  Van der Waals heterostructures have recently been identified as providing
many opportunities to create new two-dimensional materials, and in particular
to produce materials with topologically interesting states. Here we show that
it is possible to create such heterostructures with multiple topological phases
in a single nanoscale island. We discuss their growth within the framework of
diffusion-limited aggregation, the formation of moir\'e patterns due to the
differing crystallographies of the materials comprising the heterostructure,
and the potential to engineer both the electronic structure as well as local
variations of topological order. In particular we show that it is possible to
build islands which include both the hexagonal $\beta$- and rectangular
$\alpha$-forms of antimonene, on top of the topological insulator
$\alpha$-bismuthene. This is the first experimental realisation of
$\alpha$-antimonene, and we show that it is a topologically non-trivial
material in the quantum spin Hall class.
