CARBON nanotubes1 are expected to have a wide variety of interesting properties. Capillarity in open tubes has already been demonstrated2–5, while predictions regarding their electronic structure6–8 and mechanical strength9 remain to be tested. To examine the properties of these structures, one needs tubes with well defined morphologies, length, thickness and a number of concentric shells; but the normal carbon-arc synthesis10,11 yields a range of tube types. In particular, most calculations have been concerned with single-shell tubes, whereas the carbon-arc synthesis produces almost entirely multi-shell tubes. Here we report the synthesis of abundant single-shell tubes with diameters of about one nanometre. Whereas the multi-shell nanotubes are formed on the carbon cathode, these single-shell tubes grow in the gas phase. Electron diffraction from a single tube allows us to confirm the helical arrangement of carbon hexagons deduced previously for multi-shell tubes1.

Single-shell carbon nanotubes of 1-nm diameter

The use of individual molecules as functional electronic devices was first proposed in the 1970s (ref 1) Since then, molecular electronics2,3 has attracted much interest, particularly because it could lead to conceptually new miniaturization strategies in the electronics and computer industry The realization of single-molecule devices has remained challenging, largely owing to difficulties in achieving electrical contact to individual molecules Recent advances in nanotechnology, however, have resulted in electrical measurements on single molecules4,5,6,7 Here we report the fabrication of a field-effect transistor—a three-terminal switching device—that consists of one semiconducting8,9,10 single-wall carbon nanotube11,12 connected to two metal electrodes By applying a voltage to a gate electrode, the nanotube can be switched from a conducting to an insulating state We have previously reported5 similar behaviour for a metallic single-wall carbon nanotube operated at extremely low temperatures The present device, in contrast, operates at room temperature, thereby meeting an important requirement for potential practical applications Electrical measurements on the nanotube transistor indicate that its operation characteristics can be qualitatively described by the semiclassical band-bending models currently used for traditional semiconductor devices The fabrication of the three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics

Room-temperature transistor based on a single carbon nanotube

The major part of this chapter has already appeared in [1], but because of the length restrictions (in Science), the discussion on why we think this form is given in only brief detail. This chapter goes into more depth to try to answer the questions of why the fullerenes form themselves. This is another example of the very special behavior of carbon. From a chemist’s standpoint, it is carbon’s ability to form multiple bonds that allows it to make these low dimensional forms rather than to produce tetrahedral forms. Carbon can readily accomplish this and it is in the mathematics and physics of the way this universe was put together, that carbon is given this property. One of the consequences of this property is that, if left to its own devices as carbon condenses from the vapor and if the temperature range is just right, above 1000°C, but lower than 1400°C, there is an efficient self-assembly process whose endpoint is C60.

https://science.sciencemag.org/content/sci/273/5274/483.full.pdf

Crystalline Ropes of Metallic Carbon Nanotubes

CARBON nanotubes are predicted to have interesting mechanical properties—in particular, high stiffness and axial strength—as a result of their seamless cylindrical graphitic structure1–5. Their mechanical properties have so far eluded direct measurement, however, because of the very small dimensions of nanotubes. Here we estimate the Young's modulus of isolated nanotubes by measuring, in the transmission electron microscope, the amplitude of their intrinsic thermal vibrations. We find that carbon nanotubes have exceptionally high Young's moduli, in the terapascal (TPa) range. Their high stiffness, coupled with their low density, implies that nanotubes might be useful as nanoscale fibres in strong, lightweight composite materials.

Exceptionally high Young's modulus observed for individual carbon nanotubes

The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.

http://science.sciencemag.org/content/sci/277/5334/1971.full.pdf

Nanobeam mechanics: Elasticity, strength, and toughness of nanorods and nanotubes

We have carried out an exhaustive search of the energetics of all 87 isomers of the fullerene C44 using an empirical potential function. We find no single structural isomer with exceptional stability, suggesting that the enhanced abundance of this cluster observed in some studies may be due to a mixture of different molecules. We find in general that smaller, more spherical clusters and clusters whose pentagons are more isolated tend to be more stable, although the energy differences are not sufficiently large with our classical potential function to identify a particular criterion that distinguishes the stability of various similar isomers.

Relative Energetics of C44 Fullerene Isomers

Cold fusion enhanced by chemical confinement of deuterons has been suggested as an explanation of recent reports of the production of neutrons in electrochemically-generated palladium deuterides. To test this suggestion local-density-functional cluster calculations were used to study the coulomb barrier between two deuterons within the octahedral cage in crystalline palladium. The calculated repulsive forces were always greater than the corresponding forces between deuterons in molecular D2. These results imply that the room temperature fusion rate at this site is negligible.

Limits of chemical effects on cold fusion

Preliminary report on a local‐density functional study of polysilane chains

O’Keefe, Ross, and Baronavski, using laser vaporization of graphite and time-of-flight mass spectrometric detection have observed enhanced abundances of C+N cluster ions not only for n=50 and 60 but also for N = 44. Stimulated by this experimental result we have carried out a search for unusually stable C44 fullerene isomers. In this search, all possible 87 fullerene isomers of C44 were first generated and then classified according to the number of bonds, p, shared by abutting pentagons. We found that for C44 the minimum value of p is 8 and that there are only two C44 fullerenes with this value of p. Self-consistent geometry optimized calculations at the AM1 level show that these two special C44 fullerene isomers—although differing from one another by only about 0.1 eV in total energy—are over 1.0 eV more stable than any of the other possible 85 fullerene isomers of C44. These self-consistent-field calculations not only single out these two C44 fullerenes for special attention, but also further confirm the instability of abutting pentagons for lower fullerenes (those fullerenes with less than 60 carbon atoms).

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400363813

John W. Mintmire

Papers

Relative Energetics of C44 Fullerene Isomers

Limits of chemical effects on cold fusion

Preliminary report on a local‐density functional study of polysilane chains

Special C44 Isomers

Charge transfer in No2AsF6 intercalated graphite