Nonclassical Crystallization of an Al₂O₃ Film by Positively Charged Secondary Nanoparticles during Aerosol Deposition

Abstract

Thin film growth through nonclassical crystallization with charged nanoparticles as building blocks has been studied in chemical vapor deposition and physical vapor deposition. A similar mechanism might be applied to aerosol deposition (AD), with which the mechanism for the evolution of dense ceramic films at room temperature has not been clearly understood. Aerosol particles fracture into fragments of secondary nanoparticles during AD. In this work, secondary particles passing between the two parallel biased and grounded electrodes were captured by the transmission electron microscopy (TEM) grid membrane on each electrode, and it was revealed that they were mainly positively charged. Neutral secondary nanoparticles, not deflected by the electric field, produced a porous film on the silicon substrate, whereas charged secondary nanoparticles produced a dense film. The positive charge of the secondary nanoparticles appeared to enhance the plastic deformation required for the evolution of dense films during AD, which was supported by ab initio calculations.

Effects of Electrostatic Interaction on the Formation of a Particle Depletion Zone by Charged Nanoparticles during the Chemical Vapor Deposition of Si Processes

“…5,7,11−17 Hwang et al 18−27 showed that most nanoparticle building blocks generated in the gas-phase synthesis of thin films and nanostructures through chemical vapor deposition (CVD) are electrically charged and that the charges played a critical role in nonclassical crystallization. 28 To emphasize the role of charges in nonclassical crystallization, the authors named the underlying theory the "theory of charged nanoparticles". 19 In addition, structures with interesting morphologies, such as nanowires, nanobelts, nanorings, nanohelixes, nanosheets, and nanorods, have been grown via CVD.…”

“…Nonclassical crystallization has been studied extensively by numerous researchers in the field of crystal growth. ,,− Hwang et al − showed that most nanoparticle building blocks generated in the gas-phase synthesis of thin films and nanostructures through chemical vapor deposition (CVD) are electrically charged and that the charges played a critical role in nonclassical crystallization . To emphasize the role of charges in nonclassical crystallization, the authors named the underlying theory the “theory of charged nanoparticles” …”