We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10 12 cm −2 per graphene sheet. The most highlyordered sample exhibits Shubnikov -de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

Writing Conductive Lines with Hot Tips The interface within devices between conductors, semiconductors, and insulators is usually created by stacking patterned layers of different materials. For flexible electronics, it can be advantageous to avoid this architectural constraint. Graphene oxide, formed by chemical exfoliation of graphite, can be reduced to a more conductive form using chemical reductants. Wei et al. (p. 1373 ) now show that layers of graphene oxide can also be reduced using a hot atomic force microscope tip to create materials comparable to those of organic conductors. This process can create patterned regions (down to 12 nanometers in width) that differ in conductivity by up to four orders of magnitude.

We report an investigation on CO oxidation catalyzed by Au(8) or Pt(4) clusters on defective graphene using first-principles approach based on density functional theory. The simplest single-carbon-vacancy defect on graphene was found to play an essential role in the catalyzed chemical reaction of CO oxidation. When supported on a defect-free graphene sheet, the reaction barrier of CO oxidation catalyzed by Au(8) (Pt(4)) clusters was estimated to be around 3.0 eV (0.5 eV), and when adsorbed on defective graphene, the reaction barrier was greatly reduced to around 0.2 eV (0.13 eV).

Configurations of Pt 4 , Ag 7 , Pd 9 , Al 13 , and Au 16 nanoclusters adsorbed on graphene under a strain of 5%. Figure S1. Atomic structures of (a) tetrahedral Pt 4 , (b) pentagonal bipyramid Ag 7 , (c) triangular prismatic Pd 9 , (d) icosahedral Al 13 and (e) Au 16 clusters adsorbed on a graphene sheet under a strain of 5%. The cluster-graphene distances are also indicated in the figure.

Nanoscale chemical patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns is achieved by the iterative application of thermochemical nanolithography (TCNL) to inscribe amine patterns followed by their chemical conversion to other functional groups. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for covalent and molecular‐recognition‐based attachment of nano‐objects using standard chemical protocols. In particular, the ability of this method to attach proteins and DNA to the chemical nanopatterns and to create co‐patterns of two distinctive bioactive proteins is demonstrated.

We demonstrate measurement and control of single-asperity friction by using cantilever probes featuring an in situ solid-state heater. The heater temperature was varied between 25 and 650 °C (tip temperatures from 25 ± 2 to 120 ± 20 °C). Heating caused friction to increase by a factor of 4 in air at ∼ 30% relative humidity, but in dry nitrogen friction decreased by ∼ 40%. Higher velocity reduced friction in ambient with no effect in dry nitrogen. These trends are attributed to thermally assisted formation of capillary bridges between the tip and substrate in air, and thermally assisted sliding in dry nitrogen. Real-time friction measurements while modulating the tip temperature revealed an energy barrier for capillary condensation of 0.40 ± 0.04 eV but with slower kinetics compared to isothermal measurements that we attribute to the distinct thermal environment that occurs when heating in real time. Controlling the presence of this nanoscale capillary and the associated control of friction and adhesion offers new opportunities for tip-based nanomanufacturing.

Based on first-principles calculations, we have investigated electronic structures and magnetic properties of SnO 2 doped with V, Mn, Fe, and Co. Our results show that ferromagnetism is the ground state and that the Curie temperatures are expected to have high values for Fe-and Co-doped SnO 2 , which is in good agreement with the experimental observations (Ogale et al 2003 Phys. Rev. Lett. 91 077205; Coey et al 2004 Appl. Phys. Lett. 84 1332). However, in V-and Mn-doped SnO 2 , paramagnetism is more stable than ferromagnetism. In addition, we also probe the effect of an oxygen vacancy. The results exhibit that an oxygen vacancy strongly influences the magnetic properties of these doped systems, and an oxygen vacancy strongly attracts Fe and Co ions. As a result, transition metal-oxygen vacancy-transition metal groups will be common in Fe-and Co-doped SnO 2 , but this tendency does not exist in the cases of V and Mn doping. In V-doped SnO 2 , ferromagnetism becomes more stable than antiferromagnetism after inducing additional n-type carriers and the Curie temperature increases with increasing density of n-type carriers. Hence, raising the density of n-type carriers is a practical way to realize high Curie temperatures in V-doped SnO 2 .

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