Subwavelength direct-write nanopatterning using optically trapped microspheres.

A number of non-lithographic techniques are now available for processing materials on the nanoscale, including optical techniques capable of producing features that are much smaller than the wavelength of light used. However, these techniques can be limited in speed, ease of use, cost of implementation, or the range of patterns they can write. Here we report how Bessel beam laser trapping of microspheres near surfaces can be used to enable near-field direct-write subwavelength nanopatterning. Using the microsphere as an objective lens to focus the processing laser, we demonstrate arbitrary patterns and individual features with minimum sizes of approximately 100 nm (which is less than one-third the processing wavelength) and a positioning accuracy better than 40 nm in aqueous and chemical environments. Submicron spacing is maintained between the near-field objective and the substrate without active feedback control. If implemented with an array of optical traps, this approach could lead to a high-throughput probe-based method for patterning surfaces with subwavelength features.