Synthesis of nanoscale clusters using atmospheric arc evaporation and measurement of cluster-substrate interactions
Abstract
This research consists of two parts: (1) aerosol synthesis of nanoscale clusters using arc evaporation, and (2) measurement of the interaction of nanoscale gold clusters with single crystal substrates. A novel aerosol reactor designed to produce nanoscale metal, metal oxide, metal nitride and metal carbide clusters of controlled mean size is described. This reactor operates by evaporating a metal by means of an atmospheric pressure DC arc. The vaporized atoms are entrained in a steady stream of inert gas and quickly transferred to a quench region where the hot stream from the arc plasma is mixed with a second stream of cold gas. The role of the quench gas is to suppress cluster aggregation by both rapid cooling and dilution. Metal oxide, nitride, and carbide particles are formed by the addition of oxygen, nitrogen, and methane or acetylene, respectively, to the inert gas flow in either the arc or the quench region. Clusters are collected for analysis by three methods: (1) by supersonic impaction, (2) by spray-capture and (3) by thermophoretic deposition. High evaporation rates are achieved with this cluster source. Cluster size is controlled by varying the metal atom density and residence time in the arc plasma, in the quench region and in the flow downstream from the quench region. The interaction of nanoscale gold clusters with single crystal substrates is studied by means of TEM and SPM. Small, single crystal gold clusters are deposited onto various substrates including $\alpha\ -$ Al$\sb2$O$\sb3$, MgO, mica, HOPG, and MoS$\sb2$. The behavior of both bare gold clusters and gold clusters encapsulated by dodecanethiol is studied. For bare clusters, observations of cluster mobility, epitaxy, deformation, and selective binding with surface defects are interpreted in terms of cluster-substrate interaction. The behavior of the encapsulated clusters is studied in the context of assembling ordered monolayer arrays of metallic quantum dots.
Degree
Ph.D.
Advisors
Andres, Purdue University.
Subject Area
Chemical engineering|Materials science
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