Scanning tunnelling spectroscopy and ab initio calculations of single-walled carbonnanotubes interfaced with highly doped hydrogen-passivated Si(100) substrates

Abstract

The electronic properties of isolated single-walled carbon nanotubes (SWNTs) adsorbed onton- and p-doped hydrogen-passivated Si(100) surfaces are studied by ultrahigh vacuum scanningtunnelling spectroscopy and ab initio density-functional methods. SWNTs identified assemiconductors (s-SWNTs) have well-defined conduction and valence band edges separated by a≈1 eV gap, with the mid-gap Fermi level implying that the s-SWNTs areundoped. Relative s-SWNT/H-Si(100) band alignments inferred fromdI/dV plots are sensitive to the polarity of the substrate doping. Band structure calculations for a(12,4) s-SWNT corroborate experimental data: n-type (p-type) doping of the substrateleads to a shift of the surface bands lower (higher) in energy relative to those of thes-SWNT. The adsorption energy and charge transfer calculated for the (12,4) s-SWNTphysisorbed onto H-Si(100) are considerably less than values reported for the same tube onunpassivated Si(100) and are registration independent. The atomistic results presented herehave critical implications to hybrid electronic and photonic devices that rely upon a directinterface between a SWNT and a technologically relevant semiconductor such as Si orGaAs.