ABSTRACT
Wolfson Catalysis Centre (Carbon Nanotechnology Group), Inorganic Chemistry Laboratory, South Parks Road, Oxford 0X1 3QR, UK. * Department of Materials Science, Pembroke Street, Cambridge CB2 3QZ, UK. department of Materials, Parks Road, Oxford 0X1 3PH, UK
ABSTRACT: The growth behaviour and crystallography of metal halides incorporated within single walled carbon nanotubes (SWNT) has been studied by an enhanced image restoration technique which restores the object wave from a focal series of HRTEM images. This allows the structural characterisation of the encapsulated crystals with a precision not normally achievable from single HRTEM images. The restored phase provides information about the atomic thickness in projection of individual atom columns, and reveals precise structural data concerning lattice distortions within the crystal fragments relative to the bulk structures. In most cases, substantial overall lattice contractions of the crystal along the tube axis were observed. The smallest observed crystals were as thin as two atomic layers in projection along the image plane normal. 12
1. INTRODUCTION
A full ‘atom-by-atom’ characterisation of a KI/SWNT inclusion composite has been achieved using the restored exit plane wave (Meyer et al. 2000). In this previous example, the crystal was imaged along the unit cell diagonal resulting in a restored phase, in which all the atom columns consisted of either potassium of iodine atoms. It was therefore possible to assign the precise number of atoms superimposed in each column, as the phase shift in the restored phase image is directly proportional to the electron density in projection. The encapsulated crystal fragment consisted of a sequence of 1I-2K-3I-2K-1I and 1K-2K-3K-2I-1K {10 0} layers, alternating perpendicular to the tube axis. In comparison to the bulk structure of KI, the encapsulated crystal fragment was subject to overall lattice distortions given in Table 1.
