Europhys. Lett.
Volume 61, Number 6, March 2003
Page(s) 762 - 768
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 March 2003
DOI: 10.1209/epl/i2003-00299-3
Europhys. Lett., 61 (6) , pp. 762-768 (2003)

Time-resolved X-ray diffraction on laser-excited metal nanoparticles

A. Plech1, S. Kürbitz2, K.-J. Berg2, H. Graener2, G. Berg2, S. Grésillon3, M. Kaempfe4, J. Feldmann4, M. Wulff1 and G. von Plessen5

1  ESRF - BP 220, F-38043 Grenoble, France
2  Fachbereich Physik der Martin-Luther-Universität Halle-Wittenberg Friedemann-Bach-Platz 6, D-06108 Halle, Germany
3  ESPCI - 10 rue Vauquelin, F-75005 Paris, France
4  Physics Department and CeNS, University of Munich Amalienstrasse 54, D-80799 München, Germany
5  I. Physikalisches Institut, RWTH Aachen - D-52056 Aachen, Germany

(Received 9 August 2002; accepted in final form 3 January 2003)

The lattice expansion and relaxation of noble-metal nanoparticles heated by intense femtosecond laser pulses are measured by pump-probe time-resolved X-ray scattering. Following the laser pulse, shape and angular shift of the (111) Bragg reflection from crystalline silver and gold particles with diameters from 20 to 100 $\un{nm}$ are resolved stroboscopically using 100 $\un{ps}$ X-ray pulses from a synchrotron. We observe a transient lattice expansion that corresponds to a laser-induced temperature rise of up to 200 $\un{K}$, and a subsequent lattice relaxation. The relaxation occurs within several hundred picoseconds for embedded silver particles, and several nanoseconds for supported free gold particles. The relaxation time shows a strong dependence on particle size. The relaxation rate appears to be limited by the thermal coupling of the particles to the matrix and substrate, respectively, rather than by bulk thermal diffusion. Furthermore, X-ray diffraction can resolve the internal strain state of the nanoparticles to separate non-thermal from thermal motion of the lattice.

61.10.Nz - Single-crystal and powder diffraction.
65.80.+n - Thermal properties of small particles, nanocrystals, nanotubes.
78.47.+p - Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter.

© EDP Sciences 2003

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