Simultaneous determination of inclusion crystallography and nanotube conformation for a Sb 2 O 3 Õsingle-walled nanotube composite S. Friedrichs, J. Sloan,* and M. L. H. Green Wolfson Catalysis Centre (Carbon Nanotechnology Group), Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom J. L. Hutchison Department of Materials, Parks Road, Oxford, OX1 3PH, United Kingdom R. R. Meyer and A. I. Kirkland ² Department of Materials Science, Pembroke Street, Cambridge CB2 3QZ, United Kingdom ~Received 30 January 2001; published 29 June 2001! We report the structural solution of a one-dimensional Sb 2 O 3 crystal incorporated within a helical ~21,-8! single-walled carbon nanotube. The structures of both the encapsulated crystal and nanotube have been quan- tified using the phase image recovered via a modified object wave restoration scheme. DOI: 10.1103/PhysRevB.64.045406 PACS number~s!: 61.48.1c, 07.05.Pj, 68.37.Lp, 61.46.1w I. INTRODUCTION We recently showed that a 3 33 atomic layer one- dimensional ~1D! crystal of KI incorporated within a single- walled carbon nanotube ~SWNT! could be characterized on an ‘‘atom-by-atom’’ basis from the phase image restored from a focal series of images. 1 In this previous example the crystal was imaged along the unit-cell diagonal ~i.e., ^110&! relative to the bulk KI structure, which meant that all the imaged atom columns consisted of either pure K or pure I. 2 In the restored phase image, the phase shift produced by each atom column and by the SWNT walls was proportional to the electron density in projection and it was possible, there- fore, to determine the precise number and type of atoms in each column in a repeating sequence of 1I-2K-3I-2K-1I and 1K-2I-3K-2I-1K $100% layers formed along the SWNT axis. In addition, atom column positional shifts relative to the bulk structure were measured. These were attributed to local dis- tortions imposed by a reduction in coordination for the sur- face atoms of the inclusion crystal and also to constraints imposed by the confining surface of the SWNT. In spite of this level of structural characterization, information regard- ing the structural conformation of the host SWNT was absent as atomic detail from the SWNT was not resolved. In the absence of such information, a complete ab initio determina- tion of the physical properties of such a composite ~and therefore subsequent experimental verification! is impos- sible. In this paper we report the characterization of an encap- sulated nanocrystal of Sb 2 O 3 based on the valentinite struc- ture in which the atomic thickness in projection of individual antimony columns has been determined. Within the nano- crystal there is evidence for both local structural distortion and a substantial overall lattice contraction of the crystal along the tube axis. A detailed analysis of asymmetric fringe contrast in the tube walls has provided strong evidence for the chiral conformation ~including the handedness! of the nanotube itself. The conformation is determined simulta- neously together with the inclusion crystallography. II. EXPERIMENTAL A. Synthesis and specimen preparation SWNT’s were produced using a metal catalyzed arc syn- thesis procedure similar to the method previously reported 3 and filled according to the capillary technique. 4 A ground mixture of as-prepared SWNT’s ~0.030 g! and Puratronic Sb 2 O 3 ~ALFA, 99.999%!~0.150 g! was sealed into a quartz ampoule, heated at 1 K min 21 to 1033 K, held at that tem- perature for 180 min, and then allowed to slowly cool to room temperature inside the furnace. The product was re- ground, dispersed in Analar pentane and placed dropwise onto a holey carbon support grid. The product was examined at 300 kV in a Japan Electron Optics Laboratory ~JEOL! JEM-3000F field emission gun transmission electron microscope ~FEGTEM!, with a spheri- cal aberration coefficient ( C S ) of 0.57 mm and a point reso- lution of 0.16 nm. 5 In order to confirm the composition of the filling material, energy dispersive x-ray microanalysis ~EDX! spectra were recorded from discrete filled SWNT’s with an Oxford Instruments ISIS 300 system equipped with a LINK ‘‘Pentafet’’ detector and utilizing a minimum 0.5-nm-diam probe. High resolution images of individual filled nanotubes were acquired at a magnification of 3600 000 using a GATAN 794 ~1k31 k pixel! charge-coupled device ~CCD! camera. The microscope alignment was corrected for axial coma and twofold astigmatism using power spectra obtained from amorphous regions of the carbon support film. 6 The direct magnification at the plane of the CCD camera was independently calibrated at a known objective lens current using Si $110% lattice fringes. For suitable nanotubes a focal series of 20 images was recorded at an exposure of 1 s with a nominal focal increment between each image of 11 nm together with a final image with the nominal starting defocus in order to assess the specimen drift and beam damage. B. Image processing and simulation From each series of images, the exit plane wavefunction was restored using a linear Wiener filter restoration algo- PHYSICAL REVIEW B, VOLUME 64, 045406 0163-1829/2001/64~4!/045406~8!/$20.00 ©2001 The American Physical Society 64 045406-1