The production of novel electronic structures assembled from coupled nanometer-sized metal clusters
Abstract
Two types of electronic structures consisting of capacitively coupled metal clusters have been fabricated using nanometer diameter particles. These structures exhibit unique quantum size effects, including room temperature single electron tunneling (SET), and have potential application in the development of nanoelectronic devices. Colloidal metal clusters used in the fabrication of these new structures are made using a Multiple Expansion Cluster Source (MECS) and Metal Cluster Colloid Reactor (MCCR). Bare metal clusters of a controlled size in the 2 to 10 nm diameter size range are produced in the gas phase in the MECS and are then stabilized as colloidal particles in an organic solvent in the MCCR. Stabilization is achieved through the adsorption of surfactant molecules onto the surface of the clusters. Alkanethiols, dialkyl sulfides, alkyl disulfides, alkanenitriles and fatty acids are found to stabilize silver and gold clusters in both aliphatic and aromatic solvents. The first type of structure that has been produced consists of a single gold cluster that is electrically coupled to an atomically flat gold film by means of a self-assembled monolayer of organic molecules. This structure has been characterized with TEM, STM and STS. The I-V response of this structure exhibits, at room temperature, a "coulomb gap", characteristic of SET. The second type of structure that has been produced consists of a 2-D array of gold clusters that are separated from each other by an organic layer that surrounds each cluster. In order to fabricate this second structure, techniques have been developed for self-assembly of hexagonal close-packed arrays of capacitively coupled metal clusters. These arrays can span several hundred square nanometers. The clusters within such an array can be covalently and electronically linked with charge transfer ligands which displace the surfactant originally adsorbed on each cluster and bridge the space between nearest neighbors in the cluster array. This displacement process has been characterized in solution with UV-Visible absorption. It has also been studied using RAIR, Raman spectroscopy, ellipsometry, and contact angle measurements on flat gold surfaces. Flat SiO$\sb{\rm x}$ substrates patterned with conducting gold pads separated by 100 nm have been produced using e-beam lithography. Deposition of an electrically linked cluster array between these pads permits study of the electrical properties of the metal cluster arrays.
Degree
Ph.D.
Advisors
Andres, Purdue University.
Subject Area
Chemical engineering
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