We present theoretical, numerical, and experimental analyses on the non-linear dynamic behavior of superparamagnetic beads exposed to a periodic array of micro-magnets and an external rotating field. The agreement between theoretical and experimental results revealed that non-linear magnetic forcing dynamics are responsible for transitions between phase-locked orbits, sub-harmonic orbits, and closed orbits, representing different mobility regimes of colloidal beads. These results suggest that the non-linear behavior can be exploited to construct a novel colloidal separation device that can achieve effectively infinite separation resolution for different types of beads, by exploiting minor differences in their bead's properties. We also identify a unique set of initial conditions, which we denote the ''devil's gate'' which can be used to expeditiously identify the full range of mobility for a given bead type.
We demonstrate a novel self-aligned diffraction-based photolithographic technique, that uses embedded masks and backside exposure through transparent substrates, to fabricate sub-wavelength features with conventional photolithography tools. To demonstrate one potential application of this lithography tool, we produce arrays of metallic rings, split rings, and nanowires with feature sizes ranging from 130 nm and above, by modulating the exposure intensity, photoresist thickness, and etch time. The ability to produce both continuous and split rings composed of noble metals over wafer-sized areas has promise in low-cost techniques for fabricating metamaterials and other advanced optical devices.
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