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According to phase transition theory, a solid crystal will fluctuate between two equilibrium structures near the phase transition point before reaching a stable configuration, and that this region of transition broadens in small crystals. To test this theory, Zheng, Alivisatos and their co-authors zapped copper sulphi- de nanorods with an electron beam from the TEAM 0.5 microscope then watched for and saw the pre- dicted fluctuations.

“Before the TEAM microscopes, such details of the fluctuations between two solid-state phases in a nanocrystal could not have been observed,” says Zheng. “Our results should be of interest to theorists attempting to simulate structural transformations in solids as neither a study on bulk materials nor on the ensemble of nanomaterials has the capability of re- vealing such specific features of the phase transition pathways.”

TEAM stands for Transmission Electron Aberration- corrected Microscope. TEAM 0.5 and its sister in- strument TEAM 1.0 are capable of producing images with half-angstrom resolution – less than the diame- ter of a single hydrogen atom. Both microscopes are housed at Berkley Lab in DOE’s National Center for Electron Microscopy (NCEM).

The next step for her, Zheng says, will be to address questions concerning the transport of ions with battery material changes at the electrode/electrolyte inter- face, and structural changes of nanoparticle catalysts.

“Such studies share the same aim of developing mi- croscopic understanding of the structural transforma- tions of materials, especially those that are important for energy applications,” Zheng says. “In situ trans-

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HRTEM micrographs showing the low-chalcocite (left) and high-chalcocite atomic structures of a copper sulfide nanorod. © Image taken at TEAM 0.5, National Center for Electron Microscopy, Berkeley Lab

mission electron microscopy, especially our recent technical advances in dynamic imaging through liquids or gases, as well as at the applied electric bia- sing, provides a powerful tool for such studies.”

Haimei Zheng, Jessy B. Rivest, Timothy A. Miller, Bryce Sadtler, Aaron Lindenberg, Michael F. Toney, Lin-Wang Wang, Christian Kisielowski, A. Paul Alivisatos: Observa- tion of Transient Structural-Transformation Dynamics in a Cu2

S Nanorod, In: Science, Vol. 333(2011), No. 6039, July

08, 2011, Pages 206-209, DOI:10.1126/science.1204713: http://dx.doi.org/10.1126/science.1204713

http://www.lbl.gov

Paul Alivisatos: http://www.cchem.berkeley.edu/pagrp/

National Center for Electron Microscopy: http://ncem.lbl.gov/