Braun Group People 
Sidhartha Gupta
Graduate Student in Materials Science and Engineering
B.S. in Materials Science & Engineering, Georgia Institute of Technology (2006)
Design and Fabrication of Novel Structures using Proximity Field Nano-Patterning (PnP)
PnP is a large-area, low cost interference lithographic technique that is used to fabricate three-dimensionally periodic microstructures, typically for photonic crystals or microfluidic mixing elements. This technique utilizes an optical grating to generate a three-dimensional interference pattern (arising due to the diffraction caused by the optical grating) which is subsequently recorded in an underlying thick film of photoresist material. Here, the characteristic dimensions of the structure are a function of the grating pitch and geometry, the laser wavelength and the material properties of the photoresist and the optical grating. My research focuses on expanding the scope of this technique by developing comprehensive design and fabrication strategies for fabrication of functional structures.
I. Inverse Design for PnP
We have developed and demonstrated the use of a genetic algorithm (GA) based design approach to target unique and functional motifs for structures produced using PnP. The technique designs for the optical grating and the electromagnetic field of exposure supersedes the earlier heuristic approach towards inverse PnP design that was limited to motifs with high symmetry.
Figure 1. Helices with various aspect ratios are obtained for gratings optimized via GA.2
II. ‘3D Gratings’ for PnP
Structures fabricated using PnP are intricately related to the optical grating used. The design room available for motif design is strictly limited by the binary gratings that are typically used with PnP. In collaboration with the King Research Group (MechSE, Illinois), we are developing a technique for fabricating large-area pseudo-3D gratings. Such gratings now allow for the creation of motifs via PnP that were previously not realizable.
[1] Seokwoo Jeon et al., “Fabricating complex three-dimensional nanostructures with high-resolution conformable phase masks,” Proc Natl Acad Sci U S A 101, no. 34 (August 2004): 12428-12433.
[2]
James W. Rinne, Sidhartha Gupta, and Pierre Wiltzius, “Inverse design for phase mask lithography,” Opt. Express 16, no. 2 (January 2008): 663–670.