Gold Clusters and Colloids in Alumina Nanotubes

Abstract

Abstract: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 forming one-dimensional configurations of zz 15 nm gold colloids and 2.4 nm gold clusters via template methods of synthesis has now been demonstrated. The template host material consisted of porous alumina membranes formed by an electrochemical anodic process. The pores of the membrane, and hence the parallel pore channels, were packed in a hexagonal array. Alumina membranes are excellent template materials because of their high degree of order, thermal and chemical stability, and optical clarity. Pore diameter was controlled by regulation of the applied anodic potential (ca. 1.4 nm V -I ) . The pore channels were filled by one of three methods: vacuum induction (colloids only), electrophoresis (clusters only), or immersion (clusters, which were then converted 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 Keywords clusters * colloids * goldnanostructures * quantum wires 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. Composites (consisting of the gold-alumina system) were a bright scarlet color with an absorption maximum (A, , , , , ) at 519.5 nm. This is an unexpected result for spherical and small-diameter (10 nm) gold colloids, which normally absorb at i , , , 525-530 nm, a ruby-red color. Possible causes of this small but remarkable blue shift are discussed below. A new Au,, cluster ligand system consisting of a silsesquioxanederivatized thiol is also described.

Metal Clusters and Colloids

“…Some more or less accidental observations on various substrates have been made, but the purposeful design of wires of nanoparticles (quantum wires) was not achieved until recently when we used well-ordered pore channels in alumina membranes. [43] Porous aluminum oxide is formed by anodic oxidation of high-purity aluminum plates or foils.…”

Physical and Chemical Properties of Nano‐Sized Metal Particles

“…Hornayak et al [85] used the ordered channels of porous alumina as templates to obtain linear arrangements of Au nanocrystals. By varying the pore size, the diameter of the nanowire could be controlled.…”

Template synthesis of nanomaterials

“…When, however, the building blocks are a few nanometers in diameter, such as carbon encapsulated cobalt nanoparticles [201], convincing them to move into the pores becomes more difficult. A few physical techniques are available for filling nanopores with nanoparticles: mechanically forcing the particles into the pores, hydrodynamic pressure; using the pores as filters for the particles [202,203], eletrophoretic deposition; using the electrophoretic mobility of particles in a liquid, subjected to an electric field gradient, to drag the particles into the pores [204], and magnetophoretic deposition; using the magnetophoretic mobility of magnetic particles in a liquid, under the influence of a magnetic field gradient, to pull the particles into the pores. The first method is destructive and inefficient since only a shallow portion of the pores is filled.…”

“…the particles fill the pores from the side with the highest field. Electrophoretic deposition has been used to place Au nanoparticles in alumina pores, but only a small percentage of the pores were filled [204]. Also, electrophoretic deposition often requires relatively clean, H 2 O free systems because water will electrolyse at voltages differences greater than 2 V [169] and normally electrophoretic deposition requires 10 V or more.…”

“…The use of nanoparticles to change properties of thin-films is well known [217,[220][221][222][223][224][225][226][227][228]. The idea of using nanoparticles to modify and change the properties of nanowires and nanopores, however, is relatively unexplored [204]. The methods described here to put nanoparticles into nanopores to form the granular nanowires are the only ones that the authors know of.…”