Nonthermal plasma synthesized silicon-silicon nitride core–shell nanocrystals with enhanced photoluminescence

Abstract

Enhanced optical properties of silicon quantum dots (QDs) are pertinent for light-emitting applications including luminescent solar cell concentrators. Surface passivation plays a crucial role in improving photoluminescent quantum yield and effective carrier lifetimes of silicon nanocrystals and is often achieved by surface grafting of organic ligands. However, organically passivated silicon QDs often suffer from a deterioration of the optical properties when exposed to the environment. In this work, we explore the effect of an inorganic amorphous silicon nitride (SiN x ) shell on silicon QDs and their optical properties. Utilizing a dual plasma approach with dual injection ports, we synthesized Si/SiN x core-shell nanoparticles using SiH 4 , NH 3 , H 2 , and Ar. The core-shell nanocrystals were characterized using optical and structural methods, which revealed that higher nitridation plasma powers could lead to Si precipitation altering the composition of SiN x shell. While as-synthesized Si/SiN x core-shell nanocrystals did not exhibit photoluminescence, oxidized Si/SiN x core-shell nanocrystals show significantly higher quantum yield (35%) and longer carrier lifetime compared to their bare oxidized Si analogues even after an environmental exposure of six months.

Photoluminescent Si/SiO2 Core/Shell Quantum Dots Prepared by High-Pressure Water Vapor Annealing for Solar Concentrators, Light-Emitting Devices, and Bioimaging

“…This is distinctly different from organically capped Si QDs, which require hydrogen injection during synthesis to reach high PLQY values . Furthermore, these findings indicate the difference between studying natively oxidized Si QDs and HWA-treated Si QDs as other studies have indicated that natively oxidized Si QDs synthesized with hydrogen gas have reduced defect densities relative to those synthesized without hydrogen gas. ,,, For example, Pereira et al found that Si QDs synthesized with hydrogen gas in their work had a more thermally relaxed, network-structured silica shell, similar to the HWA-treated Si QDs synthesized without hydrogen gas in this work . In contrast, Si QDs synthesized without hydrogen gas had a more cage-structured silica shell after native oxidation, similar to the HWA-treated Si QDs synthesized here with hydrogen gas.…”

Nonthermal Plasma Synthesis of Composition-Tunable Silicon Nitride Nanoparticle Films for Passive Radiative Cooling

“…To this end, particles are extracted from the reactor through a nozzle and captured on a substrate by impact deposition, enabled by the pressure differential between the plasma (upstream) and beneath the nozzle in a deposition chamber (downstream). Hunter et al 29 and Mandal et al 30 have shown promising results using this method for synthesis of Si/SiN x core/shell NPs to prevent surface oxidation for optoelectronic applications. This work aims to build on the previous studies to produce composition-tunable, homogeneous SiN x NPs in this single-step, all gas-phase approach.…”

Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

“…Therefore, passivation defects in a suitable range would be a powerful strategy to regulate the luminescence of QDs. The surface-generated defects could become more stable to induce effective radiative recombination of region-confined electrons and holes. − The chemical treatment of the raw particle surface has been frequently covered by organic shells or polymeric materials, including polyethylene glycol (PEG), carboxymethyl cellulose, and polyvinyl alcohol. Nonetheless, the presence of an external passivating agent would certainly increase the complexity of the operation, and the molecular structure with long alkyl chains might improve its insulating feature to impede the electron transfer.…”