Self-Assembled Nanostructure Formation in Chemical Vapor Deposition

TL;DR

This paper models the formation of nanostructures during chemical vapor deposition using reaction-diffusion dynamics, explaining pattern emergence and growth mechanisms of thin films on substrates.

Contribution

It introduces a dynamical reaction-diffusion model for nanostructure formation in CVD, highlighting pattern selection without variational principles and linking structures to growth modes.

Findings

Instability of uniform layers leads to nanostructure patterns.

Pattern types depend on reaction-diffusion nonlinearities.

Different growth mechanisms are associated with specific structures.

Abstract

When thin films are grown on a substrate by chemical vapor deposition, the evolution of the first deposited layers may be described, on mesoscopic scales, by dynamical models of the reaction-diffusion type. For monoatomic layers, such models describe the evolution of atomic coverage due to the combined effect of reaction terms representing adsorption-desorption and chemical processes and nonlinear diffusion terms which are of the Cahn-Hilliard type. This combination may lead, below a critical temperature, to the instability of uniform deposited layers. This instability triggers the formation of nanostructures corresponding to regular spatial variations of substrate coverage. Patterns wavelengths and symmetries are selected by dynamical variables and not by variational arguments. According to the balance between reaction- and diffusion-induced nonlinearities, a succession of self-assembled structures including hexagonal arrays of dots, stripes and localized structures of various types may be obtained. These structures may initiate different types of growth mechanisms, including Volmer-Weber and Frank-Van der Merwe type of growth. The relevance of this approach to the study of different types of deposited monolayers is discussed.