Carbon nanotubes have many material properties that make them attractive for applications. In the context of nanoelectronics, interest has focused on single-walled carbon nanotubes (SWNTs) because slight changes in tube diameter and wrapping angle, defined by the chirality indices (n, m), will shift their electrical conductivity from one characteristic of a metallic state to one characteristic of a semiconducting state, and will also change the bandgap. However, this structure-function relationship can be fully exploited only with structurally pure SWNTs. Solution-based separation methods yield tubes within a narrow structure range, but the ultimate goal of producing just one type of SWNT by controlling its structure during growth has proved to be a considerable challenge over the last two decades. Such efforts aim to optimize the composition or shape of the catalyst particles that are used in the chemical vapour deposition synthesis process to decompose the carbon feedstock and influence SWNT nucleation and growth. This approach resulted in the highest reported proportion, 55 per cent, of single-chirality SWNTs in an as-grown sample. Here we show that SWNTs of a single chirality, (12, 6), can be produced directly with an abundance higher than 92 per cent when using tungsten-based bimetallic alloy nanocrystals as catalysts. These, unlike other catalysts used so far, have such high melting points that they maintain their crystalline structure during the chemical vapour deposition process. This feature seems crucial because experiment and simulation both suggest that the highly selective growth of (12, 6) SWNTs is the result of a good structural match between the carbon atom arrangement around the nanotube circumference and the arrangement of the catalytically active atoms in one of the planes of the nanocrystal catalyst. We anticipate that using high-melting-point alloy nanocrystals with optimized structures as catalysts paves the way for total chirality control in SWNT growth and will thus promote the development of SWNT applications.

We present a theoretical study on the determination of graphene orientation on the catalyst surface in chemical vapor deposition growth. Our study reveals that the interaction between the graphene wall and catalyst surface is weak and not sensitive to the orientation of graphene. The graphene edge–catalyst interaction is strong and sensitively depends on the graphene orientation. Therefore, the graphene edge–catalyst interaction is responsible for the orientation determination of a small graphene island in the early stage of graphene growth, and such an orientation can be inherited by the matured graphene due to the high barrier of graphene island rotation. On the basis of the mechanism of graphene orientation determination, various controversial-like experimental puzzles have been well-explained, and a potential of synthesizing large-area single-crystalline graphene on either single-crystalline or polycrystalline catalyst surfaces is revealed.

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Enriching near-zigzag single-walled carbons, which have a small tube-catalyst interface, by a “tandem plate” CVD method.

The routes towards carbon nanotube's chirality control during growth was revealed by kinetic modelling.

Aligned single-walled carbon nanotube arrays provide a great potential for the carbon-based nanodevices and circuit integration. Aligning single-walled carbon nanotubes with selected helicities and identifying their helical structures remain a daunting issue. The widely used gas-directed and surface-directed growth modes generally suffer the drawbacks of mixed and unknown helicities of the aligned single-walled carbon nanotubes. Here we develop a rational approach to anchor the single-walled carbon nanotubes on graphite surfaces, on which the orientation of each single-walled carbon nanotube sensitively depends on its helical angle and handedness. This approach can be exploited to conveniently measure both the helical angle and handedness of the single-walled carbon nanotube simultaneously at a low cost. In addition, by combining with the resonant Raman spectroscopy, the (n,m) index of anchored single-walled carbon nanotube can be further determined from the (d,θ) plot, and the assigned (n,m) values by this approach are validated by both the electronic transition energy Eii measurement and nanodevice application.

The atomistic simulation of defect-free SWCNT growth is realized for the first time after 12 years of continuous effort.

Atomistic simulations and a dislocation-based analysis reveal the mechanism of carbon peapod fusion into double-walled nanotubes. They explain the trend of diameter increase for the emerging inner wall, driven by the reduction in its strain energy and the interwall van der Waals energy. Surprisingly, this is also accompanied by the systematic bias in the nanotube chirality, changing from zigzag toward armchair. This prediction agrees well with our experimental data and is further supported by the analysis of earlier observations. [5][6][7][8][9] where the encapsulated fullerenes coalescence into an inner tube at high temperature. The peapod route is the preferred method for preparing relatively pure DWNTs with welldefined structures. 1 There has been considerable effort to understand the mechanism of fullerene coalescence and the transformations of sp 2 carbon networks. 8,[10][11][12][13][14] It is well established that that rotation of a C-C bond in a sp 2 carbon network, known as the Stone-Wales ͑SW͒ transformation, is the key step of such a transformation. 10,12,13 The calculated barrier of such a bond rotation is as high as 5-9 eV ͑Refs. 11 and 15͒ which explains the requirement of high temperature for the formation of peapod-derived DWNTs. 9 Because of the high barrier, it is impossible to simulate a defect-free DWNT structure by conventional molecular-dynamics simulation due to the limited simulation time ͑time scale from picosecond to nanosecond͒. 8,14 Although a full route from two fullerenes to a short SWNT has been demonstrated in previous studies, the final SWNT formation was predetermined and thus information about the inner-tube chiral angle cannot be determined correctly by these methods. [10][11][12][13] In this Rapid Communication, we study the formation of peapod-derived DWNTs. An atomic simulation successfully reproduces the transformation from peapods into a defectfree DWNT through the SW mechanism. It is found that most of the simulated inner tubes have large chiral angles ͑e.g., Ͼ 20°͒ and detailed theoretical analysis has shown that the preference for large chiral angles is dominated by the driving force of the SW transformation during tube fattening. Through careful analyzing experimental data, we have confirmed that the abundance of large chiral-angle tubes is in agreement with most experimental observations.It is well established that the kinetic Monte Carlo ͑KMC͒ method can simulate a long-time process by neglecting the thermal vibrations of atoms and considering the process of overcoming barriers directly. In mimicking the KMC method, we propose a similar method to study the coalescence of fullerenes but by considering instead the energy change in the barrier between two states. In detail, the sp 2 carbon network is described by the most used second generation Tersoff-Brenner potential in which the van der Waals interactions have been properly incorporated 15 and the energy of the relaxed initial structure is denoted as E i . A C-C bond is then selected randomly and rotated by 90°. Th...