Keywords: scanning transmission electron microscopy, aberration correction, Z–contrast, semiconductor devices, silicon nanowires, point defects, lens aberrations, nanotechnology
Seeing inside materials by aberration–corrected electron microscopy
The recent successful correction of lens aberrations in the electron microscope has improved resolution by more than a factor of two in just a few years, bringing many benefits for the study of materials. These benefits extend significantly beyond enhanced resolution alone. Aberration correction gives higher resolution by allowing the objective lens to have a wider aperture, which also results in a reduced depth of field. This effect can be used to only focus specific sections inside materials for the first time. In this contribution we describe recent results exploiting this capability. Additionally, we show how combining the microscopy data with first–principles theory gives new insights into materials properties. We cover two applications, both involving heavy atoms in a lighter host. The first shows how single Hf atoms can be mapped in three dimensions inside the 1 nm–wide SiO
2region of a high dielectric constant device structure, and how a link to macroscopic device properties results through theoretical calculations. The second example is from the field of nanoscience, where individual Au atoms are imaged inside Si nanowires grown by a vapour–liquid–solid mechanism. The majority of Au atoms are probably injected by the highly energetic electron beam. However, their observed sites and atomic configurations represent at least meta–stable configurations and match well to results from density functional calculations.