title: Multiscale imaging and tip-scratch studies reveal insight into the plasma oxidation of graphite.
abstract: The plasma oxidation process of highly oriented pyrolytic graphite (HOPG) has been investigated through a combination of multiscale (micrometric to atomic) imaging by atomic force and scanning tunneling microscopies (AFM/STM) and STM tip-scratching of the HOPG substrate. Complementary information was obtained by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Repetitive imaging of the same HOPG location following a series of consecutive plasma treatments allowed an accurate determination of the plasma etch rates along both the a and c crystallographic directions of the graphite lattice. The etch rates were typically in the range of a few nm per min along the a axis, and the equivalent of 1-6 graphene layers per min along the c axis. The results pointed to the existence of two main plasma etching regimes, related to short (<20-30 min) and long (> or =30 min) treatment times. This was inferred not only from the measured plasma etch rates but also from the observation of fundamental differences in the atomic-scale surface structure of the plasma-treated HOPG samples, and from the general mechanical behavior of the materials under the action of the AFM tip. In particular, atomic-scale STM imaging suggested a change from a defected, but essentially graphitic, surface in the first regime to an amorphous carbon surface in the second regime. Together with AFM and STM, Raman spectroscopy and XPS provided a consistent picture of the surface structure and chemistry of the plasma-modified HOPG in the two regimes. The implications of these results as well as the possible mechanism that drives the plasma etching process in the two regimes are discussed.
authors.affiliation: Instituto Nacional del Carbón, CSIC, Apartado 73, 33080 Oviedo, Spain. paredes@incar.csic.es
authors.forename: J I
authors.initials: JI
authors.lastname: Paredes
authors.forename: A
authors.initials: A
authors.lastname: Martínez-Alonso
authors.forename: J M D
authors.initials: JM
authors.lastname: Tascón