Katarzyna Dziedzic-Kocurek

Wave propagation of induced radiation in microcapillary holes of a glass microchannel plate

Soft x-ray reflection and transmission spectra of radiation propagating inside microchannel plates have been analyzed in the framework of the wave approximation. X-ray and fluorescence yields due to the grazing incidence reflection phenomenon have been investigated with respect to the geometry of the channel walls. We also discuss x-ray absorption near-edge structure spectra collected at the exit of microcapillaries under the total x-ray reflection condition, taking into account a surface transition layer at the sample surface. The fine structures and the angular distribution of the transmitted radiation have been interpreted in the energy range of the anomalous dispersion of the Si L2,3 edges.

Excitation and propagation of X-ray fluorescence through thin devices with hollowed ordered structures: comparison of experimental and theoretical spectra

The lack of models describing the propagation of X-rays in waveguides and the interference mechanism between incident and reflected radiation waves hamper the understanding and the control of wave propagation phenomena occurring in many real systems. Here, experimental spectra collected at the exit of microchannel plates (MCPs) under the total X-ray reflection condition are presented. The results are discussed in the framework of a theoretical model in which the wave propagation is enhanced by the presence of a transition layer at the surface. The angular distributions of the propagating radiation at the exit of these MCPs with microchannels of ∼3u2005µm diameter will also be presented and discussed. These spectra show contributions associated with the reflection of the primary monochromatic beam and with the fluorescence radiation originating from the excitation of atoms composing the surface of the microchannel. The soft X-ray fluorescence spectra collected at the exit of microcapillaries were analyzed in the framework of a wave approximation while diffraction contributions observed at the exit of these hollow X-ray waveguides have been calculated using the Fraunhofer diffraction model for waves in the far-field domain. Data collected at the Si L-edge show that in glassy MCPs the fluorescence radiation can be detected only when the energy of the primary monochromatic radiation is above the absorption edge for grazing angles higher than half of the critical angle of the total reflection phenomenon. Experimental data and simulations of the propagating radiation represent a clear experimental confirmation of the channeling phenomenon of the excited fluorescence radiation inside a medium and point out that a high transmission can be obtained in waveguide optics for parameters relevant to X-ray imaging.

Spectroscopic study and electronic structure of prototypical iron porphyrins and their μ-oxo-dimer derivatives with different functional configurations

Metalloporphyrins are networking molecules with strong internal N-H hydrogen bonds that may be used to substitute a metal ion inside a porphyrin ring, forming a metallo complex. The understanding of electronic structures and charge dynamics of porphyrin based molecular architectures is mandatory to clarify biological functions, catalytic processes, and opto-electrical responses in which these molecules are involved. We present here a systematic analysis of the electronic structures and the charge dynamics of two different iron-porphyrins (i.e. protoporphyrin IX and meso-tetraphenylporphine) with different functional architectures. We investigated these prototypical porphyrins and their mu-oxo-dimer derivatives by means of Fe K-edge X-ray Absorption Near-Edge Spectroscopy (XANES) combined with theoretical calculations. The electronic structure, namely the partial projected density of states and the polarization components were discussed in terms of orbital hybridizations among metal and local ligands. Data show that hydrogens are electron donors while the central metal irons accept electrons. Moreover, the metal axial ligands exhibit different electron behaviors: donors for Cl in prototypical porphyrins and acceptors for O in mu-oxo-dimer derivatives. Actually, the charge dynamics are affected by local metal ligands, but also strongly depend on the mid-range atomic ordering of the porphyrins network. The charge dynamics, evaluated from the self-consistent local potential, is associated with charge transfer mechanisms involving interactions with the axial ligands as well as with the substituents. The quantum chemical topology analysis of the electron localization function (ELF) has been used to identify the distribution of the electron pairs. They are localized around Cl atoms regardless of porphyrin configurations. Charge dynamics and electron localization are fundamental information for a deep understanding of the role of porphyrin and porphyrin-like molecules in a wide range of molecular biophysical mechanisms and in materials science processes.

Mobility of interacting inorganic nanoparticles

Abstract The mobility of the 110 nm-Fe2O3 particles in a viscous sucrose solution depends on the concentration of the nanoparticles. When the average particle–particle nearest neighbor distance is less than 250 nm, the particle interaction slows down their mobility. When is more than 170 nm, the small mobility of nanoparticles does not depend on their concentration. The critical distance is approximately equal to 2Rh = 260 nm, where Rh is the hydrodynamic radius, determined by the dynamic light scattering (DLS) method.

Mössbauer study of a tetrakis (pentafluorophenyl) porphyrin iron (III) chloride in comparison with the fluorine unsubstituted analogue

Abstract Mössbauer investigations, in association with density functional theory (DFT) calculations, have been conducted for the molecular and electronic structures of iron (III) [tetrakis (pentafluorophenyl)] porphyrin chloride [(F20TPP)Fe:Cl], as a Fe(III)-tetraphenylporphyrin complex containing chloride axial ligand and substituted hydrogen atoms by fluorine ones in the four phenyl rings, in comparison with its fluorine unsubstituted analogue [(TPP)Fe:Cl]. It was found that the parameters of Mössbauer spectra of both complexes are close to one another, and correspond to the high-spin state of Fe(III) ions, but they show the different temperature dependence and the quadrupole doublets in Mössbauer spectra show different asymmetry at low temperatures. Results of DFT calculations are analyzed in the light of catalytic activity of the halogenated complex.