posted on 2021-07-22, 14:17authored byRenae
N. Gannon, Danielle M. Hamann, Jeffrey Ditto, Gavin Mitchson, Sage R. Bauers, Devin R. Merrill, Douglas L. Medlin, David C. Johnson
Layered
van der Waals heterostructures provide extraordinary opportunities
for applications such as thermoelectrics and allow for tunability
of optical and electronic properties. The performance of devices made
from these heterostructures will depend on their properties, which
are sensitive to the nanoarchitecture (constituent layer thicknesses,
layer sequence, etc.). However, performance will also be impacted
by defects, which will vary in concentration and identity with the
nanoarchitecture and preparation conditions. Here, we identify several
types of defects and propose mechanisms for their formation, focusing
on compounds in the ([SnSe]1+δ)m(TiSe2)n system prepared
using the modulated elemental reactants method. The defects were observed
by atomic resolution high-angle annular dark-field scanning transmission
electron microscopy and can be broadly categorized into those that
form domain boundaries as a result of rotational disorder from the
self-assembly process and those that are layer-thickness-related and
result from local or global deviations in the amount of material deposited.
Defect type and density were found to depend on the nanoarchitecture
of the heterostructure. Categorizing the defects provides insights
into defect formation in these van der Waals layered heterostructures
and suggests strategies for controlling their concentrations. Strategies
for controlling defect type and concentration are proposed, which
would have implications for transport properties for applications
in thermoelectrics.