Two different straightforward synthetic approaches are presented to fabricate long-range-ordered monolayers of a covalent organic framework (COF) on an inert, catalytically inactive graphite surface. Boronic acid condensation (dehydration) is employed as the polymerization reaction. In the first approach, the monomer is prepolymerized by a mere thermal treatment into nanocrystalline precursor COFs. The precursors are then deposited by drop-casting onto a graphite substrate and characterized by scanning tunneling microscopy (STM). While in the precursors monomers are already covalently interlinked into the final COF structure, the resulting domain size is still rather small. We show that a thermal treatment under reversible reaction conditions facilitates on-surface ripening associated with a striking increase of the domain size. Although this first approach allows studying different stages of the polymerization, the direct polymerization, that is, without the necessity of preceding reaction steps, is desirable. We demonstrate that even for a comparatively small diboronic acid monomer a direct thermally activated polymerization into extended COF monolayers is achievable.
Plasma treatment at atmospheric pressure using a dielectric barrier discharge was carried out to increase the surface hydrophilicity of wood and wood-based materials. Surface energy determination by contact angle measurement revealed an increase in the polar component of surface energy and in total surface energy following plasma treatment. X-ray photoelectron spectroscopy revealed the generation of polar groups and consequently an increase in O/C ratio. The feasibility of plasma polymerization on wooden substrates at atmospheric pressure to create water-repellent characteristics was also investigated. An atmospheric-pressure plasma jet using hexamethyldisiloxane as precursor and air as process gas was used for thin-layer deposition. Treatment parameters for the layer deposition were investigated, as well as the layer topography and chemical composition. Atomic force microscopy revealed a closed surface layer consisting of silicon, oxygen, carbon and hydrogen that exhibited low water permeability.
The initial stage of thermal oxidation of bare Zr within the temperature range of 373-773 K at a pO 2 of 2 × 10 −6 Pa was investigated by combined application of angle-resolved XPS (AR-XPS) and in situ spectroscopic ellipsometry (SE). A model description of the oxide-film growth kinetics was achieved adopting coupled currents of cations and electrons within a surface-charge field. The model could be fitted very well to the experimental data, thereby yielding profound knowledge of the relation between the oxidation mechanism and the developing oxide-film microstructure.
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