Lithography-free approach to highly efficient, scalable SERS substrates based on disordered clusters of disc-on-pillar structures

Abstract

We present a lithography-free technological strategy that enables fabrication of large area substrates for surface-enhanced Raman spectroscopy (SERS) with excellent performance in the red to NIR spectral range. Our approach takes advantage of metal dewetting as a facile means to create stochastic arrays of circular patterns suitable for subsequent fabrication of plasmonic disc-on-pillar (DOP) structures using a combination of anisotropic reactive ion etching (RIE) and thin film deposition. Consistent with our previous studies of individual DOP structures, pillar height which, in turn, is defined by the RIE processing time, has a dramatic effect on the SERS performance of stochastic arrays of DOP structures. Our computational analysis of model DOP systems confirms the strong effect of the pillar height and also explains the broadband sensitivity of the implemented SERS substrates. Our Raman mapping data combined with SEM structural analysis of the substrates exposed to benzenethiol solutions indicates that clustering of shorter DOP structures and bundling of taller ones is a likely mechanism contributing to higher SERS activity. Nonetheless, bundled DOP structures appeared to be consistently less SERS-active than vertically aligned clusters of DOPs with optimized parameters. The latter are characterized by average SERS enhancement factors above 10(7).

The process of solid-state dewetting of Au thin films studied by in situ scanning transmission electron microscopy

“…Approaches include pre-patterning the substrate [10][11][12][13][14][15] or the thin film [16][17][18][19] and the introduction of a sacrificial layer [20,21]. Applications of the produced particle arrays are envisaged to range from templates for the growth of nanostructures [22,11,23,24], magnetic storage arrays [25,26], optical sensors [27,28] and plasmonic systems [29,30], over photocatalytic reactors [31] to plasmon-enhanced back reflectors in solar cells [32,33].…”

Centrifugal‐driven, reduced‐dimension, planar chromatography

“…The film was then rapidly heated to approximately 900°C in a cold wall furnace (Easy Tube 3000, First Nano, NY, USA) using a 10:1 mixture of argon and hydrogen at 735 torr. The thermally created Pt islands were subsequently used as a selective mask for anisotropic reactive ion etching (Oxford Plasma Lab, Oxford Instruments, UK) of the substrate material as described and characterized previously .…”

Length Scale Selects Directionality of Droplets on Vibrating Pillar Ratchet

“…[ 28 ] A 10 nm to 15 nm thick layer of platinum (Pt) was deposited onto a single side polished single crystal silicon (Si) wafer (100) with 100 nm of thermally grown silicon oxide (SiO 2 ) using physical vapor deposition in a vacuum evaporator equipped with an electron gun source (Thermonics Laboratory, VE-240). Wafers with a Pt layer were then thermally processed at ≈ 850 °C for 8 seconds in a mixture of argon and hydrogen (10:1) at a pressure of 735 Torr in a cold wall furnace (Easy Tube 3000, First Nano, Ronkonkoma, NY) equipped with a radiative heat source set to its maximum power (22 kW).…”

“…The resulting dewet Pt layer then served as a mask during anisotropic reactive ion etching (RIE) of the SiO 2 and Si. [27][28][29][30] The RIE was carried out in an Oxford PlasmaLab system (Oxford Instruments, UK) using glancingangle RIE with the wafer sitting on an aluminum holder bent to an angle of 70° relative to the surface of a silicon carrier wafer. A perfl uorinated oil (Fomblin 25/5) was placed between the wafer and the aluminum holder to ensure even heat transfer during etching.…”

“…The ideas of designing and using asymmetric micro-or nanostructures are often mimics of biological objects, such as the hierarchical method based on metal dewetting. [27][28][29][30] Microscale diameter pillars were fabricated using common photolithography masking techniques. The fabrication method, shown schematically in Figure 1 , resulted in arrays tilted nominally 30° off normal.…”