91福利

The Magic of Microscopy: Investigating the World’s Smallest Crystals (and Single Molecules)

Dr. Jeremy Sloan
 Department of Physics, 91福利, Coventry, CV4 7AL UK

Abstract

A wide variety of materials, including both low dimensional crystals, clusters and molecules, can form inclusions in both single and multiple walled carbon nanotubes, structures that permit the direct imaging of the contained species by high resolution transmission electron microscopy (HRTEM) [1]. From the points of view of both solid state physics and HRTEM these encapsulates are both interesting and challenging because all of the inclusions so formed are on the molecular scale and, in microscopy terms, correspond to weak phase objects of ‘known’ atomic thickness. In terms of our understanding of the relationships between structure and properties, these materials are also valuable because their small size scale makes them tractable to comparative theoretical tools such as Molecular Dynamics (MD) and Density Functional Theory (DFT) calculations. As a result, we have been able to obtain detailed crystal structure information from HRTEM of low dimensional crystal growth and then cross-correlate the obtained, sometimes modified, crystallography with DFT calculations. For example, for low dimensional semimetals/semiconductors grown within nanotubes (e.g. HgTe and SnSe) we show both modified crystal growth behaviour and modified electronic structure as a result of nanotube confinement [2]. For molecules formed within carbon nanotubes, it has been comparatively difficult to obtain such detailed correlation between structure and properties due to the relative difficulty of obtaining precise structural data from these species as they are frequently not rigidly bound within the interior of the nanotubes when imaged by HRTEM. However, for the asymmetric polyoxometalate anion [W6O19]2-, steric locking of this species within nanotubes permits direct observation of structural distortions, permitting detailed correlation with theoretical calculations (i.e. MD) for the first time [3].

References
1. J. Sloan, D.E. Luzzi, A.I. Kirkland, J. L. Hutchison, and M.L.H. Green, MRS Bull. 2004, 29, 265.
2. R. Carter, J. Sloan, A. Vlandas, M. L. H. Green A. I. Kirkland, R. R. Meyer, J. L. Hutchison P. J. D. Lindan, G. Lin, J. Harding, Phys. Rev. Lett., 2006, 96, 215501.

3 J. Sloan G. Matthewman, C. Dyer-Smith, A-Y. Sung, Z. Liu, K. Suenaga, A. I. Kirkland, and E. Flahaut, ACS Nano, 2008, 2, 966.