Direct and Reliable Patterning of Plasmonic Nanostructures with Sub-10-nm Gaps

Abstract

Nanoscale gaps in metal films enable strong field enhancements in plasmonic structures. However, the reliable fabrication of ultrasmall gaps (<10 nm) for real applications is still challenging. In this work, we report a method to directly and reliably fabricate sub-10-nm gaps in plasmonic structures without restrictions on pattern design. This method is based on a lift-off process using high-resolution electron-beam lithography with a negative-tone hydrogen silsesquioxane (HSQ) resist, where the resulting nanogap size is determined by the width of the patterned HSQ structure, which could be written at less than 10 nm. With this method, we fabricated densely packed gold nanostructures of varying geometries separated by ultrasmall gaps. By controlling structure sizes during lithography with nanometer precision, the plasmon resonances of the resulting patterns could be accurately tuned. Optical and surface-enhanced Raman scattering (SERS) measurements on the patterned structures show that this technique has promising applications in the fabrication of passively tunable plasmonic nanostructures with ultrasmall gaps.

Three-dimensional plasmonic stereoscopic prints in full colour

“…Here, we varied the gap size and nanosquare width. When the incident illumination is polarized along the axis of two closely spaced nanosquares, a coupled-dipole mode is excited with strong fields within the gap 30 . In the orthogonal direction, another resonance at a different wavelength is excited with the field localized at the aligned edges of the nanosquares, producing a slightly different colour.…”

Fabrication of sub-10 nm gap arrays over large areas for plasmonic sensors

“…8 The fabrication of nanogap arrays has been demonstrated with a variety of techniques. Electron-beam lithography (EBL) is used for direct writing 9 or patterning of shadow masks for angular evaporation. 10,11 With EBL, the pattern can be designed and realized with an exceptional degree of freedom.…”

“…Due to proximity effects of the electron beam and limitations set by the photoresist liftoff, the resulting metal nanogap dimensions are limited to above roughly 10 nm and a metal layer thickness of below 30 nm. 9,12 The serial writing process of EBL makes this technique unfavorable for the fabrication of large area and low-cost sensors. Other lithography-based techniques have been used, including molecular rulers 13,14 or atomic layer deposition (ALD), 7 as effective methods to tune the nanogap size even below 2 nm.…”

Contact Transfer Printing of Side Edge Prefunctionalized Nanoplasmonic Arrays for Flexible microRNA Biosensor

“…One is a direct control of the interparticle gap and the location among purposed particles 39, 45. The next challenge is an efficient post‐process12, 46 of keeping functional terminals on nanostructures for biorecognition while removing residual terminals from the polymer substrate 8, 47, 48.…”