  Exploring new two-dimensional (2D) van der Waals (vdW) systems is at the
forefront of materials physics. Here, through molecular beam epitaxy on
graphene-covered SiC(0001), we report successful growth of AlSb in the
double-layer honeycomb (DLHC) structure, a 2D vdW material which has no direct
analogue to its 3D bulk and is predicted kinetically stable when freestanding.
The structural morphology and electronic structure of the experimental 2D AlSb
are characterized with spectroscopic imaging scanning tunneling microscopy and
cross-sectional imaging scanning transmission electron microscopy, which
compare well to the proposed DLHC structure. The 2D AlSb exhibits a bandgap of
0.93 eV versus the predicted 1.06 eV, which is substantially smaller than the
1.6 eV of bulk. We also attempt the less-stable InSb DLHC structure; however,
it grows into bulk islands instead. The successful growth of a DLHC material
here opens the door for the realization of a large family of novel 2D DLHC
traditional semiconductors with unique excitonic, topological, and electronic
properties.

Materials Science;Mesoscale and Nanoscale Physics