Optical Characterization of Ultrasmall Si Nanoparticles Prepared through Electrochemical Dispersion of Bulk Si

Abstract

Studying the properties and stability of silicon nanoparticles (Si-np) in aqueous environments may lead to novel applications in biological systems. In this work, we use absorption and photoluminescence (PL) spectroscopy to characterize ultrasmall Si-np prepared through anodic etching and ultrasonic fractionation of a crystalline Si wafer. Their behavior is studied over time in 2-propanol and during treatments with water, NaOH, HCl, and H 2 O 2 . The observed population is divided into two types of material: bright species consisting of well-etched Si-np, ∼1 nm in diameter, and dark species derived from partially etched or aggregated Si structures. The dark material is seen by its scattering in the 2-propanol and water solutions and is largely removed via precipitation with the NaOH or HCl treatment. The bright material includes three distinct species with their respective emissions in the UV-B, UV-A, and hard-blue regions of the spectrum. The hard-blue PL is shown to have a simple pH dependence with a pK a ∼3, providing an important insight into its chemical origin and signaling for possible application of Si-np as environmental probes. Our results offer some potential for tailoring the PL properties of ultrasmall Si-np through control of their surface chemistry.

Synthesis and characterisation of Gossypium hirsutum seeds extract nanoencapsulated in silica microparticles

“…8b). Previous studies on silica have suggested that the fluorescence sources in the UV-B range are nanosized hydrogen-passivated silica species [54]. During the synthesis of our samples, similar species could be obtained along with the prevalent 1.1 lm (for SiO 2 -FD) and 1.2 lm (for SiO 2 -HD) particles identified by DLS.…”

Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation

“…26 Researchers have developed many routes for preparing organically functionalized Si-np. However, the products have been generally limited to aliphatic surface chemistries stable only in nonpolar organic solvents.…”

“…56,57 In a recent work, we reported similar, but much more substantial increases in redshifted PL after treatment of unmodified Si-np-H with NaOH under nearly identical conditions to the base hydrolysis. 26 The results were attributed to oxidation of the nanoparticle surface with possible formation of Si-O-Si bridge structures. Note that the relative lack of redshifted PL for the H 2 O fraction suggests that the carboxyl modification provides some additional protection against surface oxidation.…”

Capillary electrophoresis of ultrasmall carboxylate functionalized silicon nanoparticles

“…The red-tail emissions at 335 nm and greater were much more prominent after aqueous treatments and have been attributed to various species of oxidized and aggregated material. 12 The carboxyl functionalized Si-np-COOH were prepared via hydrosilylation of the Si-np-H with the bi-functional ester methyl 4-pentenoate, CH 2 = CHCH 2 CH 2 C͑O͒OCH 3 . 10 The reaction proceeds with insertion of the alkene into a thermally activated Si-H bond to form a stable Si-C linkage with the ester exposed to the solvent.…”