Synthesis and On-line Size Control of Silicon Quantum Dots

Abstract

The synthesis of silicon quantum dots is performed in the [3–5 nm] range using CO₂ laser pyrolysis of SiH₄. This size range is particularly relevant for potential applications in photovoltaic devices and biomedical imaging. The laser pyrolysis technique offers convenient control of the synthesis parameters in the case of nanoparticle production. However, controlling the size of small silicon objects remains difficult. The original approach consists here in a time-control of the energy injected into the reaction by gating the laser. The laser gate-on duration is adjusted in the range of 10 to 80 μs while keeping the average power constant. In parallel, supersonic expansion and on-line time-of-flight mass spectrometry are performed for on-line size characterization. A monotonic increase of the size as a function of the gate-on duration is observed for several SiH₄ volume concentrations. The results are discussed qualitatively.