Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

Abstract

The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS 2 nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS2 nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism.aberration-corrected high-resolution transmission electron microscopy ͉ inorganic closed-cage structures

The quest for inorganic fullerenes

“…Alternatively, the particles could be octahedral as indicated by the TEM pictures of nested inorganic fullerenes. 10 Such a cluster can be viewed as eight triangular platelets assembled to an octahedron. For the platelets, there is a minimum size.…”

“…The smallest such structure seems to have three walls. 10,20 In contrast to carbon, these structures are not spherical. The smallest ones have octahedral geometries.…”

“…There are many materials that form nanotubes and nested fullerenes similar to carbon, [6][7][8][9][10][11][12][13][14][15][16][17] but so far, no "single-wall" nano-spheres analogous to C 60 and B 40 have been observed. MoS 2 and WS 2 are layered materials which exhibit a certain similarity to carbon.…”

“…Both materials easily form nanotubes again similar to carbon. 18 Also, both materials form nested fullerenes, 10,19 which can be viewed as "multiwall" fullerenes. The smallest such structure seems to have three walls.…”

Insights into the capping and structure of MoS2 nanotubes as revealed by aberration-corrected STEM

“…Aberration-corrected electron microscopy for the study of inorganic nanotubes, especially those of the transition metal chalcogenides (ex: WS 2 ) is a very recent area of exploration. 15,16 The elucidation of structure and chirality is essential to the understanding of how nanotubes can have suitable electronic, mechanical and other related properties. This thereby can help the preferential and improved synthesis of nanotubes suited for specific applications.…”