Robin Nicholas

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.

Abstract:

The room temperature electroluminescence (EL) between 1.7-2.6 μ from coupled quantum dots and quantum wells in the InAs/InSb/GaSb materials system was investigated. The samples which were investigated consisted of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix. It was found that the thickness of the GaSb space layer lowers the energy from that of a quantum well alone. The results reveal the occurrence of a sharp transition after a single monolayer coverage of GaSb either due to structural changes in the quantum dots or from the shrinkage of the quantum well.