Page 41 - Read Online

Page 6 of 29 Teng et al. Microstructures 2023;3:2023019 https://dx.doi.org/10.20517/microstructures.2023.07

Figure 2. Multistep synthesis performed in carbon nanotubes: (A) Multistep in organic synthesis. The encapsulation and conversion of
2-
Mo(CO) and iodine molecules into [Mo I ] nanocluster and regenerate [MoS ] nanoribbons (Reproduced with permission [70] .
2 n
6 14
6
Copyright 2016, American Chemical Society). (B) Multistep organic synthesis. The encapsulation and conversion of the organic
molecule perylene or coronene into graphene nanoribbons (Reproduced with permission [16] . Copyright 2011, American Chemical
Society).
Morphological structure of filled CNTs heterostructures
As mentioned in Table 1, various inorganic as well as organic materials have been filled in the CNTs until
today. To study the morphological structure of the heterostructures, transmission electron microscopy
(TEM) is a basic research method. Studies have shown that when the accelerating voltage of TEM is less
than 86 kV, the carbon nanotubes can still maintain structural integrity under the action of high-energy
[73]
electron beams . High-resolution transmission electron microscopy (HR-TEM) provides clearer internal
structure information than TEM, such as interplanar spacing, atomic arrangement, and other
information . HR-TEM allows researchers to directly "observe" chemical reactions in nanoscale space.
[74]
Aberration-corrected transmission electron microscopy (AC-TEM) is more powerful than HR-TEM in
structure information. The biggest advantage of AC-TEM is that spherical aberration correction reduces
aberration and thus improves resolution. The resolution of traditional TEM is at the nanometer scale, while
[75]
the resolution of AC-TEM can reach the Å scale . Improved resolution means a deeper understanding of
the material, making observations of single atoms possible. Here, we attempt to provide a brief review of the
previous efforts made in the compounding of X@CNTs based on the chemical composition of the filling
objects.

Element materials
Element materials with low sublimation temperatures can be filled using the gas phase method by placing
opened CNTs and bulk powder under a high vacuum and high temperature directly. Guan et al. introduced
[76]
iodine to SWCNTs by heating the opened SWCNT and iodine elemental in a clean glass tube [Figure 3A] .
The structure of the filled iodine transitions from the helical atomic chain to the crystalline phase as the
diameter of the SWCNT becomes larger from Figure 3B. Phase transitions of I from chains to crystalline
structures are observed inside the SWCNT around the critical diameter of 1.45 ± 0.05 nm. Furthermore, the
structure of the host SWCNT is elliptically distorted by the helical I chains because of the repulsive
n
interaction between I or I species and the SWCNT. In the Te@SWCNT system, the single-chain or few-
-
-
5
3
chain limit Te nanowire also exhibits a helical structure, but the behavior maintains the structural