Energy - Research - Department of Materials Science & Engineering

Carbon Nanotube Transparent Conductors

A. A. Green and M. C. Hersam, “Colored semi-transparent conductive coatings consisting of monodisperse metallic single-walled carbon nanotubes,” Nano Letters, in press, 2008.

Carbon nanotubes are promising materials for many high-technology applications due to their exceptional mechanical, thermal, chemical, optical and electrical properties.
In this project, monodisperse metallic single-walled carbon nanotubes (SWNTs) have been incorporated into transparent conductive coatings. In particular, the ability to control nanotube diameter allows optical filtering while maintaining high electrical conductivity. The electrical and optical tunability of these SWNT thin films allow their incorporation into a variety of technologies including photovoltaic devices.

Conductive, flexible carbon nanotube films on plastic substrates. The carbon nanotube films are arranged in order of increasing average diameter. The ability to control nanotube diameter leads to the visible colors that are apparent in the photograph.

This research was supported by the National Science Foundation, U.S. Army, and Sloan Foundation.

Nanoscale precipitates in Aluminum

Aluminum alloys with Li additions (to increase strength and stiffness and to decrease density), and rare earth element (RE) additions (to improve creep resistance) have the potential to replace some heavier Ti-based components in energy generation applications. Addition of Li results in the precipitation of a large volume fraction of the strengthening Al₃Li phase, as well as significantly increasing the elastic modulus and reducing density. Dilute additions of Sc and rare earth elements (RE) to Al result in the precipitation of nanometric ordered Al₃(Sc,RE) precipitates, greatly improving the strength and creep resistance of Al alloys.

M.E. Krug, D.C. Dunand, D.N. Seidman, "Composition Profiles within Al₃Li and Al₃Sc/Al₃Li Nanoscale Precipitates in Aluminum", Applied Physics Letters, 92, 124107 (2008).

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Local electrode atom-probe reconstruction of a doubly aged Al-11.3Li-0.11Sc (at. %) specimen shows 11 single-phase Al₃Li precipitates and 4 core-shell Al₃Sc/Al₃Li precipitates. (Li = blue, Sc = red, Al atoms omitted for clarity).

This research is supported by the United States Department of Energy through Grant No. DE-FG02-98ER45721. The LEAP tomograph was purchased with funding from the NSF-MRI Grant No. DMR-0420532 and ONR-DURIP Grant No. N00014-0400798 programs.

High-strength nanocrystalline alloys

An important aspect of our current research is the study of microstructural stability of high purity nanocrystalline and ultra-fine grain metals under stress. We have seen that a remarkable stress-induced grain growth takes place, whether the applied stress is uniaxial, time dependent (fatigue), or caused by a microhardness indenter. The plots below show the rapid grain growth in a high purity nanocrystalline Cu sample under a Vickers indenter. An initial distribution with average grain size about 20 nm and maximum grain size of about 40 nm, has increased by about a factor of 6 within 10 seconds under the indenter, and is still growing after 30 min. Strangely enough, the growth is even more rapid at liquid nitrogen temperatures! (From, K. Zhang, J.R. Weertman and J.A. Eastmen, Appl. Phys. Lett. 87 (2005) 061921.)

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