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Page 10 of 29 Teng et al. Microstructures 2023;3:2023019 https://dx.doi.org/10.20517/microstructures.2023.07

Figure 4. Organic compounds filling: (A) A series of high-resolution images of C molecules gradually bonded (Reproduced with
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permission [61] . Copyright 2010, Springer Nature). (B) A series of successive HRTEM images of (Ce@C )@SWCNT and their schematic
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representation (Reproduced with permission [93] . Copyright 2004, Wiley). (C) Structural diagram of octasiloxane Si H O ; HRTEM
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8
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micrograph and structural diagram of Si H O @SWCNT (Reproduced with permission [95] . Copyright 2005, American Chemical
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Society). (D) AC-HRTEM and simulated images of @SWCNT and {W }@SWCNT, respectively (Reproduced with permission [89] .
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Copyright 2019, Wiley). (E) Model illustration of Viol inside a metallic SWCNT, representative AC-HRTEM image of Viol@SWCNT and
SEM image of a Viol@SWCNT (Reproduced with permission [21] . Copyright 2017, Wiley).
previously studied examples such as metal oxide [44,101] , carbides [61,84] , and halides [102-104] . This section will
concentrate on some novel structures and systems, such as transition metal dichalcogenides
[53]
(TMDs) [18,50,56,57,70,101,105-108] and perovskite .
Many materials, which are hard to stabilize under normal conditions, form new phases with unique
coordination properties in the lumen of CNTs. Under high temperatures, a PbI SWCNT with a diameter
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ranging from ~3 to 7 nm is first realized inside the hollow nanospace of MWCNT [Figure 5A] . The
[109]
SWCNTs are expected to be steady in the absence of carbon atom protection, and their electronic structure
is diameter independent. Recently, Kashtiban et al. reported the formation of four isolated halide perovskite
nanowires inside ~1.2-1.6 nm SWCNTs via melt insertion of CsPbBr and CsSnI [Figure 5B] . One of the
[53]
3
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four nanowires has a perovskite-like lamellar structure with polyhedral Sn Ix layers, while the other three
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are ABX perovskite archetypes. Vasylenko et al. created SnTe nanowires that filled in CNTs with
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monatomic, curvilinear chains, hyperbolic chains, and 2 × 2 rock structures by varying the diameter of the
CNTs . The study of halide perovskite nanowires and SnTe nanowires filled in CNTs revealed that the
[18]
structure of the internal filling can be manipulated to design its electronic behavior by changing the
diameter of the CNTs.