Proximity field nano-patterning
Prof. John Rogers and Prof. Paul Braun at UIUC developed “proximity field nanopatterning” (PnP), a fabrication technique that relies on a conformable phase mask with sub-wavelength features of relief embossed onto its surface. The approach is intrinsically simple because all of the optics are built into this single element. Soft lithographic procedures of casting and curing of elastomers based on polydimethylsiloxanes (PDMS) or perfluoropolyethers (a-PFPE) against patterns of relief on a ‘master’ yield masks with relief structures in the geometry of the resist. A single master can yield many such masks; each mask can be used many times. A key feature of the masks is their ability to establish intimate, conformal contact with the surface to be patterned, thereby achieving optical alignment with nanometer precision in the out of plane direction, through the action of generalized adhesion forces, dominated by van der Waals interactions, without the use of applied pressure or precision alignment stages. Light passing through the mask generates a distribution of intensity that can expose a layer of a photosensitive material, throughout its thickness. Only the spot size of the light source and the size of the phase mask limit the size of the patterned areas – areas of square meters are conceivable. In addition to certain operational advantages (e.g. low cost setups, large area and high speed patterning), the PnP method offers capabilities that are extremely well suited to the field of photovoltaics. Developing and applying this method to transformation optics structures for trapping, focusing and dispersion are central elements of the LMI-EFRC current and future work.