Posted: Jun 03, 2015 |
Transient melting of a nanocrystal: seeing is believing
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(Nanowerk News) Jesse Clark, working as a postdoc in the LCN group of Ian Robinson, has discovered a spectacular transient melting phenomenon in nanocrystals. Coherent X-ray diffraction experiments, carried out at the LCLS X-ray free electron laser facility at Stanford, have allowed snapshot imaging of a single 300 nm gold nanocrystal in the picosecond time interval after the particle was excited with a laser. The crystal was found to expand uniformly following the excitation and to reach the melting point about 50 ps later ("Imaging transient melting of a nanocrystal using an X-ray laser").
What is striking about the result, shown in the figure, is that the crystal melts from the outside and then re-solidifies in synchrony with the induced acoustic vibrations.
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Imaging transient melting of a nanocrystal using an x-ray laser. Snapshot projection images of a gold nanocrystal, 300nm across, before and after excitation with a femtosecond laser. The second image, 50 picoseconds after excitation, displays a low density skin that returns to the original density at later times
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This result has significant implications beyond our basic understanding of the melting process. A reproducible molten state of a metal such as platinum could have useful catalytic properties, while preserving the integrity and large surface area of the particle.
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Ian Robinson, coordinator of the project said "Bragg Coherent Diffraction Imaging is an emerging X-ray technique with great potential for probing the dynamics of matter. The dynamic imaging of the melting transition, visualised in this work, anticipates a whole new field of materials science in the time domain. I would expect there will be surprise discoveries in the transition regions between classical thermodynamic phases, with the possibility of entirely new transient phases of matter."
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The work was supported by a European Research Council Advanced grant entitled "nanosculpture".
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