RESUMEN
Oleophobic surfaces have been so far realized using complex microscale and nanoscale re-entrant geometries, where primary and secondary structures or overhang geometries are typically required. Here, we propose a new design to create them with noninteracting cavities. The suspension of liquid droplets relies on the mechanism of compression of air under the meniscus leading to stable composite oil-air-solid interfaces. To demonstrate the concept, we make oleophobic surfaces, with contact angle for oleic acid of about 130° (and hexadecane about 110°), using both microholes in silicon and nanoholes in glass. Thanks to the subwavelength dimensions and antireflection effect of the nanoholes, the glass substrate also shows a high degree of optical transparency with optical transmission exceeding that of the initial bare substrate. Crockmeter tests without any significant change in morphology, optical and wetting properties after more than 500 passes also confirm the high mechanical durability of the nanohole surface. The results indicate the possibility of using the proposed oleophobic surfaces for a wide range of applications, including self-cleaning transparent windows and windshields for automobiles and aircrafts.
RESUMEN
As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193 and 157 nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide bandgap metal fluorides become the materials of choice for the laser optics applications. To understand the optical properties of nanostructure fluoride films, thin GdF(3) films grown on CaF(2) (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the GdF(3) film was revealed with improved ellipsometric modeling, suggesting the existence of multilayer structure, a densified bottom layer, middle layers with increasing porosity, and a rough surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nanostructure to environmental contamination was experimentally demonstrated.