Enhanced-Raman scattering from silicon nanoparticle substrates

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Anatase TiO2 as a Cheap and Sustainable Buffering Filler for Silicon Nanoparticles in Lithium-Ion Battery Anodes

The design of effective supporting matrices to efficiently cycle Si nanoparticles is often difficult to achieve and requires complex preparation strategies. In this work, we present a simple synthesis of low-cost and environmentally benign aAnatase TiO₂ nanoparticles as buffering filler for Si nanoparticles (Si@TiO₂ ). The average anatase TiO₂ crystallite size was approximately 5 nm. A complete structural, morphological, and electrochemical characterization was performed. Electrochemical test results show very good specific capacity values of up to 1000 mAh g^-1 and cycling at several specific currents, ranging from 500 to 2000 mA g^-1 , demonstrating a very good tolerance to high cycling rates. Postmortem morphological analysis shows very good electrode integrity after 100 cycles at 500 mA g^-1 specific current.

Resonant Raman scattering from silicon nanoparticles enhanced by magnetic response

Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have a much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of the Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions.

Probing the spatial extension of light trapping-induced enhanced Raman scattering in high-density Si nanowire arrays

This paper reports an experimental investigation of surface-enhanced Raman scattering in high-density Si nanowire arrays obtained by electroless etching. A direct relationship between light trapping capabilities of Si nanowires and enhanced Raman scattering was demonstrated. Optimized arrays allowed for a remarkable increase of Raman sensitivity in comparison to reference planar samples. As a result, the detection limit of molecular probes under resonant excitation (e.g. methylene blue) can be extended by three orders of magnitude. In addition, continuous ultrathin films, that cannot be analyzed in conventional Raman experiments, are made detectable. In the case of anatase thin films, the detection limit of 5 nm was reached. Raman spectra of Si/TiO₂ core/shell heterostructures demonstrate that the enhanced field resulting from surface multiple scattering is characterized by a large spatial extension (about fifty nanometers), making these materials a potential alternative to plasmonic metals for SERS experiments.

Retardation assisted enhanced Raman scattering from silicon nanostripes in the visible range

Patterned silicon on insulator structures representing evenly spaced parallel 15 nm-thick nanostripes exhibit an enhanced Raman scattering response when excited in the visible range in an oblique incidence backscattering configuration. The enhancement phenomenon in two structures having different stripe widths, 200 and 50 nm, is investigated at various sample azimuthal orientations, excitation radiation polarizations as well as laser wavelengths and is shown to be of resonant nature. The enhanced Raman response of the patterned structures is attributed to the presence of Mie resonances, essentially resulting in the enhancement of the internal electric field within the nanostripes. It is quantitatively described in terms of the spheroid particle model extended beyond the electrostatic limit to include field retardation effects that are shown to be responsible for the resonant behaviour in the visible range.

Enhanced Raman scattering from individual semiconductor nanocones and nanowires

We report strong enhancement (approximately 10(3)) of the spontaneous Raman scattering from individual silicon nanowires and nanocones as compared with bulk Si. The observed enhancement is diameter (d), excitation wavelength (lambda(laser)), and incident polarization state dependent, and is explained in terms of a resonant behavior involving incident electromagnetic radiation and the structural dielectric cross section. The variation of the Raman enhancement with d, lambda(laser), and polarization is shown to be in good agreement with model calculations of scattering from an infinite dielectric cylinder.