Open Access

Show Abstract ▼

Abstract: Conjugated polymers are an important class of chromophores for optoelectronic devices. Understanding and controlling their excited state properties, in particular, radiative and non-radiative recombination processes are among the greatest challenges that must be overcome. We report the synthesis and characterization of a molecularly encapsulated naphthalene diimide-based polymer, one of the most successfully used motifs, and explore its structural and optical properties. The molecular encapsulation enables a detailed understanding of the effect interpolymer interactions. We reveal that the non-encapsulated analogue P(NDI-2OD-T) undergoes aggregation enhanced emission; an effect that is suppressed upon encapsulation due to an increasing p-interchain stacking distance. This suggests that decreasing p-stacking distances may be an attractive method to enhance the radiative properties of conjugated polymers in contrast to the current paradigm where it is viewed as a source of optical quenching.

Show Abstract ▼

Abstract: Electronic states within the HOMO–LUMO gap of organic semiconductors play a key role in the energy level alignment of substrate–organic and organic–organic interfaces and therefore are a defining parameter for device functionality and efficiency. They are thought to result from structural defects influencing the specific environment of a molecule. Varying the substrate temperature for samples grown by molecular beam deposition, we are able to control their density. Using atomic force microscopy and X-ray scattering techniques, we can differentiate defects depending on their length scale and effective direction. Comparison of the respective defect density with the density of gap states, measured directly via ultra-low-background ultraviolet photoelectron spectroscopy, enables to correlate structural and electronic properties for different prototypical organic semiconductors. We investigate the impact of gap states on the energy level alignment and find a direct link between structural defects and the interface dipole.

Open Access

Show Abstract ▼

Abstract: The oxidation of copper is essential for several fields, such as corrosion, catalytic methanol synthesis, and CO electroreduction. However, the understanding of the oxidation of copper under various conditions is not complete. Here, we study the oxidation of the vicinal Cu(911) surface by O with in-situ Surface X-ray Diffraction. It was found that the surface facets to (410), (401), and (100) which are stable in the parameter range of =25-400 C and mbar O . The (410) and (401) facets are present until the surface is further oxidized to Cu O, at mbar and above. These results further the knowledge on the oxidation of copper and its surfaces, which may be of importance for a wide range of applications.

Show Abstract ▼

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.

Open Access

Show Abstract ▼

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 .