Synthesis and On-line Size Control of Silicon Quantum                    Dots

Xavier Paquez,Olivier Sublemontier,Cécile Reynaud,Harold Kintz,Yann Leconte,Vincent Maurice,Dominique Porterat,Nathalie Herlin-Boime,Frédéric Lacour

doi:10.14356/kona.2011024

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.

Highlights

Controlling the size of quantum dots is a key issue for applications requiring materials with precisely adjustable properties brought about by nanostructuration 1)
The band gap can be adjusted as a function of the size below 8 nm according to the quantum confinement model prediction 5), which correctly fits the experimental observations for sizes down to about 3 nm
We assume that the maximum reaction temperature during gate-on slots in our case is between 770 K and 1687 K, and depends on Ton

Summary

Introduction

Controlling the size of quantum dots is a key issue for applications requiring materials with precisely adjustable properties brought about by nanostructuration 1). A typical example is the case of Silicon. Quantum Dots (Si-QDs), which exhibit strong sizedependent properties. Various applications are expected in dif ferent domains including optical and electronic devices 2), photovoltaic solar cells 3) and markers for in vivo biological structures imaging[4]). The band gap can be adjusted as a function of the size below 8 nm according to the quantum confinement model prediction 5), which correctly fits the experimental observations for sizes down to about 3 nm. In the case of silicon, the spatial confinement of the exciton induced by an incident UV photon leads to an efficient photoluminescence (PL). Of surface-passivated Si-QDs at room temperature[6]).

Objectives

Methods

Findings

Discussion

Conclusion