Building Carbon Nanotube based Network Architectures
Contacts: Jean-Christophe Charlier
Introduction
Due to the remarkable electronic and mechanical properties of SWNTs, various applications for them in nanoscale devices can be envisaged. However, little progress has been reported on techniques related to connecting such tubular structures, which is a key issue because both electronic devices and strong nano-mechanical systems need the establishment of molecular connections among SWNTs. In particular, theory predicts that a "Y" or a "T" junction could act as multi-terminal electronic device involving SWNTS. Therefore, it is imperative to join and connect nanotubes in a controllable way.
In this account, controlled electron beam exposure at elevated temperatures is found to be an interesting technique to connect SWNTs. During continuous, uniform atom removal, surfaces of isolated single-wall nanotubes heavily reconstruct leading to drastic dimensional changes. In bundles, coalescence of single-wall nanotubes is observed and induced by vacancies via a zipper-like mechanism. X, Y, and T carbon nanostructures are also fabricated by covalently connecting crossed single-wall nanotubes in order to pave the way toward controlled fabrication of nanotube based molecular junctions and network architectures. Each experiment is followed by quantum modeling in order to investigate the effect of the irradiation process at the atomic level. Our results will pave the way to the construction of nove 2D and 3D SWNT networks induced by controlled irradiation at elevated temperatures.
Coalescence of single-wall nanotubes
The coalescence of single-walled nanotubes is studied in-situ under electron irradiation at high temperature in a transmission electron microscope. The merging process is investigated at the atomic level using tight-binding molecular dynamics simulations. Vacancies induce coalescence via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices along adjacent tubes.
HRTEM images of a SWNT rope cross section, consisting of 15 nanotubes. The starting bundle is exposed to high-intensity electron irradiation (1.25 MeV) at 800C. After a few seconds, Two of the outer tubes coalesced into a larger one (see arrows).
Sequences of coalescence [side (left) and sectional (right) views] between two adjacent (10,10) carbon nanotubes into a unique single-walled tube of larger diameter.
Carbon nanotube molecular junctions
Crossing single-wall carbon nanotubes can be joined by electron beam welding to form molecular junctions. Stable junctions of various geometries are created in situ in a transmission electron microscope. Electron beam exposure at high temperatures induces structural defects which promote the joining of tubes via cross-linking of dangling bonds. The observations are supported by molecular dynamics simulations which show that the creation of vacancies and interstitials induces the formation of junctions involving seven- or eight-membered carbon rings at the surface between the tubes.
High-resolution transmission electron microscopy image and molecular model of X , Y and T junctions created by electron irradiation of two crossing nanotubes. It is remarkable that irradiation with energetic particles promotes a molecular connection between the two nanotubes, thus forming a molecular junction.
Coalescence of Nanopeapods
A fascinating structural transformation occurring inside single-walled carbon nanotubes (SWNTs) is the fullerene coalescence, which is responsible for forming stable zeppelinlike carbon molecules. In situ transmission electron microscope (TEM) observations reveal sequences of fullerene coalescence induced by electron irradiation on pristine nanotube peapods. TEM images indicate that the merging of fullerenes results in stable but corrugated tubules (5 to 7 in diameter) confined within SWNTs.
Extensive theoretical investigations of the microscopic mechanism suggest that the underlying process occurs via the polymerization of C60 molecules followed by surface reconstruction, which can be triggered either by the formation of vacancies (created under electron irradiation) or by surface-energy minimization activated by thermal annealing. These novel tubular forms of carbon contain hexagons, pentagons, heptagons, and octagons. The stability, electronic properties, and electron conductance of the novel tubules are strongly affected by the final geometry of the coalesced fullerene complex. The possibility of forming highly conducting and semiconducting tubular structures suggests new avenues in designing carbon nanowires with specific electronic characteristics.
Boron interstitials triggering connections in double-wall carbon nanotubes
Creating direct links or networks between carbon nanotubes can be applied in the development of new electronic components or nanotube-nanotube composites. But in order to fabricate these junctions or networks, exhibiting novel electronic properties, a better understanding is needed of the nanotube reactivity and their coalescence mechanism. Nanotube bridging Si pillars could be achieved by controlling the growth of carbon nanotubes using chemical vapour deposition methods in conjunction with organometallic precursors. Carbon nanotubes could subsequently be linked at defect sites, but a better control of the introduction and type of these interconnections is still needed in order to use this route. An alternative way to achieve nanotube coalescence or inter-connect carbon nanotubes can also be achieved by introducing novel types of imperfections to catalyse the formation of covalent nanotube interconnections.
Novel possibilities for carbon nanotube coalescence have been investigated, using high-resolution transmission electron microscopy (HRTEM) and resonance Raman studies. In particular, the unusual Raman feature known as the coalescence-inducing mode (CIM) observed at ∼1850 cm−1 during the coalescence of double-walled carbon nanotubes is studied, and the role played by hetero-atoms in substitution or as interstitials in the nanotube lattice is analysed. In order to gain insight in the mechanisms involved, a theoretical analysis was performed using ab initio calculations and AM1 Molecular Dynamics simulations at different temperatures.
Related publications
1) Surface reconstructions and dimensional changes in single-walled carbon nanotubes
P.M. Ajayan, V. Ravikumar, and J.-C. Charlier
Physical Review Letters 81, 1437-1440 (1998)
2) Coalescence of single-walled carbon nanotubes
M. Terrones, H. Terrones, F. Banhart, J.-C. Charlier, and P.M. Ajayan
Science 288, 1226-1229 (2000)
3) Molecular junctions by joining single-walled carbon nanotubes
M. Terrones, F. Banhart, N. Grobert, J.-C. Charlier, H. Terrones, and P.M. Ajayan
Physical Review Letters 89, 075505 (2002)
4) Fullerenes coalescence in nanopeapods : a path to novel tubular carbon
E. Hernandez, B.W. Smith, R. Rurali, H. Terrones, V. Meunier, T. Zacharia,
M. Terrones, D.E. Luzzi, and J.-C. Charlier
Nano Letters 3, 1037-1042 (2003)
5) Zipper mechanism of nanotube fusion : theory and experiment
M. Yoon, S. Han, G. Kim, S.B. Lee, S. Berber, E. Osawa, J. Ihm, M. Terrones,
F. Banhart, J.-C. Charlier, N. Grobert, H. Terrones, P.M. Ajayan, and D. Tomanek
Physical Review Letters 92, 075504 (2004)
6) Atomic nanotube welders: boron insterstitials triggering connections in double-walled
carbon Nanotubes
M. Endo, H. Muramatsu, T. Hayashi, Y. A. Kim, G. Van Lier, J.-C. Charlier,
H. Terrones, M. Terrones, and M. S. Dresselhaus
Nano Letters, 5, 1099-1105 (2005).
7) Resonance raman study of linear carbon chains formed by the heat treatment of
double-wall carbon nanotubes
C. Fantini, E. Cruz, A. Jorio, M.Terrones, H. Terrones, G. Van Lier, J.-C. Charlier,
M. S. Dresselhaus, R. Saito, M. Endo, Y. A. Kim, T. Hayashi, and M. A. Pimenta
Submitted for publication (Phys. Rev. Lett. - 2006).
Main collaborations
Profs M. Terrones and H. Terrones, IPICYT, San Luis Potosi, MEXICO
Prof. M.S. Dressehaus and Dr. G. Dresselhaus, Massachusetts Institute of Technology, USA
Prof. Pulickel M. Ajayan, Rensselaer Polytechnic Institute, New York, USA
Prof. Morinobu Endo, Faculty of Engineering, Shinshu University, JAPAN
Prof. Florian Banhart, Universitt Mainz, GERMANY
Dr. Eduardo Hernandez, Universidad Autonoma de Barcelona, SPAIN
Dr. Vincent Meunier, Oak Ridge National Laboratories, USA
Main funds
Research Training Network, contract N HPRN-CT-2000-00128, COMELCAN : coupled
mechanical and electronic properties of carbon nanotubes based systems , 2000–2003.
Ple dAttraction Interuniversitaire P5/01, Quantum size effects in nanostructured materials (UCL-FUNDP-KUL-RUCA-UIA) 2002–2006.
European Network of Excellence (N NMP3-CT-2004-500159) FAME : Functionalized Advanced Materials and Engineering : Hybrids and Ceramics 2004–2008.
European Network of Excellence (N NMP4-CT-2004-500198), NANOQUANTA : Nanoscale Quantum Simulations for Nanostructures an Advanced Materials 2004–2008.