Access to nanofabrication strategies for crafting three-dimensional plasmonic structures is limited. In this work, a fabrication strategy to produce 3D plasmonic hollow nanopillars (HNPs) using Talbot lithography and I-line photolithography...

Convex cylindrical silicon nanostructures, also referred to as silicon nanocones, find their value in many applications ranging from photovoltaics to nanofluidics, nanophotonics, and nanoelectronic applications. To fabricate silicon nanocones, both bottom-up and top-down methods can be used. The top-down method presented in this work relies on pre-shaping of silicon nanowires by ion beam etching followed by self-limited thermal oxidation. The combination of pre-shaping and oxidation obtains high-density, high aspect ratio, periodic, and vertically aligned sharp single-crystalline silicon nanocones at the wafer-scale. The homogeneity of the presented nanocones is unprecedented and may give rise to applications where numerical modeling and experiments are combined without assumptions about morphology of the nanocone. The silicon nanocones are organized in a square periodic lattice, with 250 nm pitch giving arrays containing 1.6 billion structures per square centimeter. The nanocone arrays were several mm2 in size and located centimeters apart across a 100-mm-diameter single-crystalline silicon (100) substrate. For single nanocones, tip radii of curvature < 3 nm were measured. The silicon nanocones were vertically aligned, baring a height variation of < 5 nm (< 1%) for seven adjacent nanocones, whereas the height inhomogeneity is < 80 nm (< 16%) across the full wafer scale. The height inhomogeneity can be explained by inhomogeneity present in the radii of the initial columnar polymer mask. The presented method might also be applicable to silicon micro- and nanowires derived through other top-down or bottom-up methods because of the combination of ion beam etching pre-shaping and thermal oxidation sharpening. Graphic abstract A novel method is presented where argon ion beam etching and thermal oxidation sharpening are combined to tailor a high-density single-crystalline silicon nanowire array into a vertically aligned single-crystalline silicon nanocones array with < 3 nm apex radius of curvature tips, at the wafer scale.

We report on the fabrication and modification of a top-down nanofabrication platform for enormous parallel silicon nanowire-based devices. We explain the nanowire formation in detail, using an additive hybrid lithography step, optimising a reactive ion etching recipe for obtaining smooth and vertical nanowires under a hybrid mask, and embedding the nanowire in a dielectric membrane. The nanowires are used as a sacrificial template, removal of the nanowires forms arrays of well-defined nano-pores with a high surface density. This platform is expected to find applications in many different physical domains, including nanofluidics, (3D) nanoelectronics, as well as nanophotonics. We demonstrate the employment of the platform as field emitter arrays, as well as a state-of-the-art electro-osmotic pump.

Surface-enhanced Raman spectroscopy (SERS) substrates are of utmost interest in the analyte detection of biological and chemical diagnostics. This is primarily due to the ability of SERS to sensitively measure analytes present in localized hot spots of the SERS nanostructures. In this work, we present the formation of 67 ± 6 nm diameter gold nanoparticles supported by vertically aligned shell-insulated silicon nanocones for ultralow variance SERS. The nanoparticles are obtained through discrete rotation glancing angle deposition of gold in an e-beam evaporating system. The morphology is assessed through focused ion beam tomography, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The optical properties are discussed and evaluated through reflectance measurements and finite-difference time-domain simulations. Lastly, the SERS activity is measured by benzenethiol functionalization and subsequent Raman spectroscopy in the surface scanning mode. We report a homogeneous analytical enhancement factor of 2.2 ± 0.1 × 10 7 (99% confidence interval for N = 400 grid spots) and made a comparison to other lithographically derived assemblies used in SERS. The strikingly low variance (4%) of our substrates facilitates its use for many potential SERS applications.

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Gold nanoparticles (AuNPs) were the basis for the earliest research in the field of surface enhanced Raman scattering (SERS). Coupling of their surface plasmon resonances creates hot-spots of high electromagnetic intensities found to be very useful for sensing applications. However, chemically synthesized AuNPs in suspension are usually polydisperse and when arranged on a SERS substrate, lack periodic spatial organization. This leads to large variations in the enhancement factor (EF) which is detrimental to the sensing capabilities of the SERS substrate. Here, we showcase reproducible fabrication of an array of spherical AuNPs at the apices of shell isolated silicon nanocones with a homogeneous EF for SERS. The AuNPs are produced through discrete rotation glancing angle deposition of Au on shell isolated silicon nanocones (SI-SiNC) with square lattice periodicity and 250 nm pitch. By tuning the substrate tilt angle, substrate rotation angle and deposition thickness, the location and the size of the AuNPs formed can be controlled. Using this method, we successfully fabricated 60 nm AuNPs positioned at the apices of the nanocone array. Finite-Difference Time-Domain (FDTD) simulations were performed to visualize the electric field enhancement and verify conditions such as tip radius and oxide shell thickness to optimize the same. The EF was then experimentally calculated by performing SERS measurements on benzenethiol (BT) functionalized AuNPs at 400 unique points over the SI-SiNC substrate and compared to measurements of pure BT solution. A homogeneous substrate EF of (2.05 ± 0.05) •10 7 (99% confidence interval) at par with literature was calculated for the C-S in-plane deformation mode, δCS, of the BT molecule excited at 1077 cm -1 . Our work highlights the advantages of nanofabrication for homogeneous SERS EF substrates.

The pressure stability of microfluidic glass chips was tested experimentally, with a special focus on the inserts for glued capillary connections. Destructive high-pressure experiments with demineralized water conducted at room temperature showed a difference in mean fracture pressure between the two tested glass types BF33 and D263T, with values of 192 ± 25 and 159 ± 25 bar, respectively. For BF33, hydrofluoric acid (HF) etching of the powder blasted (abrasive jet machined) chip insert increased the mean fracture pressure with 43 ± 9 bar, whilst for D263T a decrease of −22 ± 8 bar resulted. Contrary to the expected surface smoothening of the HF treatment, a rougher surface was obtained, particularly for the case of D263T, which is thought to be due to the opening of median (radial) cracks caused by the powder impact during the blasting process. The roughness obscures the effect of the tapering of the insert, preventing that factor from having a statistically significant effect on the mean fracture pressure. Nevertheless, a decrease in the mean fracture pressure and a decrease in the variance of the mean fracture pressure was observed when a taper is introduced, whereas the fracture location tends to move away from the insert-microchannel intersection towards the glue meniscus. A practical solution for cases where a high-pressure stability is required is found in applying a metal clamp around the capillary insert section. This significantly increased the fracture pressure of the chip insert section with 50 ± 21 bar, by preventing bond release.

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