Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single-layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O 2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of approximately 0.5 eV. These oxygen species desorb partially in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O 2 atmosphere at room temperature. This strongly doped graphene is very different from "graphene oxide" made by mineral acid attack.

We present scanning tunneling microscopy (STM) images of singlelayer graphene crystals examined under ultrahigh vacuum conditions. The samples, with lateral dimensions on the micrometer scale, were prepared on a silicon dioxide surface by direct exfoliation of crystalline graphite. The single-layer films were identified by using Raman spectroscopy. Topographic images of single-layer samples display the honeycomb structure expected for the full hexagonal symmetry of an isolated graphene monolayer. The absence of observable defects in the STM images is indicative of the high quality of these films. Crystals composed of a few layers of graphene also were examined. They exhibited dramatically different STM topography, displaying the reduced threefold symmetry characteristic of the surface of bulk graphite.two-dimensional ͉ graphite ͉ nanoscience S ince the first reports of experiments on stand-alone, singlelayer graphene crystals, (1) this remarkable two-dimensional material has attracted great scientific interest (2-5). There are two alternative approaches for producing graphene layers. In the first method, sample layers are mechanically exfoliated from bulk graphite crystals; in the second method, a surface, such as silicon carbide, is ''graphitized'' under vacuum conditions (6, 7). The strength of interaction between the underlying substrate and the graphene film is an issue of importance in the study of these materials of monolayer thickness. Very recent results using angle-resolved photoemission spectroscopy (7, 8) on single-and few-layer graphene samples have, for example, shown that interactions between a graphene film and a SiC substrate can be considered weak. On the other hand, several earlier scanning tunneling microscopy (STM) studies of graphitized surfaces, such as Ir(1 1 1) (9), Pt(1 1 1) (10, 11), and SiC (6), also have been performed. In these experiments, the structure observed by STM was strongly influenced by the interaction between the graphitic layer and the underlying substrate, and features unambiguously associated with the electronic properties of an isolated graphene layer could not be identified. The purported differences in the strength of the graphene-substrate coupling may reflect different sample preparation methods and/or various sensitivities of the STM and angle-resolved photoemission spectroscopy techniques to these interactions.Here we present results of an STM study of single-layer graphene films prepared by mechanical exfoliation and probed on an insulating substrate. For these micrometer-sized samples, the STM topographic images show the hexagonally symmetric honeycomb structure expected for an ideal, unperturbed graphene crystal. STM images for multilayer graphene films prepared in the same fashion display the reduced, threefold symmetry characteristic of the surface of bulk graphite crystals. In addition to the local atomic-scale structure of single-layer graphene samples, we present measurements on the film's topography over the 100-nm length scale. Height variation on the o...

Mechanically exfoliated graphene mounted on a SiO2/Si substrate was subjected to HF/H(2)O etching or irradiation by energetic protons. In both cases gas was released from the SiO2 and accumulated at the graphene/SiO2 interface resulting in the formation of "bubbles" in the graphene sheet. Formation of these "bubbles" demonstrates the robust nature of single layer graphene membranes, which are capable of containing mesoscopic volumes of gas. In addition, effective mass transport at the graphene/SiO2 interface has been observed.

We present a scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS) study of a model catalyst system consisting of supported gold nanoparticles on a reduced Fe3O4(111) surface in ultrahigh vacuum. Gold forms two electrically distinct nanoparticles on an iron oxide surface upon annealing multilayer Au/Fe3O4(111) at 500 °C for 15 min. I (V) curves taken via STS measurements show that large gold nanoparticles (∼8 nm) exhibit a metallic electronic structure and, thus, are likely neutral. Single gold adatoms appear to be strongly bonded to the oxygen sites of the Fe3O4(111) surface, and tunneling electrons are observed to flow predominantly from the STM tip to the Au adatoms and into the oxygen sites of the surface. The site-specific adsorption of the gold adatoms on oxygen surface atoms and the size-sensitive nature of the electronic structure suggest that Au adatoms are likely positively charged. When this Au/Fe3O4(111) system is dosed with CO at 260 K, adsorption of CO molecules normal to the surface atop the gold adatom sites takes place. CO adsorption on the large Au nanoparticles (∼8 nm) could not be confirmed by STM. These observations indicate that nonmetallic, positively charged Au species may play a key role in reactions involving CO, such as the CO oxidation and the water−gas-shift reaction on Au/metal oxide surfaces.