Nanosphere lithography for optical fiber tip nanoprobes

Abstract

This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips. The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet. Polystyrene (PS) nanospheres are initially self-assembled in a hexagonal array on the surface of water. The created pattern is then transferred onto an optical fiber tip (OFT). The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber, such as metal coating, nanosphere size reduction and sphere removal. Ordered dielectric and metallo-dielectric sphere arrays, metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach. Furthermore, the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions. The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost. The method can be easily extended to simultaneously produce multiple fibers, opening a new route to the development of fiber-optic nanoprobes. Finally, we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes.

Mechanical Deformation–Assisted Fabrication of Plasmonic Nanobowties with Broken Symmetry and Tunable Gaps

“…A 10:1 ratio of silicone elastomer base and curing agent (Sylgard 184, Dow Corning Co.) was well mixed, degassed by centrifuging for 5 min at 6000 rpm, cast as a 1.5 mm thick film into a petri dish, and allowed to cure at room temperature for at least 24 h. The PDMS film was removed from the petri dish and prestretched to the desired strain. Next, a hexagonally close‐packed PS colloidal sphere monolayer was formed on the prestretched PDMS substrate by a gas/liquid interface self‐assembly process . In brief, commercial sulfate latex beads (ThermoFisher Scientific Inc., diameter = 500 nm) were diluted to 2% w/w in a 1:1 ethanol/water solution.…”

“…Next, a hexagonally close-packed polystyrene (PS) colloidal sphere monolayer was formed on the prestretched PDMS substrate by a gas/liquid interface self-assembly process. [7,22,23] 3 nm of chromium and 50 nm of gold were then e-beam deposited on the colloid coated substrate, followed by removal of the colloidal mask with scotch tape. Finally, the prestretch was released, breaking the symmetry and tuning the apex-to-apex gap of the gold nanobowties.…”

“…The prestretch ratios are 0% (unstretched), 10%, 20%, and 30%, respectively. Next, a hexagonally close‐packed polystyrene (PS) colloidal sphere monolayer was formed on the prestretched PDMS substrate by a gas/liquid interface self‐assembly process . 3 nm of chromium and 50 nm of gold were then e‐beam deposited on the colloid coated substrate, followed by removal of the colloidal mask with scotch tape.…”

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patches placed apex-to-apex show some of the greatest field confinements and enhancements among plasmonic nanoantenna designs, due to a combination of localized surface plasmon resonances in sharp apex geometries and a near field electrodynamic coupling between the two apex-to-apex nanotriangles of the bowtie.Many schemes have been used to fabricate the bowtie nanoantannas, including e-beam lithography, [5,[18][19][20] focused ion beam lithography, [12] metal nanotriangle self-organization, [21] and nanosphere lithography. [7,22,23] E-beam lithography and focused ion beam lithography offer the greatest degree of control, but at the cost of requiring sophisticated equipment. While self-organization of nanoantennas appears attractive, the defects inherent to self-assembly of complex objects can be considerable in particular when the building blocks are nonspherical.

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“…Many schemes have been used to fabricate the bowtie nanoantannas, including e-beam lithography, [5,[18][19][20] focused ion beam lithography, [12] metal nanotriangle self-organization, [21] and nanosphere lithography. [7,22,23] E-beam lithography and focused ion beam lithography offer the greatest degree of control, but at the cost of requiring sophisticated equipment. While self-organization of nanoantennas appears attractive, the defects inherent to self-assembly of complex objects can be considerable in particular when the building blocks are nonspherical.…”