Time-resolved spectroscopy of silver nanocubes: observation and assignment of coherently excited vibrational modes

The response of single crystal, cubic silver particles to ultrafast laser-induced heating has been examined experimentally and theoretically. The transient absorption traces display clear modulations due to coherently excited vibrational modes. Nanocube samples with edge lengths smaller than 50 nm s...

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Bibliographic Details
Published in:The Journal of chemical physics 2007-03, Vol.126 (9), p.094709-094709
Main Authors: Petrova, Hristina, Lin, Chien-Hua, de Liejer, Suzanna, Hu, Min, McLellan, Joseph M, Siekkinen, Andrew R, Wiley, Benjamin J, Marquez, Manuel, Xia, Younan, Sader, John E, Hartland, Gregory V
Format: Article
Language:English
Subjects:
CUBIC LATTICES
FINITE ELEMENT METHOD
FREQUENCY MODULATION
LASER RADIATION
MATERIALS SCIENCE
MONOCRYSTALS
NANOSTRUCTURES
PARTICLES
SILVER
SPECTRA
SPECTROSCOPY
TIME RESOLUTION
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Summary:The response of single crystal, cubic silver particles to ultrafast laser-induced heating has been examined experimentally and theoretically. The transient absorption traces display clear modulations due to coherently excited vibrational modes. Nanocube samples with edge lengths smaller than 50 nm show a single modulation, whereas samples larger than 50 nm show two vibrational modes. The results are compared to finite element calculations, where the cubes are modeled as having cubic crystal symmetry with the principal axes parallel to the sides of the particle. The action of the laser pulse is treated in two ways, first, as creating a uniform initial strain. In this case the predominant mode excited is the breathing mode. The period of this mode is in reasonable agreement with the vibrational periods measured for the smaller cubes and with the higher frequency modulation observed for the larger cubes. A nonuniform initial strain is also considered, which could arise from nonuniform heating for particles larger than the optical skin depth of the metal. In this case the predominant mode excited is a nontotally symmetric mode. The calculated periods from this analysis are in reasonable agreement with the lower frequency modulations observed for the larger samples. The results from this study show that, to within the accuracy of these measurements, the elastic constants of cubic silver nanoparticles are the same as bulk silver.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.2672907