Modifying the Density of States of Single-Walled Carbon Nanotubes by Reversible Wrapping with Organometallic Nanofoils: A Scanning Tunneling Spectroscopy Study

Tuning the charge carrier mobility in carbon nanotubes is a key issue for applications in novel electronic or spintronic devices. This property is directly related to the electronic density of states, which is usually modified by introduction of defects or doping with metallic atoms. Both methods can induce strong localization of electronic states, disturbing the overall nanotube conductivity and enhancing electron and spin scattering. Wrapping with organometallic nanofoils is an alternative method which preserves its charge carrier density. In this work, we have prepared single-walled carbon nanotubes (SWCNTs) wrapped with nanofoils of a cobalt-coordinated polymer (NCoDPS). Transmission electron microscopy and Raman scattering reveal that the nanotubes remain intact and are homogeneously covered by the polymer. The electronic structure of SWCNT-NCoDPS was investigated by scanning tunneling spectroscopy. This technique shows that the electronic density of states of these wrapped nanotubes increases, as compared with uncapped reference samples. We also show that the wrapping process is reversible once the carbon nanotubes are swept by the scanning tunneling microscope applying an electric potential exceeding 0.5 V.