Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 26: Transport - Poster Session

TT 26.34: Poster

Wednesday, March 29, 2006, 14:30–18:30, P1

Transport properties of carbon nanotubes synthesized by chemical vapor deposition — •T. Pietsch, I. Mönch, J. Schumann, K. Biedermann, H. Vinzelberg, and B. Büchner — IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany

The electrical properties of multiwalled carbon nanotubes (MWCNT) synthesized by chemical vapor deposition (CVD) depend on the used CVD method. In this work we investigate MWCNT with outer diameters from 30 to 60 nm and length over 6 µm grown by a thermal-catalytic CVD method. TEM images show that the concentric layers of the nanotubes are not perfect. The MWCNT devices for the transport measurement with low ohmic contacts were prepared by using an ac-electrophoresis deposition either on Ti-microfinger structures followed by a HV annealing at 800^∘C or on oxidized silicon wafers with prestructured leads, electron beam lithography, oxygen plasma treatment and evaporated Cr/Au contacts on the nanotubes. The contact resistance are for the Ti contacts about 50 kΩ and for the Cr/Au contacts smaller than 1 kΩ. The average intrinsic room temperature resistance of the MWCNT measured in four-point configuration is 1500 µΩcm and comparable to that of natural graphite of 1350 µΩcm. At room temperature the current-voltage characteristics are linear but at low temperatures not linear. The temperature coefficient of the zero-bias resistance in the temperature range between 300K and 4.2K is negative. Positive magnetoresistances at 4.2K of about 2 % at 8T were measured. The results show that - caused by the defect structure of the MWCNT walls - the conduction is diffusive.