PhD Thesis


Shane D Bergin



physics ph d raman spectroscopy ph d trinity college dublin dispersions single walled carbon nanotubes large scale photoluminescence spectroscopy phase

Dispersions and solutions of single walled carbon nanotubes (2008)

Abstract Large scale exfoliation of single walled carbon nanotubes (SWNTs) has beenshown in various media. Debundling of SWNTS has been demonstrated by dilution ofnanotube dispersions. On making the initial dispersions, large aggregates (~100s ofmicrons) are removed by a mild centrifugation step resulting in an isotropic phasecontaining bundles of nanotubes. The root mean square bundle diameter, of bundles in thisisotropic phase, has been shown to be concentration dependent. Such debundling has beendemonstrated in the solvents N-methyl-2-pyrrolidone (NMP) and for the narcotic drug y-Butyrolactone, sometimes referred to as 'liquid ecstasy'. After centrifugation, thedispersions are stable against sedimentation and further aggregation for a period of weeksat least. Atomic-force-microscopy studies on deposited films reveal that the bundlediameter distribution decreases dramatically as concentration is decreased. Detailed dataanalysis suggests the presence of an equilibrium bundle number density and that thedispersions self-arrange themselves to always remain close to the dilute/semi-diluteboundary. A population of individual nanotubes is always observed which increases withdecreasing concentration until almost seventy percent of all dispersed objects areindividual nanotubes at a concentration of 0.004 mg/ml in the NMP dispersions and for y-Butyrolactone forty percent of all dispersed objects are individual nanotubes at aconcentration of 6x10'-4 mg/ml. The presence of individual nanotubes in NMP dispersionwas confirmed by photoluminescence spectroscopy. Concentration dependence of thephotoluminescence intensity confirms that the AFM measurements reflect the diameterdistributions in-situ. In addition, Raman spectroscopy confirms the presence of largequantities of individual nanotubes in the deposited films.
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Full list of authors on original publication

Shane D Bergin

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Shane D Bergin
Trinity College Dublin
Total Publications: 12