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In order for next generation solar technologies to continue to improve, detailed chemical and electronic information is essential. Core-level spectroscopies, such as X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and resonant photoelectron and Auger spectroscopies are capable of providing this information. These techniques have been used for decades across many systems but are limited to ultra-high vacuum pressures, however more recently measurements at ambient pressures have become possible. The thesis presented herein applies core-level spectroscopies to two systems: dye sensitised solar cells and solar water splitting. In the former, ultra-high vacuum core-level spectroscopies are employed to probe the chemical and electronic coupling between the dye and substrate. For the latter, ambient-pressure X-ray photoelectron spectroscopy allows the oxidation of a potential solar water splitting catalyst to be monitored. To begin, a relatively simple dye, C343, is investigated on different mesoporous substrates; TiO2 and SrTiO3. These samples were prepared ex-situ and, in the case of TiO2, compared to samples prepared by thermally evaporating C343 in-situ. By also comparing to a multilayer of dye, a detailed description of how the dye is bonded to the substrates is presented and the density of states probed. To assist in the dye's analysis, a similar dye, C334, is also investigated. Next, core-level spectroscopies are applied to a more complicated dye-TiO2 system involving the well-known dye N3 as the sensitiser. Here, the bonding to the surface is confirmed by X-ray photoelectron spectroscopy. In addition, resonant Auger electron spectroscopy is used to quantify both charge delocalisation within the molecule as well as injection into the substrate conduction band. Hard X-rays are used to study excitations from both the S 1s and Ru 2p3/2 core levels. The effect of the substrate is seen on the calculated charge transfer dynamics, and a picture of charge transfer from the thiocyanate ligand discussed. Two further dye-TiO2 systems are investigated using core level spectroscopies; RuP and RuC. These dyes are qualitatively very similar, differing only in their anchoring group. Resonant Auger electron spectroscopy is again employed, alongside resonant photoelectron spectroscopy, to quantify the charge injection and delocalisation times of both dyes. In this context, the measurements are a probe of how the anchoring group influences the injection dynamics of dye-sensitised solar cells. It is found that both dyes are capable of sub- femtosecond charge injection in the Ru 2p3/2 excited regime, however that RuP is favoured for its slower relaxation. Finally, ambient pressure X-ray photoelectron spectroscopy is used to study the oxidation chemistry of a prospective solar water splitting catalyst: TiSi2. Both powder and thin film samples are investigated, where the latter were employed in order to remove the natural oxidation caused by air. To do so, different passivation layers were investigated to preserve the TiSi2 layer. From the measurements, it is suggested that the reported catalytic activity of TiSi2 is related to the growth of a sub- stoichiometric silicon oxide, and the minimisation of SiO2 at the TiSi2 surface.

Antibiotic resistance is fast becoming a global health crisis, with the increase in resistant bacteria outpacing the generation and translation of new antibiotics. Bacteria at interfaces can produce a self-made architecture called a biofilm that acts as a physical barrier, significantly reducing the efficacy of antibiotics. The aim of this part of the project was to assess the material properties of developing biofilms non-invasively. Passive microrheology was used investigate biofilms produced by Staphylococcus aureus under various hydrodynamic shears and when exposed to different anti-biofilm enzymes. Biofilms grown under any shear stress were harder (i.e. had a lower creep compliance) than equivalent biofilms grown in stationary media. Furthermore, statistical analysis of the spatial arrangement of bacteria during biofilm growth revealed clustering as a function of height away from the interface surface. The cationic peptide G3 has been shown to be a potential antimicrobial peptide, however the exact mechanism of action is unknown. Two methods were used to probe the interaction of the peptide with the bacteria membrane. Firstly, a novel 3-dimensional tracking method incorporating photoswitchable fluorophores and an adaptive optics-based super-resolution imaging technique was used to investigate the spatial distribution of G3 following exposure in Staphylococcus aureus and Escherichia coli. No preferential localisation of G3 could be observed (i.e. G3 was homogeneously distributed within the cell) for both bacteria. Diffusion kinetics were approximated from short trajectories using a newly developed neural net software package; however no spatial dependences were observed suggesting a weak binding to the membrane. To further investigate the strength of the interaction between G3 and the cell membrane, solid state nuclear magnetic resonance was employed. Using a model phospholipid system, increased disorder (i.e. spatial fluctuations) was observed in bilayers exposed to G3, suggesting a transient interaction with the membrane. From this and the tracking data, we hypothesise that G3 transiently interacts broadly with the entire membrane to cause accumulative strain disruption. No significant clustering or decreases in order parameters suggesting a strong binding with the membrane were observed, however no positive control was assessed in this study.