Understanding the role of intermolecular interaction on through-space charge transfer characteristics in π-stacked molecular systems is central to the rational design of electronic materials. However, a quantitative study of charge transfer in such systems is often difficult because of poor control over molecular morphology. Here we use the core-hole clock implementation of resonant photoemission spectroscopy to study the femtosecond charge-transfer dynamics in cyclophanes, which consist of two precisely stacked π-systems held together by aliphatic chains. We study two systems, [2,2]paracyclophane (22PCP) and [4,4]paracyclophane (44PCP), with inter-ring separations of 3.0 and 4.0 Å, respectively. We find that charge transfer across the π-coupled system of 44PCP is 20 times slower than in 22PCP. We attribute this difference to the decreased inter-ring electronic coupling in 44PCP. These measurements illustrate the use of core-hole clock spectroscopy as a general tool for quantifying through-space coupling in π-stacked systems.
COBISS.SI-ID: 26125351
A method of sample surface topography reconstruction is described based on the asymmetry in the X-ray yields acquired by a pair of X-ray detectors positioned at opposite sides of the probing beam. The yield asymmetries in the two simultaneously acquired elemental maps are caused by differences in the X-ray absorption along the X-ray exit route in the sample with a topographically structured surface. The approach presented introduces an asymmetry factor of the X-ray intensity in each of the image pixels to obtain an image asymmetry matrix. The dependence of the asymmetry factor on the local target inclination in the detector plane is calculated for a flat sample surface model. The image asymmetry matrix is then converted into the local inclination angle matrix. As the last step, the surface topography is then reconstructed from the local inclination angle. The method is based on X-ray absorption phenomena and could be applied equivalently in X-ray elemental mapping methods using excitation beams with a well-defined direction in the sample. This includes micro-X-Ray Fluorescence analysis (micro-XRF) and micro-Proton Induced X-ray Emission (micro-PIXE). We demonstrated the method by topographic analysis of engraved metallic samples with stereo-PIXE and compared it with the results of stylus profilometry. The smallest value of the X-ray production depth and the characteristic X-ray attenuation length determines the lateral resolution of the proposed topography reconstruction method.
COBISS.SI-ID: 25740839
The effect of γ-radiation on a variety of model vitreous wasteforms applied to, or conceived for, immobilisation of UK intermediate and high level radioactive wastes was studied up to a dose of 8 MGy. It was determined that γ-irradiation up to this dose had no significant effect upon the mechanical properties of the wasteforms and there was no evidence of residual structural defects. FTIR and Raman spectroscopy showed no evidence of radiation directly affecting the silicate network of the glasses. The negligible impact of this γ-irradiation dose on the physical properties of the glass was attributed to the presence of multivalent ions, particularly Fe, and a mechanism by which the electron–hole pairs generated by γ-irradiation were annihilated by the Fe2+–Fe3+ redox mechanism. However, reduction of sulphur species in response to γ-radiation was demonstrated by S K-edge XANES and XES data.
COBISS.SI-ID: 26062631
Wet hydrogen peroxide catalytic oxidation (WHPCO) is one of the most important industrially applicable advanced oxidation processes (AOPs) for the decomposition of organic pollutants in water. It is demonstrated that manganese functionalized silicate nanoparticles with interparticle porosity act as a superior Fenton-type nanocatalyst in WHPCO as they can decompose 80% of a test organic compound in 30 minutes at neutral pH and room temperature. By using X-ray absorption spectroscopic techniques it is also shown that the superior activity of the nanocatalyst can be attributed uniquely to framework manganese, which decomposes H2O2 to reactive hydroxyls and, unlike manganese in Mn3O4 or Mn2O3 nanoparticles, does not promote the simultaneous decomposition of hydrogen peroxide. The presented material thus introduces a new family of Fenton nanocatalysts, which are environmentally friendly, cost-effective, and possess superior efficiency for the decomposition of H2O2 to reactive hydroxyls (AOP), which in turn readily decompose organic pollutants dissolved in water.
COBISS.SI-ID: 4863514
A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.
COBISS.SI-ID: 25706535