TEM and XPS studies to reveal the presence of cobalt and palladium particles in the inner core of carbon nanofibers

In this paper, the presence of a considerable number of Co (3-4 nm) and Pd (1-4 nm) particles in the inner tube (4-9 nm inner diameter) of carbon nanofibers is demonstrated with TEM and XPS. Oxidation of freshly grown fibers in nitric acid resulted in opening of the inner tube of the fibers and in creating adsorption sites on the internal and external surface of the fibers needed for anchoring of the metal precursors. It is demonstrated that analysis with TEM tilt series is a very powerful tool to locate the actual position of the metal particles, i.e. on the external or internal surface of the fibers. The fraction of metal present in the inner core of the fibers varied from 10-15% for Pd to 28-34% for Co, depending on the synthesis method.