Spectroscopy Beyond the Single-Particle Limit

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Science  05 Jul 2013:
Vol. 341, Issue 6141, pp. 36-37
DOI: 10.1126/science.1240500

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Scientists can now routinely detect and study single molecules and nanoparticles (1). However, direct observation of chemical processes and/or atomic motions in real time remains a challenge, primarily because ultrafast (subpicosecond) time resolution is needed. Optical techniques have recently been developed to study the dynamics of individual molecules or nanoparticles where two laser beams (a pump and a probe) are focused onto a single nano-object under a microscope (2, 3). The spatial resolution of these measurements is limited by the diffraction of light, so that the movements of the individual atoms can only be inferred. On page 56 of this issue, Clark et al. (4) present a study of the lattice motions of individual gold nanoparticles recorded using ultrafast coherent x-ray pulses as a probe. These measurements yield three-dimensional images of the atomic displacements in the particles as a function of time, with a spatial resolution that is orders of magnitude better than what can be achieved with optical microscopes.