Large Field Enhancement of Nanocoral Structures on Porous Si Synthesized from Rice Husks

Abstract

Silicon (Si) is a highly abundant, environmentally benign, and durable material and is the most popular semiconductor material; and it is used for the field enhancement of dielectric materials. Porous Si (PSi) exhibits high functionality due to its specific structure. However, the field enhancement of PSi has not been clarified sufficiently. Herein, we present the field enhancement of PSi by the fluorescence intensity enhancement of a dye molecule. The raw material used for producing PSi was rice husk, a biomass material. A nanocoral structure, consisting of spheroidal structures on the surface of PSi, was observed when PSi was subjected to chemical processes and pulsed laser melting, and it demonstrated large field enhancement with an enhancement factor (EF) of up to 545. Confocal microscopy was used for EF mapping of samples before and after laser melting, and the maps were superimposed on nanoscale scanning electron microscope images to highlight the EF effect as a function of microstructure. Nanocoral Si with high EF values were also evaluated by analyzing the porosity from gas adsorption measurements. Nanocoral Si was responsible for the high EF, according to thermodynamic calculations and agreement between experimental and calculation results as determined by Mie scattering theory.

Fast, Economical, and Reproducible Sensing from a 2D Si Wire Array: Accurate Characterization by Single Wire Spectroscopy

“…Si microstructures with roughness exhibit higher EFs. 36 Time and Cost of Preparing the 2D-SiWA Enhancement Substrate. We evaluated the production time and cost of fabricating a 2D-SiWA as a sensing substrate.…”

“…For this reason, many researchers have experimentally and theoretically investigated the field enhancement of submicron-structured Si materials for various shapes, including spheres, 30,31 dimers, 32 disks, 33 doughnuts, 34 pillars, 35 and coral structures. 36 Research has demonstrated a large field enhancement in the visible to near IR regions, whereby the performances of solar cells, 37−45 biomedical sensors, 46−49 optical tweezers, 50 and high-color light sources 51 are improved in a wide spectral region.…”

“…In particular, the high refractive index and low absorption coefficient of Si are responsible for a large field enhancement because of Mie resonance. , Submicron-structured Si exhibits strong Mie resonance coupling with incident light, and the magnitude of the field enhancement is close to that of a noble metal. For this reason, many researchers have experimentally and theoretically investigated the field enhancement of submicron-structured Si materials for various shapes, including spheres, , dimers, disks, doughnuts, pillars, and coral structures . Research has demonstrated a large field enhancement in the visible to near IR regions, whereby the performances of solar cells, − biomedical sensors, − optical tweezers, and high-color light sources are improved in a wide spectral region.…”

“…However, several drawbacks are associated with feasibly fabricating the structure. First, the size of an active area for field enhancement, typically <10 × 10 μm 2 , − ,− is too small to be used for a practical sensor. Almost all submicron-structured Si is prepared using an electron beam lithography (EBL) method, which severely limits the size.…”

Orange–Red Si Quantum Dot LEDs from Recycled Rice Husks

“…The reduction reaction of SiO 2 was conducted using magnesiothermic reduction. − Namely, SiO 2 powders (300 mg) were mixed with Mg (350 mg) and NaCl (846 mg) powders in an Ar atmosphere, and Mg and NaCl were used as a reduction reagent and a heat bath, respectively. The mixed powders were placed in a reaction vessel purged with Ar gas and were heated at 650 °C for 2 h using a tube furnace.…”