Silicon and silicon oxide core-shell nanoparticles: Structural and photoluminescence characteristics

Abstract

We report the synthesis of spherical core-shell structures of silicon and silicon oxide by a novel route of forced external oxidation of ball milled silicon. Structural investigations reveal the formation of a crystalline silicon core surrounded by an amorphous oxide shell, with core and shell dimensions varying approximately between 4–10 and 55–170 nm, respectively. The observations suggest partial amorphization of crystalline silicon, invasive oxygen induced passivation of dangling bonds, and formation of different types of defects in the nanocrystalline silicon/silicon oxide core-shell structure, particularly at the interfaces. No detectable photoluminescence (PL) is obtained from the as-milled silicon, but the oxidized core-shell structures exhibit strong room temperature PL, detectable with unaided eye. The peak energy of the PL spectra blueshifts with an increase in excitation energy, with the peak positions varying from 2.24 to 2.48 eV under external excitation ranging from 2.41 to 3.5 eV. The observed PL characteristics are explained in terms of dominant electronic transitions between the localized defect states and quantum confinement induced widened band states.

Tracking the Fate of Porous Silicon Nanoparticles Delivering a Peptide Payload by Intrinsic Photoluminescence Lifetime

“…Use of a “perforation etching” anodization waveform yielded PSiNPs with a well‐defined mesoporous structure (pore size ≈10 nm) and narrow nanoparticle size distribution with a mean diameter of ≈180 nm ( Figure a). Photoluminescence was activated by growth of a native oxide on the porous silicon skeleton, generating a Si‐SiO 2 core–shell type of structure that passivates nonradiative surface defects and increases quantum yield from the quantum‐confined crystalline silicon core . The resulting PSiNPs displayed a relatively broad PL emission spectrum in the red/near‐infrared region (500–950 nm; Figure b).…”

Self‐Sealing Porous Silicon‐Calcium Silicate Core–Shell Nanoparticles for Targeted siRNA Delivery to the Injured Brain

“…The mechanism of degradation of porous silicon (pSi) involves oxidation of the silicon skeleton to form silicon oxide, followed by hydrolysis of the resulting oxide phase to water‐soluble orthosilicic acid (Si(OH) 4 ) or its congeners . To prevent rapid degradation of pSi nanoparticles, various “core–shell” types of structures have been synthesized, where an inner core of a pSi skeleton is surrounded by a shell of more stable silicon oxide, titanium oxide, carbon, or other kinetically stable substances . Core–shell structures are attractive platforms for slow releasing drug delivery formulations because the synthesis of the shell can be performed in concert with drug loading in order to more effectively trap the therapeutic in the nanostructure .…”

Xylene-Capped Luminescent Silicon Nanocrystals: Evidence of Supramolecular Bonding

“…33 Because deposition of the HFetched samples on the substrate and subsequent imaging were carried out under ambient conditions, it is obvious that we get Si NC/Si-oxide core/shell structures as previously evidenced. 32 However, in this case, the size of the oxide shell estimated from the line profile varies from 1 to 8 nm (and the core size from 1 to 4 nm), which is significantly smaller than the thickness previously reported 32 for samples that were not HF-etched. Moreover, the formation of this oxide layer is prevented for the xylene-treated samples because the etched NCs are not allowed to come in contact with ambient oxygen.…”

“…31,32 In an attempt to remove the oxide shell, we treated ∼30 mg of the oxidized Si NCs with 10% aqueous buffered HF solution for ∼20 min with intermittent stirring. HF was then allowed to evaporate at ∼70°C in an inert (nitrogen) atmosphere until dry deposits of Si NCs (with H termination as well as exposed unsaturated and dangling bonds) were obtained.…”