Charge transfer between semiconducting carbon nanotubes and their doped GaAs(110) and InAs(110) substrates detected by scanning tunnelling spectroscopy

Ultrahigh vacuum (UHV) scanning tunnelling microscopy (STM) and spectroscopy (STS) have been used to examine the role of substrate doping and composition in determining the electronic behaviour of semiconducting single-walled carbon nanotubes (SWNT) deposited onto III-V(110) surfaces. Hybrid SWNT/III-V(110) systems were created through sample cleavage and subsequent nanotube transfer in UHV. Room temperature STS spectra indicate electron transfer from the n-GaAs substrate to the supported SWNT and from the SWNT to the p-GaAs substrate, resulting in the respective n-type and p-type doping of the nanotube upon adsorption. STS measurements on InAs(110) supported carbon nanotubes are less uniform, with selected SWNTs on the n-InAs(110) surface exhibiting distinct electronic changes when shifted into registration with the substrate lattice. No such orientation sensitivity is detected in nanotubes on GaAs surfaces. The potential for systematic modification of a SWNT's electronic behaviour through intentional substrate engineering could present a new avenue for the design and fabrication of nanotube-based device structures.