Robin Nicholas

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.

Abstract:

Bandgap-selective p doping of single-walled carbon nanotubes (SWCNTs) in aqueous surfactant suspensions is reported. Nanotubes with narrower bandgaps are preferentially doped by hexacyanoferrate (III), as observed by optical absorption. The bandgap absorption characteristics, which are controlled by the chemical potential, can be reversibly adjusted by controlling the oxidation potential of the dopants through the pH value. The origin of the selective modification of bandgap absorption is electron transfer between the carbon nanotubes and the hexacyanoferrate (III), which preferentially depopulates the valence band in narrower gap nanotubes.

Abstract:

Vertical magnetotransport measurements are used to investigate resonant transport processes in strongly coupled InAs/GaSb superlattices. Sample I-V curves display Stark-Cyclotron resonance and longitudinal-optic (LO) phonon mediated transport features. Resonant tunnelling features change dramatically above the magnetophonon condition suggesting that the Landau levels are renormalized due to interaction between LO phonon's and electrons.

Abstract:

We have studied the mangeto-photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) with different chiral vector indices (n,m). A novel strain method is used to assign the quantum number q and chiral vector indices. The PL intensities and energies were found to be a strong function of magnetic field at low temperature, but were field independent up to 19.5T at 300K. All emission energies show a significant red shift caused by the action of Aharanov-Bohm flux threading the tubes.