Aspects of crystal growth within carbon nanotubes

The comparative crystallisation and HRTEM imaging properties of simple binary halides formed by the alkali iodides MI (M = Li, K, Na, Rb and Cs) within single walled carbon nanotubes (SWNTs) are described. The most common structure type observed within SWNTs is the rocksalt archetype, although CsI was observed to form both bcc and rocksalt structure types. In SWNTs forming in the 1.2-1.6 nm diameter range, all of the incorporated halides showed preferred orientation, with the (100) growth direction predominating for rocksalt-type packing and (112) so far observed exclusively for bcc packing. Crystals with dimensions spanning 2-6 atomic layers thickness in projection invariably exhibited lattice expansions that were attributed predominantly to a net reduction in coordination at the crystal-carbon interface. The crystallisation behaviour Of UCl4-KCl and AgI-AgCl eutectic melts was compared in carbon nanotubes of different diameters and a pronounced ordering influence over the normally glassy melts was observed in narrower capillaries. HgI2 crystallised within nanotubes with ultra-narrow (i.e., 0.8 nm) capillaries were observed to form helical 2 x 1 layer crystals. (C) 2003 Academie des sciences. Published by Elsevier SAS. All rights reserved.