Abstract
Silicon microspheres produced in gas-phase by hot-wall CVD offer unique quality in terms of sphericity, surface smoothness, and size. However, the spheres produced are polydisperse in size, which typically range from 0.5 μm to 5 μm. In this work we show through experiments and calculations that thermophoretic forces arising from strong temperature gradients inside the reactor volume effectively sort the particles in size along the reactor. These temperature gradients are shown to be produced by a convective gas flow. The results prove that it is possible to select the particle size by collecting them in a particular reactor region, opening new possibilities towards the production by CVD of size-controlled high-quality silicon microspheres.
Highlights
Silicon microspheres produced in gas-phase by hot-wall Chemical Vapor Deposition (CVD) offer unique quality in terms of sphericity, surface smoothness, and size
In this work we show through experiments and calculations that thermophoretic forces arising from strong temperature gradients inside the reactor volume effectively sort the particles in size along the reactor
Gas convection is a key point among the complex physico-chemical processes for understanding the obtained particle size distributions, since it is responsible of the transport of particles through large distances and of inducing strong temperature gradients in the gas volume as we show below
Summary
In the CVD route based on disilane[8,9] particles nucleate and growth in gas-phase, yielding particles with very good spherical perfection, surface smoothness and material purity These are important features specially in the field of optoelectronics because they enable the particles to behave as both proper semiconductors and high-quality-factor Mie resonators. It is highly desirable to achieve size and dispersion control with the CVD method It constitutes a challenging goal because particles grow in an aerosol process where several phenomena occur at the same time, namely nucleation, coalescence, convection, and settlement by gravity[31,32,33]. Supporting substrate, the second one is a particle size sorting effect where microspheres are deposited in different substrate zones depending on their diameter These effects produce areas containing well separated microspheres. We provide a quantitative study of these effects and we give a qualitative explanation based on the equilibrium between convection, gravity, and thermophoretic forces
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