126 research outputs found
Manipulation of Ultralong Single-Walled Carbon Nanotubes at Macroscale
A parallel, controllable yet simple approach was developed to manipulate single-walled carbon nanotubes (SWNTs) and create complex architectures of SWNTs. This approach was based on the utilization of flexible poly(methyl methacrylate) (PMMA) film as a mediator for indirectly manipulating the SWNTs. With this PMMA-mediated manipulation approach, SWNTs were bended at controlled bending angles without degrading their pristine properties. Meanwhile, crossbar arrays with controlled crossing angle were created. Moreover, complex two-dimensional (2D) architectures, such as steplike and zigzag structures of SWNTs were obtained without complicated lithographic processes. Our manipulation technique paves the way to fabricate novel 2D configuration of SWNTs, induce controllable strain in SWNTs and then build new devices based on them
Bandgap Opening in Graphene Antidot Lattices: The Missing Half
The electronic structure of graphene antidot lattices (GALs) with zigzag hole edges was studied with first-principles calculations. It was revealed that half of the possible GAL patterns were unintentionally missed in the usual construction models used in earlier studies. With the complete models, the bandgap of the GALs was sensitive to the width W of the wall between the neighboring holes. A nonzero bandgap was opened in hexagonal GALs with even W, while the bandgap remained closed in those with odd W. Similar alternating gap opening/closing with W was also demonstrated in rhombohedral GALs. Moreover, analytical solutions of single-walled GALs were derived based on a tight-binding model to determine the location of the Dirac points and the energy dispersion, which confirmed the unique effect in GALs
A General Approach to Chemical Modification of Single-Walled Carbon Nanotubes with Peroxy Organic Acids and Its Application in Polymer Grafting
The previous work on the functionalization of single-walled carbon nanotubes (SWCNTs) with peroxytrifluoroacetic acid under ultrasonication is extended to other peroxy organic acids including m-chloroperbenzoic
acid and 2-bromo-2-methylperpropionic acid (BMPPA). Systematic characterization of the treated SWCNTs
shows that oxygen-based functional groups and the ester groups with Cl or Br substituents were introduced
to the nanotubes, demonstrating that the peroxy organic acid treatment is a general approach to chemical
modification of SWCNTs. The extent of functionalization depends on the acidity, oxidizability, and
concentration of the peroxy organic acids. Furthermore, the attached reactive moieties allow the chemical
coupling of SWCNTs to other materials. By using BMPPA-SWCNTs as the initiator, poly(methyl methacrylate)
was grafted to SWCNTs through atom transfer radical polymerization
Wrinkle Engineering: A New Approach to Massive Graphene Nanoribbon Arrays
Wrinkles are often formed on CVD-graphene in an uncontrollable way. By designing the surface morphology of growth substrate together with a suitable transfer technique, we are able to engineer the dimension, density, and orientation of wrinkles on transferred CVD-graphene. Such kind of wrinkle engineering is employed to fabricate highly aligned graphene nanoribbon (GNR) arrays by self-masked plasma-etching. Strictly consistent with the designed wrinkles, the density of GNR arrays varied from âź0.5 to 5 GNRs/Îźm, and over 88% GNRs are less than 10 nm in width. Electrical transport measurements of these GNR-based FETs exhibit an on/off ratio of âź30, suggesting an opened bandgap. Our wrinkle engineering approach allows very easily for a massive production of GNR arrays with bandgap-required widths, which opens a practical pathway for large-scale integrated graphene devices
âCloningâ of Single-Walled Carbon Nanotubes via Open-End Growth Mechanism
Using the concept of âcloningâ, we report herein a rational approach to grow single-walled carbon nanotubes (SWNTs) with controlled chirality via an open-end growth mechanism. Specifically, by using open-end SWNTs as âseeds/catalystsâ (without metal catalysts), ânew/duplicateâ SWNTs could be grown and cloned from the parent segments via an open-end growth mechanism. Using this strategy, we have measured more than 600 short seed segments and have found that the yield of cloning is relatively low (around 9%). This yield can be greatly improved up to 40% by growing SWNTs on quartz substrate. Atomic force microscopy and micro resonance Raman spectroscopy characterization indicate that the parent nanotube and the duplicate nanotube have the same structure. These findings provide a potential approach for growing SWNTs with controlled chirality, which are important for the application of SWNTs in nanoelectronics
Nano-Welding by Scanning Probe Microscope
A novel method, nano-welding, analogous to spot welding at the nanoscale level using scanning probe microscopy (SPM) is presented. Using SPM oxidation of the underlying silicon, single-walled carbon nanotubes (SWNTs) have been immobilized to the surface at point sites along their lengths by the nano-welding. It is shown that this nano-welding process nearly has no structural damage to the SWNTs. This immobilization makes the SPM manipulation of SWNTs controllable and desirable, which is helpful for the construction of SWNT-based nanodevices
Evolutionary Chlorination of Graphene: From Charge-Transfer Complex to Covalent Bonding and Nonbonding
Density functional theory (DFT) studies were performed to investigate the chlorination of graphene. Unlike hydrogenation and fluorination, where the adsorption of H and F is always by covalent CâH/CâF bonding, Cl atoms generate various states when single-sided graphene exposed. In the initial reaction stage, it forms Clâgraphene charge-transfer complex, where the C orbitals keep <i>sp</i><sup>2</sup> hybridization and the graphene is <i>p</i>-type doped. Further chlorination may form two adsorption configurations: one is covalent bonding Cl pairs, where the structure of the C atom is close to <i>sp</i><sup>3</sup> hybridization. With the Cl coverage increases, this configuration may further cluster into hexagonal rings, and the resulting coverage is less than 25%. The other configuration is nonbonding. This configuration is energy preferable, while Cl atoms will form Cl<sub>2</sub> molecules and escaped. When both sides of the graphene are exposed, the most stable adsorption configuration is a homogeneous ordered pattern with a Cl coverage of 25% (C<sub>4</sub>Cl) rather than collective clusters. The electronic properties of various chlorinated forms were also obtained; these showed that it is possible to tune the graphene bandgap by chlorination in a range of 0â1.3 eV
Raman Spectral Measuring of the Growth Rate of Individual Single-Walled Carbon Nanotubes
We report, herein, a rational approach to measure the growth rate of individual SWNTs. Intramolecular junctions
could be produced controllably by temperature-mediated chemical vapor deposition (CVD) and used as a
Raman-identifiable mark to confirm the starting and finishing position of a SWNT. Thus, the growth rate of
SWNTs could be calculated by ν = LCNT/t, where ν is the growth rate, L is the length of the segment, and
t is its growth time. The results show that the growth rates of SWNTs growing at 950 °C are higher than
those at 900 °C, and the growth rate at 950 or 900 °C decreases with the passage of time. We believe this
approach provides an easy way to measure the growth rate of an individual SWNT and that it is a good
starting point to study the growth behavior of SWNTs and for constructing SWNT-based device
Chirality-Dependent Raman Frequency Variation of Single-Walled Carbon Nanotubes under Uniaxial Strain
By using a homemade setup, the length of uniaxial strained single-walled carbon nanotubes (SWNTs) was directly measured by scanning electron microscopy (SEM), and quantitative relations between uniaxial strain and Raman frequency were obtained. It was found that RBM frequency was not affected, but G-band frequency variation was diameter and chirality-dependent under uniaxial strain. The G-band frequency shift rate increased with diameter increasing and chiral angel decreasing. Also G+ and Gâ frequency shift rates were related to chiral angle due to chirality-dependent CâC bonds elongation. A surprising finding that intermediate frequency mode (IFM) frequency upshifted with uniaxial strain increasing indicates that lattice transformation needs to be considered in phonon properties under uniaxial strain. These studies provide valuable information about geometric structure variation of SWNTs under uniaxial strain
Measurement of the Rate of Water Translocation through Carbon Nanotubes
We present an approach for measuring the water flow rate through individual ultralong carbon nanotubes (CNTs) using field effect transistors array defined on individual tubes. Our work exhibits a rate enhancement of 882â51 and a slip length of 53â8 nm for CNTs with diameters of 0.81â1.59 nm. We also found that the enhancement factor does not increase monotonically with shrinking tube diameter and there exists a discontinuous region around 0.98â1.10 nm. We believe that these single-tube level results would help understand the intrinsic nanofluidics of water in CNTs
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