In the past decades, group IV nanowires
and nanoparticles have
been the subject of extensive research. Beside tremendous progress
in morphological control and integration in advanced device architectures,
research on allotropes and metastable compositions has gained considerable
interest. Several new approaches now allow the controlled formation
of specific allotropes in the nanostructured form as well as chemical
compositions not attainable by traditional synthesis protocols. The
conditions applied to form these metastable solid solutions and allotropes
are usually far from thermodynamic equilibrium or rely on unconventional
templates. The increased interest in the field of metastable group
IV nanostructures arises from their altered physical properties, including
tunable, direct bandgaps with energies equivalent to the near- to
mid-infrared spectral region as described for materials such as Ge1–x
Sn
x
and
hexagonal Si1–x
Ge
x
. The implementation of these material characteristics in complementary
metal oxide semiconductor (CMOS) processes are desirable for applications
in electronics, optoelectronics, sensors, optics, etc. but also their
use as nonsurface bound nanoparticles in sensing, nanobiotechnology
and nanomedicine can offer additional opportunities. This review article
highlights both the important advancements and still open questions
for the continued development of these nanoscaled materials for next-generation
device concepts.