thickness of Si–O–C interlayer make a contribution to this at RT while the thinner interlayer and unstable structure of Si–O–C interphase do it above 1300 °C.     

Deposition of ultrahard Ti–Si–N coatings by pulsed high-current reactive magnetron sputtering

We report on the results of investigation of properties of ultrahard Ti–Si–N coatings deposited by pulsed high-current magnetron reactive sputtering (discharge pulse voltage is 300–900 V, discharge pulse current is up to 200 A, pulse duration is 10–100 μs, and pulse repetition rate is 20–2000 Hz). It is shown that for a short sputtering pulse (25 μs) and a high discharge current (160 A), the films exhibit high hardness (66 GPa), wear resistance, better adhesion, and a lower sliding friction coefficient. The reason is an enhancement of ion bombardment of the growing coating due to higher plasma density in the substrate region (10¹³ cm^–3) and a manifold increase in the degree of ionization of the plasma with increasing peak discharge current (mainly due to the material being sputtered).     

Studies on differential cross-sections of e–N2 scattering

The differential cross-sections (DCS) of the low-energy electron–N ₂ scattering are studied using the vibrational close-coupling (VCC) method and vibrational scattering potentials which include static, exchange and polarization contributions. The polarization is obtained based on the ‘better than adiabatic dipole’ (BTAD) and the ‘distributed spherical Gaussian’ (DSG) respectively. The converged (0 → 0, 0 → 1, 0 → 2, 0 → 3) DCS are obtained with the impact energies being the resonance's first two elastic scattering peaks?–?approximately 1.90 eV and 2.10 eV. Calculations from both polarization potentials agree with experimental results.     

高能质子–核反应中N(1440)激发

在相对论的理论框架下,对高能质子在自旋为零、同位旋为零的原子核上的p+A(S=0,T=0)→p′+A′+π反应进行了理论分析.讨论了在入射质子上的N?(1440)激发机制的特点.以12C靶核为例,计算了在入射能量为2.5GeV的情况下,通过N(1440)激发及衰变产生单π的反应过程,并讨论了核扭曲效应对反应的影响和在我国兰州重离子冷却储存环上开展实验研究的意义和可能性.