Defects and the structure of a manganite La0.85Sr0.15MnO3 crystal

Defects in a ferromagnetic crystal of manganite La_0.85Sr_0.15MnO₃ were created by irradiation with fast neutrons (E > 0.1 MeV). Fast neutrons produce defect clusters in a crystal lattice. The volume fraction of the clusters in the crystal after irradiation to a dose F = 2 × 10¹⁹ cm^?2 (T _irr = 340 K) was ?40%. The structural and magnetic states of the modified manganite were studied using thermal-neutron diffraction and magnetic measurements. It was revealed that neutron irradiation of a crystal suppresses the cooperative Jahn-Teller effect and the initial charge modes and decreases the temperature of ferromagnetic ordering. Under irradiation with fast neutrons, the crystalline structure of the manganite changes from the orthorhombic O′ to the pseudocubic O* phase. Arguments are advanced in favor of the specific features of the irradiated-manganite structural state being determined by long-wavelength strains induced in the crystal by antisite defects.     

Graphitization of a Polycrystalline Diamond under High-Fluence Irradiation with Noble Gas and Nitrogen Ions

To analyze the process of the ion-induced graphitization of a polycrystalline diamond, the surfacelayer conductivity and microstructure are studied experimentally after high-fluence irradiation with Ne⁺, Ar⁺, N⁺, and ions with energies of 20–30 keV at irradiation and heat-treatment temperatures ranging from 30 to 720°R in vacuum. After irradiation with argon ions at room temperature and subsequent heat treatment, the resistivity ? of a modified layer decreases exponentially with increasing treatment temperature T _ht and reaches the graphite value ? at Tht = 700°R. Such a temperature T _ht is insufficient for surface-layer graphitization by nitrogen ions. The increase in the diamond temperature under irradiation leads to a decrease in the ion-induced thermal graphitization temperature T _g by several hundred degrees. It is found that the temperature T _g is almost coincident with the corresponding temperature T_a of the dynamic annealing of radiation-induced damage in graphite. Analysis of the irradiated layer using Raman spectroscopy reveals the heterogeneous structure of the modified layer containing graphite and amorphous phases, the ratio between which correlates with the layer resistivity. Under argon-ion irradiation at diamond temperatures of 500°R or more, an increase in ? of the irradiated layer is observed, which is related to the formation of nanocrystalline graphite. This effect is not observed under nitrogen-ion irradiation.     

Initiation of nuclear reactions under laser irradiation of metal nanoparticles in the presence of thorium aqua ions

Laser irradiation of tungsten and gold nanoparticles in aqueous solutions of Th(NO₃)₄ was experimentally studied. Picosecond Nd:YAG lasers with a wavelength of 1.06 μm and a peak power from 10¹¹ to 10¹³ W cm⁻² were used. The composition of colloidal solutions before and after laser irradiation was analyzed using atomic absorption and gamma spectrometry. It was found that laser irradiation initiates nuclear reactions involving thorium nuclei, occurring via two different channels. Radioactive decay of thorium nuclei within its radioactive series is enhanced under laser irradiation in D₂O; one of the fission fragments is ¹³⁷Cs. Possible mechanisms of the process are discussed.     

Optical properties of UV-induced color centers in a KY3F10:Ce3+ crystal

The evolution of color centers induced in a KY₃F₁₀:Ce³⁺ crystal by UV radiation has been observed and interpreted. It has been revealed that, initially, the UV irradiation of the KY₃F₁₀:Ce³⁺ crystal induces the formation of color centers predominantly of the F-type, which, in a short time period of about ten minutes, are transformed into complex color centers of the F ₂-type, as well as into impurity color centers. Based on the data obtained, a diagram of energy states of the crystal, dopant, and color centers has been constructed, on which most probable processes that are caused by electronic transitions occurring in the KYF:Ce³⁺ crystal after its UV irradiation have been indicated.     

Development of a saturated transient X-ray laser at 13.9 nm in LSAI

We summarise the progress achieved at LSAI in the understanding and optimisation of the transient collisional pumping of X-ray lasers using an ultra-short sub-ps heating pulse. The effect of travelling-wave irradiation on the lasing signal on the 4d¹S₀→4p¹P₁ Ni-like Ag line at 13.9 nm is studied in detail. Under specific irradiation conditions strong laser emission is also obtained on another spectral line at 16.05 nm, which is identified as the 4f¹P₁–4d¹P₁ transition in Ni-like Ag.     

SURFACE PHASE DECOMPOSITION IN Bi2Sr2CaCu2O7-y SINGLE CRYSTALS UNDER NITROGEN IONS IRRADIATION

The influence of irradiation by 30 keV nitrogen ions with a fluence 1×10¹⁸N⁺·cm^-2 on the crystal structure of single crystal Bi₂Sr₂CaCu₂O_7-y was investigated by means of X-ray photoelectron spectroscopy and X-ray diffraction. The irradiation caused a transformation from Bi₂Sr₂CaCu₂O_7-y (2212 phase) to Bi₂Sr₂CuO_5-x (2201 phase). It was observed that. a small amount of metallic bismuth with an average thickness of about 6.3nm appeared after the irradiation. The possible reaction mechanism under nitrogen-ion irradiation was discussed.     

Local crystallization in an oxyfluoride glass doped with Er3+ ions using a continuous argon laser

Local crystalline formation in erbium doped oxyfluoride glass has been obtained under a cw Argon laser irradiation up to 1.8 W pumping power. By exciting at 514 nm, the emission from 800 nm and 850 nm corresponding to the ⁴S_3/2(²H_11/2)→⁴I_13/2 electronic transitions have been analyzed both inside and outside the irradiated area. The changes in the emission spectra indicate that the high power Ar laser irradiation has resulted in a localized desvitrification process. The temperature dependence of the fluorescence intensity ratio of the 800 nm and 850 nm emission bands has been used to determine the temperature of the irradiated zone. Moreover, the average lifetime of the ⁴S_3/2(²H_11/2) thermalized levels have been measured as a function of the excitation spot position. An important decrease is observed at the irradiated area. These results confirm that a localized cristalline phase has been created by the laser action.     

Thermoluminescence response as a function of irradiation temperature

Thermoluminescence response at different irradiation temperatures and photon energies has been studied. Analyses of the glow curve and the peak height of TLD 200, 600, 700 and CaSO₄:Dy for irradiations using ⁶⁰Co, ¹³⁷Cs and ²²⁶Ra were made.     

Observation of a chemical reaction reversibly triggered by a structural phase transition

Two distinct radical species, (AsO₄)^4- and (AsO₃)^2-, created by irradiation in crystals of ND₄D₂AsO₄, undergo (taking into account the deuterons) the following chemical reaction: AsO₃D^- + OD^- ? AsO₄D^2-₂The effect occurs at the antiferroelectric-paraelectric phase transition of the compound. Its essential feature is that the reaction is completely reversible i.e. that it can be triggered by the phase transition, the direction of the reaction depending on the direction of passage of the Curie point. An analogy is presented with a biological process, namely the second step of the cooperative binding of oxygen on haemoglobin.     

Structural features of aluminium alloy 1441 irradiated by Ar+ ions

Using electron microscopy it was found that irradiation of clad cold-worked specimens made of commercial aluminium-lithium alloy 1441 by the Ar ⁺ ions of energy 40 keV at low doses of irradiation (10¹⁵ cm⁻², irradiation time 1 s, T < 70 °C) and ion-current density of about 100 μA/cm² results in the transformation of the cellular structure formed in the alloy under deformation. As the dose of irradiation is increased up to 10¹⁶ cm⁻², a transition from a cellular to a subgrain structure close to a polygonal one is observed. The efficiency of the process is increased with ion-current density. Furthermore, under ion irradiation at increased ion-current densities, the β′(Al ₃ Zr) and Al ₈ Fe ₂ Si particles present in the deformed alloy dissolve, and disperse particles of a new Al ₂ LiMg phase of platelet shape are formed. The changes in the dislocation structure and phase composition in alloy 1441 are observed several seconds after irradiation not only in the surface layer adjacent to the ion incorporation band but also through the thickness of the specimen tens of thousands times greater than ion projective ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–81, February, 2007.     

Effective activation energy of 16MeV proton irradiated QMG-YBCO

Ion irradiation effects on improvement of flux-pinning properties for quenched and melt growth YBCO samples (QMG-materials) were studied. Irradiation with 16MeV protons was performed up to a dose of 1×10¹⁶ p/cm². The effective activation energies of vortices are expressed with the formula, U_eff=g(T)h(H)f(J) ∝ (J/J_c)^−∝* [1-(T/T_x)²]^2/3*H^−1/3 at lower irradiation doses below 5×10¹⁵ p/cm². The J-dependence of U_eff changes from power-law to quesi-exponential dependence with an increment of irradiation dose.     

Gamma-ray irradiation effect on the absorption and luminescence spectra of Nd:GGG and Nd:GSGG laser crystals

Laser crystals Nd³⁺:Gd₃Ga₅O₁₂ (Nd:GGG) and Nd³⁺:Gd₃Sc₂Ga₃O₁₂ (Nd:GSGG) were grown by Czochralski method. The influence of gamma-ray irradiation on their absorption and luminescence spectra has been investigated. Two additional absorption (AA) bands induced by gamma-ray irradiation appear in the spectra of Nd:GGG crystal while only a very weak AA band appears for the Nd:GSGG crystal. This indicated that Nd:GSGG crystal has stronger ability to resist the color center formation by irradiation. The intensity of the excitation and emission spectra of Nd:GGG crystal decrease after the irradiation of 100 Mrad gamma-ray. In contrast, a luminescence strengthening effect was observed in Nd:GSGG crystal after exposure to the same irradiation dose. The results showed that the Nd:GSGG crystal is a promising candidate used under radiation environments such as in outer space.     

Comparison of the transmission behavior of a triazeno-polymer with a theoretical model

The threshold fluence,F _Th, of ablation of a triazeno-polymer was measured in the low fluence range for thin films using conventional UV-spectroscopy. It was found that there is a clearly definedF _Th for 308 nm irradiation between 20 and 25 mJ cm^–2. In the case of 248 nm irradiation, a threshold fluence range between 16 and 32 MJ cm^–2 was found. The ablation rate for both irradiation wavelengths depends on film-thickness. For the XeCl excimer-laser, the point at which the rate becomes independent of thickness was observed to lie at a value which did not correspond to the calculated laser penetration depth, whereas for the KrF laser the independence was not reached within the applied thickness range (up to 0.35 m). Additional transmission measurements have been performed showing that the target transmission at 248 nm increases only slightly, whereas for 308 nm the transmission increases by a factor of approximately 4. This result shows that dynamic target absorption properties are very important for describing the ablation process. The results derived from the transmission studies and etch rates were analyzed theoretically with a two-level model of chromophore absorption. For 248 nm irradiation this model can describe the transmission behavior and the ablation rate. In the case of 308 nm irradiation, it was only possible to match one data set. A good agreement with the experimental transmission ratio does not match the ablation rate and vice versa.     

IR,UV and visible absorption of X irradiated single crystals of sodium nitrite

X irradiation of NaNO₂ single crystals, induces a motion of some NO₂^? ions, mainly around the axis perpendicular to their planes (a axis). The change in the orientation of NO₂^? is observed on the v₂ vibration of NO₂^? (by IR absorption) and on the vibronic structures associated with the NO₂^? electronic transitions (by UV and visible absorption). Other centers, like no₃^?, are also produced by irradiation. Their evolution with temperature is studied.     

Effect of oxide surface metallization under ion-beam irradiation

Changes in the surface chemical composition of WO₃, Ta₂O₅, MoO₃, and Nb₂O₅ oxides after Ar⁺ ion irradiation and those of the WO₃ surface after He⁺ ion irradiation under high vacuum were investigated by X-ray photoelectron spectroscopy. Upon Ar⁺ ion irradiation with an energy of 3 keV, the pronounced effect of ion-beam metallization was observed on the WO₃ oxide surface; a moderate effect was found for the Ta₂O₅ oxide surface; a weak one for the MoO₃ oxide surface; and no effect was discovered for the Nb₂O₅ oxide surface. At the saturation dose, 44 at % W, 12 at % Ta, and 2 at % Mo form on the oxide surfaces. Irradiation by light He⁺ ions with energies of 1 and 3 keV results in WO₃ surface metallization. At the saturation dose, 2 and 10 at % W (at 1 and 3 keV, respectively) forms on the oxide surface. The nature, mechanisms, and features of the oxide surface metallization effect induced by ion-beam irradiation are discussed.     

Ion-beam reduction of the surface of higher oxides of molybdenum and tungsten

The process of reduction of the surface of oxides MoO₃ and WO₃ under irradiation by Ar⁺ and O ₂ ⁺ ions with an energy of 3 keV in high vacuum is investigated by X-ray photoelectron spectroscopy. It is shown that upon irradiation by Ar⁺ ions, lower and intermediate oxides and unoxidized metals are formed in the surface layers of higher oxides. Irradiation by O ₂ ⁺ ions mainly leads to formation of intermediate oxides with an insignificant content of lower oxides. It is found that the process of ion-beam reduction of the surface of oxides MoO₃ and WO₃ substantially depends on the ion type, irradiation dose, and difference in energy of the metal-oxygen bond in oxides.     

Damage induced in garnets by heavy ion irradiations: a study by optical spectroscopies

The damage induced by heavy-ion irradiation has been studied in yttrium iron garnet (Y₃Fe₅O₁₂ or YIG) films, doped with Ca, Tb and Tm, grown by liquid-phase epitaxy on gadolinium gallium garnet (Gd₃Ga₅O₁₂ or GGG) substrates. Irradiations of doped-YIG epitaxial films and GGG substrates with 36-MeV ¹⁸³W and 12-MeV ¹⁹⁷Au ions were applied for fluences between 1 × 10¹³ and 3 × 10¹⁵ cm^–2 near room temperature. The radiation damage was monitored by micro-Raman spectroscopy and UV–visible optical absorption spectroscopy. Raman spectra revealed that amorphisation was achieved in YIG for both ions, whereas a high lattice disorder was induced in GGG without reaching amorphisation for the Au ion irradiation. Raman spectra also showed that a major damage of the tetrahedral sites was induced in GGG, as previously found for YIG. It is concluded that with such ions reaching the stopping power threshold of track formation in YIG and GGG the observed rate of amorphisation may result from a combination of electronic and nuclear energy losses as calculated using the unified thermal spike model.     

Effects of ultrasound irradiation on Au nanoparticles deposition on carbon-coated LiNi0.5Mn1.5O4 and its performance as a cathode material for Li ion batteries

LiNi_0.5Mn_1.5O₄ (LMNO) has attracted considerable attention as a Li-ion battery cathode material, owing to its high discharge voltage of 4.7 V (vs. Li/Li⁺) and high energy density. However, the electronic conductivity of LMNO is low, resulting in a low discharge capacity at high current density. To overcome this limitation, we deposited Au nanoparticles (NPs), which have a high conductivity and chemical stability at high battery voltages, on carbon-coated LMNO (LMNO/C) using ultrasound irradiation. Consequently, Au NPs that are ∼16 nm in size were deposited on LMNO/C, and ultrasound irradiation was reported to disperse the NPs on LMNO/C more effectively than stirring. Furthermore, the deposition of Au NPs on LMNO/C using ultrasound irradiation improved its electronic conductivity, which is related to an increase in the discharge capacity due to the reduction of Ni⁴⁺ to Ni²⁺ in LMNO/C at a high current density.     

Design and fabrication of a TiO2/nano-silicon composite visible light photocatalyst

Nano-silicon (nc-Si) was utilized as the charges generator to promote the photocatalytic and super-hydrophilic reactivity of TiO₂ film under visible light irradiation. The photocatalytic ability of TiO₂/nc-Si composite photocatalyst was evaluated by a set of experiments to photodecompose 100 ppm methylene blue (MB) in aqueous solution. And the super-hydrophilic property was characterized by measuring the water droplet contacts angle, under visible light irradiation in atmospheric air and at room temperature. Under 100 mW/cm² visible light irradiation, the droplet contact angles were reduced to 0° within 4 h with nc-Si charge generator. Additionally, the rate constant of MB photo-degradation was promoted 6.6 times.     

Surface composition modification of tungsten higher oxide under He<Superscript>+</Superscript> ion bombardment

The surface reduction of higher oxide WO₃ under irradiation by He⁺ ions with the energies 1 and 3 keV in a high vacuum is investigated by X-ray photoelectron spectroscopy. It is found that lower WO₂ and intermediate WO _x (2 < x < 3) oxides form first in WO₃ surface layers under He⁺ ion bombardment, and with an increase in the irradiation dose metallic tungsten forms. It is shown that the degree of irradiated oxide surface metallization increases with an increase in the energy of the bombarding He⁺ ions. A comparison of WO₃ oxide surface composition modification under He⁺ and Ar⁺ ion irradiation is presented.