Spectroscopy and Dynamics of Nanometer-Sized Noble Metal Particles

Abstract

Electron-phonon coupling in 11 ( 2 nm diameter Au particles and 10 ( 3 nm and 50 ( 10 nm Ag particles has been examined by ultrafast pump-probe spectroscopy. The observed relaxation times are strongly dependent on the pump laser power. At the lowest pump powers used, the time constants for relaxation are 0.8 ( 0.1 ps for the 11 nm Au particles, 1.1 ( 0.1 ps for the 10 nm Ag particles, and 1.0 ( 0.1 ps for the 50 nm Ag particles. The measured relaxation times are similar to those for bulk metals, which implies that there are no size-dependent effects in the dynamics for particles in this size region. The transient absorption/ bleach recovery signals for the particles were modeled using the theory developed by Rosei et al. (Surf. Sci. 1973, 37, 689). These calculations yield the transient absorption spectrum as a function of the temperature of the electron distribution. The time dependence of the electronic temperature after pump laser excitation was calculated using the two-temperature model for electron-phonon coupling. The experimental signal versus time traces at selected wavelengths were then simulated by combining the two calculations. The results from the simulations are in semiquantitative agreement with the experimental results. In particular, the low-power relaxation times are correctly predicted by the model calculations. At very high pump laser power (>5 mJ/cm 2 ) the transient bleach signal for Ag shows an unusual 10 ps growth. This growth is attributed to either a change in the dielectric constant of the surrounding medium due to heat transfer from the particles or thermally induced dissociation of adsorbed molecules.

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.…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…Faster electronic relaxation is attributed to greater electron-phonon coupling [141]. The transfer of energy between hot electrons and the nanoparticles can be observed as coherent vibrational oscillations which are indicative of the breathing modes of the nanoparticle lattice [57,152,153]. The amplitude of the coherent oscillations of HGNs can be correlated to aspect ratio since amplitude is inversely proportional to the electron-phonon coupling constant g [153,154].…”

“…It has been reported that low aspect ratio nanoparticles have g values comparable to their solid counterparts while high aspect ratio ones have enhanced g values [14,85,140,152,182]. In this work, as the aspect ratio increased from 3.5 to 9.5, the g value increased from 1.67 × 10 16 ± 0.22 to 3.33 ± 0.45 × 10 16 W m −3 k −1 , while solid NPs maintained an average g of 1.90 ± 0.20 × 10 16 W m −3 k −1 over a range of diameters (20,40, and 80 nm) [149].…”

“…Following excitation, electrons relax via electron-electron, electron-phonon, and phonon-phonon interactions [9,36,172,194]. During this process, most of the energy is converted to thermal energy [2,152]. Stronger light absorption leads to more heat generation.…”

Highly Sensitive Surface-Enhanced Raman Scattering Sensing of Heparin Based on Antiaggregation of Functionalized Silver Nanoparticles

“…It can provide 10-fold to 100-fold higher SERS signals than the similar Au NPs, which is mainly due to its d-s band gap, is in the ultraviolet (UV) region, giving rise to less damping of the plasmon mode. 30,31 Accordingly, in the present study, we applied SERS technique to the sensitive and selective detection of heparin based on antiaggregation of 4-MPY functionalized Ag NPs upon the presence of protamine. Protamine is a kind of natural peptide with polypositive ion, which has ∼20 charges; 32 its special structure could lead to the aggregation of 4-MPY functionalized Ag NPs, thus resulting in the changes in colors, surface plasmon resonance absorption and Raman intensity of 4-MPY.…”