Abstract (eng)
The aim of this thesis was the investigation of the electrical and galvanomagnetic properties of highly oriented pyrolytic graphite.
There has been a huge interest in graphite and related carbon-structures, after the revelation of unusual and unexpected phenomena on separated graphene in 2004. Plenty of examinations have been done on graphite, unclarities still remain in many transport properties.
In this work (magneto)resistance- and Hall-measurements were performed, to examine the concentrations and mobilities of electrons and holes by using a two-band-model. The changes in the transport properties due to lattice-defects, contaminations and orientation of crystallites in terms of magnetic field and temperature will be discussed, also in comparison to other samples.
Due to the appearance of anomalies in the Hall-effect and the magnetic-field-dependence of the magnetoresistance we will discuss a possible involvement of the effects of trigonal warping and Dirac-fermions.
Measurements of the resistance along the graphite planes and perpendicular to them in the temperature range of 10 to 300K are presented. In addition, a magnetic field is applied parallel and perpendicular to the planes for magnetoresistance measurements. The Hall-effect is evaluated at constant field in the conventional in-plane arrangements, as well as for out-of-plane Hall fields.
The resistance in the graphite planes shows metallic behaviour over the entire temperature range. The c-axis-resistance exhibits the same behaviour to 36K. For higher temperatures a semi-conductor-like dependence is seen. A magnetoresistive effect of 11000% has been measured at 11K and 1T (applied perpendicular to the graphite planes) – for parallel fields no effect could be detected. Hall-effect measurements are successful only at perpendicular fields – resulting in a negative Hall coefficient for 1T.