Laser-Induced Inter-Diffusion in AuAg Core−Shell Nanoparticles

Abstract

The preparation of gold-silver nanoparticles with a core-shell structure by radiation chemistry is described. The optical properties of particles containing Au cores and Ag shells are compared to those of the reverse system for a variety of overall particle compositions. Nanosecond and picosecond laser-induced heating (at 532 nm) is used to melt the Au core Ag shell particles into homogeneous alloyed nanoparticles. The transition from the kinetically stable core-shell structure to the alloy is demonstrated by TEM and by the spectral changes accompanying melting. It is found that the particles must accumulate many laser pulses to completely mix into the alloy. In the case of nanosecond excitation, alloying and reshaping from faceted and irregular particles into smooth spheres occurs at absorbed energies of 5-6 mJ/pulse, and fragmentation takes place at higher energies, >10 mJ/pulse. In the case of 30 ps laser excitation, the thresholds for alloying/reshaping and fragmentation are lower: 1 and 4 mJ/pulse, respectively. The higher energy threshold for nanosecond excitation compared to the picosecond case is due to dissipation of the absorbed energy to the solvent during excitation, which is estimated to occur on a 100-200 ps time scale. Thus, the temperatures reached in the particles by nanosecond excitation are lower than those achieved by picosecond excitation for equal pulse energies.

Hybridized Organic Nanocrystals for Optically Functional Materials

“…Both deposited Ag NP and Au NP domains formed inside the metal shell are much smaller than the wavelength in vis light, and the effective dielectric constant may correspond to AgAu alloy. That is to say, the LSP in Figure 16b may reflect the dielectric constant of AgAu alloy, 107,108 being not the simply additive extinction spectra from individual Ag NPs and Au NPs. 91 However, the powder XRD pattern has not been measured, because the fcc lattice constant of Au (a = 0.408 nm) is almost the same as that of Ag (fcc: a = 0.409 nm).…”

Photon Emission Spectroscopy of Single Oxide-Supported Ag-Au Alloy Clusters

“…Due to their perfect miscibility and distinct optical properties, they represent a model system to obtain a principle understanding of the alloy formation in small particles. Mixed Ag-Au colloids have been prepared in aqueous solution, 11,[14][15][16][17][18] and solid matrices, such as glass, 12,13 silica, 19 and alumina. 20 Optical absorption and extinction spectroscopy was employed to analyze the cluster ensembles.…”

Hybridization of Polydiacetylene Core and Metal Shell

“…11 (b). Since Ag-and Aunanoparticle domains in the shell are smaller than wavelength, effective dielectric constant of the shell can be regarded as alloy of Ag and Au metals (42,43). As a result, extinction spectra of the present core-shell-type nanoparticles reflected effective dielectric constant of Ag-Au alloy, not the additive extinction spectra from Au and Ag nanoparticles, and PDA nanocrystals.…”