Photochemically-induced electronic switching in carbon nanotubes

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The central goal of the present project is the fabrication and investigation of nanowires that are able to undergo a reversible switch between two states of high and low electrical conductivity, respectively. The electronic switch shall be realised within single-wall carbon nanotubes (SWCNT) on the basis of light-induced reactions that decrease the extension of the pi-conjugated system of the tubes and hence their conductivity. To obtain stable devices capable of repeated reversible switches, the SWCNTs will be enclosed in a compact surfactant shell consisting of an anthracene derivative. This type of compound is chosen since preliminary experiments revealed the possibility of photo-induced cycloaddition of anthracene to SWCNTs, which can be reversed by thermal activation. The chemical structure of the anthracene-based surfactants will be optimised to achieve sufficiently strong pi-interaction with the graphene layer of the SWCNTs, combined with a well-balanced hydrophobic/hydrophilic character.Transmission electron microscopy, fluorescence spectroscopy, and atomic force microscopy will be performed to determine the molecular arrangement of the amphiphiles on the SWCNT and the stability of the SWCNT/complexes against aqueous solutions, both as a function of pH value, the presence of different ions, temperature, as well as photo-irradiation. The electronic structure of the SWCNT/surfactant complexes will be compared before and after photo-irradiation by detailed charge transport measurements, scanning tunnelling spectroscopy and spatially high-resolved Raman spectroscopy. Since in all three methods the same individual SWCNTs will be examined, the obtained data will allow an unequivocal interpretation of the radiation effect. The same types of investigation will be employed to determine whether the back reaction, consisting of cycloreversion to the starting configuration, can be thermally induced or achieved via irradiation with a shorter wavelength. In addition, thermal- or photo-cycling studies will be carried out to investigate the long term stability of the devices.