Ion tracks as electrically conducting nanowires

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Ion tracks in matter are generated during irradiation with swift heavy ions by high and very local electronic energy loss. The structural changes induced in this way often yield to amorphous tracks or defect enriched latent tracks. In very few cases one finds a local phase transformation form an electrically insulating to a conductive phase. This is the case for tetrahedral amorphous carbon (ta-C) which locally converts to a sp2 bonded conductive phase upon irradiation with e.g. GeV 238U ions. The diameter of the conducting tracks is only 8 nm. Thus, conducting ion tracks possess the potential to realize novel nanoscale electronic devices. It seems that beside ta-C other materials like VO2 , rare earth nickelates and Fe3O4, which undergo an insulator-metal transition as function of temperature, are also suited to generate conducting ion tracks. Such systems may be of interest for all-oxide electronic devices and because of their thermoelectric behaviour. The aim of the proposal is to tailor the track conductivity in ta-C towards high and uniform conductivity with Ohmic conduction. This shall be achieved by doping of the ta-C matrix with suited metal atoms and also by ion irradiation with high charge state ions (high energy loss). Furthermore, the formation, the microstructure and the properties of conducting ion tracks in VO2 thin films shall be investigated. The potential of ion track electronics shall be studied for interrupted tracks, prepared by irradiating layered film structures of ta-C and insulating BN spacer layers. In this way conducting ion tracks provide the contacts to a small volume of few nm3 in size which may exhibit Coulomb blockade effects even at room temperature.