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Ultrafast laser spectroscopy has been used to measure the electron-phonon coupling constant in PtAu core-shell bimetallic nanoparticles. A chemical reduction method was used to prepare Pt cores of 12.5 nm diameter and a γ-radiolytic deposition technique was then used to grow Au shells of variable thickness. The resulting nanoparticles have a spectrum that is characteristic of Au. It is found that the electron-phonon coupling time for these hybrid nanoparticles (τ[sub e-ph]∼200 fs) is over a factor of 3 shorter than that for plain Au nanoparticles (τ[sub e-ph]∼650 fs). The faster dynamical response is due to the large electron-phonon coupling constant for Pt, which provides efficient scattering of the excited electrons. Platinum dominates the temporal response, even for a 1:6 molar ratio of Pt to Au, because it has a much larger density of states near the Fermi level compared to Au. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ultrafast laser experiments were used to study electron-phonon coupling in Au nanoparticles in the 2.5 to 8 nm size range in aqueous solution. The electron-phonon coupling constants for these samples were found to be independent of the particle size. This is attributed to a weak interaction between the electron gas and the surface phonon modes in Au. Calculations were performed which show that the coupling between the hot electrons and the surface accounts for less than 10% of the total electron energy losses for these particles. Thus, bulk electron-phonon coupling dominates the relaxation of excited electrons in Au particles, for particles as small as several hundred atoms. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]