# Dresden 2009 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 15: Correlated Electrons: Metal-Insulator Transition 2

### TT 15.6: Vortrag

### Dienstag, 24. März 2009, 11:00–11:15, HSZ 301

**Metal-insulator transition in polymer surfaces modified by low-energy ion irradiation** — •Yuri Koval, Irina Lazareva, and Paul Müller — Department für Physik, Universität Erlangen-Nürnberg, Germany

The surface of several polymers like polyimide, PMMA, or PET was graphitized by low-energy (0.15-1.5 keV) ion irradiation at different temperatures (150-700 K). Due to the small penetration depth of ions the thickness of conducting layers is substantially less than 10 nm. Depending on the energy of ions and the temperature of irradiation the sheet conductance can be changed from 10^{−}^{1}^{1} S to 10^{−}^{4} S. We show that with increase of the sample conductance the electric transport changes from variable range hopping to semi-metallic type.

Semi-metallic behavior was observed for samples with sheet conductances higher than the quantum conductance g. For samples with lower sheet conductance an exponential law σ=σ_{0}exp(-(T_{0}/T)^{x}) typical for variable range hopping transport was found. For samples with a power x=0.5 we have found a correlation between σ_{0} and T_{0} in the form σ_{0}=σ_{0}_{0}exp(T_{0}/T^{*})^{0}^{.}^{5} with σ_{0}_{0} equal to the quantum conductance g. Analyzing the low temperature current-voltage characteristics, a similar correlation between the pre-exponential factor and the numerator in the exponent j=j_{0}exp(-(E_{0}/E)^{0}^{.}^{5}) was observed, where j is the current density and E is the electric field.