Transport properties of spiral carbon nanofiber mats containing Pd metal clusters using Pd2(dba)3 as catalyst

We have grown spiral carbon nanofibers containing Pd metal clusters using the Pd2(dba)3 catalyzed decomposition of gaseous acetylene on molecular sieves (AlPO4-5) support. The microstructure and composition of the spiral carbon nanofibers were examined by the powder x-ray diffractometer and transmission electron microscope. The conductivity of the mat in the temperature range from 14 to 250 K could be described by the form of exp[-(T-1/4)]. The thermopower shows a remarkably linear behavior down to 40 K, reminiscent of some conducting polymers. The sign change of the thermopower suggests there exists more than one type of charge carrier, which could be ascribed to the different types of nanotube with various sizes of radius. The transport behavior of spiral carbon nanofibers containing Pd metal clusters will be discussed in the framework of the heterogeneous model.