Orientation and shape selection of self-assembled epitaxial Ce1−xGdxO2−y nanostructures grown by chemical solution deposition

Abstract

The extended use of self-assembling approaches for the generation of oxide nanostructures with engineered functional properties firstly relies on the ability to control their growth processes. In this paper, we focus on the growth of Ce1−xGdxO2−y (CGO) nanoislands on ABO3 substrates (i.e. LaAlO3 (LAO)) as a model system to investigate the nucleation and kinetic evolution of epitaxial nanostructures grown by high-throughput ex situ methods based on chemical solution deposition. Fine-tuning of growth conditions enables us to select the crystallographic orientation of CGO leading to two systems with different equilibrium shapes and kinetics. Self-assembled (001)CGO‖(001)LAO nanostructures grow with stable uniform square-based nanopyramid shape, whereas the nucleation of (011)CGO‖(001)LAO leads to highly elongated nanowires with enhanced diffusive mobility. At high temperatures, shape selection is merely achieved through a modified growth atmosphere (oxidizing or reducing). However, a temperature-induced nucleation orientation crossover occurs under the reducing growth atmosphere, allowing the tuning of a nanodot-to-nanowire ratio through kinetic control. We prove by XPS that an enhanced concentration of oxygen vacancies in the nanowires is linked to their ultrafast coarsening. The nucleation processes are scrutinized through thermodynamic analysis, and it is concluded that the supersaturation degree controls the nanoislands' orientation.