David Batchelor

A gas-phase photoelectron spectroscopy and X-ray absorption spectroscopy study of 1,2,3-benzotriazole and methyl derivatives was undertaken to investigate the influence of the tautomerism on the spectroscopic signature in greater detail. Soft X-ray photoelectron spectroscopy of the nitrogen core level, nitrogen K-edge near-edge X-ray absorption fine-structure measurements, and mapping of the resonant Auger spectroscopy were performed. High-energy ultraviolet photoemission spectroscopy was also undertaken to compare with the previous studies using low-energy low-energy Helium I and Helium II excitation. The gas-phase characterization is an essential step for interpreting adsorbed molecular phases and thin films on surfaces. The results also served as a test of STOBE density functional theory calculations, in particular the near edge.

To characterize an electron beam, visible synchrotron light is often used and dedicated beamlines at synchrotron sources are becoming a more common feature as instruments and methods for the diagnostics are, along with the accelerators, further developed. At KARA (Karlsruhe Research Accelerator), such a beamline exists and is based on a typical infrared/visible-light configuration. From experience at such beamlines no significant radiation was expected (dose rates larger than 0.5 µSv h−1). This was found not to be the case and a higher dose was measured which fortunately could be shielded to an acceptable level with 0.3 mm of aluminium foil or 2.0 mm of Pyrex glass. The presence of this radiation led to further investigation by both experiment and calculation. A custom setup using a silicon drift detector for energy-dispersive spectroscopy (Ketek GmbH) and attenuation experiments showed the radiation to be predominantly copper K-shell fluorescence and is confirmed by calculation. The measurement of secondary radiation from scattering of synchrotron and other radiation, and its calculation, is important for radiation protection, and, although a lot of experience exists and methods for radiation protection are well established, changes in machine, beamlines and experiments mean a constant appraisal is needed.

N-donor ligands such as n-Pr-BTP [2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine] preferentially bind trivalent actinides (An³⁺) over trivalent lanthanides (Ln³⁺) in liquid–liquid separation. However, the chemical and physical processes responsible for this selectivity are not yet well understood. Here, an explorative comparative X-ray spectroscopy and computational (L ₃-edge) study for the An/Ln L ₃-edge and the N K-edge of [An/Ln(n-Pr-BTP)₃](NO₃)₃, [Ln(n-Pr-BTP)₃](CF₃SO₃)₃ and [Ln(n-Pr-BTP)₃](ClO₄)₃ complexes is presented. High-resolution X-ray absorption near-edge structure (HR-XANES) L ₃-edge data reveal additional features in the pre- and post-edge range of the spectra that are investigated using the quantum chemical codes FEFF and FDMNES. X-ray Raman spectroscopy studies demonstrate the applicability of this novel technique for investigations of liquid samples of partitioning systems at the N K-edge.

X-SPEC is a high-flux spectroscopy beamline at the KIT (Karlsruhe Institute of Technology) Synchrotron for electron and X-ray spectroscopy featuring a wide photon energy range. The beamline is equipped with a permanent magnet undulator with two magnetic structures of different period lengths, a focusing variable-line-space plane-grating monochromator, a double-crystal monochromator and three Kirkpatrick–Baez mirror pairs. By selectively moving these elements in or out of the beam, X-SPEC is capable of covering an energy range from 70 eV up to 15 keV. The flux of the beamline is maximized by optimizing the magnetic design of the undulator, minimizing the number of optical elements and optimizing their parameters. The beam can be focused into two experimental stations while maintaining the same spot position throughout the entire energy range. The first experimental station is optimized for measuring solid samples under ultra-high-vacuum conditions, while the second experimental station allows in situ and operando studies under ambient conditions. Measurement techniques include X-ray absorption spectroscopy (XAS), extended X-ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X-ray PES (HAXPES), as well as X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS).

Transition metal porphyrazines are a widely used class of compounds with applications in catalysis, organic solar cells, photodynamic therapy, and nonlinear optics. The most prominent members of that family of compounds are metallophtalocyanines, which have been the subject of numerous spectroscopic and theoretical studies. In this work, the electronic structure and X‐ray absorption characteristics of three Cu‐porphyrazine derivatives are investigated by means of modern electronic structure theory. More precisely, the experimentally observed N K‐edge and Cu L‐edge features are presented and reproduced by time‐dependent density functional theory, restricted open‐shell configuration interaction, and a restricted active space approach. Where possible, the calculations are used to interpret the observed spectroscopic features in terms of electronic transitions and, furthermore, to connect spectral differences to chemical variations. Part of the discussion of the computational results concerns the impact of various parameters and approximations that are used for the calculations, for example, the choice of active space.

The reactivity of benzotriazole with copper on a gold surface has been studied by a combination of surface sensitive methods with support from DFT (density functional theory) calculations. For some time benzotriazole has been known to enhance the corrosion resistance of copper at the monolayer level, although the exact mechanism is still a matter of discussion and disagreement in the literature. A single crystal Au(111) surface allows evaluation of the interaction of weakly physisorbed, intact benzotriazole molecules with copper atoms dosed to sub-monolayer amounts. These interactions have been characterised, in the temperature range ca. 300–650 K, by scanning tunnelling microscopy, high resolution electron energy loss spectroscopy and synchrotron-based X-ray photoemission spectroscopy and near-edge X-ray absorption fine structure studies. Supporting DFT calculations considered the stability of isolated, gas-phase, benzotriazole/Cu species and their corresponding spectroscopic signature at the N K absorption edge. In agreement with previous investigations, benzotriazole physisorbs on a clean Au(111) surface at room temperature forming a hydrogen-bonded network of flat-lying BTAH molecules, relatively weakly bonded to the underlying gold surface. However, in the presence of co-adsorbed copper atoms, proton removal from the molecules leads to species better described as BTA⁻ interacting directly with Cu atoms. In these situations the molecules adopt a more upright orientation and Cu(BTA)₂ and –[Cu(BTA)]_n– species are formed, depending on temperature and coverage of the adsorbed species. These species are stable to relatively high temperatures, 550–600 K.

Geometrical structure and electronic characteristics of ultrathin metallic films of one metal on another are strongly influenced by factors such as lattice mismatch and formation of near-surface alloys. Doped systems often show modified chemico-physical properties which may be amenable to different reactivity routes. Copper–gold surface alloys have received the attention of several studies, only a few of which have been undertaken in an ultra-high vacuum environment, using surface sensitive techniques. In this contribution, systems produced upon room temperature deposition of copper on the (22 × √3)-Au(111) surface, at various copper loadings and annealed to different temperatures, are investigated using scanning tunneling microscopy and synchrotron radiation based techniques (X-ray photoelectron diffraction, photoemission), with comparison with some theoretical modeling. Overall the fcc lattice is essentially maintained on preparation. Upon thermal treatments structural and compositional changes, in favor of alloyed structures with tetragonal packing, are seen.