  Understanding structure at the interface between two-dimensional (2D)
materials and 3D metals is crucial for designing novel 2D/3D heterostructures
and improving the performance of many 2D material devices. Here, we quantify
and discuss the 2D/3D interface structure and the 3D morphology in several
materials systems. We first deposit facetted Au nanoislands on graphene and
transition metal dichalcogenides, using measurements of the equilibrium island
shape to determine values for the 2D/Au interface energies and examining the
role of surface reconstructions, chemical identity, and defects on the grown
structures. We then deposit the technologically relevant metals Ti and Nb under
conditions where kinetic rather than thermodynamic factors govern growth. We
describe a transition from dendritic to facetted islands as a function of
growth temperature and discuss the factors determining island shape in these
materials systems. Finally, we show that suspended 2D materials enable the
fabrication of a novel type of 3D/2D/3D heterostructure and discuss the growth
mechanism. We suggest that emerging nanodevices will utilize such versatile
fabrication of 2D/3D heterostructures with well-characterized interfaces and
morphologies.
