The low-magnetic-field feature in the magnetic field dependence of the luminescence of negatively charged nitrogen-vacancy (NV−) centers in diamond has been experimentally observed for the first ...time. This feature, centered at the zero magnetic field-henceforth the zero field line-and observed with a magnetic field sweep of NV− center luminescence (magnetic spectrum), is quite narrow. The properties of this line are considerably different from those of other narrow NV− magnetic spectrum lines. Its amplitude is weakly dependent on the orientation of the single-crystal sample with respect to the external magnetic field. This line is also observed in a powdered sample. The shape of the line changes drastically with a change in the polarization of excitation light. The amplitude of the line non-linearly depends on excitation light intensity. For low intensities this dependence is close to the square law. We attribute the occurrence of this line to the dipole-dipole interaction between different NV− centers.
The effect of X-ray (0.07 nm) and ultraviolet radiation (207 nm) on the electrodeposition rate, structure, and properties of composite coatings based on nickel with gold nanoparticles is studied. It ...is found that exposure of the electrolyte to X-ray and ultraviolet radiation during the electrodeposition of Ni/Au composite coatings leads to an increase in the weight gain per unit area and contributes to the formation of continuous compact coatings. An increase in the electrocrystallization rate upon exposure to radiation is attributed to the occurrence of radiation-induced chemical reactions in the irradiated aqueous electrolytes, which intensify diffusion processes and the reduction rate of the metal at the cathode. It is shown that the deposition rate of a substance on the cathode depends on the wavelength of the radiation acting during deposition, the energy effect of which determines the degree of radiolysis of aqueous solutions and the respective intensity of radiation-induced chemical reactions, which in turn are responsible for the structure and properties of composite coatings. Analysis of the surface morphology and elemental and phase composition of Ni/Au composite coatings shows that the action of X-ray and ultraviolet radiation during coating deposition contributes to the incorporation of gold nanoparticles into the nickel matrix and the formation of Ni/Au composite coatings with modified properties. It is found that the microhardness and adhesion of Ni/Au coatings irradiated during deposition are higher than the respective parameters of the nonirradiated samples. The dependences of the microhardness of Ni/Au composite coatings formed under X-ray and ultraviolet radiation on the deposition current density are determined.
Ti–Zr–N coatings were formed by the method of vacuum arc deposition using combined Ti and Zr plasma flows in a N
2 atmosphere at different ratios of arc currents of Ti and Zr cathodes. After ...deposition, obtained samples were annealed in vacuum at the temperature of 850 °C. The element and phase composition, residual stresses and nanohardness were studied by Auger-Electron Spectroscopy, X-ray diffraction (XRD) and nanoindentation, respectively.
XRD analysis reveals the formation of ternary Ti–Zr–N nitride coatings with the structure of solid solutions. It is shown that Ti–Zr–N coatings possess high hardness in comparison with TiN and ZrN binary nitrides. An increase in hardness is observed with increasing Zr content. However, it is established that after annealing coatings keep better stability of hardness with decrease of Zr content. The intrinsic stress in the as-deposited coatings is found to be largely compressive (−
4 GPa) and almost independent of Zr content, but much higher than in ZrN and TiN binary nitrides (−
2 GPa). After annealing, a significant stress relaxation is observed in all coatings due to relief of growth-induced point defects. Stress analysis on as-grown and annealed samples enabled us to determine the stress-free lattice parameter
a
0. This latter is expanded by ∼
0.4–0.7% as compared to Vegard's law.
The thermal stability of Ti–Zr–N coatings will be discussed in terms of evolution and interdependence between structure, composition and hardness after annealing.
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•Magnetic-field dependent photoluminescence of NV− centers in diamonds is modelled.•A calculation method is proposed to account for coherent polarization transfer.•The method ...reproduces sharp dips from avoided crossings in the field dependence.•Groups of such dips, LAC lines, can be modelled theoretically.
We propose an efficient method for calculating level anti-crossing spectra (LAC spectra) of interacting paramagnetic defect centers in crystals. By LAC spectra we mean the magnetic field dependence of the photoluminescence intensity of paramagnetic color centers: such field dependences often exhibit sharp features, such as peaks or dips, originating from LACs in the spin system. Our approach takes into account the electronic Zeeman interaction with the external magnetic field, dipole-dipole interaction of paramagnetic centers, hyperfine coupling of paramagnetic defects to magnetic nuclei and zero-field splitting. By using this method, not only can we obtain the positions of lines in LAC spectra, but also reproduce their shapes as well as the relative amplitudes of different lines. As a striking example, we present a calculation of LAC spectra in diamond crystals containing negatively charged NV centers.
The influence of x-ray radiation on the protective properties of ZnNi/SiO
2
composite coatings has been investigated experimentally, and the optimal regimes of their electrodeposition on irradiation ...by the method of complete factor experiment have been revealed. It is shown that the action of x-ray radiation on the electrolytes used for electrodeposition of ZnNi/SiO
2
leads to an increase in their dispersive power, which makes it possible to form composite coatings with the metal uniformly distributed over the surface and, correspondingly, with elevated corrosion resistance. It has been found that the action of x-ray radiation on the process of electric deposition of ZnNi/SiO
2
coatings promotes formation of layers with enhanced anticorrosion properties. Based on experimental data and according to the method of complete factor experiment, the influence of variations in the x-ray radiation exposure dose power and concentration of SiO
2
nanoparticles in the electrolyte on the dispersive power of electrolytes and corrosion resistance of ZnNi/SiO
2
coatings has been considered. Regression equations have been obtained, an analysis of the coefficients of which allowed the conclusion that a maximum increase in the dispersive power and a decrease in the rate of appearance of corrosion products on ZnNi/SiO
2
coatings are achieved on combination of two factors: addition of SiO
2
nanoparticles to the electrolyte and irradiation of the electrolyte by x-ray radiation in the process of coating deposition. The developed statistical model allows one to adequately determine the optimal concentrations of SiO
2
nanoparticles in an electrolyte and the regime of x-ray irradiation for obtaining coatings with enhanced anticorrosive properties.
Ti–Zr–N coatings were grown by the method of condensation from a plasma phase in a vacuum with ion bombardment of sample surfaces while combining Ti and Zr plasma flows in a residual nitrogen ...atmosphere. The coatings were deposited at different arc currents of Ti and Zr cathodes. The elemental and phase composition, preferred orientation and residual stresses were studied by X-ray microanalysis (XMA) and X-ray diffraction (XRD), respectively.
XMA studies show that multicomponent systems of different compositions are obtained, and the control of plasma flows gives the possibility to synthesize ternary nitrides of any composition. XRD analysis reveals the formation of ternary Ti–Zr–N solid-solution nitrides with a (111) preferred orientation. A correlation between the lattice parameter and elemental composition of Ti–Zr–N coatings is observed.
It is found that the stress-free lattice parameter increases with decreasing Ti arc current. The residual stress is compressive and relatively large (∼
6.5 GPa). The relation between the composition and the stress using the model of formation of ternary solid-solution nitrides with combination of plasma flows of Ti and Zr is discussed.
The influence of the nitrogen compression plasma flow impact on the phase and element composition and tribological properties of AISI M2 and AISI T1 high-speed steels was investigated in this work. ...The bank capacitor initial voltage, the number of pulses and nitrogen pressure in the vacuum chamber varied during experiments, providing the change of energy deposited in the surface layer within the limits of 5–13 J/cm
2 per pulse. X-ray diffraction analysis, Auger electron spectroscopy, Rutherford backscattering analysis, scanning electron microscopy, optical microscopy, friction coefficient and microhardness measurements were used for the characterization of the treated samples. It was found that the treatment of both types of steel resulted in austenite formation in the surface layer and carbide partial dissolution. The growth of energy deposited in the surface layer leads to the increase of thickness of the affected by treatment layer up to 24 μm and to the decrease of MC and M
6C carbides volume fraction in the analyzed layer. Treatment leads to nitrogen penetration into the steel up to the depth of 400 nm and the redistribution of the alloying elements in the surface layer. The decrease of hardness due to dissolution of carbides was observed almost in all range of treatment parameters, thus making unsuitable the usage of the compression plasma flow treatment for high-speed steels tribological properties improvement as a stand-alone technique.
This paper reports on the investigation of Ti–Cr–N gradient coatings deposited by cathodic arc vapor deposition. The Ti–Cr–N coatings were formed by the method of condensation from a plasma phase in ...a vacuum with ion bombardment of sample surfaces with combined Ti and Cr plasma flows in a residual nitrogen atmosphere. Auger Electron Spectroscopy (AES) investigations showed that the deposited coatings exhibited compositional gradient: a Cr-rich transition layer was formed during pretreatment of the substrate with Cr ions and a main Ti–Cr–N layer of varying Ti and Cr composition along the coating thickness was obtained by changing the arc current of Ti and Cr cathodes during deposition. Transmission Electron Microscopy (TEM) observations showed that TixCr1−xN solid solutions, with 0.60<x<0.84 and 0.25<x<0.67 were formed, depending on the relative cathode current change. The grains size of coating was ∼ 10 nm.
The biaxial stress, determined from X-ray Diffraction using the sin2ψ method, was compressive and varied from −2.2 to −2.7 GPa for gradient coatings grown on silicon and from −4.1 to −4.3 GPa for the samples grown on carbon steel substrates. Gradient coatings exhibited reduced internal stresses in comparison with coatings of constant composition (−3.9 and −5.6 GPa, for samples grown on Si and steel substrate, respectively). It is established that the mechanical properties (hardness and the modulus of elasticity) of gradient coatings are the superposition of the solid solutions TixCr1−xN of different concentration (0.60<x<0.84 and 0.25<x<0.67).
Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films have been deposited on silicon substrates by a hybrid technique combining microwave plasma-enhanced chemical vapor ...deposition and sputter-deposition processes from argon–methane and argon–acetylene mixtures of various compositions. The size of crystallites, ratio between sp
2 and sp
3 types of carbon bonds, hardness, friction coefficient, and wear resistance of composite films were investigated as functions of the carbon content in the films expressed by the atom number ratio C/(C
+
Cu). The size of crystallites decreased down to 2 nm in films having high carbon contents (60%, C/(C
+
Cu)). Composite films formed from Ar–C
2H
2 mixtures with a carbon content of 78% (C/(C
+
Cu)) exhibited relatively high hardness (6.1 GPa) and very high elastic recovery upon unloading (90%). However, the wear resistance of hard Cu/a-C:H films was very low ((5.7
±
0.6)
×
10
−6 mm
3/Nm). During the friction tests, a very low resistance to crack formation and cross-sectional propagation was observed. Cu/a-C:H films formed from Ar–CH
4 mixtures and containing 75% of carbon (C/(C
+
Cu)) possessed low friction coefficients (0.02–0.04) and volume wear coefficients ((0.11
±
0.02)
×
10
−6 mm
3/Nm). The intensity Raman peak ratio
I
D/
I
G (0.71) proved to be much lower for the films having a low value of volume wear coefficient. This is the result of the presence of nanosized carbon clusters in the polymer-like matrix and copper crystallites that provides very low shear stresses during friction tests and forms nanosized wear debris.
The effect of compressive plasma flows of nitrogen on the mechanical properties, phase and element composition of a WC hard alloy (6 wt.% of Co) has been investigated in this work. Compression plasma ...flows were obtained using a quasistationary plasma accelerator. X-ray diffraction analysis, Auger electron spectroscopy, scanning electron microscopy and X-ray microanalysis were used as investigation techniques.
It was found that the whole depth of the modified layer amounted to 15 μm. The phase composition analysis showed that plasma treatment resulted in the transformation of a WC phase into a W2C one. The formation of a graphite phase was also found in the surface layer. The element composition analysis revealed surface segregation of carbon and cobalt. The findings also showed that microhardness of the hard alloy increased 1.7 times after treatment.
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