Инновационные методы в области управления персоналом

Целью статьи является обоснование инновационных методов в области управления персоналом

Overhauser Effect of 67Zn Nuclear Spins in ZnO via Cross Relaxation Induced by the Zero-Point Fluctuations of the Phonon Field

Biological and Soft Matter Physic

Hydrogen a relevant shallow donor in Zinc Oxide

Biological and Soft Matter Physic

Comments on the cross-relaxation effect between adsorbed ³He and PrF₃ nanoparticles

The spin kinetics data of ³He in contact with PrF₃ and LaF₃ nanosized powders are reported. All experiments have been carried out by pulse NMR methods at temperature 1.5 K. The analysis of obtained data testifies in favor of cross-relaxation presence in the nuclear spin–lattice relaxation data, which takes place between ³He and ¹⁴¹Pr nuclei

Size-dependent concentration of N⁰ paramagnetic centres in HPHT nanodiamonds

Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT) technique were studied by high-frequency W- and conventional X-band electron paramagnetic resonance (EPR) spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of structures in the nanodiamond shell

Dynamic nuclear polarization of 67Zn and 1H spins by means of shallow donors in ZnO nanoparticles

Dynamic nuclear polarization DNP effects are observed of 67Zn I=5/2 nuclear spins in ZnO nanoparticles and of 1H I=1/2 spins of the Zn OH 2 capping layer. The almost complete polarization of these nuclear spins is achieved by saturating the electron paramagnetic resonance transition of the shallow interstitial Li donor present in the ZnO nanoparticles. The remarkable aspect is that this DNP is caused by an Overhauser mechanism although the phonons mediating the polarization process do not fit into the nanoparticles. An explanation of this DNP process is presented, and it is shown that this allows for a measurement of the distribution of phonon modes in the nanoparticles. The enhancement of the nuclear polarization also opens the possibility to study semiconductor nanostructures with NMR techniques

Probing Wave Functions of Electrically Active Shallow Level Defects by Means of High-Frequency Pulsed ENDOR in Wide Bandgap Materials: SiC, AlN, ZnO, and AgCl

In the high-frequency ENDOR experiments, the hyperfine (HF) interaction between the unpaired electron of the shallow donor or shallow acceptor and the nuclear spins of the Coulombic center and the surrounding atoms is determined, which is then translated into the spin density of the electronic wave function at the various atomic positions. The results of studying the spatial distribution of wave functions for shallow donors in ZnO, AgCl, AlN, and SiC crystals, ZnO-based nanostructures, and shallow boron acceptors in SiC will be presented. The change of the electronic wave function of a shallow donor in ZnO quantum dots (QDs) when entering the regime of quantum confinement by using the nuclear as probes has been observed. The model, based on the effective mass approximation (EMA), that describes a 1s-like wave function with the Bohr radius of ~ 1.5 nm for distant shells was tested. The EMA does not yield an appropriate description of the electronic wave function when the radius of the QD is reduced below the Bohr radius. The direct reconstruction of the wave function of the intrinsic shallow electronic center (SEC) and self-trapped excitons in AgCl was presented. The SEC was suggested to be an electron that is shallowly trapped by two adjacent silver ions on a single cationic site (split-interstitial position), so-called “latent image” in silver halides. The shallowly trapped electron of the STE is shown to behave like a hydrogen 1s electron, centered on the Ag+ lattice position, with a Bohr radius r0 = 1.51 nm that is in agreement with Bohr radius of SEC (r0 = 1.66 nm). For SEC in AgBr, r0 = 2.48 nm. It was demonstrated that dynamic nuclear polarization of nuclear spins due to hyperfine interactions with ligand nuclei can be achieved in ZnO (and based QDs) and AgCl by saturating the high-frequency EPR transition of a shallow donor at low temperatures corresponding to a high Boltzmann factor. Several types of shallow donors were indicated in AlN crystals: (i) affected by the DX-relaxation and (ii) with normal behavior. The strong HF interaction for light-induced SD in AlN support the assignment to the impurity in anionic sublattice (e.g. oxygen in N position). At the same time, a shallow donor with normal behavior can belong to Si or C in the Al position. The electronic structure of shallow donors and shallow acceptors in silicon carbide was investigated by the ENDOR method. The spin density of the N donor corresponding to the observed ENDOR lines was established to be p like in character and located mainly on the Si atoms for the k site in 4H-SiC, whereas for the three sites in 6H-SiC the spin density is s-like in character and located mainly on the C atoms. An explanation for the difference in the electronic wave function of the N donor in 4H-SiC and 6H-SiC can be found in the large difference in the band structure of the two polytypes and in the position of the minima in the Brillouin Zone. The electronic density for shallow B acceptor substituting Si in the k position is distributed in an ellipsoidal shape with the main symmetry axis making an angle of 70° with the c axis, i.e., along the direction of the B–C with main spin density

EPR of Radiation-Induced Nitrogen Centers in Hydroxyapatite: New Approaches to the Study of Electron-Nuclear Interactions

© 2020, Pleiades Publishing, Ltd. Abstract: Radiation-induced impurity nitrogen centers (NO32-) in nanosized powders of synthetic hydroxyapatite are studied by pulse EPR and pulse double-frequency EPR, which is named the NMR detected by electron–electron double resonance (ELDOR detected NMR, EDNMR) method. The EPR signals caused by the interaction of the electron of (NO32-) with the environmental nuclei (1H, 14N, and 31P) are identified, and the parameters of the hyperfine and quadrupole interactions of the electron with the 14N nuclei are determined. The possibility of using the EDNMR method in the X-band of microwave frequencies (νmw ≈ 9 GHz) at room temperature to obtain a detailed information about peculiarities of electron-nuclear interactions in hydroxyapatite is demonstrated

Spin polarization induced by optical and microwave resonance radiation in a Si Vacancy in SiC: a promising subject for the spectroscopy of single defects

Depending on the temperature, crystal polytype, and crystal position, two opposite schemes have been observed for the optical alignment of the populations of spin sublevels in the ground state of a Si vacancy in SiC upon irradiation with unpolarized light at frequencies of zero-phonon lines. A giant change by a factor of 2¿3 has been found in the luminescence intensity of zero-phonon lines in zero magnetic field upon absorption of microwave radiation with energy equal to the fine-structure splitting of spin sublevels of the vacancy ground state, which opens up possibilities for magnetic resonance detection at a single vacancy