Multi-layer structures in binary systems as, e.g., InAs/AlSb and AlSb/GaSb as well as ternary InGaAs/AlGaAs quantum wells grown by molecular beam epitaxy and studied by HREM demonstrate the importance of strain relaxations to physical properties and image contrast. This is true also for the HREM and TEM determination of the structure (geometry, size, shape, etc.) of nm-scale objects as, e.g., quantum dots (QD) and quantum wires. Different shapes, and materials systems are investigated (e.g. InAs/GaAs, CdSe/ZnSe, Ge/Si) to separate shape and misfit related effects the properties. For instance, pyramidal shape InGaAs islands always seem to be truncated owing to the lower In content on top of the pyramid and to the high level of strains. The relaxations observed may be described by relatively simple interatomic potentials within classical MD simulations.
Related to the shape – strain problems a very actual topic considers the additional influence of migration of point defects at the interfaces and nanostructures, e.g. the influence of C at twins in Si.
The Figure shows relaxed models of an pyramidal quantum dot configuration and an sphere (without embedding matrix) as well as experimental and corresponding simulated plan view (100)-bright field images (left and right rows) in comparison with experimental details for stacked quantum dots (cross section upper left).