Misfit layered compounds
(MLCs) MX-TX
2
, where M, T =
metal atoms and X = S, Se, or Te, and their nanotubes are of significant
interest due to their rich chemistry and unique quasi-1D structure.
In particular, LnX-TX
2
(Ln = rare-earth atom) constitute
a relatively large family of MLCs, from which nanotubes have been
synthesized. The properties of MLCs can be tuned by the chemical and
structural interplay between LnX and TX
2
sublayers and
alloying of each of the Ln, T, and X elements. In order to engineer
them to gain desirable performance, a detailed understanding of their
complex structure is indispensable. MLC nanotubes are a relative newcomer
and offer new opportunities. In particular, like WS
2
nanotubes
before, the confinement of the free carriers in these quasi-1D nanostructures
and their chiral nature offer intriguing physical behavior. High-resolution
transmission electron microscopy in conjunction with a focused ion
beam are engaged to study SmS-TaS
2
nanotubes and their
cross-sections at the atomic scale. The atomic resolution images distinctly
reveal that Ta is in trigonal prismatic coordination with S atoms
in a hexagonal structure. Furthermore, the position of the sulfur
atoms in both the SmS and the TaS
2
sublattices is revealed.
X-ray photoelectron spectroscopy, electron energy loss spectroscopy,
and X-ray absorption spectroscopy are carried out. These analyses
conclude that charge transfer from the Sm to the Ta atoms leads to
filling of the Ta 5
d
z
2
level, which is confirmed by density functional theory (DFT)
calculations. Transport measurements show that the nanotubes are semimetallic
with resistivities in the range of 10
–4
Ω·cm
at room temperature, and magnetic susceptibility measurements show
a superconducting transition at 4 K.