  Galvanic replacement reactions on metal nanoparticles are often used for the
preparation of hollow nanostructures with tunable porosity and chemical
composition, leading to tailored optical and catalytic properties. However, the
precise interplay between the three-dimensional (3D) morphology and chemical
composition of nanostructures during Galvanic replacement is not always well
understood as the 3D chemical imaging of nanoscale materials is still
challenging. It is especially far from straightforward to obtain detailed
information from the inside of hollow nanostructures using electron microscopy
techniques such as SEM or TEM. We demonstrate here that a combination of
state-of-the-art EDX mapping with electron tomography results in the
unambiguous determination of both morphology transformation and elemental
composition of nanostructures in 3D, during Galvanic replacement of Ag
nanocubes. This work provides direct and unambiguous experimental evidence
leading to new insights in the understanding of the galvanic replacement
reaction. In addition, the powerful approach presented here can be applied to a
wide range of nanoscale transformation processes, which will undoubtedly guide
the development of novel nanostructures.
