Graphene nanoribbons (GNRs) are materials with properties distinct from those of other carbon allotropes. The all-semiconducting nature of sub-10-nm GNRs could bypass the problem of the extreme chirality dependence of the metal or semiconductor nature of carbon nanotubes (CNTs) in future electronics. Currently, making GNRs using lithographic, chemical or sonochemical methods is challenging. It is difficult to obtain GNRs with smooth edges and controllable widths at high yields. Here we show an approach to making GNRs by unzipping multiwalled carbon nanotubes by plasma etching of nanotubes partly embedded in a polymer film. The GNRs have smooth edges and a narrow width distribution (10-20 nm). Raman spectroscopy and electrical transport measurements reveal the high quality of the GNRs. Unzipping CNTs with well-defined structures in an array will allow the production of GNRs with controlled widths, edge structures, placement and alignment in a scalable fashion for device integration.

We develop a simple chemical method to obtain bulk quantities of N-doped, reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia. X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various reaction temperatures reveals that N-doping occurs at a temperature as low as 300ºC, while the highest doping level of ~5% N is achieved at 500ºC. N-doping is accompanied by the reduction of GO with decreases in oxygen levels from ~28% in as-made GO down to ~2% in 1100ºC NH 3 reacted GO. XPS analysis of the N binding configurations of doped GO finds pyridinic N in the doped samples, with increased quaternary N (N that replaced the carbon atoms in the graphene plane) in GO annealed at higher temperatures (>900ºC). Oxygen groups in GO were found responsible for reactions with NH 3 and C-N bond formation.Pre-reduced GO with fewer oxygen groups by thermal annealing in H 2 exhibits greatly reduced reactivity with NH 3 and lower N-doping level.2 Electrical measurements of individual GO sheet devices demonstrate that GO annealed in NH 3 exhibits higher conductivity than those annealed in H 2 , suggesting more effective reduction of GO by annealing in NH 3 than in H 2 , consistent with XPS data. The N-doped reduced GO shows clearly n-type electron doping behavior with Dirac point (DP) at negative gate voltages in three terminal devices. Our method could lead to the synthesis of bulk amounts of N-doped, reduced GO sheets useful for various practical applications.3

Graphene nanoribbons have attracted attention for their novel electronicand spin transport properties [1][2][3][4][5][6] , and because nanoribbons less than 10 nm wide have a band gap that can be used to make field effect transistors 1-3 . However, producing nanoribbons of very high quality, or in high volumes, remains a challenge 1, 4-18 . Here, we show that pristine few-layer nanoribbons can be produced by unzipping mildly gas-phase oxidized multiwalled carbon nanotube using mechanical sonication in an organic solvent. The nanoribbons exhibit very high quality, with smooth edges (as seen by high-resolution transmission electron microscopy), low ratios of disorder to graphitic Raman bands, and the highest electrical conductance and mobility reported to date (up to 5e 2 /h and 1500 cm 2 /Vs for ribbons 10-20 nm in width). Further, at low temperature, the nanoribbons exhibit phase coherent transport and Fabry-Perot interference, suggesting minimal defects and edge roughness. The yield of nanoribbons was ~2% of the starting raw nanotube soot material, which was significantly higher than previous methods capable of producing high quality narrow nanoribbons 1 . 2The relatively high yield synthesis of pristine graphene nanoribbons will make these materials easily accessible for a wide range of fundamental and practical applications. Fig S1). The yield of nanoribbons was estimated to be ~2 % of the starting raw soot material through the two step process, which could be further improved by repeating the unzipping process for remaining nanotubes in the centrifuged aggregate, increasing the calcination temperature and prolonging the sonication time. The yield and quantity of high quality nanoribbons (width 10-30 nm) far exceeds previous methods capable of making high quality nanoribbons 1,13 .We used atomic force microscope (AFM) to characterize multiwalled carbon nanotubes and the unzipped products deposited on SiO 2 /Si substrates. Nanoribbons were easily distinguished from multiwalled carbon nanotubes due to obvious decreases in apparent heights (1-2.5 nm in height for nanoribbons, Fig Our method produced a high percentage of nanoribbons with ultra-smooth edges by simple calcination and sonication steps, which can be performed in many laboratories. The mechanism of the unzipping differs from previous methods that involved extensive solution-phase oxidation 14 . We proposed that our calcination step led to gas phase-oxidation of pre-existing defects on arc-discharge grown multiwalled carbon nanotubes. A low density structural defect was known to exist on the sidewalls and the ends of high quality arc-derived multiwalled carbon nanotubes 19. The defects and ends were more reactive with oxygen than pristine sidewalls during 500 o C calcination, a condition used for purifying arc-discharge multiwalled carbon nanotubes without introducing new defects on sidewalls 19,20 . Similar to oxidation of defects in the plane of graphite by oxygen 21,22 , etch pits were formed at the defects 5 and extended from the outmost sidewall ...

As a single-atom thick carbon material with light-weight, high surface area and conductivity, graphene 1,2 could be ideal substrates for growing and anchoring of functional nanomaterials for high performance electrocatalytic or electrochemical devices. Nanocrystals grown on graphene could have enhanced electron transport rate, high electrolyte contact area and structural stability, all of which could be useful for various fundamental and practical applications. 3 Although decoration of nanoparticles on graphite oxide (GO) sheets has been shown, 4-6 it remains unexplored and highly desirable to synthesize nanocrystals on more pristine graphene with high electrical conductivity, control the morphologies of the nanocrystals by tuning the oxidation degrees of the graphene sheets, and rationalize the nanocrystal growth behavior.Here, we show a general two-step method to grow hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized GO in hydrothermal reactions. Small particles pre-coated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline nanoplates or nanorods with well defined shapes. In contrast, particles pre-coated on GO were pinned by the high-concentration oxygen groups and defects on GO without recrystallization into well-defined morphologies. Our results suggest an interesting approach to controlling the morphology of nanocrystals by tuning the surface chemistry of graphene substrates used for crystal nucleation and growth.Our GS with low degree of oxidation were made by an exfoliation-reintercalation-expansion method, 7-9 and GO was produced by a modified Hummers method 10 (Figure 1). The resistivity of our

We study the effect of remote hydrogen plasma on graphene deposited on SiO₂. We observe strong monolayer selectivity for reactions with plasma species, characterized by isotropic hole formation in the basal plane of monolayers and etching from the sheet edges. The areal density of etch pits on monolayers is 2 orders of magnitude higher than on bilayers or thicker sheets. For bilayer or thicker sheets, the etch pit morphology is also quite different: hexagonal etch pits of uniform size, indicating that etching is highly anisotropic and proceeds from pre-existing defects rather than nucleating continuously as on monolayers. The etch rate displays a pronounced dependence on sample temperature for monolayer and multilayer graphene alike: very slow at room temperature, peaking at 400 °C and suppressed entirely at 700 °C. Applying the same hydrogen plasma treatment to graphene deposited on the much smoother substrate mica leads to very similar phenomenology as on the rougher SiO₂, suggesting that a factor other than substrate roughness controls the reactivity of monolayer graphene with hydrogen plasma species.