Assembly of Large-Area Aligned Gold Trimers with Sub-5 nm Air-Filled Vertical Nanogaps

The subwavelength confinement of optical energy within the nanogap formed between adjacent plasmonic nanostructures leads to a multitude of fascinating properties that act as the foundation for new nanotechnologies. Here, we demonstrate a nanofabrication process for the assembly of substrate-based gold trimers with sub-5 nm air-filled vertical nanogaps. The stepwise process proceeds along a pathway that sees (i) the high-temperature vapor-phase assembly of standalone gold nanostructures, (ii) the formation of a conformal sacrificial oxide layer around each nanostructure using atomic layer deposition (ALD) where the role of the oxide is to precisely define the nanogap width, (iii) the glancing angle deposition (GLAD) of a gold-antimony bilayer that, when heated, assembles into a linear Au-oxide-Au-oxide-Au trimer as the sacrificial antimony layer is lost to sublimation, and (iv) an etching process that selectively removes the oxide to form air-filled vertical nanogaps. The trimers show a high degree of alignment that leads to a polarization dependent extinction spectrum. The work advances the possibility of using low-cost, high-throughput, and scalable vapor-phase techniques to form plasmonic nanostructures separated by nanogaps and, in doing so, provides the building blocks needed to enable on-chip plasmonic devices.