Physical phenomena of thin surface layers
This thesis explores different physical phenomena observed in, or involving thin surface ﬁlms. Thin surface layers are ubiquitous. Found in nature and used in almost every aspect of daily life, thin surface ﬁlms are invaluable. While the applications and roles may be varied, to be used effectively, the physical properties of these ﬁlms and the factors inﬂuencing their stability need to be well understood. Surfaces can have a strong effect on the stability of thin ﬁlms. In thin ﬁlms of polymer blends, wetting layers rich in one component often form at the ﬁlm interface prior to phase separation. Here the formation of these wetting layers are seen to result in destabilisation of the ﬁlm, even when the blend is far from phase coexistence. A spinodal like instability with a characteristic wavelength is shown to form. A theoretical model is developed, which describes the observed behaviour in terms of coupled height and composition ﬂuctuations in the wetting layer. Spin coating is a common technique for the formation of thin polymer ﬁlms. Films formed in this way however, are often seen to exhibit anomalous properties, which strongly differ from that of the bulk behaviour of the material. Here the rheological properties and stored stresses in spin cast ﬁlms are explored, with focus on the role that the casting solvent plays in the properties of the ﬁlm. The results suggest that the observed deviation comes from a lowered density of chain entanglements. The effective viscosity and residual stresses in the as-spun ﬁlm are seen to strongly depend on the casting solvent properties and the solvent-polymer interactions. The use of organometallic polymers as precursors for the formation of magnetic ceramics is investigated. Emphasis is placed on doping the polymers with metallic compounds prior to pyrolysis, allowing for the formation of technologically interesting metallic alloys, without the need for new polymers to be synthesised. The formation of iron-palladium alloys is demonstrated using this method. These are highly desirable due to their potential use in hard-disk drive technologies. Thin ﬁlms can be used to inﬂuence the optical signature of a material and are widely used in nature to produce vibrant, pure, iridescent colours. Here the optical properties of the tropical plant Selaginella willdenowii are explored. The bright blue colouration is seen to arise from a multilayer lamella structure on the upper surface of the leaves. Light is important to plants, who use it both as an energy source and an environmental signal. Blue iridescence occurs in a wide range of plant species, suggesting that it has some adaptive beneﬁt. These are considered and discussed.