Yuebing Zheng, The University of Texas at Austin, TX, USA, and colleagues have developed bubble-pen lithography, a technique that "writes" colloidal particles onto plasmonic substrates. Optically controlled microbubbles capture and guide the particles using thermal and surface tension gradients, gas pressure, and substrate adhesion.
The researchers focused a laser underneath a sheet of gold nanoislands to produce a hot spot. This formed a microbubble in a suspension of polystyrene beads in water overhead, which attracted the beads to its surface and could be steered across the substrate by moving the laser beam. After the laser was removed, the microbubble disappeared, leaving the beads attached to the substrate. Increasing the laser power makes larger vapor bubbles, producing hollow spheres of beads.
The team tested their technique using suspended CdSe/ZnS core/shell quantum dots. The fluorescence lifetime of the dots fixed onto the substrate indicated a strong coupling between quantum dot excitons and substrate plasmons. This method could be used for nanofabrication, chemical recognition devices, and basic research on interactions between zero-dimensional and two-dimensional materials.
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