Crystal structure of 1 DC u C l@ SWCNT s determined by low voltage high resolution transmission electron microscopy

Abstract

A wide variety of metal oxides, metal halides and other materials may be introduced into opened multiwalled or single‐walled carbon nanotubes (SWCNT). These experiments have permitted the study of the crystal growth of low‐dimensional materials whereby the incorporated crystals are constrained to just a few atomic layers in cross‐section by the internal van der Waals surface of the carbon nanotubes. The type of encapsulated crystal and its interaction with the carbon nanotube determines the electronic properties of the entire system. Change in the local crystal chemistry of incorporated crystals has been observed directly by HRTEM and has also been predicted from ab initio calculations. Therefore, the precise the composition and structure data of the encapsulated crystal is important for a correct interpretation of the filled nanotubes electronic properties. In this work, the structure and composition of SWCNTs filled by CuCl molecules from gas‐phase was characterized by High‐Resolution Transmission Electron Microscopy (HRTEM), Scanning Transmission Electron Microscopy (STEM) and X‐ray Energy Dispersion Spectroscopy (EDS). The measurements were carried out on a Titan 60‐300 TEM/STEM microscope (FEI, The Netherlands) at acceleration voltage of 80 kV equipped with monochromator and Cs spherical aberration corrector. Characterization and interpretation of the experimental images were performed by comparison with simulated HRTEM images. The CuCl@SWCNT films were characterized by Raman spectroscopy (Ar–Kr ion laser at the wavelengths of 488 nm (2.54 eV), 514.5 nm (2.41 eV), 568 nm (2.18 eV), and 647 nm (1.92 eV)). The spectral resolution was 0.5 cm ‐1 . A series of HRTEM images with different orientations of encapsulated CuCl crystal inside the nanotubes was obtained and analyzed. The chemical composition of the filled nanotubes was evaluated by EDS. It is shown that the composition ratio of copper and chlorine is 1:1. A typical fragment of filled CuCl@SWCNT is shown in Fig. 1. Fast Fourier transform was applied for the interplanar distances and angles between the vectors of reciprocal lattice estimation. The good coincidence between the calculated and experimental values of interplanar distances of encapsulated CuCl was observed for the case of NaCl type crystal lattice deformed along the [110] direction. Simulation of CuCl@SWCNT HRTEM images revealed a good correspondence of calculated and experimental data. It was found the significant changes in the Raman spectra of the CuCl@SWCNT films relative to unfilled nanotubes. The G Raman mode had a large shift (up to 20 cm ‐1 ) and a different shape. This could be explained by efficient charge transfer between the nanotube surface and the encapsulated CuCl crystal. The work was supported by RSF‐15‐12‐30041.