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Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

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Figure 6 Electron–phonon dynamics in 48- and 15-nm spherical gold nanoparticlesand gold nanorods with a mean aspect ratio of 3.8. These data suggest that the electron–phononcoupling is independent of the size and shape of gold nanoparticles.in the momentum (and hence phase), they do not change the energy of theexcited electrons.V. PHOTOTHERMAL SHAPE CHANGES OF GOLDNANORODSLarge extinction coefficients of gold nanoparticles and their small massesresult in a significant increase of the lattice temperature even at low laserexcitation powers [several nanojoules (nJ) per pulse]. If the excitationintensity is increased above a few microjoules level, changes of the nanoparticleshape can be observed [26–30]. Figure 7 shows TEM images of goldnanorods before (Fig. 7a) and after (Fig. 7b) exposure to 50-AJ femtosecondlaser pulses at 800 nm. The particles do not precipitate after laser exposurebut, rather, a selective heating of gold nanorods in the aqueous solution leadsto transformation of rodlike particles into particles of almost spherical shape.A comparison of the particle volume before and after laser exposure is shown<strong>Copyright</strong> <strong>2004</strong> <strong>by</strong> <strong>Marcel</strong> <strong>Dekker</strong>, <strong>Inc</strong>. <strong>All</strong> <strong>Rights</strong> <strong>Reserved</strong>.

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