Outer Nanotube Research Articles

Coulomb blockade oscillation in a multiwalled carbon nanotube with internanotube tunnel junctions

Internanotube charge transport in a multiwalled carbon nanotube (MWNT) was investigated. We directly measured electrical transport from the outer nanotube to the inner nanotubes in a MWNT with two electrodes. The outer nanotubes between the two electrodes were disconnected, leaving the innermost nanotube, so that the current flows into the innermost nanotube via the internanotube junctions. The transport properties of this device clearly showed Coulomb blockade oscillation with a charging energy of 15 meV at 4.2 K. The observed Coulomb blockade oscillation was nonperiodic to the gate voltage, indicating that the multiple internanotube tunnel junctions were formed underneath the electrodes.

Chemistry of Carbon Nanotubes

Judicious application of site-selective reactions to non-aligned and aligned carbon nanotubes has opened a rich field of carbon nanotube chemistry. In order to meet specific requirements demanded by particular applications (e.g. biocompatibility for nanotube biosensors and interfacial strength for blending with polymers), chemical modification of carbon nanotubes is essential. The tips of carbon nanotubes are more reactive than their sidewalls, allowing a variety of chemical reagents to be attached at the nanotube tips. Recently, some interesting reactions have also been devised for chemical modification of both the inner and outer nanotube walls, though the seamless arrangement of hexagon rings renders the sidewalls relatively unreactive. This review provides a brief summary of very recent progress in the research on chemistry of carbon nanotubes.

An atomic-scale analysis of catalytically-assisted chemical vapor deposition of carbon nanotubes

Growth of carbon nanotubes during transition-metal particles catalytically-assisted thermal decomposition (also referred to as chemical vapor deposition or CVD) of methane in hydrogen as a carrier gas has been analyzed at the atomic scale using a kinetic Monte Carlo method. The method is parameterized by the rates of various nanotube surface and edge reactions (e.g. adsorption of hydrocarbons and hydrogen onto the surface of the transition-metal particles and onto the surface of carbon nanotubes, carbon atom attachment to the growing end of nanotubes, nucleation and growth of the outer nanotubes walls, etc.). Simulations of the carbon nanotubes growth are found to yield predictions regarding the effect of nominal and local processing conditions on the nanotubes morphology and growth rates in very good (qualitative and quantitative) agreement with their experimental counterparts. In addition, formation of new walls during growth is found to take place quite readily suggesting that the fabrication of single walled carbon nanotubes by CVD may be a formidable task.

Anomalous potential barrier of double-wall carbon nanotube

The stable structure of a double-wall carbon nanotube (DWNT) is calculated for various chirality pairs, (n,m) – (n ′,m ′) , of inner and outer constituent layers. The stability of a double-wall nanotube is found not to depend on chirality, but rather on the diameter difference between inner and outer layers. However, the potential barrier for the relative displacement of the inner and outer nanotube layers is found to depend significantly on the chirality difference of the pair. Mechanical motions like a bolt–nut pair or discrete rotations can be expected for special pairs of chiralities in double-wall nanotubes, and these special motions will be important for nano-technology.

Axially compressed buckling of a doublewalled carbon nanotube embedded in an elastic medium

An elastic double-shell model is presented for infinitesimal buckling of a double-walled carbon nanotube embedded in an elastic matrix under axial compression. The analysis is based on a Winkler model for the surrounding elastic medium and a simplified model for the van der Waals interaction between the inner and outer nanotubes. An explicit formula is derived for the critical axial strain, which indicates the effects of the surrounding elastic matrix combined with the intertube van der Waals forces. In particular, the present model predicts that the critical axial strain of the embedded double-walled nanotube is lower than that of an embedded single-walled nanotube under otherwise identical conditions. This implies that inserting an inner tube lowers the critical axial strain of an embedded single-walled carbon nanotube, although the total critical compressive force could be increased due to the increase in the cross-sectional area of the nanotube. The reduced critical axial strain is attributed to the intertube slips between the inner and outer tubes. This result indicates that embedded multi-walled carbon nanotubes could be even more susceptible to infinitesimal axial buckling than embedded single-walled carbon nanotubes.

Resonance Raman Scattering of Multi-Walled Carbon Nanotubes

ABSTRACTMulti-walled carbon nanotubes synthesized by the carbon arc in hydrogen gas have very thin core channels. We have measured resonance Raman scattering of some samples synthesized in different conditions, and have observed radial breathing mode (RBM) peaks from 200 to 500 cm−1. Resonance effect of each peak is similar to that of single-walled nanotube. However, the peak frequencies are about 5 % higher than those of single-walled nanotubes, which is probably due to the inter-layer interaction. Further, the highest RBM peak splits in three peaks. The result on the resonance effect and the zone-folding band calculation suggest that the thinnest core nanotube is (4,3) that have four candidates of second outer nanotubes. This suggests that the different outer nanotube gives different degree of the interlayer interaction.

Docking envelopes for the assembly of molecular bearings

To design a process for the assembly or self-assembly of a nanomachine requires knowing the degree of spatial control needed to put the components together. A useful starting point in this area of study is the concept of a docking envelope, which is a continuous region of initial condition parameter space for which two structures will dock. In this paper docking envelopes, determined from molecular dynamics simulation, are presented for the assembly of a molecular bearing consisting of two concentric carbon nanotubes. In the beginning of each simulation the outer nanotube (sleeve) is held in place and the inner nanotube (shaft) starts far away from, but is given an initial velocity toward, the sleeve. The docking envelope in this case is delineated by the initial offset from a coaxial geometry. In order to address recent concerns about the effects of zero-point energy leakage and chaos in classical simulations of nanomachine components, docking envelopes from two types of simulations are presented: fully atomistic (all degrees of freedom included) and rigid body (each nanotube rigid but shaft allowed to rotate and translate).