Scientists engaged in a multi-institution project based in Albuquerque, N.M., have found that UV light can be used to make precise size adjustments to nanopores. The study, which involves Sandia National Labs and the University of New Mexico, is aimed at developing a comprehensive method to adjust the sizes of trillions of nanoscopic pores in fine filters, sensors, and diffraction gratings to improve the efficiency of these devices.
Led by Jeff Brinker, a senior scientist at Sandia and professor at UNM, the project's long-term goal is to develop a method for the membrane-based separation of oxygen from nitrogen. This involves a size difference of 0.2 Ω, or 0.02 nm. According to the researchers, it's now possible to use a beam of UV light to go from pores of 3.4 to 3.6 Ω in diameter, tuning the membrane to optimize oxygen-nitrogen separation.
Known as a type of nanostructural engineering, the use of UV light influences pore size and connectivity in the heart of self-assembled, repeated-pattern nanostructures. This process varies pore sizes continuously over a range within the illuminated pattern. The UV process creates a kind of tunable zeolite, a crystalline structure with tiny but unalterable pore sizes. This enhances the membranes' ability to separate molecules by size.
The membrane used in this experiment was self-assembled, thin-film, photosensitive silica. When exposed to the proper amount of light, a 10-Ω hole could be tuned to 8 or 9 Ω. Photoacid molecules uniformly incorporated within the nanostructure break apart to form an acid when light is shone on them (see the figure). This process causes the silica to solidify locally. The amount of solidification is proportional to the amount of light shown on the membrane.
Possible uses of this experimental process include "gray-scale" patterning, or shining light through a lithographic mask that varies its intensity. This theoretically allows for a broad spatial variation of the materials' structure and properties. The same process can be used to produce optical diffraction gratings, devices that can redirect and filter light, made entirely of laser-damage-resistant silica.
Research is ongoing. Currently, the team is attempting to improve control demonstrated over a dynamic range. Scientists from the Vienna University of Technology and Applied Materials Corp. in Santa Clara, Calif., have also contributed to the project. Sandia and UNM have filed a joint patent application on the process.
For details, go to www.sandia.gov.