John Fink

Spontaneous ordering of bimodal ensembles of nanoscopic gold clusters

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 nanocrystals. For example, monodisperse fractions of thiol-stabilized gold nanoparticles have been crystallized into two- and three-dimensional superlattices. Metal particles stabilized by quaternary ammonium salts can also self-assemble into superlattice structures,. Gold particle preparations with quite broad (polydisperse) size distributions also show some tendency to form ordered structures by a process involving spontaneous size segregation,. 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).

Synthesis and reactions of functionalised gold nanoparticles

Stable functionalised gold nanoparticles are prepared by simultaneous reduction of tetrachloroaurate ions and attachment of bifunctional organic thiol molecules to the growing gold nuclei leading to a material whose chemical behaviour is characterised by the vacant functionality of the bifunctional thiol ligand.

Adoption of near-coincident-site lattice orientations by contacting monolayer rafts of metallic nanoparticles with different superlattice periodicities

A hexagonal raft of monodisperse alkane-thiol-stabilized Au nanoparticles has been self-assembled from solution on to an amorphous C substrate and then subsequently a second layer of monodisperse but differently sized gold nanoparticles deposited on top of the first. Detailed analysis of electron micrographs obtained from various regions of this bilayer revealed the presence of several distinct epitaxial interface structures. A simple near-coincident-site lattice model is used to rationalize the existence of the observed characteristic nanoparticle interface structures.

What are the Limitations in the Characterization of Self-Assembled Metamaterials using Advanced Microscopy Techniques?

C.J. Kiely,* M. Watanabe,* A. Burrows,* P. Clasen,* M.P. Harmer,* B.Rodriguez-Gonzalez,** L. Liz-Marzan,** I. Hussain,*** J. Fink*** and M. Brust *** * Center for Advanced Materials and Nanotechnology, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195, USA. ** Departmento de Quimica Fisica, Universidad de Vigo, 36200, Vigo, Spain. *** Center for Nanoscale Science, University of Liverpool, Liverpool, Merseyside, L69 7ZD, UK. The controlled manipulation of materials on the nanometer scale is an important task for the production and precision positioning of ever more compact electronic, optical and magnetic components. It is now possible to create thin films, nanowires and 3-D supercrystals by exploiting the order inducing chemical interactions that are inherent to a particular system. For instance, ordered structures comprised of monosized ligand stabilized nanoparticles (of most materials) can be ‘self-assembled’ from a solution of their components simply by evaporating a drop of such solution onto a suitable substrate. The current state-of-the-art is the production of