Predicting nanocrystal morphology governed by interfacial strain

TL;DR

This paper presents a model predicting the shape of NiO nanocrystals on substrates based on interfacial strain, explaining experimental observations and aiding design of hetero-epitaxial nanostructures.

Contribution

It introduces a quantitative model using the GWK theorem to predict nanocrystal shapes governed by interfacial strain, validated by experimental data.

Findings

Fully pseudomorphic interfaces lead to smooth embedded morphologies.

Relaxed interfacial strain results in truncated pyramidal shapes.

The model accurately predicts nanocrystal shapes and sizes.

Abstract

The shape dependence for the technologically important nickel oxide (NiO) nanocrystals on (001) strontium titanate substrates is investigated under the generalized Wulff-Kaichew (GWK) theorem framework. It is found that the shape of the NiO nanocrystals is primarily governed by the existence (or absence) of interfacial strain. Nanocrystals that have a fully pseudomorphic interface with the substrate (i.e. the epitaxial strain is not relaxed) form an embedded smooth ball-crown morphology with {001}, {011}, {111} and high-index {113} exposed facets with a negative Wulff point. On the other hand, when the interfacial strain is relaxed by misfit dislocations, the nanocrystals take on a truncated pyramidal shape, bounded by {111} faces and a {001} flat top, with a positive Wulff point. Our quantitative model is able to predict both experimentally observed shapes and sizes with good accuracy. Given the increasing demand for hetero-epitaxial nanocrystals in various physio-chemical and electro-chemical functional devices, these results lay the important groundwork in exploiting the GWK theorem as a general analytical approach to explain hetero-epitaxial nanocrystal growth on oxide substrates governed by interface strain.