Ultra-Narrow Metallic Nano-Trenches Realized by Wet Etching and Critical Point Drying

Abstract

A metallic nano-trench is a unique optical structure capable of ultrasensitive detection of molecules, active modulation as well as potential electrochemical applications. Recently, wet-etching the dielectrics of metal–insulator–metal structures has emerged as a reliable method of creating optically active metallic nano-trenches with a gap width of 10 nm or less, opening a new venue for studying the dynamics of nanoconfined molecules. Yet, the high surface tension of water in the process of drying leaves the nano-trenches vulnerable to collapsing, limiting the achievable width to no less than 5 nm. In this work, we overcome the technical limit and realize metallic nano-trenches with widths as small as 1.5 nm. The critical point drying technique significantly alleviates the stress applied to the gap in the drying process, keeping the ultra-narrow gap from collapsing. Terahertz spectroscopy of the trenches clearly reveals the signature of successful wet etching of the dielectrics without apparent damage to the gap. We expect that our work will enable various optical and electrochemical studies at a few-molecules-thick level.

Suppressed terahertz dynamics of water confined in nanometer gaps

“…It should be noted that the gap is always filled with aluminum oxide, KOH, or water, so that liquid water can be guaranteed to fill the gap after the whole process is completed. An empty gap is prepared as a reference by vaporizing the gap-filling water by critical point drying (CPD) ( 57 ). Detailed fabrication processes are shown in Materials and Methods.…”

Plasmonic refractive index nano sensor based on triplet coupled stub resonators based Fano resonances

“…One potential solution can be using extreme ultraviolet lithography (EUV) to pattern waveguides and cavity resonators on a photoresist [65], followed by either a dry etching, like the inductively coupled plasma (ICP) method [66], or wet etching, using a selective etchant of silver. However, wet etching of nano‐slits can be associated with a high surface tension of water in the process of drying in which slits are prone to collapsing unless applying unique methods, like lowering the applied stress to the gap using the critical point drying technique [67]. Another straightforward method for extracting specified TCSRs in Figure 2a can be applying the FIB method, which is based on the vertical bombardment of a target layer using heavy ions [68].…”