Resonant Gap Nanoparticle Chains, with Application to Surface Enhanced Raman Scattering

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Objective:Metal dimer, slot-cavity, and nanoparticle chain optical structures that operate based on resonant gap modes will be designed and compared using numerical electromagnetic simulations, in order to arrive at candidate designs for fabrication. Dielectric gratings with 2-10 nm line width will be fabricated with high-resolution lithography, atomic layer deposition and selective etching. Such gratings will be imprinted into metal films to form smooth and narrow trenches, thereby achieving designed resonant slot and chain waveguides. Fabricated structures will be tested using near-field and far-field approaches as a function of wavelength, in order to evaluate field enhancement and guiding performance. Raman measurements will be performed to determine the enhancement.Intellectual Merit:Nanoparticles with resonant gaps can provide large field enhancement for nonlinear optics and spectroscopy. The fabrication techniques to be developed will achieve line widths of a few nanometers, a length scale of tremendous interest yet not accessible with standard top-down lithography.Broader Impacts:Two Ph.D. students will be supported, and this research will constitute a substantial part of their theses. An undergraduate research student will be invited to work on this project each year. Material from this research will be used as demonstrations in entry-level graduate and senior-level undergraduate classes taught by Webb and Qi, and incorporated, as appropriate, into Purdue EPICS (engineering projects in community service), a design experience for undergraduates. Simulation tools developed will be accessible through the investigators Purdue web sites.