Facile synthesis of high-quality graphene nanoribbons

Abstract

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 ...

Nanotomy-based production of transferable and dispersible graphene nanostructures of controlled shape and size

“…On comparing with the literature data on GNRs with similar dimensions, these values are close to that reported for GNRs produced via sonochemical unzipping of CNTs 10 and are significantly lower than that for lithography and other GNR production techniques ( Fig. 3g) [1][2][3]34 .…”

“…S11). The carrier mobilities ranged from 20-130 cm 2 34 , are attributed to carrier scattering at GNRs' overlapping junctions and three-dimensional transport over large channel length.…”

Edge states in graphene-like systems

“…Graphene ribbons are interesting by their own sake, and there has been enormous progress in the fabrication of ribbons with smooth edges [53][54][55][56][57] , so that inter-edge coupling is also an interesting topic [30][31][32]35,37,38,40,42,51,57,58 .…”

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

“…In research, bottom-up synthesis is usually adopted which is based on oxidizing organic precursors, such as oxidative cyclodehydrogenation of oligophenylene and polyphenylene [45].…”

“…As mentioned above, graphene quantum dots (GQDs) and nanoribbons (GNRs) can enable the further engineering on the properties of graphene specifically the band structure for optoelectronic applications. In research, bottom-up synthesis is usually adopted which is based on oxidizing organic precursors, such as oxidative cyclodehydrogenation of oligophenylene and polyphenylene [45]. It should also be mentioned that a variety of precursors have been employed for the synthesis of graphene, such as ethylene, usually with the assistance from hydrogen at ambient [46].…”