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Letters to Nature

Nature 396, 444-446 (3 December 1998) | doi:10.1038/24808; Received 22 June 1998; Accepted 24 August 1998

Spontaneous ordering of bimodal ensembles of nanoscopic gold clusters

C. J. Kiely1, J. Fink1,2, M. Brust2, D. Bethell2 & D. J. Schiffrin2

  1. Materials Science and Engineering, Department of Engineering, The University of Liverpool, Liverpool L69 3BX, UK
  2. Department of Chemistry, The University of Liverpool, Liverpool L69 7ZD, UK

Correspondence to: C. J. Kiely1 Correspondence and requests for materials should be addressed to C.J.K. (e-mail: Email: kiely@liv.ac.uk).

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The controlled fabrication of very small structures at scales beyond the current limits of lithographic techniques is a technological goal of great practical and fundamental interest. Important progress has been made over the past few years in the preparation of ordered ensembles of metal and semiconductor nanocrystals1, 2, 3, 4, 5, 6, 7. For example, monodisperse fractions of thiol-stabilized gold nanoparticles8 have been crystallized into two- and three-dimensional superlattices5. Metal particles stabilized by quaternary ammonium salts can also self-assemble into superlattice structures9,10. Gold particle preparations with quite broad (polydisperse) size distributions also show some tendency to form ordered structures by a process involving spontaneous size segregation11,12. Here we report that alkanethiol-derivatized gold nanocrystals of different, well defined sizes organize themselves spontaneously into complex, ordered two-dimensional arrays that are structurally related to both colloidal crystals and alloys between metals of different atomic radii. We observe three types of organization: first, different-sized particles intimately mixed, forming an ordered bimodal array (Fig. 1); second, size-segregated regions, each containing hexagonal-close-packed monodisperse particles (Fig. 2); and third, a structure in which particles of several different sizes occupy random positions in a pseudo-hexagonal lattice (Fig. 3).

Figure 1: An ordered raft comprising Au nanoparticles of two distinct sizes with RB/RA approximately 0.58.
Figure 1 : An ordered raft comprising Au nanoparticles of two distinct sizes with RB/RA |[ap]| 0.58. Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com

Shown are electron micrographs at low (a) and higher (b) magnification. c, The low-angle superlattice electron diffraction pattern obtained from this bimodal raft structure.

High resolution image and legend (575K)