In situ structural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres.

Anna Rosa Ziefuss,Matteo Levantino,Anton Plech,Stefan Reich,Sven Reichenberger

doi:10.1039/c9cp05202j

Abstract

Fragmentation of colloidal 54 nm gold nanoparticles by picosecond laser pulses is recorded by time-resolved X-ray scattering, giving access to structural dynamics down to a 80 ps resolution. Lattice temperature and energy dissipation have been quantified to verify that the maximum applied fluence of 1800 J m-2 heats up the particles close to boiling. Already within 30 ns, particles with significantly lower particle sizes of 2 to 3 nm are detected, which hints towards an ultrafast process either by a thermal phase explosion or Coulomb instability. An arrested growth is observed on a microsecond time scale resulting in a final particle size of 3-4 nm with high yield. In this context, the fragmentation in a NaCl/NaOH solution seems to limit growth by electrostatic stabilization of fragments, whereas it does not modify the initial product sizes. The laser-induced fragmentation process is identified as a single-step, instantaneous reaction.

Highlights

Fragmentation of colloidal 54 nm gold nanoparticles by picosecond laser pulses is recorded by timeresolved X-ray scattering, giving access to structural dynamics down to a 80 ps resolution
1.1 Gold particle colloidal synthesis Gold nanoparticles have been produced by pulsed laser ablation in liquids (LAL) by ablating a gold target in ultra-pure water (MilliQ, Millipore) in a batch chamber with a Nd:YAG laser (Ekspla, Atlantic Series, 10 ps, 1064 nm, 9.6 mJ, 100 kHz, 10 min), containing typically a multimodal size distribution.[39,40,41]
Exemplary Transmission electron micrographs (TEM) images of the educt particles can be found in Fig. 1 together with extinction spectra (Thermo Scientific: Evolution 201 spectrometer) of the educt and product particles below. 1.2 Ex situ analysis of fragmentation Fragmentation for an analysis of the irradiated final particles has been done by a picosecond laser (Edgewave) with 10 ps pulses at 532 nm and 80 kHz

Summary

Introduction

Fragmentation of colloidal 54 nm gold nanoparticles by picosecond laser pulses is recorded by timeresolved X-ray scattering, giving access to structural dynamics down to a 80 ps resolution. The effect of near-field enhancement even led to more exotic and specialized fragmentation, like near-field ablation,[20] which has been discussed in case of rod-like Au nanoparticles.[21] On the other hand, ultrashort-pulse excitation may lead to a non-equilibrium pathway in the phase diagram that eventually would allow to cross the spinodal line of the material.[22] The consequence would be a violent explosion, or spinodal decomposition This may directly lead to small particles with a distribution in sizes. Femtosecond-resolved diffraction experiments on single particles have witnessed such a behaviour.[31]

Methods

Results

Conclusion