Fabrication of Split-Rings via Stretchable Colloidal Lithography

Herein, a facile new patterning method is demonstrated for creating pairs of split-ring resonators (SRRs) in a scalable manner over large surface areas. This method is based on a novel variation of colloidal lithography called stretchable colloidal lithography (SCL), which combines conventional colloidal lithography and stretchable poly(dimethylsiloxane) (PDMS) molds. To fabricate SRRs, arrays of circular polystyrene (PS) rings were fabricated by conventional colloidal lithography. The circular ring features could be transferred to a PDMS stamp, forming negative features, circular apertures on the stamp. The PDMS stamp was then stretched, thereby transforming the circular apertures into elliptical ones. By using the stretched PDMS molds for polymer imprinting, elliptical rings with nonuniform heights could be fabricated. Each elliptical ring could be transformed into a pair of PS SRRs by controlled O₂ reactive ion etching. Through a subsequent chemical wet etching step, PS SRRs could be readily transferred into an underlying gold film. The SRRs exhibited multiple modes of polarization-dependent plasmonic resonances in the visible and infrared spectral regions. Experiments and corresponding theoretical modeling demonstrated that these multiple resonances could be tuned in a predictable manner. All optical data compared well with results from electromagnetic simulations. (Graph Presented).