Ultrafast electron-electron scattering and energy exchanges in noble-metal nanoparticles

Abstract

International audienceThe conduction electron energy exchanges are investigated in gold and silver nanoparticles with average size ranging from 2 to 26 nm, embedded in different matrices. The experimental studies were performed by following the internal thermalization dynamics of photoexcited nonequilibrium electrons with a femtosecond pump-probe technique. The probe wavelength dependent measurements are in qualitative agreement with the results of a theoretical model based on bulk metal electron kinetics and band-structure modeling. In both metals, the measured electron thermalization times are close to the bulk ones for nanoparticles larger than 10 nm and sharply decrease for smaller ones. The results are independent of the nanoparticle environment and synthesis technique showing that the observed size behavior reflects an increase of the efficiency of the electron-electron energy exchanges in small nanoparticles. It is in agreement with a simple model based on a bulk metal approach of the electron kinetics modified to introduce surface effects. The observed increase of the electron-electron interaction with size reduction is ascribed to reduction of the screening of the Coulomb interaction by the conduction and core electrons close to the nanoparticle surface

Role of adsorbates on dynamics of hot-electron (type I and II) thermalization within gold nanoparticles

“…On the opposite, the internally hot thermalized electron gas shows a narrow bleach with a positive absorption for wavelengths longer than 590 nm. The observed differential transient absorption spectra are in excellent accordance with calculations reported in the literature [13,14]. Upon comparison of the spectra recorded at 250 fs and times longer than 3 ps, a time dependent shift of the crosspoint of the signal with the baseline from 630 to 585 nm is clearly observed between these spectra.…”

“…2A and B are fits of the experimental data according to equations (1) and (2), respectively. [14]. In accordance with the information from the nonclassical broadening of the surface plasmon, we attribute the retardation of the internal thermalization to the presence of an additional decay channel for NNEs in these small gold nanoparticles.…”

Hot Adsorbate-Induced Retardation of the Internal Thermalization of Nonequilibrium Electrons in Adsorbate-Covered Metal Nanoparticles

“…At present, the internal thermalization dynamics has been mainly investigated in bulk metals [19][20][21] and naked metal nanoparticles. 22,23 However, until now, information on electronelectron scattering dynamics in adsorbate-covered metal nanoparticles cannot be found in the literature.Here, we wish to address the following question: How can adsorbates affect the dynamical behavior of NEs in a metal? For this purpose, we approach this problem for the first time with adsorbate/metal nanosystems (AMNs) by femtosecond transient absorption spectroscopy.…”

“…At present, the internal thermalization dynamics has been mainly investigated in bulk metals [19][20][21] and naked metal nanoparticles. 22,23 However, until now, information on electronelectron scattering dynamics in adsorbate-covered metal nanoparticles cannot be found in the literature.…”

Characterization of two dimensional self-organized Au nanoparticles embedded in Si3N4

“…Magnetron sputtering has been used for example to prepare films to study nonlinear susceptibility 9,10 and transport properties. 11 Electron beam evaporation 12 or cluster deposition 13 allowed electron dynamics characterization. Ion beam techniques appeared to be successful in embedding metallic NPs in matrices.…”