Polarization photosensitivity of Schottky barriers on monoclinic ZnAs<Subscript>2</Subscript> crystals

Pioneering experiments on creating Cu(In)/p-ZnAs₂ photosensitive Schottky barriers on monoclinic ZnAs₂ single crystals grown by directional crystallization from a near-stoichiometric melt are described. Photosensitivity spectra are taken from the structures in natural and linearly polarized radiations. The structures are found to be sensitive to polarization. From the photoactive absorption spectra of the monoclinic ZnAs₂, it follows that most minimal direct band-to-band transitions in these crystals are allowed in the E ∥ z axis polarization and can be used, specifically, in designing novel devices-polarization—controlled switches of spectral ranges of incident radiation photorecording.     

Polarized optical absorption of MnGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Optical absorption of MnGa₂S₄ single crystals is studied at two light polarizations (E ||C and E⊥ C). The polarization splitting of the absorption edge points to a splitting of the valence band of MnGa₂S₄. A contribution to the crystal-field splitting is made by two factors, namely, by a difference in the pseudopotential of cationic sublattice atoms and by tetragonal compression of the lattice along the C axis. A scheme of optical transitions in MnGa₂S₄ in the Brillouin zone center is suggested, according to which the optical transitions Г₃ + Г₄ → Г₁ occur in the polarization E ⊥ C, and the Г₂ → Г₁ transitions occur in the polarization E || C.     

Polarized spectral properties of Er<Superscript>3+</Superscript> ions in NaGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Polarized spectral properties of Er³⁺:NaGd(WO₄)₂ single crystal are reported. The crystal was grown by the Czochralski method. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios. Fluorescence decay curves of the ⁴ I _13/2, ⁴ I _11/2, and ⁴ S _3/2 multiplets for the Er³⁺ ions were measured. Stimulated emission cross-sections of the ⁴ I _13/2→⁴ I _15/2 transition obtained by the Fuchtbauer–Ladenberg formula and the reciprocity method were compared. Multi-phonon relaxation rates of the crystal were estimated. Green up-conversion fluorescence around 531 and 552 nm was observed, and the possible up-conversion mechanisms were proposed. PACS 78.20.-e; 42.70.Hj     

The synthesis of graphene-TiO<Subscript>2</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> super-thin heterojunctions with enhanced visible-light photocatalytic activities

In this paper, an efficient strategy for the synthesis of graphene nanobelt-titanium dioxide/graphitic carbon nitride (graphene-TiO₂/g-C₃N₄) heterostructure photocatalyst was applied to fabricate a kind of visible-light-driven photocatalyst. The heterostructure shows higher absorption edge towards harvesting more solar energy compared with pure TiO₂ and pure g-C₃N₄ respectively. Furthermore, the as-prepared graphene-TiO₂/g-C₃N₄ heterostructure can show enhanced photocatalytic activity under visible-light irradiation. These outstanding performances of photocatalytic activities for graphene-TiO₂/g-C₃N₄ composites can be attributed to the heterojunction interfaces which can separate the electron-hole pairs and impede the recombination of electrons and holes more efficiently. This study conclusively demonstrates a facile and environmentally friendly new strategy to design highly efficient graphene-TiO₂/g-C₃N₄ heterostructure photocatalytic materials for potential applications under visible-light irradiation.

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Photoelectric parameters of the heterojunctions ITO-CdGeP2

Photosensitive n-n and n-p structures based on CdGeP₂ crystals and layers of indium and tin oxides were prepared by the method of reactive cathodic sputtering. The photoelectric properties of the structures in natural and linearly polarized light were studied, and the temperature dependence of the photosensitivity in the interval 80–400 K was also measured. The polarization parameters of heterojunctions were determined, and the results were analyzed based on a model of the band spectrum and the selection rules for interband transitions in CdGeP₂. It is shown that n-n heterojunctions can be employed as polarimetric photodetectors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 39–44, August, 1988.     

Investigation of heterojunctions in the system SnO2-CdGeP2

Photosensitivity spectra of heterojunctions on the basis of SnO₂ layers and n- and p-type conductivity CdGeP₂ crystals are investigated in natural and linearly polarized radiation in the 160–360 K temperature range. Temperature coefficients of the change in interband energies of A- and B-junctions are determined. The temperature dependence of the photosensitivity of the obtained n-n and n-p-heterojunctions is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 23–27, July, 1989.     

Fabrication and some properties of ZnO/<Emphasis Type="Italic">A</Emphasis><Superscript>III</Superscript>N heterojunctions

n-ZnO/p-A ^IIIN (A ^III = Ga, Al) heterojunctions have been fabricated, which exhibit relatively strong electroluminescence in the blue-violet spectral range under forward bias. It is shown that ZnO layers grown with rf-discharge activation have a less developed surface with a significant decrease in the sizes and number of zinc clusters. The current-voltage characteristics of the heterostructures obtained have rectifying properties with a cutoff voltage corresponding to the ZnO band gap.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

III. Electron-impact dissociative ionization of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

The dynamics of cold atoms in conservative optical lattices obviously depends on the geometry of the lattice. But very similar lattices may lead to deeply different dynamics. In a 2D optical lattice with a square mesh, it is expected that the coupling between the degrees of freedom leads to chaotic motions. However, in some conditions, chaos remains marginal. The aim of this paper is to understand the dynamical mechanisms inhibiting the appearance of chaos in such a case. As the quantum dynamics of a system is defined as a function of its classical dynamics – e.g. quantum chaos is defined as the quantum regime of a system whose classical dynamics is chaotic – we focus here on the dynamical regimes of classical atoms inside a well. We show that when chaos is inhibited, the motions in the two directions of space are frequency locked in most of the phase space, for most of the parameters of the lattice and atoms. This synchronization, not as strict as that of a dissipative system, is nevertheless a mechanism powerful enough to explain that chaos cannot appear in such conditions.     

I. Electron-impact ionization and dissociation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact ionization and dissociation of C₂H₂⁺ and C₂D₂⁺ have been measured for electron energies ranging from the corresponding thresholds up to 2.5 keV. The animated crossed beams experiment has been used. Light as well as heavy fragment ions that are produced from the ionization and the dissociation of the target have been detected for the first time. The maximum of the cross-section for single ionization is found to be (5.56 ± 0.03)× 10^-17 cm² around 140 eV. Cross-sections for dissociation of C₂ H₂⁺ (C₂D₂⁺) to ionic products are seen to decrease for two orders of magnitude, from C₂D⁺ (12.6 ± 0.3) × 10^-17 cm² over CH⁺(9.55 ± 0.06) × 10^-17 cm², C⁺ (6.66 ± 0.05) × 10^-17 cm², C₂⁺ (5.36 ± 0.27) × 10^-17 cm², H⁺ (4.73 ± 0.29) × 10^-17 cm² and CH₂⁺ (4.56 ± 0.27) × 10^-18 cm² to H₂⁺ (5.68 ± 0.49) × 10^-19 cm². Absolute cross-sections and threshold energies have been compared with the scarce data available in the literature.     

Polarization modes in the Ba<Subscript>2</Subscript>Mg<Subscript>2</Subscript>Fe1<Subscript>2</Subscript>O<Subscript>22</Subscript> multiferroic

The spectra of complex permittivity of a Ba₂Mg₂Fe₁₂O₂₂ single crystal belonging to the family of Y-type hexaferrites have been measured over a wide temperature range (10–300 K) with the aim of determining the dynamic parameters of the phonon and magnetic subsystems in the terahertz and infrared frequency ranges (3–4500 cm⁻¹). A factor-group analysis of the vibrational modes has been performed, and the results obtained have been compared with the experimentally observed resonances. The oscillator parameters of all nineteen phonon modes of E _u symmetry, which are allowed by the symmetry of the Ba₂Mg₂Fe₁₂O₂₂ crystal lattice, have been calculated. It has been found that, at temperatures below 195 and 50 K, the spectral response exhibits new absorption lines due to magnetic excitations.     

Polarized Raman scattering in helimagnetic β‐MnO2

A rutile β‐MnO₂ film was grown on MgO substrate using plasma‐assisted molecular beam epitaxy (PAMBE) monitored by reflection high‐energy electron diffraction (RHEED). Polarized Raman spectra at various temperatures were obtained to investigate the influence of the helimagnetic structure on the vibrational modes of β‐MnO₂. A red shift of E_g modes indicates a gradual formation of spin angles between neighboring Mn⁴⁺ ions. The intensities of the E_g and A_1g modes with y‐polarized incidence increase remarkably below the Néel temperature. A new view as vibrational mode projection (VMP) indicates the interactions between the magnetic component of incident light and the helimagnetic structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Stereodynamics of the reactions Ne+H₂⁺/Ne+D₂⁺/Ne+T₂

The vector correlations between products and reagents for the reactions Ne+H + 2 , Ne+D + 2 , and Ne+T + 2 are calculated by means of the quasi-classical trajectory method on a new potential energy surface constructed by Lü et al. [J. Chem. Phys. 2010 132, 014303]. The polarization-dependent differential cross-sections (2π/σ)(dσ 00 /dω t ), (2π/σ)(dσ 20 /dω t ), (2π/σ)(dσ 22+ /dω t ), and (2π/σ)(dσ 21 /dω t ), and the distributions of P (θ r ), P (φ r ), and P (θ r ,φ r ) are calculated. The isotopic effect, which is associated with the difference in mass factor among the three reactions, is revealed.     

Magnetic properties of the tetranitrosyl-iron complex Fe<Subscript>2</Subscript>(SC<Subscript>3</Subscript>H<Subscript>5</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>(NO)<Subscript>4</Subscript>

The magnetic properties of the binuclear nitrosyl-iron complexes Fe₂(SC₃H₅N₂)₂(NO)₄ are investigated. It is demonstrated that several types of particles, such as dimers with a pair of spins 1/2, dimers with a pair of spins 5/2, and paramagnetic particles with spin 3/2, make a contribution to the magnetic properties of the complexes. A decrease in the temperature below 25 K leads to a change in the shape of the EPR spectra corresponding to these dimers, so that Lorentzian lines (homogeneous broadening) transform into Gaussian lines (inhomogeneous broadening). This is accompanied by a stepwise change in the EPR line width and g factors. The change in the line shape indicates that complexes become asymmetric at low temperatures, possibly, due to the decrease in the spin exchange frequency below the frequency of the microwave field of the spectrometer.     

NMR study of the paramagnetic state of low-dimensional magnets LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> and NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript>

A comprehensive NMR study of the magnetic properties of single crystal LiCu₂O₂ (LCO) and NaCu₂O₂ (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for ^63,65Cu, ⁷Li, and ²³Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.     

Blocking of coupling to the 0<Subscript>2</Subscript><Superscript>+</Superscript> excitation in <Superscript>154</Superscript>Gd by the [505]11/2<Superscript>-</Superscript> neutron in <Superscript>155</Superscript>Gd

The concept that the first excited 0⁺ states in N = 90 nuclei are not a b \beta -vibration but a second vacuum formed by the combination of the quadrupole pairing force and the low density of oblate orbitals near the Fermi surface is supported by the blocking of this collective mode in ¹⁵⁴Gd from coupling to the [505]11/2^- single-particle quasi-neutron orbital in ¹⁵⁵Gd . The coupling of this orbital to the 2⁺ g \gamma -vibration in ¹⁵⁴Gd is observed since this coupling is not Pauli-blocked.     

Natural photopleochroism of n-In2O3-n-CdGeP2 heterojunctions

The photosensitivity of isotypical heterojunctions n-In₂O₃n-CdGeP₂ in natural and linearly polarized light at temperatures in the range 160–370 K was studied. It was found that the photosensitivity to natural light exhibits a window effect; a conclusion is drawn regarding the character of the interband A and B transitions in CdGeP₂ and about their temperature dependence. The temperature dependence of the polarization photosensitivity of heterojunctions was studied, and its numerical parameters were determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 27–31, July, 1989.     

Some properties of n-CdS-p-Cu2S film heterojunctions

Some n-CdS-p-Cu₂S film heterojunctions have been obtained which differ from previously studied hetero junctions in the anomalous sign of the rectification and the presence of photo sensitivity only in the fundamental-absorption region of Cu₂S. These features of the characteristic are associated with the effect of the surface states at the boundary on the energy structure of the hetero junction. The results are interpreted on the assumption that the main mechanism involved in the passage of current across the hetero junction is the tunneling of the electrons through the barrier at the boundary into the Cu₂S.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 74–76, June, 1972.     

Optical characteristics of plasma of I*<Subscript>2</Subscript>, Cl*<Subscript>2</Subscript>, Br*<Subscript>2</Subscript> halogen dimer barrier-discharge excilamps

Barrier-discharge excilamps operating in homonuclear chlorine, bromine, and iodine and their mixtures with inert gases have been studied. The spectral and energy characteristics of the barrier-discharge plasma have been obtained. The conditions have been determined at which the band D′ → A′ predominates in the spectra of molecules I*₂ (342 nm), Cl*₂ (257.8 nm), and Br*₂ (291 nm). The efficiencies of I₂, Cl₂, and Br₂ excilamps were found to be 1.6, 2, and 3.8%.