Silicon Nanopillars for Field-Enhanced Surface Spectroscopy

Abstract

Silicon nanowire and nanopillar structures have drawn increased attention in recent years due in part to their unique optical properties. Herein, electron beam lithography combined with reactive-ion etching is used to reproducibly create individual silicon nanopillars of various sizes, shapes, and heights. Finite difference time domain analysis predicts local field intensity enhancements in the vicinity of appropriately sized and coaxially illuminated silicon nanopillars of approximately 2 orders of magnitude. While this level of enhancement is modest when compared to plasmonic systems, the unique advantage of the silicon nanopillar resonators is that they enhance optical fields in substantially larger volumes. By analyzing experimentally measured strength of the silicon Raman phonon line (500 cm(-1)), it was determined that nanopillars produced local field enhancements that are consistent with these predictions. Additionally, we demonstrate that a thin layer of Zn phthalocyanine on the nanopillar surface with a total amount of <30 attomoles produced prominent Raman spectra, yielding enhancement factors (EFs) better than 2 orders of magnitude. Finally, silicon nanopillars of cylindrical and elliptical shapes were labeled with different fluorophors and evaluated for their surface-enhanced fluorescence (SEF) capability. The EFs derived from analysis of the acquired fluorescence microscopy images indicate that silicon nanopillar structures can provide enhancements comparable or even stronger than those typically achieved using plasmonic SEF structures without the limitations of the metal-based substrates, such as fluorescence quenching and an insufficiently large probe volume. It is anticipated that dense arrays of silicon nanopillars will enable SEF assays with extremely high sensitivity, while a broader impact of the reported phenomena is anticipated in photovoltaics, subwavelength light focusing, and fundamental nanophotonics.

Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

“…While the spectral range for localized plasmonic modes has been successfully pushed into the infrared using such materials, the plasmonic origin of the modes implies that they are still limited by the relatively fast electron/plasma scattering (typically on the order of 10-100 fs) [41][42][43]. On the other hand, the use of dielectric materials can dramatically reduce optical losses [44][45][46][47][48][49][50], but resonators with sub-diffraction optical confinement cannot be achieved using positive permittivity materials.…”

Selectively assaying CEA based on a creative strategy of gold nanoparticles enhancing silver nanoclusters' fluorescence

“…SEF is believed to occur through the coupling of the fluorophores with radiating plasmons from the metallic particles (Kawasaki and Mine, 2005;Wells et al, 2012;Zhang et al, 2005). Nevertheless, fluorescence is also quenched once the fluorophore is excessively close to the metal core, and maximum enhancement occurs at about 10 nm away from the metal surface (Kulakovich et al, 2002).…”

Adding colors to polydimethylsiloxane by embedding vertical silicon nanowires

“…Incorporation of vertical silicon nanowires into PDMS devices also opens up other interesting possibilities for optical sensing in microfluidic chips, e.g., silicon nanopillar-based field-enhanced surface spectroscopy. 16 The process by which the etched nanowires are transferred from the silicon substrate to the PDMS is of key importance. Several previous works have demonstrated the transfer of vertical silicon micro-and nanowires to PDMS.…”