6 research outputs found
Microsphere Lithography on Hydrophobic Surfaces for Generating Gold Films that Exhibit Infrared Localized Surface Plasmon Resonances
Evaporation induced self-assembly
is an established method for
producing close-packed two-dimensional sphere masks on hydrophilic
surfaces such as glass. In sphere lithography, gold or silver is deposited
over sphere masks to generate a film-over-nanospheres or a nanoprism
array that can be used as a sensing surface in localized surface plasmon
extinction and surface enhanced Raman spectroscopy experiments. Sphere
lithography is less commonly used to prepare sphere masks on hydrophobic
surfaces associated with infrared window materials, in part because
it is challenging to find solvents with wetting and evaporation characteristics
that are appropriate for such surfaces. This wetting challenge can
be overcome with appropriate surfactants. However, surfactant residues
are then left behind on the sensing surface. We report methods for
depositing monolayer crystalline sphere masks onto CaF<sub>2</sub> windows that minimize surfactant residue by either using ethanol
as a volatile cosolvent that enhances wetting, or by increasing the
concentration of colloid to compensate for the reduced attractions
between spheres and surface. The rate of evaporation of solvents from
the colloid drop is controlled by fixing the headspace partial pressure
of ethanol and/or water