Chemical doping of individual semiconducting carbon-nanotube ropes

We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)]

Highly conducting carbon nanotube/polyethyleneimine composite fibers

Single-walled carbon nanotube/ polyethyleneimine (SWNT/PEI) composite fibers are fabricated by coagulation-based spinning of SWNTs dispersed in aqueous solution by various surfactants. The spun SWNT/PEI composite fibers are either solid or hollow (see Figure), and have useful mechanical properties and over a hundred times the electrical conductivity of supertough SWNT/polyvinyl alcohol composite fibers.Partially supported by the Defense Advanced Research Projects Agency Grant MDA972-02-C-0005, the Texas Higher Education Coordinating Board Grant 009741-0130-2003, and the Robert A. Welch Foundation. E. M. acknowledges funding from MEC (Ramón y Cajal Program). B. G. K. acknowledges support from University IT Research Center Project.Peer reviewe

Spin splitting and even-odd effects in carbon nanotubes

The level spectrum of a single-walled carbon nanotube rope, studied by transport spectroscopy, shows Zeeman splitting in a magnetic field parallel to the tube axis. The pattern of splittings implies that the spin of the ground state alternates by 1/2 as consecutive electrons are added. Other aspects of the Coulomb blockade characteristics, including the current-voltage traces and peak heights, also show corresponding even-odd effects.Comment: Preprint, pdf format only, 4 pages including figure

Length sorting cut single wall carbon nanotubes by high performance liquid chromatography

Semi-preparative, HPLC based, size exclusion chromatography (SEC) was used to length sort single wall carbon nanotubes previously cut by an acid based process. In contrast to prior reports of nanotube length separation by gravity fed SEC, mean nanotube lengths in the present study were shorter than the controlled pore glass media pore diameter used (400 nm). The results indicate that prep scale HPLC can provide a viable method for efficient length separation with good resolution. Features observed in the chromatogram are attributed to a dependence of the light scattering efficiency on the lengths of the nanotubes relative to the wavelength of the light used for detection

Method of making ropes of single-wall carbon nanotubes

This invention provides a method of making single-wall carbon nanotubes by laser vaporizing a mixture of carbon and one or more Group VIII transition metals. Single-wall carbon nanotubes preferentially form in the vapor and the one or more Group VIII transition metals catalyzed growth of the single-wall carbon nanotubes. In one embodiment of the invention, one or more single-wall carbon nanotubes are fixed in a high temperature zone so that the one or more Group VIII transition metals catalyze further growth of the single-wall carbon nanotube that is maintained in the high temperature zone. In another embodiment, two separate laser pulses are utilized with the second pulse timed to be absorbed by the vapor created by the first pulse