Silicon nitride is a ubiquitous and well-established nanofabrication material with a host of favourable properties for creating nanofluidic devices with a range of compelling designs that offer extraordinary discovery potential. Nanochannels formed between two thin silicon nitride windows can open up vistas for exploration by freeing transmission electron microscopy to interrogate static structures and structural dynamics in liquid-based samples. Nanopores present a strikingly different architecture—nanofluidic channels through a silicon nitride membrane—and are one of the most promising tools to emerge in biophysics and bioanalysis, offering outstanding capabilities for single molecule sensing. The constrained environments in such nanofluidic devices make surface chemistry a vital design and performance consideration. Silicon nitride has a rich and complex surface chemistry that, while too often formidable, can be tamed with new, robust surface functionalization approaches. We will explore how a simple structural element—a ∼100 nm-thick silicon nitride window—can be used to fabricate devices to wrest unprecedented insights from the nanoscale world. We will detail the intricacies of native silicon nitride surface chemistry, present surface chemical modification routes that leverage the richness of available surface moieties, and examine the effect of engineered chemical surface functionality on nanofluidic device character and performance.

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses <100 nm were grown at 3 and 10 °C between 0.5 and 3 h, with mean grain sizes between ∼20 and 30 nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200 nm thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces.

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Surface enhanced Raman spectroscopy; SERS; electroless plating; metallization.ABSTRACT Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for sensing molecules proximal to suitable coinage metal surfaces. The physical structure of the SERS-active metal layer and its support is a key design parameter inspiring considerable, and frequently specialized, efforts in substrate fabrication. The necessary gold film structure can arise from both the metallization process and the underlying support structure, and the structure of the support can deliver additional functions including analytical capabilities such as physical filtering. We used electroless plating as a general approach to create a library of SERS substrates: SERSactive gold films on a range of supports made from a variety of materials, made with a mixture of simple and complex fabrication histories, and offering a selection of structurally-derived functions. The result was that supports with existing functions had their capabilities enhanced by the addition of SERS sensing. Electroless plating thus offers a host of beneficial characteristics 3 for nanofabricating multifunctional SERS substrates, including: tolerance to substrate composition and form factor; low equipment overhead requirements; process chemistry flexibility-including compatibility with conventional top-down nanofabrication; and a lengthy history of commercial application as a simple metallization technique. We gold-plated standard nanofabrication-compatible silicon nitride support surfaces with planar and porous architectures, and with native and polymer-grafted surface chemistries. We used the same plating chemistry to form SERS-active gold films on cellulose fibers arrayed in commercial filter paper and formed into nanocellulose paper. In a functional sense, we used electroless plating to augment nanoporous filters, chromatography platforms, and nanofabrication building blocks with SERS capability.

Silicon nitride fabricated by low-pressure chemical vapor deposition (LPCVD) to be silicon-rich (SiN x ), is a ubiquitous insulating thin film in the microelectronics industry, and an exceptional structural material for nanofabrication. Free-standing <100 nm thick SiN x membranes are especially compelling, particularly when used to deliver forefront molecular sensing capabilities in nanofluidic devices. We developed an accessible, gentle, and solution-based photodirected surface metallization approach well-suited to forming patterned metal films as integral structural and functional features in thin-membrane-based SiN x devicesfor use as electrodes or surface chemical functionalization platforms, for exampleaugmenting existing device capabilities and properties for a wide range of applications.