Investigating defect-induced changes on the topographic and electronic structure of graphite is a current topic for both, experimental and theoretical physicists. It has been shown that defects, consisting of atomic vacancies or adsorbed atoms, produce long-range electronic effects around the affected lattice sites [1,2]. With scanning probe microscopy (SPM) it is possible to directly investigate these defects with atomic resolution. The important long-range changes in the electronic structure make it very difficult to determine the actual defect size with scanning tunneling microscopy (STM) only. However, scanning the surface with a conductive cantilever has the advantage of imaging both, the changes in topography and the local density of states (LDOS) simultaneously.
Defects have been created in an electron cyclotron resonance (ECR) hydrogen plasma on highly oriented pyrolithic graphite (HOPG). Plasma treatment is a powerful tool for surface cleaning and modification. By changing the pressure in the plasma chamber one can control the ion energy from about 20 eV (10-4 mbar) down to about 2eV (10-1 mbar) [3].
Our measurements give indication that the defects consist of adsorption of hydrogen on the graphite and not of atomic vacancies created by the low energetic ions. Differences between treatments with different pressures (and thus different ion energies) will be discussed.
References
[1] K.F. Kelly and N.J. Halas, Surface Science, 416, L1085 - L1089, 1998
[2] H.A. Mizes and J.S. Foster, Science, 244, 559 - 562, 1989
[3] S. Nowak et al, J. Vac. Sci. Technol. A 10 (6), 3419 [Dhatch] 3425, 1992