Tuning the spectral and temporal response in PtAu core–shell nanoparticles

JOSE´ H. HODAK; ARNIM HENGLEIN; GREGORY V. HARTLAND

JOURNAL OF CHEMICAL PHYSICS

Año: 2001 vol. 114 p. 2760 - 2765

0021-9606

Ultrafast laser spectroscopy has been used to measure the electron–phonon coupling constant inPtAu core–shell bimetallic nanoparticles. A chemical reduction method was used to prepare Ptcores of 12.5 nm diameter and a g -radiolytic deposition technique was then used to grow Au shellsof variable thickness. The resulting nanoparticles have a spectrum that is characteristic of Au. It isfound that the electron–phonon coupling time for these hybrid nanoparticles (t e – ph;200 fs! is overa factor of 3 shorter than that for plain Au nanoparticles (t e – ph;650 fs!. The faster dynamicalresponse is due to the large electron–phonon coupling constant for Pt, which provides efficientscattering of the excited electrons. Platinum dominates the temporal response, even for a 1:6 molarratio of Pt to Au, because it has a much larger density of states near the Fermi level compared to Au.