Electron dynamics in gold and gold–silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron–phonon relaxation

Abstract

Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electronelectron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band ͑i.e., when the excitation wavelength is 630 or 800 nm͒. However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electronphonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas ͑low excitation powers͒. No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy ͑HRTEM͒ reveals that these gold nanoparticles possess defect structures. The effect of this on the electron-phonon relaxation processes is discussed. 18 nm gold-silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system.

High electrical conductance enhancement in Au-nanoparticle decorated sparse single-wall carbon nanotube networks

“…These are: i) the particle diameter at which, for a given number per unit area, the nanoparticles are in intimate contact and form a continuous metallic pathway larger than an individual nanoparticle, and ii) the diameter that is equal to electron mean free path within the individual nanoparticle. The electron mean free path in bulk Au is approximately 50 nm [42].…”

Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses

“…[25][26][27] The electron-phonon coupling was found to be size 3,7 and shape 7,8 independent for gold nanoparticles in the size range from 8 to 120 nm. The measured electron-phonon relaxation times depend on the laser pump power 2,3,7 and are on the order of a few picoseconds (1-4 ps). [1][2][3][4][5][6][7][8][9][10][11][12][13] The results obtained for the nanoparticles furthermore compare well with the electronphonon coupling constant measured for bulk gold 28 using similar time-resolved laser techniques.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In particular, silver 1,2,9 and gold [2][3][4][5][6][7][8][10][11][12][13] nanoparticles have been studied intensively as they show a strong absorption band in the visible region, which is due to the excitation of the surface plasmon resonance. [25][26][27] The electron-phonon coupling was found to be size 3,7 and shape 7,8 independent for gold nanoparticles in the size range from 8 to 120 nm. The measured electron-phonon relaxation times depend on the laser pump power 2,3,7 and are on the order of a few picoseconds (1-4 ps).…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Time-resolved transient absorption spectroscopy allows one to follow the electronphonon relaxation dynamics in thin metal films [21][22][23][24] and small metal particles. [1][2][3][4][5][6][7][8][9][10][11][12][13] In particular, silver 1,2,9 and gold [2][3][4][5][6][7][8][10][11][12][13] nanoparticles have been studied intensively as they show a strong absorption band in the visible region, which is due to the excitation of the surface plasmon resonance. [25]…”

Interference Effects in Nanocrystalline Systems

“…[1][2][3][4][5] Besides loose nanocrystalline powders, where the above conditions can arise from special growth or coalescence phenomena, [6,7] these effects are important also in polycrystalline aggregates as they can influence the overall properties of the system. [3] Models have been proposed to describe the special condition when the diffracted intensity distributions from small and closely oriented domains overlap in Reciprocal Space (RS), thus affecting the observed powder patterns in different ways.…”