Synthesis of nanostructures using charged nanoparticles spontaneously generated in the gas phase during chemical vapor deposition

Abstract

Nonclassical crystallization is the process in which crystals grow by deposition of nanoparticles rather than by the layer-wise deposition of atoms/ions/molecules on a crystal surface. A spontaneous generation of charged nanoparticles (CNPs) in the gas phase has been experimentally confirmed during many chemical vapor deposition (CVD) processes. The fact that crystals grown by CNPs have smooth surfaces without any void indicates that CNPs have a liquid-like or superplastic property. Based on this understanding of nonclassical crystallization in CVD processes, the synthesis of nanoparticles, thin films and nanowires can be approached systematically. Since electrical field, drag effect, size and the number of charges per particle affect the behavior of CNPs, electric bias, gas velocity, the size of the nanoparticles and the amount of charge can be new processing parameters. The size distribution of CNPs depends on the process conditions.The nanoparticles can be attracted or repelled by applying an electric bias to a substrate. If the nanoparticles are made to land on the substrate in a suitable number density, they can be used as quantum dots. In addition, nanopowders, nanowires, and nanostructures can be synthesized by CNPs with or without metallic catalysts on substrates. Herein, we will review recent results of the synthesis of nanostructures such as nanoparticles, thin films, and nanowires in the CVD process. We will also discuss the role of charge in these syntheses.