GOLD CLUSTERS AND COLLOIDS IN ALUMINA NANOTUBES

The fabrication of a supported and insulated quantum wire would be of great interest, especially if electronic information could be accessed to determine charging and conductivity profiles. The feasibility of f orming one-dimensional configurations of approximate to 15 nm gold col loids and 1.4 nm gold clusters via template methods of synthesis has n ow been demonstrated. The template host material consisted of porous a lumina membranes formed by an electrochemical anodic process. The pore s of the membrane, and hence the parallel pore channels, were packed i n a hexagonal array. Alumina membranes are excellent template material s because of their high degree of order, thermal and chemical stabilit y, and optical clarity. Pore diameter was controlled lation of the app lied anodic potential (ca. 1.4 nm V-1). The pore channels were filled by one of three methods: vacuum induction (colloids only), electrophor esis (clusters only), or immersion (clusters, which were then converte d into colloids by heating). Rudimentary wires consisting of colloids and clusters were successfully formed. In both cases, the diameter of the pore channel exceeded that of the clusters or colloids. The wires thus formed conformed to the pore channel by forming helical secondary structures. It was not possible to form contiguous wires of clusters by immersion, or of colloids formed from clusters after heating. Compo sites (consisting of the gold-alumina system) were a bright scarlet co lor with an absorption maximum (lambda(max)) at 519.5 nm. This is an u nexpected result for spherical and small-diameter (10 nm) gold colloid s, which normally absorb at lambda(max) 525-530 nm, a ruby-red color. Possible causes of this small but remarkable blue shift are discussed below. A new Au-55 cluster ligand system consisting of a silsesquioxan e-derivatized thiol is also described.