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.

A central question in the field of graphene-related research is how graphene behaves when it is patterned at the nanometre scale with different edge geometries. A fundamental shape relevant to this question is the graphene nanoribbon (GNR), a narrow strip of graphene that can have different chirality depending on the angle at which it is cut. Such GNRs have been predicted to exhibit a wide range of behaviour, including tunable energy gaps 1,2 and the presence of one-dimensional (1D) edge states [3][4][5] with unusual magnetic structure 6,7 . Most GNRs measured up to now have been characterized by means of their electrical conductivity, leaving the relationship between electronic structure and local atomic geometry unclear [8][9][10] . Here we present a sub-nanometre-resolved scanning tunnelling microscopy (STM) and spectroscopy (STS) study of GNRs that allows us to examine how GNR electronic structure depends on the chirality of atomically well-defined GNR edges. The GNRs used here were chemically synthesized using carbon nanotube (CNT) unzipping methods that allow flexible variation of GNR width, length, chirality, and substrate 11,12 . Our STS measurements reveal the presence of 1D GNR edge states, the behaviour of which matches theoretical expectations for GNRs of similar width and chirality, including width-dependent energy splitting of the GNR edge state.The chirality of a GNR is characterized by a chiral vector (n,m) or, equivalently, by chiral angle θ, as shown in Fig. 1a. GNRs having different widths and chiralities were deposited on a clean Au(111) surface and measured using STM. Figure 1b shows a room temperature image of a single monolayer GNR (GNR height is determined from linescans, such as that shown in Fig. 1b inset; some multilayer GNRs were observed, but we focus here on monolayer GNRs). The GNR of Fig. 1b has a width of 23.1 nm, a length greater than 600 nm, and exhibits straight, atomically smooth edges (the highest quality GNR edges, such as those shown in Figs 1 and 2, were observed in GNRs synthesized as in ref. 11). Such GNRs are seen to have a 'bright stripe' running along each edge.This stripe marks a region of curvature near the terminal edge of the GNR that has a maximum extension of ∼3 Å above the mid-plane terrace of the GNR and a width of ∼30 Å (see line scan in Fig. 1b inset). Such edge-curvature was observed for all high-quality GNRs examined in this study (more than 150, including GNRs deposited onto a Ru (0001) is reminiscent of curved edge structures observed previously near graphite step-edges 13 . We rule out that these GNRs are collapsed nanotubes by virtue of the measured ratio (observed to be π) of GNR width to nanotube height for partially unzipped CNTs. We further rule out that the curved GNR edges observed here are folded graphene boundaries by means of a detailed comparison of terminal curved edges and actual folded edges (see Supplementary Information). Low-temperature STM images (Figs 1c and 2a) show finer structure in both the interior GNR terrace and the edge re...

The controlled synthesis of highly crystalline MoS2 atomic layers remains a challenge for the practical applications of this emerging material. Here, we developed an approach for synthesizing MoS2 flakes in rhomboid shape with controlled number of layers by the layer-by-layer sulfurization of MoO2 microcrystals. The obtained MoS2 flakes showed high crystallinity with crystal domain size of ~10 μm, significantly larger than the grain size of MoS2 grown by other methods. As a result of the high crystallinity, the performance of back-gated field effect transistors (FETs) made on these MoS2 flakes was comparable to that of FETs based on mechanically exfoliated flakes. This simple approach opens up a new avenue for controlled synthesis of MoS2 atomic layers and will make this highly crystalline material easily accessible for fundamental aspects and various applications.

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 ...

The transferring and identification of single- and few- layer graphene sheets from SiO2/Si substrates to other types of substrates is presented. Features across large areas (∼cm2) having single and few-layer graphene flakes, obtained by the microcleaving of highly oriented pyrolytic graphite (HOPG), can be transferred reliably. This method enables the fast localization of graphene sheets on substrates on which optical microscopy does not allow direct and fast visualization of the thin graphene sheets. No major morphological deformations, corrugations, or defects are induced on the graphene films when transferred to the target surface. Moreover, the differentiation between single and bilayer graphene via the G′ (∼2700 cm−1) Raman peak is demonstrated on various substrates. This approach opens up possibilities for the fabrication of graphene devices on a substrate material other than SiO2/Si.