Lajaunie Luc, Radovsky Gal, Tenne Reshef, Arenal Raul
Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón, Universidad de Zaragoza , 50018 Zaragoza, Spain.
Department of Materials and Interfaces, Weizmann Institute of Science , 76100 Rehovot, Israel.
Inorg Chem. 2018 Jan 16;57(2):747-753. doi: 10.1021/acs.inorgchem.7b02680. Epub 2017 Dec 26.
We have synthesized quaternary chalcogenide-based misfit nanotubes LnS(Se)-TaS(Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described here were reported in the literature as a bulk compound. The characterization of these nanotubes, at the atomic level, has been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy. In particular, quantification at sub-nanometer scale was achieved by acquiring high-quality electron energy-loss spectra at high energy (∼between 1000 and 2500 eV). Remarkably, the sulfur was found to reside primarily in the distorted rocksalt LnS lattice, while the Se is associated with the hexagonal TaSe site. Consequently, these quaternary misfit layered compounds in the form of nanostructures possess a double superstructure of La/Ta and S/Se with the same periodicity. In addition, the interlayer spacing between the layers and the interatomic distances within the layer vary systematically in the nanotubes, showing clear reduction when going from the lightest (La atom) to the heaviest (Ho) atom. Amorphous layers, of different nature, were observed at the surface of the nanotubes. For La-based NTs, the thin external amorphous layer (inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily, for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm) is clearly ascribed to oxidation. All of these findings helped us to understand the atomic structure of these new compounds and nanotubes thereof.
我们合成了基于硫族化物的错配纳米管LnS(Se)-TaS(Se)（Ln = 镧、铈、钕和钬）。这里描述的化合物均未在文献中作为块状化合物报道过。这些纳米管在原子水平上的表征是通过不同的透射电子显微镜技术进行的，包括高分辨率扫描透射电子显微镜、电子衍射和电子能量损失谱。特别是，通过在高能量（约1000至2500电子伏特之间）获取高质量的电子能量损失谱，实现了亚纳米尺度的定量分析。值得注意的是，发现硫主要存在于扭曲的岩盐型LnS晶格中，而硒与六方TaSe位点相关联。因此，这些纳米结构形式的四元错配层状化合物具有相同周期性的La/Ta和S/Se双超结构。此外，纳米管中层间间距和层内原子间距系统地变化，从最轻的（镧原子）到最重的（钬）原子时显示出明显减小。在纳米管表面观察到了不同性质的非晶层。对于基于镧的纳米管，薄的外部非晶层（小于10纳米）可归因于硒缺乏。相反，对于基于钬的纳米管，厚的非晶层（10至20纳米之间）明显归因于氧化。所有这些发现有助于我们理解这些新化合物及其纳米管的原子结构。
