Measurements of contact angle of ethanol-water solutions were performed on crystalline silicon and on mesoporous silicon films with porosities up to ∼72%. Water contact angles of 44 • and 76 • were measured for untreated and HF-dipped crystalline silicon, respectively, consistent with previous studies. The contact angle for ethanol-water mixtures was found to decrease with increasing ethanol concentration for both untreated crystalline silicon and also for HF-dipped crystalline silicon up to an ethanol concentration of ∼80%; at higher concentrations the contact angle approached zero. Similar behaviour was observed on mesoporous silicon surfaces for ethanol concentrations 40%, above which the contact angle dropped abruptly to an immeasurably small value. This behaviour is attributed to a decrease in surface tension with increasing ethanol concentration. For all ethanol-water solutions, a minimum value of contact angle was observed at a porosity of ∼40%, above which it remained approximately constant. The behaviour of contact angle with porosity can be explained by a change in the Wenzel roughness parameter due to changes in the specific surface area of the film.

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An overview of the inelastic laser light scattering technique of Brillouin spectroscopy and its application to the study of hypersound in a diverse set of materials systems will be presented. In particular, results obtained from recent Brillouin scattering experiments on natural gastropod mucus, layered high temperature superconductor Bi2Sr2CaCu2O8+δ, biotite micas, and satellite tobacco mosaic virus crystals will be highlighted. Collectively, these results demonstrate the utility of Brillouin light scattering spectroscopy as a sensitive non-destructive probe of hypersound velocity and attenuation in the vicinity of structural phase transitions, the influence of chemical composition and incommensurate structure on material elasticity, and of phonon dynamics in challenging materials classes.