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Electrical conduction of ion tracks in tetrahedral amorphous carbon: temperature, field and doping dependence and comparison with matrix data

Krauser, J. and Gehrke, H.-G. and Hofsäss, H. and Amani, J. and Trautmann, C. and Weidinger, A. (2015):
Electrical conduction of ion tracks in tetrahedral amorphous carbon: temperature, field and doping dependence and comparison with matrix data.
In: New Journal of Physics, IOP Publishing Ltd., p. 123009, 17, (12), ISSN 1367-2630,
[Online-Edition: http://dx.doi.org/10.1088/1367-2630/17/12/123009],
[Article]

Abstract

This paper gives an extended overview of the electrical properties of ion tracks in hydrogen-free tetrahedral amorphous carbon (ta-C) with a sp(3) bond fraction of about 80%. The films were grown by mass selected ion beam deposition of 100 eV C-12(+) ions. The ion tracks are generated by irradiation of ta-C films with uranium ions of 1 GeV kinetic energy. Along the ion path a conversion from diamondlike (sp(3)) carbon to graphite-like (sp(2)) carbon takes place. Topography and current measurements of individual ion tracks were performed by atomic force microscopy at ambient temperature. The temperature dependence of the electric conductivity was studied between 15 and 390 K by means of 0.28 mm(2) large contact pads averaging over about 10 7 tracks. For each sample and at each temperature the conductivity as a function of the applied electrical field (non-ohmic behaviour) was measured separately and the data were extrapolated to field zero. In this way, the zero-field conductivity was determined independent from the field dependence. In spite of large differences in the absolute values, the temperature dependence of the zero-field conductivities is found to be very similar in shape for all samples. The conductivities follow a T-1/4 law up to temperatures slightly below room temperature. At higher temperatures a transport mechanism based on over-barrier hopping dominates with an activation energy of about 220 meV for tracks and 260 meV for the ta-C matrix. The field dependence measurements show that the deviation of the I-V characteristics from ohmic behaviour decreases with increasing zero-field conductivity. We also tested Cu-doped ta-C samples and found that they conduct significantly better than pure ta-C. However, the doping also increases the zero-field conductivity resulting in a weaker contrast between the track and matrix. The data are interpreted within the so-called 'barrier model' where the electrons are assumed to move fairly freely in well-conducting sp(2) regions but encounter barriers in track sections consisting of more sp(3)-like bonds.

Item Type: Article
Erschienen: 2015
Creators: Krauser, J. and Gehrke, H.-G. and Hofsäss, H. and Amani, J. and Trautmann, C. and Weidinger, A.
Title: Electrical conduction of ion tracks in tetrahedral amorphous carbon: temperature, field and doping dependence and comparison with matrix data
Language: English
Abstract:

This paper gives an extended overview of the electrical properties of ion tracks in hydrogen-free tetrahedral amorphous carbon (ta-C) with a sp(3) bond fraction of about 80%. The films were grown by mass selected ion beam deposition of 100 eV C-12(+) ions. The ion tracks are generated by irradiation of ta-C films with uranium ions of 1 GeV kinetic energy. Along the ion path a conversion from diamondlike (sp(3)) carbon to graphite-like (sp(2)) carbon takes place. Topography and current measurements of individual ion tracks were performed by atomic force microscopy at ambient temperature. The temperature dependence of the electric conductivity was studied between 15 and 390 K by means of 0.28 mm(2) large contact pads averaging over about 10 7 tracks. For each sample and at each temperature the conductivity as a function of the applied electrical field (non-ohmic behaviour) was measured separately and the data were extrapolated to field zero. In this way, the zero-field conductivity was determined independent from the field dependence. In spite of large differences in the absolute values, the temperature dependence of the zero-field conductivities is found to be very similar in shape for all samples. The conductivities follow a T-1/4 law up to temperatures slightly below room temperature. At higher temperatures a transport mechanism based on over-barrier hopping dominates with an activation energy of about 220 meV for tracks and 260 meV for the ta-C matrix. The field dependence measurements show that the deviation of the I-V characteristics from ohmic behaviour decreases with increasing zero-field conductivity. We also tested Cu-doped ta-C samples and found that they conduct significantly better than pure ta-C. However, the doping also increases the zero-field conductivity resulting in a weaker contrast between the track and matrix. The data are interpreted within the so-called 'barrier model' where the electrons are assumed to move fairly freely in well-conducting sp(2) regions but encounter barriers in track sections consisting of more sp(3)-like bonds.

Journal or Publication Title: New Journal of Physics
Volume: 17
Number: 12
Publisher: IOP Publishing Ltd.
Uncontrolled Keywords: conducting ion tracks, tetrahedral amorphous carbon, conduction mechanism
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Ion-Beam-Modified Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 29 Feb 2016 12:37
Official URL: http://dx.doi.org/10.1088/1367-2630/17/12/123009
Identification Number: doi:10.1088/1367-2630/17/12/123009
Funders: Financial support for this work was provided by the DFG (HO1125/21-1) and (KR3298/2-1)., We acknowledge support by the Open Access Publication Funds of the Gottingen University.
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