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MSD - Materials Sciences Division

Nanocrystals pass through tiny constrictions unchanged

(a) TEM image of iron nanocrystal inside a multiwalled carbon nanotube. (b) The same section of nanotube after a current has been applied, causing the iron nanoparticle to squeeze into the adjacent constriction. (c) Diffraction pattern for a different iron nanoparticle while moving through a nanotube constriction, confirming its crystallinity.

Scientific Achievement

Observed an iron nanocrystal move through a constriction in a carbon nanotube with a smaller diameter than that of the nanocrystal, without melting or undergoing compression, driven by an electric current

Significance and Impact

A theoretical model based on these findings has implications for both nanomechanics and tunable synthesis of metal nanoparticles.

Summary

A team of researchers at Berkeley Lab and UC Berkeley have observed an iron nanocrystal move through a constriction in a carbon nanotube with a smaller diameter than that of the nanocrystal, driven by an electric current. The team observed the system with in situ transmission electron imaging and diffraction, and found that the nanocrystal did not melt or undergo compression while squeezing through the constriction. Using density functional calculations (DFT) and kinetic Monte Carlo simulations, the researchers determined the pattern of iron atom motion to account for the observed behavior. In their model, iron atoms in the region where the nanocrystal contacts the nanotube migrate to the front of the nanocrystal, carried by the electric current. The resulting concentration gradient drives diffusion of iron atoms from the end of the nanocrystal into the contact region. This theoretical model has implications for both nanomechanics and tunable synthesis of metal nanoparticles.

“Surface Atom Motion to Move Iron Nanocrystals through Constrictions in Carbon Nanotubes under the Action of an Electric Current,” S. Coh, W. Gannett, A. Zettl, M.L. Cohen, and S.G. Louie, Phys. Rev. Lett. 110, 198901 (2013).   DOI: 10.1103/PhysRevLett.110.185901