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Abstract: A novel neutron and X-ray reflectometry sample environment is presented for the study of surface-active molecules at solid–liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide–dodecane interface at a shear rate of 7.0×102 7.0 × 10 2 s−1 s − 1 using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of 7.0×102 7.0 × 10 2 s−1 s − 1 was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be 24.3+9.9−10.2 24.3 − 10.2 + 9.9 Å under direct shear at 7.0×102 7.0 × 10 2 s−1 s − 1 and 25.8+4.4−5.2 25.8 − 5.2 + 4.4 Å when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at 3.0×103 3.0 × 10 3 s−1 s − 1 .

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Abstract: Understanding the nanostructure and nanomechanical properties of surface layers of erucamide, in particular the molecular orientation of the outermost layer, is important to its widespread use as a slip additive in polymer materials. Extending our recent observations of nanomorphologies of erucamide layers on a hydrophilic silica substrate, here we evaluate its nanostructure on a more hydrophobic polypropylene surface. Atomic force microscopy (AFM) imaging revealed the molecular packing, thickness, and surface coverage of the erucamide layers, while peak force quantitative nanomechanical mapping (QNM) showed that erucamide reduced the adhesive response on polypropylene. Synchrotron X-ray reflectivity (XRR) was used to probe the out-of-plane structure of the surface layers. Static contact angle measurements further corroborated on the resulting wettability, also demonstrating the efficacy of erucamide physisorption in facilitating control over polypropylene surface wetting. The results show the formation of erucamide monolayers, bilayers and multilayers, depending on the concentration in the spin-cast solution. Correlation of AFM, XRR and wettability results consistently points to the molecular orientation in the outermost layer, i.e. with the erucamide tails pointing outward for the surface nanostructures with different morphologies (i.e., bilayers and multilayers). Rare occurrence of monolayers with exposed hydrophilic head groups were observed only at the lowest erucamide concentration. Compared with our previous observations on the hydrophilic surface, the erucamide surface coverage was much higher on the more hydrophobic propylene surface at similar erucamide concentrations in the spin-cast solution. Furthermore, the structure, molecular orientation and nanomechanical properties of the spin-cast erucamide multilayers atop polypropylene were also similar to those on industrially relevant polypropylene fibers coated with erucamide via blooming. These findings shed light on the nanostructural features of the erucamide surface layer underpinning its nanomechanical properties, relevant to many applications in which erucamide is commonly used as a slip additive.

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Abstract: Organic solar cells (OSCs), also known as organic photovoltaics (OPVs), are an emerging solar cell technology composed of carbon-based, organic molecules, which convert energy from the sun into electricity. Key for their performance is the microstructure of the light-absorbing organic bulk heterojunction. To study this, organic solar films composed of both fullerene C60 as electron acceptor and different mole percentages of di-[4-(N,N-di-p-tolyl-amino)-phenyl]-cyclohexane (TAPC) as electron donor were evaporated in vacuum in different mixing ratios (5, 50 and 95 mol%) on an ITO-coated glass substrate held at room temperature and at 110 °C. The microstructure of the C60: TAPC heterojunction was studied by grazing incidence wide angle X-ray scattering to understand the effect of substrate heating. By increasing the substrate temperature from ambient to 110 °C, it was found that no significant change was observed in the crystal size for the C60: TAPC concentrations investigated in this study. In addition to the variation done in the substrate temperature, the variation of the mole percent of the donor (TAPC) was studied to conclude the effect of both the substrate temperature and the donor concentration on the microstructure of the OSC films. Bragg peaks were attributed to C60 in the pure C60 sample and in the blend with low donor mole percentage (5%), but the C60 peaks became nondiscernible when the donor mole percentage was increased to 50% and above, showing that TAPC interrupted the formation of C60 crystals.

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Abstract: Organic semiconductors offer a flexibility in band gap tuning through different molecular lengths and have shown to be promising candidates for high‐performance electronic devices. While electronic properties have been extensively studied in many publications, the topic of thin film structure and molecular packing is still quite neglected. In this work, the thin film crystal structure of [6]phenacene (Fulminene) and [7]phenacene deposited on silicon substrates using the OMBD method as well as further studies with potassium deposition on [6]phenacene are investigated. Ex‐situ X‐ray and optical methods are employed to obtain an insight into the crystal structure and optical properties. The orientation of the molecules and the unit cell structure is calculated from the measured reciprocal space maps. Additionally, the influence of a possible interfacial doping mechanism by deposition of potassium on top of [6]phenacene is investigated. Thin films of [6]phenacene show a high crystallinity with a standing‐up configuration and a similar molecular structure and symmetry compared to [4]phenacene. [7]phenacene features two different apparently thickness‐dependent polymorphs (H and L) with a structure similar to [5]phenacene. These results reveal that odd/even parity, that is, even or odd number of benzene rings, directly influences the phenacene thin film structure.

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Abstract: This thesis focuses on understanding the fundamental chemistry of metal oxide and chalcogenide interfaces with potential applications to novel photovoltaic devices. Both anatase and rutile TiO2 are commonly used in photovoltaic devices, water splitting devices and sun screen. However, due to their large band gaps, 3.0 eV and 3.2 eV respectively, they require sensitisation to allow absorption of the visible range of the solar spectrum. The chemistry of this interface between the electron transport layer and sensitiser, and how it may be enhanced by the addition of small organic molecules is particularly important in solar cell research as it can be an area of significant efficiency losses or gains. Two surface sensitive techniques have been employed to probe the surface structure and interactions, X-ray photoelectron spectroscopy and surface Xray diffraction. In this thesis it has been shown that the band alignment of 2D SnS with anatase and rutile TiO2 is a type II overlap. Resonant photoemission spectroscopy was also employed to further understand the interactions between the TiO2 surfaces and 2D SnS, and elucidate the chemical states contributing to the valence band of SnS. XPS has also been used to understand the surface reactivity of PbS when exposed to O2 and H2O. It has been shown that upon exposure of PbS to O2 and H2O that PbSO4 and Pb hydroxyl species are produced in significant amounts. The adsorption of dopamine onto the PbS surface pre-exposure significantly reduces the degradation of the PbS surface. Surface X-ray diffraction was then used to further define the arrangement of dopamine on anatase TiO2 (101) surface, which is a system that has attracted a lot of research interest both theoretical and experimental. This study uses current theoretical and experimental models of the dopamine/anatase TiO2 structure to compare with surface X-ray diffraction data recorded, allowing the geometry of dopamine on the anatase TiO2 surface to be defined.