Robin Nicholas

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.

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.