[en] Atomic-force and Kelvin-probe microscopies were employed in ultrahigh vacuum to image the surface topography and contact potential of the hydrogen-terminated and unterminated surfaces of diamond. A variation of about 25 meV in the contact potential was measured on a length scale of 20 nm and ascribed to differently orientated surface domains resulting from hydrogen-plasma processing of the sample. Shifts in the work function arising from sample heating in vacuum and the adsorption of C₆₀ were measured. The Fermi level was found to be 0.7 and 1.1 eV below the valence band maximum for C₆₀ coverages of 1 and 4 monolayer, respectively.