Fine Structure Parameters Research Articles

Influence of the pulsed magnetic field of the amplitude strength on the parameters of the magnetoplastic effect in aged Al–Si–Cu–Fe aluminum alloy

The results of a comprehensive experimental study of the influence of the pulsed magnetic field of the amplitude strength on the properties and characteristics of an Al–Si–Cu–Fe aluminum alloy during aging are presented. Data are presented on the modes of thermomagnetic treatment and the results of measurements of the microhardness, lattice parameter, and fine structure parameters of the alloy aged at a temperature of 175°С for 4 h in a pulsed magnetic field with a strength amplitude of 79.6–557.2 kA/m and in its absence. The main regularities of changes in the structure and properties of the metal alloy during annealing are formulated.

Evidence of ferromagnetic coupling for manganese pairs in a layered van der Waals GaS semiconductor

Using high-frequency electron paramagnetic resonance (EPR), we have observed the ferromagnetic coupling of manganese Mn2+ pairs in a layered van der Waals GaS semiconductor. The EPR spectra of Mn2+ pairs (Mn24+) [replacing covalently bonded Ga24+ pairs oriented along the chain axis (c axis) of two gallium ions and being situated in the center of the layer] were recorded at 94 and 130 GHz. The fine structure parameters for the lower multiplets with spin S = 5 and S = 4 were determined equal to D = −0.040 cm−1 and D ≅ −0.035 cm−1, respectively. Based on the observation of additional EPR lines in the region of intersection of the levels in the magnetic field of the multiplet with S = 5 and S = 4, the energy of the isotropic exchange interaction J was estimated to be ∼−0.5 cm−1. For all transitions, a well-resolved hyperfine structure was observed, due to the interaction with two equivalent 55Mn nuclei, leading to the appearance of 11 lines with a hyperfine interaction constant A = 30(1) × 10−4 cm−1, which is approximately half the hyperfine interaction constant for single Mn2+ ions. In addition, a signal from single manganese ions Mn2+ with spin S = 5/2 and a hyperfine interaction constant A = 60(1) × 10−4 cm−1 was observed, which are characterized by extremely large fine structure splitting of D = −0.15 cm−1. Simultaneously with EPR studies, the crystals were monitored by photoluminescence and micro-Raman scattering measurements using a microscope with confocal optics.

ВЛИЯНИЕ ВЗРЫВНОЙ ОБРАБОТКИ НА ТЕРМОМЕХАНИЧЕСКИЕ СВОЙСТВА И СТРУКТУРУ ВТОРИЧНОГО ФТОРОПЛАСТА-4

In order to develop a technology for processing hard-to-recycle F-4, the thermomechanical properties and crystal structure of secondary fluoroplast-4 (F-4), obtained by explosive pressing of waste in the form of industrial chips, were studied. The heat-deformation properties, phase transition temperature, and fine structure parameters in different compaction zones are determined.

Optical Alignment and Optical Orientation of Excitons in CdSe/CdS Colloidal Nanoplatelets.

Optical alignment and optical orientation of excitons are studied experimentally on an ensemble of core/shell CdSe/CdS colloidal nanoplatelets. Linear and circular polarization of photoluminescence during resonant excitation of excitons is measured at cryogenic temperatures and with magnetic fields applied in the Faraday geometry. The developed theory addresses the optical alignment and optical orientation of excitons in colloidal nanocrystals, taking into account both bright and dark exciton states in the presence of strong electron-hole exchange interaction and the random in-plane orientation of nanoplatelets within the ensemble. Our theoretical analysis of the obtained experimental data allows us to evaluate the exciton fine structure parameters, the g-factors, and the spin lifetimes of the bright and dark excitons. The optical alignment effect enables the identification of the exciton and trion contributions to the emission spectrum, even in the absence of their clear separation in the spectra.

Increasing the Wear Resistance of Structural Alloy Steel 38CrNi3MoV Subjected to Isothermal Hardening and Deep Cryogenic Treatment

In the production of critical parts for various machines and mechanisms, expensive structural steels are used alloyed with chromium, nickel, molybdenum, and vanadium. In practice, the wear resistance of parts, especially under severe operating conditions, may be insufficient due to uneven microstructure and the content of retained austenite. Therefore, increasing the operational stability of various products made of alloy steels is an important task. The purpose of this work is to investigate the effect of isothermal hardening from the intermediate (γ+α)-area and the duration of deep cryogenic treatment on the structure formation and frictional wear resistance of 38CrNi3MoV steel. The isothermal hardening promotes the formation of the required multiphase microstructure of 38CrNi3MoV steel. The influence of the duration of deep cryogenic treatment on the microhardness, amount of retained austenite, fine structure parameters, and friction wear of 38CrNi3MoV steel are established. Complex heat treatment of 38CrNi3MoV steel, according to the proposed mode, makes it possible to achieve a significant decomposition of retained austenite to martensite, which leads to an increase in frictional wear resistance of ~58%.

EPR detection of Cr4+ centers in yttrium orthosilicate Y2SiO5

The EPR spectra of Czochralski grown Y2SiO5:Cr and Y2SiO5:53Cr crystals have been studied. In addition to the previously known spectra of Cr3+, the spectrum of the Cr4+ ion was detected and studied for the first time. The fine structure parameters of tetravalent chromium in Y2SiO5 host were obtained based on the analysis of the angular and frequency-field dependences of the EPR spectra. The conclusion about tetrahedral coordination of Cr4+ ion in this host was made. The concentrations ratio of c(Cr3+)/c(Cr4+) ions in the crystal has been evaluated.

Hyperfine-Resolved Rotational Spectroscopy of Phenyl Radical.

We present an analysis of the hyperfine-resolved rotational spectrum of gas-phase phenyl radical, c-C6H5, between 9 and 35 GHz. The isotropic and anisotropic hyperfine parameters of all five protons and the electronic spin-rotation fine structure parameters are accurately determined from this study, which allow detailed insight into the distribution and interactions of the unpaired electron in this prototypical σ-radical. The implications for laboratory and astronomical investigations of phenyl that are reliant on a precise centimeter-wave catalog are discussed, as are the prospects for detecting and assigning the hyperfine-resolved rotational spectra of other large, weakly polar hydrocarbon chain and ring radicals.

Study of Tricalcium Phosphate Ceramics Doped with Gadolinium Ions with Various EPR Techniques

Tricalcium phosphate (TCP)-based materials, such as β-Ca3(PO4)2 doped with rare earth ions (RE), have shown applications as biomaterials, lighting emitting materials, scintillating materials, in vivo imaging probes, and thermoluminescent dosimeters. Their properties are found to be dependent on the distribution of RE3+ on Ca2+ sites that can be controlled by pulsed electron paramagnetic resonance (EPR) and electron spin echo envelop modulation (ESEEM) experiments. The main spectroscopic parameters (spin Hamiltonian values) of Gd3+ and nitrogen impurity centers are quantitatively determined (g-factor, the fine structure parameters D and E, the hyperfine constants A) as well as dynamic characteristics: spin–lattice T1 and spin–spin T2 relaxation times. Based on the analysis of the EPR datasets, the interatomic distance between Gd3+ and 31P was estimated in the dipole–dipole approximation. Two structurally nonequivalent Gd3+ positions in the β-TCP structure have been identified. The obtained valuable results demonstrate applicability of modern EPR techniques to characterize Gd-TCP systems despite the powder structure of the material and high electron spin S = 7/2 of Gd3+ ions.

Production conditions and fine structure parameters of metallic glasses based on light rare-earth elements

Thermal regimes of formation and parameters of the fine structure of amorphous alloys based on light rare-earth elements (E-La, Ce, Pr) with normal metals (M-Al, Cu, Ag) obtained by rapid cooling of melt layers on the inner surface of a rotating cylindrical heat receiver are studied. It has been shown that the alloys under study belong to materials with an average level of glass-forming ability (GFA), whichsolidify without crystallization in cross sections from 35 to 65 μm during quenching from a liquid state. Based on the correlation between the sizes of coherent scattering regions and the shortest interatomic distances found by X-ray diffraction for E-M amorphous alloys with the corresponding characteristics of metallic glasses of other classes, a conclusion was made about a close analogy of the atomic structure of noncrystalline phases fixed by quenching metallic melts.

A coupled-channel deperturbation treatment of the [formula omitted] complex of the CN radical towards spectroscopic accuracy

A global deperturbation analysis of the experimental rovibronic term values of the X2Σ+, A2Π and B2Σ+ states of the 12C14N isotopomer has been performed. The inverse spectroscopic problem was directly solved in the framework of the reduced 4×4 coupled-channel (RCC) deperturbation model based on potential energy curves (PECs) as well as the spin-orbit and L-uncoupling electronic matrix elements between the X2Σ+, A2Π, and B2Σ+ states. Regular perturbations of the X∼A∼B complex by the remote doublet states manifold were taken into account by introducing of the fine-structure parameters as explicit functions of interatomic distance. The optimized PECs and non-adiabatic coupling functions describe the vast majority (5600–6570) of the empirical term values, attributed to locally and regularly perturbed levels of the complex, with a root-mean-squared deviation of 0.015-0.05 cm−1, depending on a particular set of the experimental term values included in the fitting procedure. The resulting mass-invariant RCC deperturbation parameters can straightforwardly extend a line-list of all CN isotopomers into a wide region of vibrational and rotational quantum numbers.

Spectroscopic characterization of singlet-triplet doorway states of aluminum monofluoride.

Aluminum monofluoride (AlF) possesses highly favorable properties for laser cooling, both via the A1Π and a3Π states. Determining efficient pathways between the singlet and the triplet manifold of electronic states will be advantageous for future experiments at ultralow temperatures. The lowest rotational levels of the A1Π, v = 6 and b3Σ+, v = 5 states of AlF are nearly iso-energetic and interact via spin-orbit coupling. These levels thus have a strongly mixed spin-character and provide a singlet-triplet doorway. We here present a hyperfine resolved spectroscopic study of the A1Π, v = 6//b3Σ+, v = 5 perturbed system in a jet-cooled, pulsed molecular beam. From a fit to the observed energies of the hyperfine levels, the fine and hyperfine structure parameters of the coupled states and their relative energies as well as the spin-orbit interaction parameter are determined. The standard deviation of the fit is about 15MHz. We experimentally determine the radiative lifetimes of selected hyperfine levels by time-delayed ionization, Lamb dip spectroscopy, and accurate measurements of the transition lineshapes. The measured lifetimes range between 2 and 200ns, determined by the degree of singlet-triplet mixing for each level.

Accurate 3D thermal stress analysis of thermal barrier coatings

An accurate and efficient calculation method for the thermoelastic field of thermal barrier coating structures has a great contribution to their accurate design and quality promotion. However, because of the thin coating thickness and large stress gradient in the coatings, it is too hard to guarantee the calculation accuracy especially on the interface by using the traditional commercial software. With this motivation, an accurate method for 3D thermoelastic field of thermal barrier coating structure under arbitrary heat loads is proposed in this paper. The numerical results reveal that the method has good convergence, high accuracy, and high stability. Based on this method, the effects of material parameters and coating thickness on the stress field are investigated to provide a refined guideline for the selection of coating materials. Furthermore, the optimal thickness of coating can be designed accurately by considering the interfacial failure criterion. Numerical results also reveal that the appropriate coating materials and coating thickness can largely reduce coating and interface stress. These studies indicate that the highly precise calculation method is useful for extremely fine structure design, parameter analysis and failure evaluation of the thermal barrier coating structures and enhancing their quality.

Magnetism and temperature dependence of nano-TiO2: Fe EPR spectra

Nanocrystalline TiO2 samples of various compositions (up to 5 at.% Fe) with anatase structure and an average particle size of about 20 nm were synthesized using sol-gel technology. The magnetic properties of nano-TiO2: Fe was studied by electron paramagnetic resonance (EPR) and Faraday balance. The existence of an inhomogeneous magnetic state in TiO2: Fe samples of different compositions were revealed by EPR spectroscopy in a wide temperature range. The analysis of the EPR spectra in the L -, X - and Q-bands allowed us to calculate the quadratic fine structure (D, E) parameters, “axial” and “rhombic” ones, respectively. The value of D turned out to be quite small, which indicates an insignificant anisotropy, which can be ignored describing the magnetic properties of TiO2:Fe. It was shown that the temperature behavior of different separate components of the integral EPR spectra can be qualitatively interpreted in the model of coexistence in the TiO2: Fe system, mainly, dimers with a strong negative exchange interaction and isolated paramagnetic centers. No ferromagnetic state in TiO2: Fe-based samples after etching of aE-prepared state were detected.

Modulation of virulence factors of Staphylococcus aureus by nanostructured surfaces

Investigating and understanding the response of microbes to various surfaces requires a versatile parametrisation of the surface, and multiple assays that captures the complexity of the biofilm structures. Here, Staphylococcus aureus biofilm viability, polysaccharide poly-N-acetylglucosamine, and proteins on the cell surface were analysed with agar plate- and well plate-based biofilm formation assays. Biofilms were grown on a set of nanostructured polymeric surfaces, which were thoroughly characterised for their surface chemistry and topography. Surface hydrophobicity, summit density as well as peak and valley structure were found to influence the microbial viability and exopolysaccharide abundance level in the agar plate assay. In the well plate assay, surface chemical parameters had a lesser influence on the viability, but roughness caused by valley structures increased the viability and decreased the exopolysaccharide expression. Surface proteins relating to pathogenicity were affected by the biofilm formation assay. The abundance profile of these proteins correlated clearly with several roughness parameters, especially fine structure parameters in the agar plate assay and lateral roughness in the well plate assay. These results highlight the necessity of describing the material surfaces with a versatile set of different roughness parameters to completely understand what specific features of a surface drive a certain bacterial response.

On the incorporation of nickel into hexagonal barium titanate: magnetic properties and electron paramagnetic resonance (EPR)

Systematic measurements of the magnetic moment of hexagonal 6H-BaTiO3 + 0.04 BaO + x NiO (0.005 ≤ x ≤ 0.02) ceramics were performed to study the influence of Ni ions on the magnetic properties. By temperature-dependent measurements of the paramagnetic susceptibility at 90 kOe, the Ni2+ ion was identified as the majority defect in air-sintered Ni-doped hexagonal barium titanate. Q-band EPR investigations of a 2.0 mol% Ni-doped single crystal revealed three different Ni centers located at Ti sites: first, Ni3+ ions at Ti sites in intact oxygen octahedra, second, Ni3+ associated with an oxygen vacancy and third, the presence of Ni2+ centers leading to a forbidden transition. The Ni3+—VO associate characterized by a vacancy in the face-sharing oxygen plane of the oxygen octahedra can be ruled out. The crystal field parameters of the Ni2+ defect were estimated by a combined fitting of the paramagnetic susceptibility and the EPR fine structure parameter D to B_{0}^{4} ≈ −17,300 cm−1, left| {B_{0}^{2} } right| ≈ 2500 cm−1 and B_{3}^{4} ≈ 19,000 cm−1.

Field-free, Stark, and Zeeman spectroscopy of the Ã2Π1/2−X̃2Σ+ transition of ytterbium monohydroxide

The 000A2Π1/2−X2Σ+, 110A2Π1/2−X2Σ+, and 101A2Π1/2−X2Σ+ bands of an internally cold molecular beam sample of ytterbium monohydroxide, YbOH, have been recorded at the near natural linewidth limit and analyzed to determine the fine structure parameters. Numerous lines in the 000A2Π1/2−X2Σ+ band associated with the lowest rotational levels were recorded in the presence of a static electric field and analyzed to determine the magnitude of the molecular frame permanent electric dipole moment, |μel|, for the X2Σ+(0,0,0) and A2Π1/2(0,0,0) states of 1.9(2) and 0.43(10) D, respectively. An electrostatic polarizability model is used to predict the μel for the X2Σ+(0,0,0) state. The 000A2Π1/2−X2Σ+ band is recorded in the presence of a weak static magnetic field to observe the electric dipole allowed transitions having ΔJ=−2, which are used to assist in the rotational quantum number assignment and confirm the identity of the excited state. An expression for the A2Π1/2(0,0,0) magnetic g factor is derived and shown to correctly model the observed magnetic tuning. A comparison with YbF is made and implications for the use of YbOH as a venue for symmetry violation measurements are discussed.

Вплив режимів відпуску на параметри тонкої структури, напруження і твердість сталі 25Х2М1Ф

Вплив режимів відпуску на параметри тонкої структури, напруження і твердість сталі 25Х2М1Ф

Paramagnetic Ions in Distorted Perovskite YAlO3 Doped with Europium

In crystals of yttrium orthoaluminate doped with the 151Eu isotope, Eu2+, Cr3+, Gd3+, and Мо3+ paramagnetic centers are detected. The fine structure parameters of the spin Hamiltonian are determined or refined for these centers. The orientation behavior of previously unobserved forbidden transitions is considered for the Cr3+ centers. It is shown that two Mo3+ signals that are detected in magnetic fields directed parallel to the crystallographic axes do not belong to different molybdenum centers, but are two intradoublet transitions of the same center.

Парамагнитные ионы в легированном европием искаженном перовските YAlO-=SUB=-3-=/SUB=-

In yttrium orthoaluminate crystals doped with the 151Eu isotope, the paramagnetic centers Eu2+, Cr3+, Gd3+, and Mo3+ have been detected. The fine structure parameters of the spin Hamiltonian of these centers were determined or refined. The account of the orientational behavior of previously unobserved forbidden transitions has been taken for the Cr3+ centers. It is shown that two Mo3+ signals that are detected in magnetic fields parallel to the crystallographic axes do not belong to different molybdenum centers, but are two intra-doublet transitions of the same center.

Fine-Structure Parameters, Zeeman Splitting and Its Specific Features, and Gyromagnetic Ratios for Configurations 1sng (n = 5–10) of a Helium Atom

The fine-structure parameters are calculated by a semiempirical method for six $$1sng$$ configurations of a helium atom using new refined energy values. After diagonalization of second-rank energy-operator matrices (levels $$^{3}{{G}_{4}}$$ and $$^{1}{{G}_{4}}$$ ), the discrepancies between the calculated and experimental energy values are virtually equal to zero. The main concern was with the study of the Zeeman structure in order to determine the gyromagnetic ratios for all four levels of configurations. This is topical because analogous experimental data are absent for the studied configurations. The gyromagnetic ratios can be calculated only in the linear region. This region has been established for all the considered configurations. The specific features of Zeeman splitting—crossings and anticrossings of magnetic sublevels—were also studied. The data obtained can serve as a guide for further experimental studies.