Crystal Shape Engineering of Silicon Nanoparticles in a Thermal Aerosol Reactor

Abstract

In this work, the capability of gas phase synthesis for crystal shape engineering of silicon nanoparticles (SiNPs) in a hot wall reactor is demonstrated. Therefore, the necessary boundary conditions for the formation of monodisperse spherical SiNPs as well as octahedral-shaped particles from silane pyrolysis are systematically deduced. The different shapes of the SiNPs are ascribed to different growth regimes (reaction limitation, diffusion limitation) depending on the global process parameters. Single crystalline, defect-free, spherical particles with a mean diameter of 30 nm (geometric standard deviation below 1.1) and octahedra with a mean edge length of about 100 nm could be obtained solely by process parameter adjustment. Particle size and shape as well as crystallinity were characterized by scanning electron microscopy and X-ray diffraction. The inner structure and faceting of the particles were analyzed in detail by high resolution transmission electron microscopy. A model that elucidates the orientation relation between the inner silicon structure and the particle shape is derived for the octahedra.

Silicon‐Based Dielectric Metamaterials: Focus on the Current Synthetic Challenges

“…Thec oncentration required to have supersaturation depends on the type of chemical reaction (e.g.t ype of precursor,d ecomposition kinetics) and on the synthesis conditions.W orking below the supersaturation limit produces few nuclei, that then may grow by heterogeneous growth. This trend opposes that observed by Kçrmer et al [59] which can be explained by the fact that the saturation limit was surpassed and therefore particle growth occurred by coalescence. Kçrmer and co-workers observed that asilane partial pressure inferior to 1mbar in 100 mbar of Ar allowed the production of Si objects larger than 100 nm.…”

“…[54,56,57] Thet emperature,t he total pressure in the reactor and the silane partial pressure are fundamental parameters,h aving ac onsiderable effect on the size,s ize dispersion, crystallinity [58] and even the shape of the produced particles. [59] Ostraat et al observed as ize increase from 6-7nmto40nmupon increasing the silane concentration from 10 ppb to 3300 ppb. [56] Kçrmer et al [58] investigated the effect of silane partial pressure (i.e.t he concentration) on the particle size:they observed an increase in the average size of Si particles from 25 to 40 nm by decreasing silane pressure from 1mbar to 0.5 mbar.The discrepancy in these two results arises from the particle growth mechanism, which proceeds through homogenous growth in the first case and heterogeneous growth in the latter.…”

“…[56] Kçrmer et al [58] investigated the effect of silane partial pressure (i.e.t he concentration) on the particle size:they observed an increase in the average size of Si particles from 25 to 40 nm by decreasing silane pressure from 1mbar to 0.5 mbar.The discrepancy in these two results arises from the particle growth mechanism, which proceeds through homogenous growth in the first case and heterogeneous growth in the latter. [59] Adjusting the total and silane partial pressure,heterogeneous growth can be favored over homogeneous growth, producing large,m onodisperse and crystalline particles. [59] Adjusting the total and silane partial pressure,heterogeneous growth can be favored over homogeneous growth, producing large,m onodisperse and crystalline particles.…”

Reaction Engineering Strategies for the Production of Inorganic Nanomaterials

“…The mixing of the reactants and the carrier gas also adds flexibility to this system, with a variety of possible mixing arrangements. The better control of operating conditions allows the use of this system for the production of technological materials with tailored characteristics, such as highly crystalline silicon nanoparticles . However, to obtain monodisperse nanoparticles the use of low pressure (under 25 mbar) and low precursor concentration are required, leading to low throughput rates.…”

Octahedral faceted Si nanoparticles as optical traps with enormous yield amplification

“…A completely differently shaped Si-NP formed by SiH 4 gas thermal dissociation at a high temperature (above 1100°C) has recently been reported19. The weakness of this approach is that it only leads to a few irregular crystalline nanoparticles immersed in a mess consisting of a large number of amorphous and polycrystalline particles and again inhibits the use of low cost substrates.…”