Photoinduced formation of metal nanoparticles in γ-irradiated sodium-fluoride crystals

It is established that sodium nanoparticles with sizes of several hundreds of nanometers, several tens of nanometers, and several nanometers are formed in γ-irradiated photobleached NaF crystals. Along with randomly scattered particles, areas in which nanoparticles with sizes of tens of nanometers are grouped around a particle with a size of hundreds of nanometers are revealed. Mechanisms for color-center aggregation and nanoparticle formation are discussed.     

Photoinduced Polaron-Splitting in Polymer

We simulate a relaxation process of a polaron in polymer after photo excitation, and a new state is realized by means of proper excitation. The original lattice configuration of the polaron splits into two symmetrical peaks, and consequently a double-well potential is formed, where the wavefunctions of electron localized in these two wells are entangled. Thus, this process provides a method to generate the Schroedinger cat state. According to the dynamical process of the lattice configuration, the relaxation time of splitting is about 150fs.     

Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline γ-glycine

We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline γ-glycine. Analysis of magic-angle spinning (MAS) and stationary ¹⁷O NMR spectra of [¹⁷O]-γ-glycine obtained at 9.4, 14.1, 16.4, and 18.8 T yields the magnitudes of the ¹⁷O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that ¹⁷O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary ¹⁷O NMR spectra.     

BFKL resummation effects in γ*γ* → ρρ

We calculate the leading order BFKL amplitude for the exclusive diffractive process in the forward direction, which can be studied in future high energy e ⁺ e ^- linear colliders. The resummation effects are very large compared to the fixed-order calculation. We also estimate the next-to-leading logarithmic corrections to the amplitude by using a specific resummation of higher order effects and find a substantial growth with energy, but smaller than in the leading logarithmic approximation. CPHT Unité mixte 8627 du CNRS LPT Unité mixte 8627 du CNRS An erratum to this article is available at .     

Photoinduced Phenomena in Amorphous Ge-As-S System

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Structural, dielectric and piezoelectric properties of nonlinear optical γ-glycine single crystals

Gamma glycine was synthesized and the single crystals were grown by the slow evaporation method in the presence of lithium nitrate. Structure and crystalline nature of the grown γ-glycine crystal was confirmed by X-ray diffraction technique. It was found to crystallize in the trigonal system with space group P3₁. The chemical composition was determined by NMR. Fourier transform infrared studies revealed the functional groups present in the grown crystal and UV-vis-NIR spectra revealed the transmission properties of the crystal specimen. Surface morphology of the grown crystal was studied by scanning electron microscopy (SEM) and elemental composition was confirmed by energy-dispersive spectrometry (EDS). The second-order nonlinear optical property of the material was investigated by Kurtz powder technique and the relative second harmonic efficiency of γ-glycine was estimated to be higher than that of KDP. The dielectric measurement was carried out as a function of frequencies at room temperature and the results were discussed. The samples have shown piezoelectric behavior with a fairly good piezoelectric charge coefficient (d₃₃) of 7.37 pC/N. Photoluminescence studies showed emission peak around 350 nm. Thermo gravimetric and differential thermal analyses were employed to understand the thermal and physio-chemical stability of the synthesized compound.     

Deuteron chemical shift and EFG tensors in α-glycine

By computer fitting of resonance lines in deuteron spectra of perdeuterated crystals, deuteron chemical shifts in crystals are measured with an accuracy of ±0.3 ppm. Second-order quadrupole shifts must be taken into account. An important advantage of the method is that the measured chemical shifts and the shift tensors are automatically related to EFG tensors which can be assigned easily. The method is applied to α-glycine for which a shift anisotropy Δσ = 21 ± 9 ppm has been reported for the methylene protons. Full EFG and chemical-shift tensors are reported at both methylene deuteron sites, and motionally averaged tensors are reported for the ND₃⁺ sites. The shift anisotropies Δσ for the methylene deuterons are 4.7 and 9.4 ppm, respectively. Significant differences of the isotropic shifts and quadrupole coupling constants are also observed for these two deuterons. They are interpreted as evidence for the formation of a weak CH … O hydrogen bond in α-glycine.     

Magnetic properties of γ-Fe2O3 nanoparticles encapsulated in surface-treated polymer spheres

Mössbauer and magnetic characterization of polymer-dispersed γ-Fe₂O₃ nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mössbauer spectroscopy data suggest the presence of only Fe^3?+? ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mössbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H₂O₂ and Na₂S₂O₈ modify notoriously the magnetic response of the polymer-dispersed nanoparticles.     

Growth and characterization of γ-glycine single crystals from cadmium chloride for optoelectronic applications

Single crystal of γ-glycine, an organic nonlinear optical material has been grown by solvent evaporation technique from the aqueous solutions of glycine and cadmium chloride at ambient temperature for the first time. The γ-phase of glycine is confirmed by single crystal X-ray diffraction. The crystal is in hexagonal system with non-centrosymmetric space group P31. The FTIR spectral analysis shows the functional group vibration of γ-phase glycine. UV–vis–NIR analysis reveals that the crystal has good optical transparency window in the entire visible and IR region. UV cut-off wavelength is at ∼350 nm. Thermal analysis shows the thermal stability, phase transition of the grown crystals and its melting point. Second harmonic generation efficiency of the crystal is about 1.7 times that of KDP.     

Effect of nano γ-Al2O3 addition on ion dynamics in polymer electrolytes

Polymer electrolytes, which hold the key of successful operation of all solid state ionic devices, have been investigated. An amorphous polymer was used to facsimile fast ion transport in the gel polymer electrolytes (GPE) and room temperature conductivity >10⁻³ S/cm can be attained. Further, these electrolytes were transformed into composites by dispersing inorganic particles of γ-Al₂O₃ (11 nm in size) in varying wt.%. An enhancement in the conductivity for an optimum concentration using LiClO₄ as a salt can be obtained and is described in terms of free charge carrier concentration, while the other family of Lithium salts viz. LiTf, LiIm, LiBETI decreases the conductivity marginally. FTIR spectroscopy supports the observed decrease in terms of more association between fillers and salts. It has been realized that the mechanical integrity of these composites increases manifold, without affecting the conductivity, significantly.     

Poly ethylene oxide (PEO)–LiI polymer electrolytes embedded with CdO nanoparticles

Improvement of electrical conductivity of poly ethylene oxide (PEO)–LiI polymer electrolytes is necessary for their use in solid state lithium ion battery. In this study a new kind of PEO–LiI-based polymer electrolytes embedded with CdO nanoparticles with improved electrical conductivity has been prepared and characterized. The electron microscopic studies confirm that CdO nanoparticles of average size 2.5 nm are dispersed in the PEO matrix. The glass transition temperature of the PEO–LiI electrolyte decreases with the introduction of CdO nanoparticle in the polymer matrix. X-ray diffraction, electron microscopic, and differential scanning calorimetry studies show that the amorphous phase of PEO increases with the introduction of CdO nanoparticle and that the increase in amorphous phase is maximum for 0.10 wt% CdO doping. The electrical conductivity of the sample with 0.10 wt% CdO increases by three orders in magnitude than that of the PEO–LiI electrolyte. The electrical conductivity of PEO–LiI electrolyte embedded with CdO nanoparticle exhibits VTF behavior with reciprocal temperature indicating a strong coupling between the ionic and the polymer chain segmental motions.     

Nanocrystalline soft magnetic ribbon with α″-Fe16N2 nanocrystallites embedded in amorphous matrix

A nanostructure with α″-Fe₁₆N₂ nanocrystallites embedded in an amorphous matrix was prepared by annealing Fe₉₂B₈ amorphous alloy in a NH₃+H₂ gas mixture stream with subsequent quenching and annealing. The average grain size and the volume fraction of the α″-Fe₁₆N₂ phase are found to be 18 nm and 54%, respectively. The prepared sample exhibits a saturation magnetization of 2.35 T, a coercive force of 11.4 A/m, an initial permeability of 9.1×10⁴ and a relaxation frequency of 4.1×10⁴ Hz.     

Photoinduced Reconstruction of Electronic Structure in Half-Metal CrO2

We investigate the photoinduced effects on the electronic structure for half-metallic ferromagnet CrO2 （Tc 390 K）, in which the conducting electrons are totally polarized, by using the LSDA＋U method. A significant change is found for the band structure and the density of states （DOS） for CrO2 under photo-excitation, especially for the Cr 3dt2g band： disappearance of the spin-split band, suggesting collapse of the half-metallic state. We ascribe the change of electronic structure under photo-excitation to the wider one-electron band W via the strong hybridization of the down-spin Cr 3d and O 2p states. Furthermore we discuss the magnetic properties under photo-excitation.     

Dielectric properties of crystalline binary KNO3—AgNO3 mixtures embedded in nanoporous silicate matrices

The results of dielectric studies of MCM-41 sili cate matrices with cellular pores (37.0 and 26.1 ? in diameter) filled by binary mixtures of K_1−x Ag _x NO₃ (x=0, 0.05, 0.10) are reported in comparison with those obtained for bulk salts of the same composition in the temperature range of structural phase transitions. It has been revealed that, upon heating, the nanocomposites undergo transitions from crystal modification II to phase I, as in bulk KNO₃, whereas the bulk mixtures with x=0.05 and 0.10 have a complex structure in accordance with the phase diagram. It has been shown that embedding binary salts and pure potassium nitrate in pores with a diameter of 26.1? results in the formation of an intermediate ferroelectric phase upon cooling. The permittivity and electrical conductivity are found to increase with increasing AgNO₃ concentration in bulk samples, as well as with decreasing pore size in the nanocomposites for all values of x.     

Temperature Dependence of Photoinduced Birefringence in an Azobenzene Polymer

The photoinduced birefringence in an azobenzene polymer is investigated at different temperatures between -20℃ to 50℃. It is found that there is a peak value of photoinduced birefringence in the temperature dependence of the photoinduced birefringence under a certain pumping intensity. With the pump light in 90mW/cm^2, the peak value of the photoinduced birefringence appeared at about 0℃ C. The effect of temperature on the photoinduced birefringence is discussed using the competition mechanism between the photoinduced reorientation and the thermal random motion.     

Doping effects on the stacking fault energies of the γ’ phase in Ni-based superalloys

The doping effects on the stacking fault energies(SFEs),including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault,were studied by first principles calculation of the/phase in the Ni-based superalloys.The formation energy results show that the main alloying elements in Ni-based superalloys,such as Re,Cr,Mo,Ta,and W,prefer to occupy the Al-site in Ni3 AI,Co shows a weak tendency to occupy the Ni-site,and Ru shows a weak tendency to occupy the Al-site.The SFE results show that Co and Ru could decrease the SFEs when added to fault planes,while other main elements increase SFEs.The double-packed superlattice intrinsic stacking fault energies are lower than superlattice extrinsic stacking fault energies when elements(except Co) occupy an Al-site.Furthermore,the SFEs show a symmetrical distribution with the location of the elements in the ternary model.A detailed electronic structure analysis of the Ru effects shows that SFEs correlated with not only the symmetry reduction of the charge accumulation but also the changes in structural energy.     

Photoinduced intramolecular electron transfer reactions in fullerene—phenothiazine linked compounds: effects of magnetic field and spacer chain length

Spectroscopic and electrochemical properties of two fullerene(C₆₀)-phenothiazine(PH) linked compounds with different spacer chain length have been compared in benzonitrile (polar solvent) and in benzene (non-polar solvent). Transient absorption and fluorescence spectra indicated that photoinduced intramolecular electron transfer occurred in benzonitrile, but not in benzene. The results are due to solvent effect on energy levels of the photogenerated biradical. The driving forces for the electron transfer were determined by measuring the redox potentials of the C₆₀ and PH moieties. Thermodynamic parameters for the electron transfer processes were evaluated and compared. In benzonitrile, the lifetime of the photo-generated biradical was very long, in spite of being around the top region in Marcus theory. The decay rate of the biradicals was retarded in the presence of magnetic fields. The decay rate constant decreased quickly with increasing the magnetic field and became constant above about 0.2 T. The magnetic field effects verified that the triplet biradical was generated by the intramolecular electron transfer from PH to the triplet excited state of C₆₀. The long lifetime is most probably ascribed to the spin multiplicities of the biradical.     

P-Odd effects in the γ+He4 → He4 + π0 reaction

P-Odd effects with the elastic photoinformation of neutral pions in He⁴ nuclei are due to the interference of the P-odd amplitude of weak interaction with the P-even amplitude of strong interaction, and originate only for polarized photons. It is shown that close to the reaction threshold P-odd effects should be small. The interference amplitude of the mechanisms corresponding to exchange with a Regge or-pole and a neutral Z-boson at high energies is studied. P-Odd effects in this case increase with increase of energy of the interacting particles and with the square of the imparted momentum. P-Odd effects due to interference of the s ingle-photon and Z-boson mechanisms are also investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 71–76, September, 1978.