Structural Modification in Proton-Irradiated Highly-Oriented Pyrolytic Graphite

Abstract

We have made a comprehensive study on the structural changes in highly-oriented pyrolytic graphite (HOPG) samples irradiated with 2.25-MeV proton beams. X-ray photoelectron spectroscopy showed a surface polishing effect and a graphite-to-diamond surface structural transformation, followed by regraphitization of the diamond-like surface as the proton irradiation dose was increased from 10(15) ions/cm(2) to 2 x 10(17) ions/cm(2). While the surface showed prominent changes at relatively small irradiation doses, the bulk region of the HOPG, as probed by Raman spectroscopy, manifested creation of defects only at the maximum dose employed, for which ferromagnetism takes place.