In Situ Observation of Coulomb Fission of Individual Plasmonic Nanoparticles

Abstract

Reshaping plasmonic nanoparticles with laser pulses has been extensively researched as a tool for tuning their properties. However, in the absence of direct observations of the processes involved, important mechanistic details have remained elusive. Here, we present an in situ electron microscopy study of one such process that involves Coulomb fission of plasmonic nanoparticles under femtosecond laser irradiation. We observe that gold nanoparticles encapsulated in a silica shell fission by emitting progeny droplets comprised of about 10–500 atoms, with ejection preferentially occurring along the laser polarization direction. Under continued irradiation, the emitted droplets coalesce into a second core within the silica shell, and the system evolves into a dual-core particle. Our findings are consistent with a mechanism in which electrons are preferentially emitted from the gold core along the laser polarization direction. The resulting anisotropic charge distribution in the silica shell then determines the direction in which progeny droplets are ejected. In addition to yielding insights into the mechanism of Coulomb fission in plasmonic nanoparticles, our experiments point toward a facile method for forming surfaces decorated with aligned dual-gold-core silica shell particles.

In situstructural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres

“…9,25,29,76 A current study reports on the observation of Coulomb fission in silica-shell gold particles, that show a signature of small product droplets ejected after femtosecond excitation. 30 A recent structural resolution of gold particle excitation and fragmentation in air on a substrate has shown a stress-mediated explosion at relatively low fluence just above melting. 31 Such a scenario may not be distinguishable from spinodal decomposition with the fragment size depending on the level of overheating.…”

“…This Coulomb instability (sometimes called 'explosion', referring to a related effect in molecules and clusters 24 ) has been proposed based on observed laser-induced electron ejection 9,25 and is still under debate. [26][27][28][29][30] However, it should not be forgotten that finite-size effects not only encompass thermal properties, but also the spatial mode of fragmentation can be affected by geometry. It has been predicted in simulations that a strain-induced decomposition may be induced, 29 if the photothermal excitation is faster than the particle acoustic eigenmodes.…”

A novel method forin situvisualization of the growth kinetics, structures and behaviours of gas-phase fabricated metallic alloy nanoparticles

“…Aer EAD, the micro-ball shrinks visibly as a portion of its mass has turned into alloy nanoparticles surrounding it. This EAD process has a strong signicance differing from the Coulomb explosion observed previous, [29][30][31][32] i.e. EAD growth process is consecutive and quite controllable instead of random bursts.…”

The fragmentation mechanism of gold nanoparticles in water under femtosecond laser irradiation

“…Individual progeny particles appear suddenly, from one movie frame to the next (200 ms frame duration), suggesting that they are ejected individually, in a process that closely resembles the femtosecond laser-induced fission of gold particles in a silica shell that we previously reported. 30 After they first appear, some of the progeny particles slowly increase in size, suggesting that a solution-mediated growth process occurs. A frequently observed feature of the fragmentation process is that progeny particles surround the parent at a well-defined distance ( Fig.…”