Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2x1) diamond surfaces using noncontact AFM

High-purity, type IIa diamond is investigated by noncontact atomic force microscopy (NC-AFM). We present atomic-resolution images of both the electrically conducting hydrogen-terminated C(100)-(2 x 1) : H surface and the insulating C(100)-(2 x 1) surface. For the hydrogen-terminated surface, a nearly square unit cell is imaged. In contrast to previous scanning tunneling microscopy experiments, NC-AFM imaging allows both hydrogen atoms within the unit cell to be resolved individually, indicating a symmetric dimer alignment. Upon removing the surface hydrogen, the diamond sample becomes insulating. We present atomic-resolution images, revealing individual C-C dimers. Our results provide real-space experimental evidence for a (2 x 1) dimer reconstruction of the truly insulating C(100) surface.