X-Ray induced enhancement effect in electroluminescent zinc sulphides

Enhancement effect in electroluminescent emission from ZnS∶Cu, Cl and ZnS∶Cu, Mn, Cl luminophors under the concurrent action of sinusoidal electric field and x-radiation has been investigated. Variation of the enhancement ratioR=B _E+R/B_E+B_R whereB _E+R =Light output when both electric field and x-radiation are operative;B _E=Electroluminescent output;B _R=Photoluminescent output with frequency and voltage of the applied A.C. field and with x-ray intensity has been studied. A non-linear behaviour of the enhancement with voltage and x-ray intensity has been found, which is similar to that observed in the case of ultraviolet stimulated electroluminescent emission. R _max in both the species studied, is always found to be less than 4/3 in each case.     

Resonant coherent excitation of 94 MeV/u Ar17+ ions in the $$(2\bar 20)$$ planar channel of a silicon crystal

The charge exchange and characteristic x-radiation of channeled ions under resonant coherent excitation are simultaneously described in terms of the density matrix formalism. The survival fraction of 94 MeV/u Ar¹⁷⁺ ions in the \((2\bar 20)\) planar channel of a silicon crystal is calculated, and the angular distribution of x-ray emission of these ions is analyzed.     

Influence of ligand states on the relationship between orbital moment and magnetocrystalline anisotropy

The spin and orbital moments of Au/Co/Au trilayers grown on a W(110) single crystal substrate have been investigated by means of x-ray magnetic circular dichroism. Our findings suggest that the orbital moment of Co does not obtain a maximum value along the easy axis, in contrast with previous experience. This is attributed to the large spin-orbit interaction within the Au caps. Both second order perturbation theory and first principles calculations show how the magnetocrystalline anisotropy (MCA) is dramatically influenced by this effect, and how this leads to the fact that the orbital moment anisotropy is not proportional to the MCA.     

Spectral analysis of paramagnetic centers induced in human tooth enamel by x-rays and gamma radiation

Based on study of spectral and relaxation characteristics, we have established that paramagnetic centers induced in tooth enamel by x-rays and gamma radiation are identical in nature. We show that for the same exposure dose, the intensity of the electron paramagnetic resonance (EPR) signal induced by x-radiation with effective energy 34 keV is about an order of magnitude higher than the amplitude of the signal induced by gamma radiation. We have identified a three-fold attenuation of the EPR signal along the path of the x-radiation from the buccal to the lingual side of a tooth, which is evidence that the individual had undergone diagnostic x-ray examination of the dentition or skull. We have shown that the x-ray exposure doses reconstructed from the EPR spectra are an order of magnitude higher than the applied doses, while the dose loads due to gamma radiation are equal to the applied doses. The data obtained indicate that for adequate reconstruction of individual absorbed doses from EPR spectra of tooth enamel in the population subjected to the combined effect of x-radiation and accidental external gamma radiation as a result of the disaster at the Chernobyl nuclear power plant, we need to take into account the contribution to the dose load from diagnostic x-rays in examination of the teeth, jaw, or skull.     

Effects of Ⅴ/Ⅲ ratio on species diffusion anisotropy inthe MOCVD growth of non-polar a-plane GaN films

Non-polar a-plane (110) GaN films have been grown on r-plane (102) sapphire substrates by metal organic chemical vapour deposition. The influences of Ⅴ/Ⅲ ratio on the species diffusion anisotropy of a-plane GaN films were investigated by scanning electron microscopy, cathodoluminescence and high-resolution x-ray diffraction measurements. The anisotropy of a-plane GaN films may result from the different migration length of adatoms along two in-plane directions. Ⅴ/Ⅲ ratio has an effect on the growth rates of different facets and crystal quality. The stripe feature morphology was obviously observed in the film with a high V/III ratio because of the slow growth rate along the [100] direction. When the Ⅴ/Ⅲ ratio increased from 1000 to 6000, the in-plane crystal quality anisotropy was decreased due to the weakened predominance in migration length of gallium adatoms.     

Cosmic X-ray astronomy

The results obtained from observations of the celestial x-radiation over the past nine years are reviewed. Emphasis is placed on the study of the discrete sources, particularly those which have been identified with astronomical objects known from optical and radio studies. The isotropic background x-radiation is dealt with briefly, and the theories which account for x-ray production on the astronomical scale are mentioned where applicable. Finally, the observations needed to further advance this exciting subject are discussed.     

Effects of wave propagation anisotropy on the wave focusing by negative refractive sonic crystal flat lenses

<正>In this study,wave propagation anisotropy in a triangular lattice crystal structure and its associated waveform shaping in a crystal structure are investigated theoretically.A directional variation in wave velocity inside a crystal structure is shown to cause bending wave envelcpes.The authors report that a triangular lattice sonic crystal possesses six numbers of a high symmetry direction,which leads to a wave convergence caused by wave velocity anisotropy inside the crystal.However,two of them are utilized mostly in wave focusing by an acoustic flat lens.Based on wave velocity anisotropy,the pseudo ideal imaging effect obtained in the second band of the flat lens is discussed.     

Characterization of ZnS nanoparticles synthesized by co-precipitation method

ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible(UV-Vis)absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect.The photoluminescence spectrum of Zn S nanoparticles shows a blue visible spectrum.     

Electron and phonon effects in superconducting tunnel detectors of x-radiation

Nb/Al/AlO_x/Nb superconducting tunnel junctions were investigated in the role of x-ray detectors. Amplitude spectra of pulses arising upon irradiation of tunnel junctions of different sizes by ⁵⁵Mn x-radiation were recorded at a temperature T=1.4 K. We also analyzed the temporal shape of the pulses. We considered the influence of diffuse motion of nonequilibrium quasiparticles, the inverse tunneling effect, and exchange of 2Δ phonons between electrodes, on the characteristics of the tunnel detectors. It is shown that phonon processes can bring about changes in the amplitude, duration, and polarity of the signal. Fiz. Tverd. Tela (St. Petersburg) 41, 1168–1175 (July 1999)     

Analytical method for studying terahertz vibrations in a stearic acid single crystal

The anisotropy of terahertz absorption was investigated for a B-form single crystal of stearic acid. A polarized terahertz spectrometer was used to obtain absorption spectra over the range of 1–5 THz. Seven vibrational modes were observed; four exhibited significant angular dependence. Additionally, we demonstrated a simple approach for estimating the angle of the dipole moment for each vibrational mode.     

Luminescent properties of LiCl-Cu single crystals

The absorption, photoluminescence, x-ray luminescence, and thermoluminescence spectra, and the photoluminescence excitation spectra of LiCl-Cu single crystals with different activator concentration were investigated at temperatures of 79–450°K. The absorption spectrum at room temperature has two bands with maxima at 237 and 259 nm. The absorption coefficient of the 237 nm band is proportional to the copper concentration in the crystal (C_Cu ≤ 7·10^?4 mole %). The photoluminescence and x-ray luminescence spectrum at room temperature consists of one emission band at 324 nm, which conforms with the Mollwo-Ivey rule in the homologous series RbCl → KCl → NaCl → LiCl. The copper ions create trapping levels for electrons and holes at different depths in the forbidden band of the LiCl crystal. The correlation between the thermoluminescence peaks and the recombination-luminescence excitation bands (infrared stimulation) is investigated.     

Anisotropic x-ray emission from heliumlike Fe24+ ions aligned by resonant coherent excitation with a periodic crystal potential

We have measured deexcitation x rays emitted from the resonant coherently excited 2(1)P(1) state of heliumlike Fe24+ ions of 423 MeV/amu, planar channeling through a Si crystal. Large anisotropy in the angular distribution of deexcitation x-ray emission is observed: the x-ray emission in the direction parallel to the channeling plane is favored by a factor of 2 compared to the perpendicular direction. This anisotropy originates from the direction of the periodic crystal field, which populates specific m states in resonant coherent excitation and aligns the excited states.     

Orbital and bonding anisotropy in a half-filled GaFeO3 magnetoelectric ferrimagnet

We investigated the orbital anisotropy of GaFeO3 using the Fe L2,3-edge x-ray magnetic circular dichroism and the polarization dependent O K-edge x-ray absorption spectroscopy. We found that the system shows a considerably large orbital momentum and anisotropic Fe-O bonding, which are unexpected in a half-filled d5 system such as GaFeO3. The orbital and bonding anisotropies, which turn out to be induced by the lattice distortions with exotic off-centering site movements, contribute the large magnetocrystalline energy and magnetoelasticity. These results provide critical clues on the microscopic understanding of the magnetoelectricity.     

Features of interaction of a narrow light beam with a smectic OCBP. Memory effect

1. A memory effect was observed in a smectic liquid crystal without artificially increasing its absorption in a wide temperature interval — from the nematic-phase temperature (t ≤ 35°C) to room temperature (t ⋍ 21–22°C). 2. We have shown that a narrow light beam produces in the crystal an optical inhomogeneity indicative of transverse anisotropy.     

Formation of x-ray images by the action of an optical image on a diffracting lithium niobate crystal

A possible mechanism for the formation and processing of an x-ray image using a corresponding optical image as a template is considered. The method is based on the thermal influence of light on the x-ray diffraction parameters of an LiNbO₃ crystal. A mechanism for the influence of the gradients of the temperature fields formed in the crystal on the x-ray structural parameters of the crystal is proposed. Information which permits the evaluation of some practical aspects of the application of the observed effect in technology is given. Zh. Tekh. Fiz. 67, 76–79 (September 1997)     

Analysis of the polarization dependence of the N K edge X-ray absorption fine structure in InN

The polarization dependence of the x-ray absorption near-edge structure (XANES) of InN beyond the N K edge is calculated. The XANES calculations are performed for different values of the angle θ between the XY plane of crystalline indium nitride and the incident x-radiation (θ = 15°, 30°, 45°, 60°, 75°, and 90°). It is shown that, in the case of N K XANES for InN, a strong polarization dependence of the specific features of the spectrum is observed. The calculated spectra are compared with previously measured experimental spectra. The partial densities of the electronic states of InN are calculated near the top of the valence band and near the bottom of the conduction band.     

Anisotropy of optical absorption of α-MnS single crystal

The optical absorption spectra of an α-MnS single crystal and their temperature behavior in the range from 86 to 300 K are investigated for the (100) plane in the energy range from 8×10³ to 22×10³ cm^?1 for the first time. Comparison of these spectra with those for the (111) plane reveals an essential absorption anisotropy in unpolarized light. The anisotropy is manifested in a much stronger splitting of the lowest energy band for the (100) plane in comparison with that for the (111) plane. With decreasing temperature, the splitting becomes smaller. Possible mechanisms for the anisotropy revealed are proposed.     

First observation of nonreciprocal X-Ray gyrotropy

We report the first observation of a nonreciprocal x-ray linear dichroism caused by the time-reversal odd, real part zeta of the complex gyrotropy tensor zeta(*) which is dominated by electric dipole-electric quadrupole E1E2 interference terms. A nonreciprocal transverse anisotropy was observed in the low temperature insulating phase of a Cr doped V2O3 Mott crystal when a single antiferromagnetic domain was grown by magnetoelectric annealing along the hexagonal c axis. This new element (edge) specific spectroscopy could nicely complement x-ray magnetic circular dichroism which is silent for antiferromagnetic materials.     

Ray spectra and structure of acoustic beams in crystals

Propagation of acoustic beams in crystals is theoretically investigated. The effect of acoustic anisotropy on the structure of acoustic beams is analyzed based on their ray spectra. Numerical calculations are performed for fast and slow acoustic modes in the XY crystallographic plane of paratellurite single crystal, which is characterized by very strong anisotropy of elastic properties.     

RKKY ferromagnetism with Ising-like spin states in intercalated Fe(1/4)TaS2

We investigated the magnetic nature of Fe(1/4)TaS2 using x-ray absorption spectroscopy, photoemission spectroscopy, and first principles band calculations. The results show a large unquenched orbital magnetic moment (～1.0 μ(B)/Fe) at intercalated Fe sites, resulting in a gigantic magnetic anisotropy (H(A)?60 T). The magnetic coupling is well understood in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, suggesting a novel RKKY ferromagnet with Ising-type spin states. We also found that this indirect exchange coupling between the neighboring Fe spins is ferromagnetic and maximized at the Fe-Fe distance of 2×2 superstructure.