Aggregation Phenomena in Atomic Layer Deposition

Abstract

Atomic layer deposition (ALD) is a gas-phase thin film technology that boasts atomic-level control over the amount of material being deposited. A great deal of research effort has been devoted to the exploitation of ALD precision for the synthesis of nanostructures other than thin films such as supported nanoparticles (NPs). ALD is not only precise but also scalable to high-surface-area supports such as powders, which are relevant to a wide range of applications in fields spanning catalysis, energy storage and conversion, and medicine. Yet, translating the precision of ALD of thin films to the synthesis of NPs is not straightforward. In fact, ALD is mostly understood in terms of self-limiting surface reactions leading to a layer-by-layer conformal growth. However, the formation and growth of NPs is bound to be dictated by atomistic processes other than ALD surface reactions, such as the diffusion and aggregation of atoms and NPs. Understanding the role of such non-equilibrium processes is the key to achieving atomic-level control over the morphology of ALD-grown NPs and, in particular, their particle size distribution (PSD) and shape. This thesis is aimed at expanding our atomic-scale understanding of the mechanisms behind the formation of NPs during ALD. In particular, this thesis is based on experiments and models that were devised with an eye to scalability.