Kenneth A. Smith

Gas-phase catalytic growth of single-walled carbon nanotubes from carbon monoxide

Abstract Single-walled carbon nanotubes (SWNTs) have been produced in a gas-phase catalytic process. Catalysts for SWNT growth form in situ by thermal decomposition of iron pentacarbonyl in a heated flow of carbon monoxide at pressures of 1–10 atm and temperatures of 800–1200°C. The SWNT yield and diameter distribution can be varied by controlling the process parameters, and SWNTs as small as 0.7 nm in diameter, the same as that of a C60 molecule, have been generated. This process shows great promise for bulk production of carbon nanotubes.

Catalytic growth of single-wall carbon nanotubes from metal particles

Single-walled carbon nanotubes have been synthesized by the catalytic decomposition of both carbon monoxide and ethylene over a supported metal catalyst known to produce larger multi-walled nanotubes. Under certain conditions, there is no termination of nanotube growth, and production appears to be limited only by the diffusion of reactant gas through the product nanotube mat that covers the catalyst The present invention concerns a catalyst-substrate system which promotes the growth of nanotubes that are predominantly single-walled tubes in a specific size range, rather than the large irregular-sized multi-walled carbon fibrils that are known to grow from supported catalysts. With development of the supported catalyst system to provide an effective means for production of single-wall nanotubes, and further development of the catalyst geometry to overcome the diffusion limitation, the present invention will allow bulk catalytic production of predominantly single-wall carbon nanotubes from metal catalysts located on a catalyst supporting surface.

Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes

Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt.%, which is the highest capacity of any carbon material. Hydrogen is first adsorbed on the outer surfaces of the crystalline ropes. At pressures higher than about 40 bar at 80 K, however, a phase transition occurs where there is a separation of the individual SWNTs, and hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the material of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes.

Elastic strain of freely suspended single-wall carbon nanotube ropes

We have induced large elastic strains in ropes of single-wall carbon nanotubes, using an atomic force microscope in lateral force mode. Freely suspended ropes were observed to deform as elastic strings with tension proportional to elongation. Ropes were elastically deformed over >10 cycles without showing signs of plastic deformation. The maximum strain observed, 5.8±0.9%, gives a lower bound of 45±7u200aGPa for the tensile strength (specifically, yield stress) of single-wall nanotube ropes.

Controlled deposition of individual single-walled carbon nanotubes on chemically functionalized templates

Carbon nanotubes offer great promise as molecular wires because they exhibit high electrical conductivity and chemical stability. However, constructing nanotube-based electronic devices requires a controlled means of assembling the tubes. We report procedures both for producing individual short SWNT segments and for their reliable deposition on chemically functionalized nanolithographic templates. Using this method, we have positioned individual nanotubes at specific locations and orientations in such a way that the nanotubes contact metal electrodes. This discovery is potentially very important for fabrication of simple electrical circuits with nanotubes, and provides a new tool for study of electron transport in nanotubes. q 1999 Elsevier Science B.V. All rights reserved.

Reversible sidewall functionalization of buckytubes

Abstract Single-wall fullerene nanotubes have been made soluble in various organic solvents, including chloroform, methylene chloride, and tetrahydrofuran by covalently attaching alkanes to their sidewalls. Sidewall-alkylated nanotubes are obtained by reacting sidewall-fluorinated nanotubes with alkyl magnesium bromides in a Grignard synthesis or by reaction with alkyllithium precursors. Covalent attachment to the sidewalls was confirmed by UV–visible spectroscopy, which is also used to show that the alkane sidewall groups can be removed by oxidizing them in air to recover pristine nanotubes.

In-plane-aligned membranes of carbon nanotubes

We have produced the first macroscopic objects comprised of highly aligned single-wall carbon nanotubes (SWNTs). These objects are thin membranes prepared by producing a suspension of SWNT segments, introducing the suspension to a strong magnetic field to align the segments, and filtering the suspension in the magnetic field to produce an aligned membrane of SWNT. These membranes exhibited natural cleavage planes parallel to the magnetic field. This preparation of macroscopic samples of aligned single-wall nanotubes permits exploitation of their highly anisotropic properties, and will enable measurement of the electronic, thermal, magnetic, mechanical, and optical properties of bulk nanotube materials.

Orienting Polar Molecules in Molecular Beams. Symmetric Tops

Symmetric‐top molecules exist in various orientations in even very weak electric fields, in contrast to diatomic molecules which are oriented only in fields so large as to be impractical. For symmetric tops these orientations can be separated in an inhomogeneous electric field, and calculations are presented for the separating properties of a hexapole field. The transmission and the final distributions of velocity and orientations have been calculated for several different molecules over a range of conditions. Experimental transmission measurements were made and are in good agreement with calculations. By fitting experimental points to calculated transmission curves dipole moments in good agreement with literature values have been determined. The molecules separated by the hexapole field are experimentally shown to make adiabatic transitions into a homogeneous electric field, providing evidence that the molecules can be oriented in the laboratory reference frame.

Ionization of xenon atoms in high Rydberg states by collision with molecules

Ionization of xenon atoms in single highly excited states ‖nf≳ (where 25⩽n⩽40) by collisions with CCl4, CCl3F, and SF6 has been investigated. Absolute rate constants for Xe+ production are reported together with the identities of the major negatively charged species produced in the collisions. Cross sections determined from these rate constants are also given. The data lend support to the theoretical model, which views such collisions as being dominated by the interaction between the target molecules and the excited electron, with the Xe+ ion core playing a minor role.

Vibrational relaxation times for HF due to collisions with He

Calculations of HF vibrational relaxation times in He have been performed using a theoretical model which treats the HF molecule as a simple harmonic oscillator and approximates the He–HF interaction as a separable product of a Lennard‐Jones function of the intermolecular distance and an empirical exponential function of the internal molecular coordinate. When the two state formula for the relaxation time is used, the results agree with the experimental values of Bott and Cohen near 2600 °K but have a slightly greater slope.