TEM study of aluminum superconductor growth on the in-plane selected area semiconductor nanowire network

Semiconductor nanowires with strong spin-orbit coupling, high mobility and ballistic transport such as InSb and InAs, partially covered in s-wave superconductor are one of the actively developing platforms for Majorana zero modes, building blocks for topologically protected quantum computing. The semiconductor/superconductor interface is the most crucial part of the nanowire as Majoranas should emerge there. Aluminium is one of the most promising materials for a superconductor, providing a better quality interface than, for instance, niobium titanium nitride. Here, we demonstrate how transmission electron microscopy (TEM) can assess the quality of the Al superconductor layer, in particular the orientation and size distribution of grains, interface quality and grain boundaries. This study is carried out on the in-plane selected area nanowire network covered with aluminium. Combination of nanobeam electron diffraction technique with a pixelated detector with high signal-to-noise-ratio allows to obtain the grain orientation in the Al layer with the thickness of 5-10 nm.