Luminescence properties of silver zinc phosphate glasses following different irradiations

We report on exposing a photosensitive zinc phosphate glass containing silver to different radiation (electron, gamma, optical). Laser irradiations using nanosecond ultraviolet (UV) and femtosecond infrared (IR) laser are compared with gamma and electron exposure. All irradiated glasses exhibit absorption maxima around 320 nm and 380 nm and emission in the visible spectral range. Following exposure, silver clusters are formed. The optical response of such species is investigated using absorption and fluorescence spectroscopic techniques. The mechanism of formation of these clusters is discussed.     

Synthesis and ionic conductivity of new layered perovskite compound, Ag2La2Ti3O10

A new layered perovskite compound, Ag₂La₂Ti₃O₁₀, was synthesized by an ion-exchange reaction of M₂La₂Ti₃O₁₀ (M = Na,K) with a AgNO₃ molten salt. The crystal structure and the ionic conductivity of the ion-exchanged compound were investigated. The ionic conductivities attributed to the interlayer silver ions were observed at high temperatures. The ionic conductivity of Ag₂La₂Ti₃O₁₀ was much higher than that of Na₂La₂Ti₃O₁₀, while the interlayer sodium ions in Na₂La₂Ti₃O₁₀ and silver ions in Ag₂La₂Ti₃O₁₀ have almost the same rock-salt type coordination. The higher conductivity of Ag₂La₂Ti₃O₁₀ is probably due to the higher polarizability of silver ions.     

Frequency and temperature amplitude dependence of complex heat capacity in the melting region of polymers

Amplitude and frequency dependence of reversible melting of polycaprolactone (PCL) and an ethylene octene copolymer (EOM) were studied using temperature-modulated differential scanning calorimetry (TMDSC) (2?10^?1 Hz <f < 0.05 Hz) and shear spectroscopy (dynamic mechanical analysis, DMA) (5?10^?4 Hz < f < 100 Hz). It was found that the excess heat capacity of PCL is constant for temperature amplitudes in the range 5 mK < A_T < 2 K. The excess heat capacity decreases with frequency of temperature perturbation and tends to zero at about 0.1 Hz and 100 Hz for PCL and EOM, respectively. The constant excess heat capacity and the frequency dependence support the idea that reversible melting is related to a relaxation process on the surface of the polymer crystals. The occurrence of such a relaxation process was shown by shear modulus measurements in the same frequency and temperature region. The relaxation process is, in the melting region, much slower than main relaxation (glass transition). At low temperatures, a crossover can be seen, indicating the independence of both processes because of spatial separation. The main relaxation is related to the melt, while the other is related to the crystal surface.     

Temperature dependence of the a.c. conductivity of Naβ-alumina

Low temperature a.c. conductivity of β-alumina is of the form σ(ω) = σ(ω) + Aωⁿ. Both σ(0) and A are found to be thermally activated. Simple relationships, dependent on the value of n, are shown to exist between (i) the relative magnitudes of σ(0) and A and (ii) their respective activation energies.     

Glass forming regions and dielectric properties of new phosphate glasses

The glass forming regions have been determined in the systems P₂O₅-A₂O-MO (A = Li, Na; M = Cu, Cd), P₂O₅-Bi₂O₃-Li₂O and P₂O₅-Bi₂O₃-ZnO. The largest vitreous domain has been found in the ternary diagram P₂O₅-Bi₂O₃-ZnO. The variation of the dielectric constants has been followed inside the glass regions. ε'_r increases with increasing amount of alkaline oxides and substantially diminishes with increasing percentage of either CuO or CdO.     

Investigation of the pressure dependence of band gaps for silver halides within a first-principles method

The pressure dependence of the direct and indirect band gaps in rocksalt silver halides has been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for the exchange-correlation potential. It is found that indirect band gaps (L→X and L→Γ) exhibit different responses to application of pressure. Similar trends are found for the indirect band gaps of AgCl and AgBr while the trend in AgI (L→Γ) band gap is different. In all the compounds, the effect of pressure on the direct band gaps (Γ→Γ, X→X and L→L) show qualitatively similar results. The fundamental indirect band gap (L→Γ) pressure coefficients are −4.19 meV (GPa)⁻¹ and −3.81 meV (GPa)⁻¹ for AgCl and AgBr while for AgI (L→X) it is −61.50 meV (GPa)⁻¹. The band gap pressure coefficient as well as the volume deformation potential for the various band gaps of the compounds have also been investigated.     

Concentration and temperature dependence of asphericity of 3d-electrons in f.c.c. Co-Ni and Co-Fe alloys

The asphericity of 3d-electrons was measured as a function of temperature in some f.c.c. ferromagnetic Co alloys by means of the polarized neutron technique. The asphericity, as measured by the population of the e_g and t_2g sub-levels, was found to be almost independent of temperature. Simple models failed to explain the data.     

Chaotic temperature dependence in a model of spin glasses

We address the problem of chaotic temperature dependence in disordered glassy systems at equilibrium by following states of a random-energy random-entropy model in temperature; of particular interest are the crossings of the free-energies of these states. We find that this model exhibits strong, weak or no temperature chaos depending on the value of an exponent. This allows us to write a general criterion for temperature chaos in disordered systems, predicting the presence of temperature chaos in the Sherrington-Kirkpatrick and Edwards-Anderson spin glass models, albeit when the number of spins is large enough. The absence of chaos for smaller systems may justify why it is difficult to observe chaos with current simulations. We also illustrate our findings by studying temperature chaos in the naıve mean field equations for the Edwards-Anderson spin glass. Received 27 March 2002 Published online 19 July 2002     

Rotational Brownian dynamics simulations of non-interacting magnetized ellipsoidal particles in d.c. and a.c. magnetic fields

The rotational Brownian motion of magnetized tri-axial ellipsoidal particles (orthotropic particles) suspended in a Newtonian fluid, in the dilute suspension limit, under applied d.c. and a.c. magnetic fields was studied using rotational Brownian dynamics simulations. The algorithm describing the change in the suspension magnetization was obtained from the stochastic angular momentum equation using the fluctuation-dissipation theorem and a quaternion formulation of orientation space. Simulation results are in agreement with the Langevin function for equilibrium magnetization and with single-exponential relaxation from equilibrium at small fields using Perrin's effective relaxation time. Dynamic susceptibilities for ellipsoidal particles of different aspect ratios were obtained from the response to oscillating magnetic fields of different frequencies and described by Debye's model for the complex susceptibility using Perrin's effective relaxation time. Simulations at high equilibrium and probe fields indicate that Perrin's effective relaxation time continues to describe relaxation from equilibrium and response to oscillating fields even beyond the small field limit.     

Influence of Ag2O on crystallisation and structural modifications of phosphate glasses

A series of phosphate glasses of composition 45P₂O₅–(40???x)CaO–15Na₂O–xAg₂O (x?=?0, 3, 6, 8, 10 and 12?mol%) with different Ag₂O contents were prepared using the melt-quenching technique. The incorporated Ag₂O highly influenced the increase of its transition tendency towards crystallisation and, on contrary, reduced the degree of glassification of phosphate glasses. The lowering of glass transition temperature and increase in thermal expansion were observed in glasses against Ag₂O inclusions. The crystalline phase transitions of amorphous material during thermal treatment were confirmed by employing X-ray diffraction studies. As revealed by X-ray photoelectron spectroscopy, the incorporated silver oxide into phosphate glass exists in two different oxidation states, Ag₂O and AgO. The pyrophosphate and metaphosphate units were predominantly occupied in glass and glass ceramics. The elastic moduli and Vicker's hardness values exhibited the decrease in phosphate glass structural compactness due to Ag₂O-incorporation and these values were found to improve because of crystalline transitions.     

Deposition and wettability of silver nanostructures on Si(1 0 0) substrate based on galvanic displacement reactions

A new route for silver electroless deposition on Si(1 0 0) substrate is developed based on the galvanic displacement process. The basic electroless bath contains NaF and AgNO₃ with different concentrations. The morphologies of electrolessly deposited silver nanostructures, including silver nanowires and nanoparticles, are strongly dependent on the electrolyte composition. Adding an excess dosage of polyvinylpyrrolidone into the basic electrolyte yields final silver films of porous structures composed by multitudinous Ag nanoparticles. The porous silver films possess the surface hydrophobic property after the modification with n-dodecanethiol. Unidirectional wetting and spreading of a water droplet are also demonstrated on the patterned porous Ag films.     

Formulae for temperature and concentration dependence of impurity monomers and dimers in nonreguear binary f.c.c. solid solutions

Czechoslovak Journal of Physics -     

Raman of indigo on a silver surface. Raman and theoretical characterization of indigo deposited on silicon dioxide-coated and uncoated silver nanoparticles

Raman, surface-enhanced Raman scattering, and shell isolated nanoparticles-enhanced Raman scattering techniques were used to study the indigo–nanoparticle interaction nature. Silver nanoparticles were employed with and without a silicon dioxide spacer inert layer. The SERS spectral profile, obtained using silver nanoparticles, is different from the Raman one, which led to the proposition that the indigo–silver interaction is in the range of intermolecular interactions. SERS spectral reproducibility suggests identical organization and orientation of the analyte on the metal surface. The shell isolated nanoparticles enhanced Raman scattering spectrum of indigo, obtained by using silicon dioxide coated silver nanoparticles resulted similar to its Raman spectrum. This result indicates that the indigo structure is chemically unmodified by the silicon dioxide-coated silver surface. From the shell-isolated nanoparticles-enhanced Raman scattering experiments, the electromagnetic mechanism is proposed as the reason for the spectral enhancement. Theoretical calculations allow one to infer both the indigo–silver surface interaction nature and the orientation of indigo on the surface.     

Concentration and temperature dependence of diluent dynamics studied by line shape experiments on a phosphate ester in polycarbonate

³¹P Hahn spin echo line shape and proton line shape experiments are reported on bisphenol A polycarbonate (BPAPC)-tris(2-ethylhexyl)phosphate (TOP) systems to study the concentration and temperature dependence of the local dynamics. In an earlier ³¹P line shape study a lattice model was presented as a framework to interpret the plasticization and antiplasticization behavior of the diluent based on a fractional population given by the type of nearest neighbor contacts in the mixed polymer-diluent glass. In this study, ³¹P spin echo line shapes of BPAPC, with 5%, 10% and 15% TOP, which monitor the diluent dynamics, at different temperatures and echo delay times are simulated in terms of fast- and slow-moving components, and the resulting fractional populations are compared with that predicted by the lattice model. Comparisons with the lattice model calculations are also made in the simulation of the ¹H line shapes on BPAPC with 5% and 10% TOP, which probes both the polymer and diluent dynamics, and on BPAPC with 5% and 10% perdeuterated trioctylphosphate (DTOP), which detects only the polymer motion. Fairly good line shape simulations and agreement between the lattice model and the fitting results at low diluent concentrations are obtained in all cases. Restricted cone motion best describes the slow-moving component in the ³¹P line shape fittings. For the fast component, rotational Brownian diffusion with a distribution of correlation times corresponding to a stretched exponential function is used. An activation energy E_a of 56 kJ/mol and an exponent of 0.7 for the fractional exponential correlation function are obtained and used to calculate the mechanical loss peak which was compared with the experimental loss data. The plateau character of the fractional population as a function of temperature can also be interpreted and understood in terms of the lattice model.     

The effects of a trace addition of silver upon elevated temperature ageing of an Al–Zn–Mg alloy

Microalloying additions of Ag (0.1 at.%) increase the hardening response of Al–Zn–Mg alloys to elevated temperature ageing in the range 100–200°C due to the formation of a high density of very fine η′ precipitate plates. The present study employed transmission electron microscopy (TEM) and three-dimension atom probe (3DAP) to study the early stages of ageing in the alloy Al–1.8Zn–3.4Mg–0.1Ag (at.%) in an attempt to identify the role of Ag in stimulating precipitation hardening. During isothermal ageing at 90°C, the hardening response is attributed to a high density of Zn–Mg–Ag rich solute clusters and GP zones. During ageing at 150°C, η′ precipitates nucleate at Zn–Mg–Ag rich solute clusters, the former growing as {111} platelets with an average composition of approximately 20 at.% Zn, 20 at.% Mg and 1.4 at.% Ag. The 3DAP data indicates that the co-segregation of Zn and Ag and subsequently Zn and Mg atoms precedes the formation of the Zn–Mg–Ag rich solute clusters. The GP zones and η′ precipitates were observed to possess a Zn:Mg ratio close to 1:1, whereas the equilibrium η precipitates possessed compositions consistent with MgZn₂. Furthermore, partitioning of Ag was observed inside all precipitate phases, viz. G.P. zones, η′ and η.     

Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach

Abstract  The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl₄ is greater than the AgNO₃ at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum. The case of low concentration of extract with HAuCl₄ offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal- or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state. Graphical abstract  Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent. The rate of bioreduction of AgNO₃ is lower than the HAuCl₄ at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration of phyllanthin with AgNO₃ and HAuCl₄.      

Frequency,power and temperature dependence of the off-resonance magnetoresistance spike in irradiated 2D-electron systems

We present calculated results on frequency, power and temperature dependence of the recently discovered giant radiation-induced off-resonance magnetoresistance spike obtained in ultraclean two-dimensional electron systems. This spike shows up on the second harmonic of the cyclotron resonance. We apply the radiation-driven electron orbit model to this novel ultraclean scenario. In agreement with experiments, we obtain that the spike intensity is strongly dependent on temperature and radiation power. On the other hand, the spike position is mainly dependent on radiation frequency. These results would be of special interest from the application perspective, such as nanophotonics, ultrasensitive microwave detectors or solar cells given the strong translation of radiation energy into electrical current.     

Frequency and temperature dependence of the dielectric parameters of wide temperature range TGBA and TGBC* phases of unsymmetrical liquid crystal dimers

In the present work we have carried out frequency and temperature dependent dielectric studies of an optically active dimeric compound, 4-n-undecyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy)chalcone which shows wide temperature range twist grain boundary (TGB) phases namely TGBA and TGBC*. Dielectric permittivities and DC conductivities have been determined along and normal to the TGB helix axes. Two weak collective modes of dielectric relaxations have been detected for the planar oriented sample where permittivity is measured normal to the long axes of the molecules (but along the TGB helix axis). One mode, which exists in the MHz region, has behavior similar to those of the soft mode due to the amplitude fluctuation. The second one exists in the low frequency region (～100 Hz) and appears due to phase fluctuation as happens in the case of Goldstone mode. Sample confined between electrodes treated for the homeotropic alignment (permittivity measured normal to the helix axis) does not show any mode of relaxation in the frequency range of 1 Hz to 1 MHz. Measured permittivities suggest negative dielectric anisotropy for the system.     

Wetting of a self-assembled 1,4-benzenedimethanethiol monolayer on gold and silver: An adhesion force spectroscopy study

Using atomic force microscopy we investigated how local capillary phenomena are affected by the deposition of a self-assembled 1,4-benzenedimethanethiol (BDMT) layer on epitaxially grown Au(1 1 1) and Ag(1 1 1) films. Force-distance curves monitored at varying relative humidity show clear differences in the adhesion forces on the different samples, which can be explained in terms of a change in the wetting behavior due to the presence of the molecules. Moreover, we found that not only the chemical structure of the molecules but also their orientation strongly influences the strength of the capillary forces. A detailed analysis of the measurements shows that condensation of water vapor on Au(1 1 1) films is drastically enhanced due to the vertically aligned BDMT molecules, while on Ag(1 1 1) water condensation is reduced due to a parallel molecule orientation.