ABSTRACT
This chapter discusses scanning transmission electron microscopy (STEM) tomography to reconstruct the three-dimensional structure and composition of a Si/Ge quantum dot. The optimum 3D probe was evaluated using simulation and experimental defocus series of probe images. The fidelity of the quantum dot reconstruction was slightly hampered by contamination but the initial experiments show how STEM electron tomography can examine quantum dot structures with I nm3 3D resolution. In the biological sciences, in which cell or macromolecular structures are truly three-dimensional, electron tomography has been used to reconstruct the 3D structure from a series of projections at successive angles. Arguably the most promising of the is high-angle annular dark-field STEM tomography owing to its intrinsic high spatial resolution, atomic number sensitivity and the incoherent nature of the image formation. One of the limitations of STEM tomography is the finite depth of focus, which arises from the convergent nature of the probe.
