Jacek Filipecki

Positronics of subnanometer atomistic imperfections in solids as a high-informative structure characterization tool.

Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy applied to characterize different types of nanomaterials treated within three-term fitting procedure are critically reconsidered. In contrast to conventional three-term analysis based on admixed positron- and positronium-trapping modes, the process of nanostructurization is considered as substitutional positron-positronium trapping within the same host matrix. Developed formalism allows estimate interfacial void volumes responsible for positron trapping and characteristic bulk positron lifetimes in nanoparticle-affected inhomogeneous media. This algorithm was well justified at the example of thermally induced nanostructurization occurring in 80GeSe2-20Ga2Se3 glass.

Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

The new transition-metal manganite Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

Water-sensitive positron trapping modes in nanoporous magnesium aluminate ceramics

The water-sensitive positron trapping modes in nanoporous MgAl2O4 ceramics with a spinel structure are studied. It is shown that water-sorption processes in magnesium aluminate ceramics leads to corresponding increase in positron trapping rates of extended defects located near intergranual boundaries. This catalytic affect has reversible nature, being strongly dependent on sorption water fluxes in ceramics. The fixation of all water-dependent positron trapping inputs allow to refine the most significant changes in positron trapping rate of extended defects.

Voids in mixed-cation silicate glasses: Studies by positron annihilation lifetime and Fourier transform infrared spectroscopies ☆

PALS in comparison with FTIR studies have been applied to investigate the structure of different oxide glasses. Three components of the positron lifetime τ (τ1 para- and τ3 ortho-positronium and τ2 intermediate lifetime component) and their intensities were obtained. The results of the calculation of mean values of positron lifetimes for the investigated glasses showed the existence of a long-living component on the positron annihilation lifetime spectra. From the Tao-Eldrup formula we can estimate the size of free volume. On the basis of the measurements we can conclude that the size and fraction of free volume reaches the biggest value for the fused silica glass. The degree of network polymerisation increases void size.

Studying Functional Properties of Hydrogel and Silicone-Hydrogel Contact Lenses with PALS, MIR and Raman Spectroscopy

Determination of free volume holes of the hydrogel and silicone-hydrogel polymer contact lenses were investigated. Two types of polymer contact lenses were used as materials: the first is a hydrogel contact lenses Proclear family (Omafilcon A), while the second is a silicone-hydrogel contact lens of the family Biofinity (Comfilcon A). Positron annihilation lifetime spectroscopy PALS was used to characterize geometrical sizes and fraction of the free volume holes in the investigated samples. There is a clear difference in the free volume sizes and their fractions between silicone-hydrogel and polymer hydrogel contact lenses which in turn are connected with oxygen permeability in these lenses. Apart from that, spectroscopic (middle infrared) MIR and Raman examinations were carried out in order to demonstrate the differences of the water content in the test contact lenses.

PALS as characterization tool in application to humidity-sensitive electroceramics

It is shown that positron annihilation lifetime spectroscopy is a quite promising tool for nanostructural characterisation of humidity-sensitive spinel-type MgAl2O4 ceramics, the results being achieved provided four-component fitting procedure with arbitrary lifetimes is applied to treat mathematically the measured spectra. It is shown that Tao-Eldrup model is adequate for calculation of nanopore size in MgAl2O4 ceramics using lifetime values of the third and four components.

Influence of lanthanum on structural and magneto-optic properties of diamagnetic glasses of the TeO2–WO3–PbO system

This paper is focused on the design, fabrication and characterization of tellurite glass of composition TeO2–WO3–PbO in terms of La2O3 addition. The effect of La2O3 on the structure of the obtained glasses has been investigated by means of spectrophotometric and ellipsometric measurements in the UV-Vis-NIR spectral region and then relevant optical parameters have been calculated. The DC magnetic susceptibility study has been used to investigate the influence of lanthanum ion (La3+) on the structural and magnetic properties of the investigated glass system. Based on DTA, PALS and Raman studies, it can be stated that modification of the basic structural units with La3+ ions, namely the TeO4 trigonal bipyramid (tbp) and the TeO3 trigonal pyramid (tp), both having a lone pair of electrons occupying one of the equatorial positions, affect the magnetic properties of these glasses.

Investigations of Faraday effect in oxide glasses for optoelectronics devices

Amorphous glassy materials are of great interest on account of their possible application in optical electronics and glass fiber techniques. In this article lead-bismuth-gallium oxide glasses has been investigated. These materials are characterized by the great value of refractive index and because of absence of paramagnetic ions possess good magneto-optic properties. Measurements of the Faraday effect confirm the occurrence considerable value of the Verdet constant in the group of glasses without rare-earth elements, promising for application in magneto-optic devices.

Extended defects in insulating MgAl2O4 ceramic materials studied by PALS methods

Extended positron-trapping defects in technological modified insulating nanoporous MgAl2O4 ceramics are characterized by positron annihilation lifetime spectroscopy. The results are achieved using three-component fitting procedure with arbitrary lifetimes applied to treatment of measured spectra. Within this approach, the first component in the lifetime spectra reflects microstructure specificity of the spinel structure, the second component responsible to extended defects near intergranual boundaries and the third component correspond to ortho-positronium pick-off decaying in nanopores of ceramics. It is shown that in ceramics of different technological modifications the same type of positron traps prevails.

An investigation of the effect of silicone oil on polymer intraocular lenses by means of PALS, FT-IR and Raman spectroscopies,

The effect of the polydimethylsiloxane (PDMS) based silicone oil, that is widely used in vitreoretinal surgery, on internal structures of the polymer intraocular lenses was investigated. The effect of PDMS was studied on the polymethyl methacrylate (PMMA) rigid lenses and poly(2-hydroxyethyl methacrylate) (PHEMA) flexible lenses. The research was carried out by means of the positron lifetime spectroscopy (PALS) as well as the infrared spectroscopy (FT-IR) and the Raman spectroscopy (RS). The studies involving the use of PALS and FT-IR methods have revealed that the PHEMA based lenses absorbed, whereas the PMMA lenses did not absorb, silicone oil. The results obtained with the use of the RS method were inconclusive, probably due to the too low intensity of the characteristic PDMS bands. The evidence from this study was discussed in terms of physics and related to the clinical use of both silicone oil and intraocular lenses.