Robin Nicholas

Abstract:

We report an efficient technique to separate ferromagnetic catalyst particles from an aqueous surfactant solution of single-walled carbon nanotubes (SWNTs) by the use of a 1.3 T permanent magnet. High resolution transmission electron microscopy (HRTEM) demonstrates that SWNTs are coated with a surfactant layer that stabilises the aqueous dispersions of SWNTs. The residual quantities of Fe catalyst (∼3%) can be effectively removed from a colloid solution of SWNTs in a magnetic field while absorbance spectra of the initial and purified solutions show that the nanotube diameter distribution remains unchanged. © 2005 Elsevier Ltd. All rights reserved.

Abstract:

Strain-induced band gap shifts that depend strongly on the chiral angle have been observed by optical spectroscopy in polyvinylpyrrolidone(PVP)- or Surfactin micelle-wrapped single-walled carbon nanotubes (SWCNTs). Uniaxial and torsional strains are generated by changing the environment surrounding the SWCNTs, using the surrounding D2O ice temperature or the hydration state of a wrapping polymer. These methods can be used as diagnostic tools to determine the quantum number, q, and examine chiral vector indices for specific nanotube species.

Abstract:

We investigate vertical magnetotransport measurements in strongly coupled InAs/GaSb superlattices within the miniband transport regime. Sample magnetoresistance curves display oscillations due to the successive un-nesting of Landau level minibands. This qualitative picture is strongly supported by Monte Carlo simulations, which include acoustic and optic phonon scattering as well as Umklapp processes, providing a semi-classical description of the miniband transport.

Abstract:

We report a study of the effects of various sample purification and modification techniques on the band gaps and optical properties of bulk single walled carbon nanotubes (SWNTs). These include a variety of thermal and chemical oxidation treatments and a study of nitrogen and boron doping.