Effect of UV irradiation on Cu+-containing glasses

Optical absorption spectra of copper-containing silicate glasses were determined and the effects of UV irradiation on the spectra were studied. Oxalic acid was used as a reducing agent in order to obtain monovalent copper ions. Several absorption bands were observed as a result of UV irradiation at wavelengths of 430–480, 565–570, 620–690, 720–790, 800–900 and 307–310 nm. These bands were interpreted in terms of photochemical reaction and attributed to color centers, cupric ions (Cu¹⁺⁺), metastable copper atoms (Cu^o), and aggregates of copper atoms which were induced by UV irradiation.     

Study of the Radiation Resistance of Endohedral Fullerenes of Rare-Earth Elements and Their Water-Soluble Derivatives

Endohedral metallofullerenes Me@C_2n (n = 30–50), their hydroxylated derivatives Me@C_2n(OH)_38–40 (Me = Tm, Ho, Eu, Sm, Co), and fullerenol С₆₀(OH)₃₈ have been synthesized The radiation resistance of these structures under irradiation in reactor by thermal and fast neutron fluxes in the fluence range of 1018–1019 cm^–2 (cadmium ratio of ~10) has been analyzed. Endofullerenols are shown to be more stable in comparison with initial endohedral fullerenes; the molecules containing Eu and Sm (atoms characterized by the largest slow-neutron absorption cross section) turned out to be most stable. The mechanism of the formation of secondary Eu and Sm endofullerenols is discussed taking into account the neutron capture and emission of γ quanta by excited nuclei, which acquire the recoil energy.     

An XPS study of the early stages of silver photodiffusion in Ag/a-As2S3 films

X-ray induced structural changes at the Ag/As₂S₃ interface are investigated using X-ray photoelectron spectroscopy on the samples prepared within the spectrometer. The as-prepared film consists of stable heteropolar As–S bonds as well as ∼16% S (and As) atoms in lower (higher) electron density configurations such as the –S–S– (–As–As–) segments with ‘wrong’ homopolar bonds. Two distinct stages of the X-ray induced diffusion are revealed. At first, silver reacts with atoms within –S–S– like segments to form Ag–S bonds. In the second stage, the Ag–S bonds decompose due to the reaction of S with As atoms within the –As–As– ‘wrong’ segments to form As–S heteropolar bonds, and silver diffuses away from the interface into the film. The results provide guideline for enhancing silver photodiffusion in chalcogenide glass. The irradiation of the (Ag–Te)/As₂S₃ sample with X-rays shows that not only Ag, but Te also diffuses away from the surface.     

Investigation of silver centres in glassy B2O3

B₂O₃ samples with silver impurities, X-ray irradiated at 77 K and then heated to 300 K, exhibit the presence of Ag⁺₂ molecular ions. It has been found that formation of Ag⁺₂ centres occurs with the participation of neutral silver atoms according to the reaction Ag⁰ + Ag⁺ → Ag⁺₂. The EPR spectra of Ag⁺₂ have been investigated and the parameters of the spin Hamiltonian have been determined. Under the action of light, λ = 390 nm, the Ag⁺₂ centres were observed to undergo photochemical decomposition into Ag⁰ atoms and Ag⁺ ions.The EPR spectra of Ag⁰ atoms have also been studied in great detail. The effect of light irradiation and temperature variation on the properties of these atoms has been investigated.     

Effect of proton irradiation on electrical properties of a-As2S3

This paper reports the effect of proton irradiation on the electrical properties of a-As₂S₃ in the temperature range of 323–418 K and frequency range 0.1–100 kHz. The variation of transport property is studied with proton irradiation dose (1 × 10¹³ ions/cm² and 1 × 10¹⁵ ions/cm²). It has been observed that proton irradiation changes the dc conductivity (σ_dc), dc activation energy (ΔE_dc) and ac conductivity (σ_ac(ω)). The σ_dc and σ_ac(ω) increases with dose of proton irradiation. The value of frequency exponent (s) decreases with the temperature and irradiation dose. These results are explained in terms of change in density of defect states in these glasses.     

Magnetic field dependence of the relative critical current density in γ‐irradiated polycrystalline YBa2Cu3O7

The effect of different doses of γ‐rays on the behavior of the critical current density, J_c in an YBa₂Cu₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ‐ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of Co-based amorphous alloys under the impact of the ion irradiation and recovery of the amorphous phase

Crystallization behavior of the amorphous phase in the Co–Fe–B–Si alloy system was investigated by X-ray diffraction technique under the influence both of thermal and irradiation activation. Crystallization starting temperature decreases by 200–300 ^°C under the influence of the irradiation. After partial crystallization of the amorphous alloy under the action of the irradiation annealed below the thermal crystallization temperature, the amorphous phase was again formed while annealing the alloy without irradiation. During irradiation and thermal annealing formation of the new metastable phase has been discovered with the diffraction pattern similar to the previously discovered cubic aperiodical phase in the Fe–Nb–Cu–B–Si alloy.     

Nature of radiation defects in synthetic quartz according to the small-angle neutron scattering data

The supraatomic structure of single crystals of synthetic quartz in the initial state with a dislocation density of 570 cm^?2 and after irradiation in the VVR-M reactor at the Petersburg Nuclear Physics Institute with fast neutrons having the energy E _n > 1 MeV in the range of fluences F _n = 7.7 × 10¹⁷ ?2.1 × 10²⁰ neutrons/cm² has been studied by small-angle scattering of thermal neutrons. It is established that fast neutrons form point, linear, and volume lattice defects throughout the entire sample volume. Large-volume structures (nuclei of the amorphous phase) in quartz, reaching ～100 nm in size, occupy a small total volume (～1.5%) even at the maximum fluence 2.1 × 10²⁰ neutrons/cm². The majority of damage is related to the point defects with the radius of gyration of 1–2 nm and linear defects, which give comparable contributions up to several percent.     

Lithium Intercalation into the Tetradymite-type Selenides Sulfides Bi2Se3-xSx

The reaction rate of Li intercalation into Bi₂Se_3−xS_x single crystals (x = 0, 0.025 and 0.05) increases with an increasing sulfur content in the crystals. This effect has been explained qualitatively by a change in the bond polarity in the Bi₂Se₃ due to the substitution of selenium atoms by sulfur atoms. This substitution results in a change in the electron density distribution and thus also in the width of the van der Waals gap between the structural layers, responsible for the course of intercalation. This explanation is supported by a quantum-chemical calculation of the charges on the atoms of the Bi₂Se_3−xS_x lattice manifesting and increase in the negative charge on Se atoms with an increasing value of x.     

Effect of γ-irradiation on mechanically activated and on non-activated LiF

By means of EPR spectroscopy lattice defects have been investigated, which had been produced in OH⁻ containing LiF by mechanical activation and subsequent irradiation (mainly γ-irradiation). The structure of irradiation-induced hydrogen centers shows characteristic differences dependent on the kind of LiF: H_s⁰ (hydrogen atoms in anion vacancies) are created in mechanically activated LiF powders, whereas H_i⁰ (hydrogen atoms in interstitial positions) in LiF single crystals. In both the cases also F centers are produced besides other paramagnetic defects. The observed defects can be used for an estimation of the degree of distortion in mechanically activated LiF.     

On a Hypothesis on the Molecule Vacancies in PbTe

The temperature dependence of the current carriers mobility in SnTe(I) and PbTe (I) synthesized in presence of SnI₂ or PbI₂ respectively was studied. An experimental formula was established, showing that current carriers scattering in SnTe(I) is due to vacancies at constant Hall coefficient. For PbTe (I) crystallized from tellurium solution by traveling heater method the mobility is high (between 2.10⁴ and 4.10⁴ cm²/Vs) and the Hall coefficient is constant within the interval 77 K–450 K. Only within 77 K–160 K interval the current carriers scattering is due to vacancies. A hypothesis is proposed based on the presence of molecular vacancies (V_pbTe). These vacancies do not change electron gas concentration but do change the carriers mobility. Specimens with a negligibly low lead atoms vacancies Concentration were investigated. An empirical expression is established which shows that their mobility depends on molecular vacancies concentration and explains observed weak temperature influence upon carriers mobility. These results are obtained only from Hall coefficient and electric conductivity measurements within the 77 K–160 K temperature interval.     

Elucidation of the stereochemistry of Tl+ in oxide glasses by electron spin resonance spectroscopy

The relation has been elucidated between the stereochemistry of Tl⁺ and the chemical composition of host oxide glasses by measuring the ESR of paramagnetic Tl²⁺ induced with γ-irradiation at 77 K. The spectra have been analyzed by using a new solution of the spin-Hamiltonian developed by the authors. The results indicate: (1) there are two sites for Tl⁺ in a wide variety of oxide glasses (site I and site II). Tl⁺ in site I has a heavily distorted ligand field (lone pair electrons of Tl⁺ occupy a s-p(-d) hybridized non-bonding orbital extruding in one direction). The geometry of the Tl⁺-complex in site II is nearly spherically-symmetric (lone pair electrons locate in an anti-bonding sigma orbital to which the Tl 6s atomic orbital mainly participates); (2) site I appears in the glasses where both the bridging and non-bridging oxygens coexist. Site II is observed in the other glasses; (3) a drastric change in lineshape of Tl²⁺ induced with 77 K irradiation was observed upon thermal annealing. A structural model for this change was proposed; the Tl²⁺ with an excess plus charge is stabilized by the cooperative motion of the alkali ion pairing with Tl²⁺ and intervening non-bridging oxygens, the alkali being repelled and the oxygens being attracted.     

X-ray reflectometry of the specific features of structural distortions of He+-implanted Si(001) surface layers

The structural changes in the surface layers of silicon substrates, implanted by helium ions with energies from 2 to 5 keV and doses to 6 × 10¹⁵–5 × 10¹⁷ cm^?2, has been studied by high-resolution X-ray reflectometry. The damaged layer is found to have a total thickness comparable with the total ion path length (estimated from the SRIM model) and a multilayer structure: a strongly amorphized layer with reduced density, a porous (incapsulated) layer, and a deformed layer. The thickness of sublayers, their density ρ(z), and the mean strain (～5 × 10^?3) have been determined. The characteristic pore size is estimated to be 5–20 nm. It is shown that the presence of a nanoporous layer facilitates the formation of diffuse scattering, which can be used to diagnose layers by high-resolution X-ray reflectometry.     

Structural changes of amorphous Pd80Si20 with neutron irradiation,with an interpretation in terms of the imperfections in the structure of amorphous solids

Wide and small-angle X-ray scattering measurements were made, as well as differential scanning calorimetry, for amorphous Pd₈₀Si₂₀ before and after irradiation by neutrons (5 × 10²⁰ neutrons/cm², > 1 Mev), and the structural changes thereby produced are described.Before irradiation the structure is well assimilated with a dense random packing (DRP) structure except that the coherence between neighboring Pd atoms extends farther than expected from the DRP structure, the coherent length estimated from the X-ray scattering being about 8 Å.With irradiation the coherent regions of 8 Å diameter get separated from each other by a mean distance of 20 Å, thus producing structural inhomogeneities which do not exist at all before irradiation. The glass transition temperature is found to be increased by about 10 K after irradiation.The effects of irradiation are interpreted as being due to the structural imperfections produced by particle bombardment. The DPR structure is adopted as a model structure for the perfect amorphous solids.     

Color centers and charge state change in Ce:YAG crystals grown by temperature gradient techniques

Color centers and impurity defects of Ce:YAG crystals grown in reduction atmosphere by temperature gradient techniques have been investigated by means of gamma irradiation and thermal treatments. Four absorption bands associated with color centers or impurity defects at 235, 255, 294 and 370 nm were observed in as-grown crystals. Changes in optical intensity of the 235 and 370 nm bands after gamma irradiation indicate that they are associated with F⁺-type color center. Charge state change processes of Fe³⁺ impurity and Ce³⁺ ions take place in the irradiation process. The variations of Ce³⁺ ions concentration clearly indicate that Ce⁴⁺ ions exist in Ce:YAG crystals and gamma irradiations could increase the concentration of Ce³⁺ ions. Annealing treatments and the changes in optical density suggest that a heterovalent impurity ion associated with the 294 nm band seems to be present in the crystals.     

Dislocation density in heteroepitaxial indium arsenide layers

In As layers have been grown by CVD on (111)B-oriented GaAs substrates. The dislocation density (N_D) distribution through the layer thickness has been studied. N_D is dependent on the mole fraction of AsCl₃ in the gaseous phase and, consequently, on the current carriers concentration. This results in the supposition that the decreasing of N_D in the layers after a “critical” thickness is due to the “pinning” of dislocations at impurity atoms which form stronger bonds with the host In or As atoms than the bond In–As, an effect which is known for bulk GaAs and InP crystals.     

Silver nanoclusters formation in ion-exchanged glasses by thermal annealing,UV-laser and X-ray irradiation

The Ag-exchanged commercial soda-lime silicate glasses were treated by three methods: thermal annealing, UV-laser irradiation, and X-ray irradiation, in order to promote the silver nanoclusters formation. Absorption spectrometry and electron spin resonance measurement results indicated that the silver ions transferred to silver atoms after the above three treatments. The silver atoms diffused and then aggregated to become nanoclusters after thermal annealing in air, or after UV-laser irradiation. However, X-ray irradiation, which induced defects and reduction of Ag⁰ atoms, would not promote the silver nanocluster formation. After annealing at 600 °C for 45 h, the spherical nanoclusters with a diameter of 3–8 nm were formed. The nanoclusters with a diameter of about 2 nm were formed after 30 min UV-laser irradiation without subsequent heating. The surface plasmon resonance peak position of silver nanoclusters changed from 411 nm after thermal annealing to 425 nm after UV-laser irradiation. The peak position shift was due to the nanoclusters size difference.     

Hg X n coordination polyhedra (X = F, Cl, Br, and I) in crystal structures

The crystallochemical analysis of 188 structures containing 252 crystallographic kinds of Hg(II) atoms in Hg X _n coordination polyhedra (X = F, Cl, Br, and I) has been performed by the method of intersecting spheres with the use of Vorono-Dirichlet polyhedra. It was found that halogen atoms surrounded by Hg(II) atoms are characterized by the coordination numbers from 3 to 8. It was demonstrated that, at the unvarying nature of the X atoms, the average Hg-X interatomic distance increases by 0.13–0.57 Å with an increase of the coordination number, whereas the average radius of spheres with the volume equal to that of the Vorono-Dirichlet polyhedron of a Hg atom is either independent of the coordination number (at X = F) or varies with it only by about 0.02–0.07 Å (at X = Cl, Br, and I). This allows the approximation of mercury atoms in the crystal structures by soft (deformable) spheres of a constant volume. Some results obtained in the analysis of the topology and the geometry of [Hg_m X _n ] ^z?-complexes in crystal structures are also presented.     

Photoelectrochemical solar cells based on TiS2/TiO2(TiOxSy) photoelectrodes

A new photoelectrode of TiS₂/TiO₂ alloy with a possible new TiO_xS_y phase has been synthesized for the first time in the present investigation. This photoanode exhibits improved photoelectrochemical (PEC) response as compared to either TiS₂ or TiO₂ photoelectrode. With this new photoelectrode high PEC conversion efficiency is evidenced by large photovoltage (840 mv) and significantly high photocurrent density (40 mA/cm²). The photovoltage obtained in the present system is significantly high and the photocurrent density is the highest reported so far for the TiO₂ based systems. It has been suggested that the enhancement in photoactivity in the present system is due to the reduced band gap of TiO_xS_y alloy material. Such a band gap reduction is thought to be facilitated by the downward movement of the valence band of titanium disulphide which is made up of chalcogen atoms through substitution of sulphur atoms by oxygen atoms.     

On the crystallochemical origin of the disordered form of Ba7(EuII)F12Cl2 and the structural changes induced at high temperature

The crystal structure of the disordered modification of Ba₇F₁₂Cl₂ has been carefully re‐examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ∼3 e^–/ų in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ∼800 °C. New structural data show a change in space group from P6₃/m to P6. During this process, a slight chemical change and the formation of nano‐channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)