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Carbon nanotubes are, next to molecular electronics, the most common application area for the QuantumWise software. Both academic research and industrial R&D groups use the products extensively to investigate various aspects of nanotubes, ranging from basic properties to specific device applications like diodes, switches, and sensors.
Tutorials & Resources
If you are interested in studying nanotubes with ATK, an excellent starting point will be the tutorials. A dedicated nanotube tutorial is under development, but for now the general ones, plus those for graphene, will be useful.
Virtual NanoLab contains a dedicated NanoTube Grower, allowing users to easily build ideal nanotubes of any chirality with just a few clicks. The tool also gives a quick preview of the tight-binding band structure (screenshots).
Also, feel free to download our unique carbon nanotube periodic table (PDF)!·
A multitude of different nanotube systems
The QuantumWise software platform, with the first-principles engine Atomistix ToolKit (ATK) and the graphical user interface Virtual NanoLab (VNL) allows researchers to focus on the relevant points for their projects, namely the investigation of the electrical properties of novel device structures, rather than spending time writing their own quantum-mechanical codes for the simulation, or struggling with data import/export to visualize the results.
ATK is capable of calculating a wide variety of nanotube (and related) geometries:
- ideal tubes
- truncated or capped tubes
- tube/tube heterojunctions
- metal/tube/metal junctions (i.e. a piece of a nanotube between two metal surfaces; the metals can be different)
- metal/tube junction (i.e. a nanotube attached to a metal surface)
- tube/molecule/tube junctions
- crossed tubes
- single wall or multiwall tubes
- fullerenes
- unrolled tubes - i.e. graphene sheets
- tubes with defects and impurities (see below)
- etc
Note that for transport calculations there is no periodicity along the tube axis. Thus when defects or dopants are introduced, or molecules adsorbed on the surface of the tube, the observed effect is related to the single impurity/molecule. Heterogeneous systems are also described as truly heterogeneous; the left and right tube segments extend to infinite each respective way.
Not just carbon!
Since ATK uses first-principles methods for the computations, one is not limited to just carbon tubes. Studies of more unusual tube materials involve gold, boron-nitride (BN), and silicon-carbide (SiC).
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R.T. Senger, S. Dag & S. Ciraci, Physical Review Letters 93, 196807 (2004)
Gold atoms can form both freestanding and tip-suspended chiral single-wall nanotubes composed of helical atomic strands. The mechanical stability is studied and compared to experiments. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these wires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands.
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Unlike carbon nanotubes, boron-nitride nanotubes are wide band gap semiconductors for all chiralities due to the different bonding character.
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Y.-T. Yang et al., Chinese Science Bulletin 53, 3770 (2008)
A (7,0) silicon carbide (SiC) nanotube coupled to Au (111) surfaces via Au-C bonds shows negative differential resistance (NDR).
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Basic properties of nanotubes
The ability of ATK to calulcate the electronic structure as well as the ballistic tunneling current in nanostructures enables users to study
- dependence of the electronic structure and transport properties on functionalization, e.g. for sensor applications (see below for more detailed nanoelectronic case studies)
- spin transport properties of nanotubes (see below)
- single vs. multiwall nanotubes, either free or contacted to metallic electrodes; see e.g. Q. Yan et al., Physical Review B Vol. 72, 155425 (2005) which studies the influence of side vs. edge contacting, inner vs. outer shell contacting, broken shells (inner & outer), and intershell hopping
- bias-induced forces (Y. Girard et al., Journal of Physical Chemistry C 111, 12478 (2007) and Journal of Physics: Conference Series 100, 052063 (2008))
- band structure and transport properties of tubes with defects (e.g. Stone-Wales) or impurities (including doping); see e.g. T. Yamamoto, et al., New Journal of Physics 9, 245 (2007) with extensions to phonon transport, or Y.-F. Li et al., Journal of Physics: Condensed Matter 20, 415207 (2008) which considers Haeckelite carbon nanotubes
- mechanical properties, like·Young's modulus
- Bloch states
- the details of the transport mechanisms
- and many other things!
Nanoelectronic case studies
Below we showcase some nanoelectronic device structures based on nanotubes that users of Atomistix ToolKit have studied with the software. For convenience they have been grouped in four categories:
- nanotubes as molecular detectors
- spin filter applications
- nanotube switches
- general nanoelectronics
To view all references to papers on graphene studied with ATK, see the publication list.·
Nanotubes as molecular detectors
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G. Abadir, K. Walus, R. Turner & D. Pulfrey, International Journal of High Speed Electronics and Systems 18, 879 (2008) and 8th IEEE Conference on Nanotechnology, 230 (2008)
Adsorption of single molecules of different amino acids on short carbon nanotubes is predicted to cause distinct changes in the local density of states, transmission coefficient, and current. This is promising for the prospect of CNT-based single-biomolecule sensors that might depend on the LDOS, e.g., devices that respond to changes in either conductance or electroluminescence.
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O. B. Malcioglu & S. Erkoc, Journal of Nanoscience and Nanotechnology 8, 469 (2008)
Alterations in the electronic transport properties of C(4,4) single walled carbon nanotube when several different chemical agents are introduced to the outer surface are investigated. The conductance shows a strong dependence on the geometry and aromaticity, both are which altered when the suitable agent is introduced, resulting in rather dramatic response in the I-V curve; the current is reduced significantly, and quantization effects are observed, even for a single molecule. |
Nanotubes as spin filters
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X. Q. Shi et al., Journal of Physical Chemistry C 111, 10130 (2007)
A spin-polarized current and negative differential resistance is obtained for a carbon nanowires in the core of single-walled carbon nanotube.
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Y. Girard, T. Yamamoto & K. Watanabe, e-Journal of Surface Science and Nanotechnology 6, 157 (2008)
A highly spin-dependent zero-bias conductance is obtained for a metallic single-walled (5,5) carbon nanotube with non-magnetic adatoms (carbon and boron). The microscopic origin of this phenomenon is explained by the features of the spin-dependent local density of states in the region of the adatom. The spin-dependent conductance is controllable by tuning the applied gate voltage, which would be a useful property for application in spin filters. |
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Y. Min et al., Nanotechnology 20, 095201 (2009)·
Half-metallic behavior of Au-V(Cr) quantum wires adsorbed on an armchair (5, 5) boron-nitride nanotube is obtained. The density of states shows a metallic property at the Fermi level for the majority spin channel and a semiconductor gap in the minority spin channel. The half-metallic behavior of the quantum wire/nanotube complex originates from the half-metallic behavior of the free-standing Au-V(Cr) quantum wires. The calculations indicate that such a one-dimensional half-metallic magnet can be used as a spin filter. |
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K. L. Yao et al., Physics Letters A 372, 5609 (2008)
Large tunnel magnetoresistance (several thousand percent) and perfect spin filtration effect are obtained in V doped boron nitride nanotubes. The tunnel magnetoresistance decreases monotonically when bias is applied, and eventually goes to negative values. The spin-dependent nonequilibrium transport is investigated by studying the microscopic details of the transmission coefficients.
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Nanotubes as nanoelectronic switches
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F. OuYang et al., Journal of Applied Physics 102, 064501 (2007) and Frontiers of Physics in China 2, 36 (2007) and Chinese Physics Letters 24, 2369 (2007)
Studies of nanoelectronic switches based on armchair carbon nanotubes, capped or open ended, connected to various fullerenes (C70, C20, C82). The conductance can be tuned within several orders of magnitude by changing the orientation of the molecule, the distance from the molecule to the tube, or by rotating one of the tubes around the symmetry axis of the system at fixed distances. The study also reveals that molecular configuration selection, doping, and structural relaxation plays an important role in the design of such devices. Finally, the conductance mechanisms for such a molecular device are analyzed.
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Q. Yan et al., Applied Physics Letters 88, 173107 (2006)
A nanoelectronic switch is proposed based on telescoping double-walled carbon nanotubes, which can be conveniently turned on or off via the relative motion of the tubes along the tube axis. The quantum conductance oscillates with the overlapping length of the two shells, which is mainly attributed to the variation of coupling effect between pi electronic states of the two shells. The switching of TDWCNTs is determined by the distribution of delocalized frontier molecular orbitals of this system. |
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P. Zhao et al., Physica E: Low-dimensional Systems and Nanostructures 41, 474 (2009)
The switching characteristics of an optical molecular switch based on the phenoxynaphthacenequinone (PNQN) molecule between two armchair single-walled carbon nanotube electrodes is studied. The molecule and the electrode material are shown to be promising candidates for optical molecular switches.
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B. Akdim & R. Pachter, Journal of Physical Chemistry C 112, 3170 (2008)
The switching behavior in a nitro-oligo(phenylene ethylene) molecule bridged between a silicon slab and a single wall carbon nanotube (SWCNT) mat is studied. The results suggest that the switching may be driven by conformational changes in the molecule upon the application of an electric field. The nature of the contact at the interface of the SWCNT mat also plays an important role.
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General nanotube nanoelectronics
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S. U. Lee et al., Physical Chemistry Chemical Physics 10, 5225 (2008)
M. Khazaei et al., Journal of Physical Chemistry C 111, 12175 (2007)
Creating carbon nanotube intramolecular heterojunctions with different covalent linkages (peptide bonds) exhibit Schottky rectifying behavior. This can pave the way towards the design and implementation of various electronic logic functions based on carbon nanotubes.
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W. Y. Kim, S. K. Kwon & K. S. Kim, Physical Review B 76, 033415 (2007)
Metallic carbon nanotubes coupled by molecules form asymmetric couplings even if symmetric structures are employed, giving rise to negative differential resistance (NDR).
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S. Compernolle et al., Physical Review B 77, 193406 (2008)
Carbon nanotubes (CNTs) are a promising candidate to replace copper interconnects. An ab initio study is presented on the conductance of a closed-packed bundle of very narrow metallic (4,0) CNTs, which is vertically placed on a Cu (100) surface. While the intertube interactions have no significant impact on the conductance, which however is highly dependent on the exact geometry of the interface.
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M. Khazaei et al., ACS Nano 2, 939 (2008)
A new approach for the design of functional units obtained by interconnecting carbon nanotubes (CNTs) with different numbers of zinc layers is presented. Remarkably, the zinc layers behave as a momentum filter when they are inserted within metallic CNT electrodes, thereby providing 1D heterojunctions that can act as a wire-like, negative differential resistance (NDR), or varistor-type nanoscale device. Thus it may be possible to design specific heterojunctions, which can select a conducting channel between two electrodes. This study presents for the first time a nanoscale device with the characteristics of a varistor.
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P. Bai et al., Nanotechnology 19, 115203 (2008)
Semiconducting carbon nanotube Schottky diodes are modeled as a nanotube embedded in a metal electrode, to resemble the experimental set-up. The rectification behaviour of the diode is mainly due to the asymmetric electron transmission function distribution in the conduction and valence bands and can be improved by changing metal-SCNT contact geometries. The threshold voltage of the diode depends on the electron Schottky barrier height which can be tuned by altering the diameter of the SCNT. Contrary to the traditional perception, the metal-SCNT contact region exhibits better conductivity than the other parts of the diode.
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Some further details
There are several specific features of ATK that makes it especially well suited for simulations of nanotubes:
- Full DFT (LDA and PBE/revPBE) simulation of electronic structure and transport properties, also spin-polarized
- Localized basis sets with compact support (SIESTA type) makes it effortless to describe the vacuum surrounding the nanotube, and also provides an accurate description of doping atoms without computational overhead
- The localized basis set also means ATK can handle comparatively large systems (more atoms), in fact up to 1,000 atoms can relatively easily be simulated on a laptop
- Parallelized code with linear speedup for transmission and current calculations
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Applications 
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