Films Adsorbed on Carbon Nanotubes at Low Temperatures

We study the thermodynamic, structural and dynamic properties of a single or a few atomic/molecular layer films adsorbed (deposited) on interesting surfaces. This topic is related to the behavior of matter in one- and two-dimensions (1d and 2d), the crossover from 1d to 2d, and how bulk (3d) matter grows (or doesn't grow) on selected surfaces. The research is done at temperatures between 1.5K and 300 K. At present we are working on films of  Helium, Hydrogen, Neon, Argon and Krypton, relatively simple atoms and molecules, adsorbed on carbon nanotube bundles and on films deposited on a single carbon nanotube. The progression of atoms and molecules (and isotopic varieties) has been chosen because quantum effects become extremely important in the thermodynamic properties of the helium isotopes and the molecular variations of hydrogen.  

Vapor pressure and heat capacity measurements of "films" within the first atomic/molecular layer, done in Seattle, show that on single-wall carbon nanotube bundles, atoms adsorb first on imperfect interstitial channels on the bundles, followed by adsorption on grooves formed by two nanotubes on the outside of a bundle, and finally by adsorption on the outside surface of the bundle, a progression from 1d films to 2d films. Measurements of the structure, mobility, and phonon spectrum of some of the films have been made at the neutron diffraction and inelastic neutron scattering facilities at the Institute Laue-Langevin in Grenoble, France, in collaboration with USA and European scientists. Some of the links on the margin will connect the reader to pdf versions of some of our published articles.

Measurements of adsorption on a single carbon nanotube have not been possible until rather recently. A single layer of atoms on a 2 nanometer diameter tube about a micrometer long has about thirty thousand atoms. In Prof. Cobden's lab (see his web site), single nanotube devices have been built which have the sensitivity to detect a very small fraction of an atomic layer. With these devices we have been able to measure adsorption isotherms of the first layer of Ar and Kr around 77K with a sensitivity of "tens of atoms". We are actively working on these devices, see link on margin for details.

Undergraduate (BS in Physics) and graduate (PhD and MS) students work on these projects.

All the activities of the group are funded by two grants from the National Science Foundation, with Oscar Vilches and David Cobden as co-Principal Investigators.

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Last modified: 9/22/2009 6:49 PM