14 October 2004 Coherent excitation of vibrational modes in nanospheres and nanorods
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Abstract
Ultrafast excitation of metal particles in solution coherently excites the phonon modes that correlate with the expansion coordinate of the particle. The period of the modulations yields information about the average size of the particles if their elastic constants and shape are known, or information about the elastic constants if the average size and shape is known. In this paper we describe recent experiments where we have used time-resolved spectroscopy to examine the elastic constants of: (i) gold nanorods with aspect ratios between 2 and 5; and (ii) spherical gold particles in aqueous solution at very high pump excitation levels. The first set of experiments shows that the elastic moduli (Young's modulus, and the bulk and shear modulus) of gold nanorods are significantly smaller than those of bulk gold. This is attributed to the structure of the nanorods, specifically, that they grown with a five-fold twinned structure. In the second set of experiments essentially the change in the elastic moduli with laser intensity is used to estimate the temperature of the particles. The results show that the particles can reach very high lattice temperatures (approaching the melting point of the metal). Examination of the transient absorption data suggests that the hot particles produce explosive boiling of the solvent in these experiments.
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Gregory V. Hartland, Gregory V. Hartland, Min Hu, Min Hu, Patrick Hillyard, Patrick Hillyard, Hristina Pertova, Hristina Pertova, Xuan Wang, Xuan Wang, } "Coherent excitation of vibrational modes in nanospheres and nanorods", Proc. SPIE 5513, Physical Chemistry of Interfaces and Nanomaterials III, (14 October 2004); doi: 10.1117/12.556012; https://doi.org/10.1117/12.556012
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