We present the spatially resolved modification of the topography and electronic properties of monolayer graphene by a low dosage of atomic oxygen on the nanometer scale. Using the combination of an ultrahigh-vacuum scanning tunneling microscope and a gas beam of oxygen atoms, we show that the surface O-atoms, even at a low coverage of O/C = ∼1/150, serve as p-type dopants that leads to site-dependent partial and full graphene band modifications up to a gap of a few hundred millielectronvolts. The degree of modification and the number of O-atom-induced charge-holes per area are inversely proportional to the distance between the measuring position and the location of the nearest adsorbate. However, the number of holes contributed per oxygen atom is found to be a site-independent constant of 0.15 ± 0.05. For a small population of adsorbates taller than 4 Å, the graphene energy bands are no longer resolved; instead, our tunneling spectra show very spatially localized but highly dense states over a wide potential range, which indicates a sole tunneling contribution from the tall stacks of the electron-rich O-atoms and a complete decoupling from the graphene bands.

A new method to directly modify the surface structure and energy levels of a porphyrin monolayer was examined in the molecular scale using scanning tunneling microscopy and spectroscopy (STM and STS) and presented in this communication. The exposure to atomic oxygen has induced highly ordered surface cross-linking and changed the occupied and unoccupied orbital levels of a cobalt(II) octaethyl porphyrin (CoOEP) monolayer, and as a result, the HOMO–LUMO gap was reduced by ∼10%. Counterintuitively, the STM/STS data indicated that the reactive central Co atoms did not participate in the gas–surface reactions. Reflection–absorption infrared spectroscopy (RAIRS) measurements further indicated that the STM observed intermolecular linkages are stabilized via hydrogen bonding. This CoOEP + O˙ system also illustrates an example that the six-fold surface packing symmetry predominates the four-fold molecular symmetry in producing a three-fold symmetric surface cross-linking structure.

A new method to directly modify the surface structure and energy levels of a porphyrin monolayer was examined in the molecular scale using scanning tunneling microscopy and spectroscopy (STM and STS) and presented in this communication. The exposure to atomic oxygen has induced highly ordered surface cross-linking and changed the occupied and unoccupied orbital levels of a cobalt(II) octaethyl porphyrin (CoOEP) monolayer, and as a result, the HOMO–LUMO gap was reduced by ∼10%. Counterintuitively, the STM/STS data indicated that the reactive central Co atoms did not participate in the gas–surface reactions. Reflection–absorption infrared spectroscopy (RAIRS) measurements further indicated that the STM observed intermolecular linkages are stabilized via hydrogen bonding. This CoOEP + O˙ system also illustrates an example that the six-fold surface packing symmetry predominates the four-fold molecular symmetry in producing a three-fold symmetric surface cross-linking structure.