Optically Defined Multifunctional Patterning of Photosensitive Thin-Film Silica Mesophases

Abstract

Photosensitive films incorporating molecular photoacid generators compartmentalized within a silica-surfactant mesophase were prepared by an evaporation-induced self-assembly process. Ultraviolet exposure promoted localized acid-catalyzed siloxane condensation, which can be used for selective etching of unexposed regions; for "gray-scale" patterning of refractive index, pore size, surface area, and wetting behavior; and for optically defining a mesophase transformation (from hexagonal to tetragonal) within the film. The ability to optically define and continuously control both structure and function on the macro- and mesoscales is of interest for sensor arrays, nanoreactors, photonic and fluidic devices, and low-dielectric-constant films.

Morphological control of surfactant-templated metal oxide films

“…Macroscopic patterning of these materials has been demonstrated previously using micromolding [8], differential wetting, ink jet printing, dip pen lithography [44], and even light [45]. Although the state-of-the-art in non-traditional patterning continues to evolve [46••], the last few years have seen few significant developments in patterning of thin-film inorganic mesophases.…”

Development of an efficient large-aperture high damage-threshold sol-gel diffraction grating.

“…These processes typically use an organosilane modified metal alkoxide, often in conjunction with a photoinitiator to locally polymerize the organosilane. We have recently shown [17] that the polymerization increases the refractive index of the exposed region relative to the unexposed region (Δn ≈ 0.025). Although we investigate these photosensitive sol-gel films for large area diffraction gratings, their usefulness may be limited by a number of factors: low refractive index difference, low film thickness (and questionable UV penetration through thicker films), and 450…”

“…A value of Δn=0.06 for n 0 =1.35 refers to n=n 0 ±Δn/2, allowing n to vary from 1.32 to 1.38. To date, Δn's in sol-gel have only reached 0.02 [17] while they have reached 0.25 in DCG [29]. For the average n 0 =1.35 considered, we will only consider values of Δn up to 0.2, since this is an acceptable value for DCG (although it requires a great development leap on the part of sol-gel).…”

“…Other properties of interest in addition to optical properties include mechanical strength, light scattering, and laser damage resistance. Photosensitive sol-gel films To determine if photosensitive sol-gel films could be used in high-low refractive index gratings designs, we infiltrated the aerogel film matrix with silica/surfactant/photoacid generator (PAG, [diaryl iodonium hexafluoroantimonate]) [17]. In this system, silica/UV exposure through a mask at 240-260 nm causes photolysis of the PAG, releasing a strong Brønsted acid that condenses the silica matrix (and yields higher n) in the unmasked regions.…”

“…Sol-gel films can exhibit the requisite high damage-threshold (>10 J/cm 2 for 1 ns-scale pulses) [14,15] and can have gratings written into them [16][17][18], although verification of both properties simultaneously has not been explored. We propose coating a high damagethreshold mirror (>10 J/cm 2 at the ns-scale) with sol-gel and then writing a volume phase grating into the medium (see Fig.…”