11-06/07 :: June/July 2011

nanotimes Research

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Fast Fourier transform pattern (left) and high resolution TEM images of the low-chalcocite (green) and high-chalcocite (red) domains in a copper sulfide nanorod. © Image taken at TEAM 0.5, National Center for Electron Microscopy, Berkeley Lab, USA

great interest to a broad range of scientific fields and hold important implications for numerous technolo- gies.

“In nanoscale systems, the energetic barrier to a structural transformation scales with crystal size,” says Alivisatos. “When the size of a nanocrystal is in a regime where thermal energy is comparable to the energy barrier for phase transformation, fluctuations between two stable structures occur at the transition point, and are relevant to many molecular and solid- state phenomena near equilibrium.”

Alivisatos, the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC) Berkeley, is a corresponding author of a paper in the journal Science titled “Observation of Transient Structural-Transformation Dynamics in a Cu2S Nano- rod.” Co-authoring this paper were Haimei Zheng,

Jessy Rivest, Timothy Miller, Bryce Sadtler, Aaron Lindenberg, Michael Toney, Lin-Wang Wang and Christian Kisielowski. “During the phase transitions of copper sulfide between low-chalcocite and high- chalcocite structure, the sulfur ions remain in a rigid lattice frame while the copper ions move within the sulfur ion lattice,” says Haimei Zheng, lead and co- corresponding author of the Science paper.

“We observed where the phase nucleates at the surface of the nanorod and within the core and how the phase transformation propagates,” Zheng says. “We also observed the effects of defects. For examp- le, we observed that a stacking fault creates a barrier for the movement of copper ions and thereby blocks the phase propagation. Such observations provide us with important new insights on the atomic pathways of first order structural transformations.”