Nucleation and growth of gold nanoparticles initiated by nanosecond and femtosecond laser irradiation of aqueous [AuCl₄]⁻

Abstract

Irradiation of aqueous [AuCl4]− with 532 nm nanosecond (ns) laser pulses produces monodisperse (PDI = 0.04) 5-nm Au nanoparticles (AuNPs) without any additives or capping agents via a plasmon-enhanced photothermal autocatalytic mechanism. Compared with 800 nm femtosecond (fs) laser pulses, the AuNP growth kinetics under ns laser irradiation follow the same autocatalytic rate law, but with a significantly lower sensitivity to laser pulse energy. The results are explained using a simple model for simulating heat transfer in liquid water and at the interface with AuNPs. While the extent of water superheating with the ns laser is smaller compared to the fs laser, its significantly longer duration can provide sufficient energy to dissociate a small fraction of the [AuCl4]− present, resulting in the formation of AuNPs by coalescence of the resulting Au atoms. Irradiation of initially formed AuNPs at 532 nm results in plasmon-enhanced superheating of water, which greatly accelerates the rate of thermal dissociation of [AuCl4]− and accounts for the observed autocatalytic kinetics. The plasmon-enhanced heating under ns laser irradiation fragments the AuNPs and results in nearly uniform 5-nm particles, while the lack of particles’ heating under fs laser irradiation results in the growth of the particles as large as 40 nm.

One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

“…Like PLAL, laser photochemical reduction can produce sub-5 nm Au NPs at room temperature in aqueous solution without added surfactants or stabilizers [30,31]. Laser photochemical reduction is typically performed using laser pulses of picosecond [27][28][29][30] or femtosecond [31][32][33][34][36][37][38][39][40][41][42][43] duration, although optical breakdown of water during micrometer-scale nanosecond UV laser irradiation has been identified [44], and Au NP synthesis with ns pulses at 532 nm was recently reported [43]. Femtosecond laser pulses form plasma primarily through photoionization instead of cascade ionization, which enables precise control over the plasma electron density by varying the laser peak intensity [26].…”

“…Femtosecond laser pulses form plasma primarily through photoionization instead of cascade ionization, which enables precise control over the plasma electron density by varying the laser peak intensity [26]. This ability to control reactive species formation rates with the peak intensity enables substantial control over Au NP size distributions [29,31,35,43].…”

Laser-assisted synthesis of gold–graphene oxide nanocomposites: effect of pulse duration

“…In the absence of GO, we recently reported that photoreduction of [AuCl 4 ] À with 532 nm, 8 ns or 800 nm, 30 fs pulses in water under otherwise similar conditions (average laser power, beam diameter) produce different Au NP size distributions. 47 These results are attributed to the distinct reduction mechanisms induced by the two lasers. Photoreduction with fs lasers is driven by reactive species such as hydrated electrons formed by water photolysis.…”

“…Photoreduction with fs lasers is driven by reactive species such as hydrated electrons formed by water photolysis. [47][48][49][50] In contrast, ns laser pulses induce thermal decomposition of the [AuCl 4 ] À precursor and photothermal autocatalytic reduction in the presence of AuNPs due to the 532 nm laser wavelength being resonant with the surface plasmon resonance of Au. 47 In this work, we report on the role of GO in determining Au NP size distributions, prGO chemical composition, and catalytic activity of Au-prGO nanocomposites produced using ns and fs lasers.…”

X-ray tracking of structural changes during a subnanosecond solid-solid phase transition in cobalt nanoparticles

“…The structure and shape of the nanoparticles is essential for their chemical and magnetic behavior and much effort has been put into techniques to control these properties, both during synthesis and after [11]. As an examples of postsynthesis modification of nanoparticle properties utilizing laser illumination of nanoparticle solutions, illumination with intense nanosecond laser pulses exciting plasmon modes at 532 nm has been shown to give rise to highly monodisperse nanoparticles in the case of Au [12]. For characterizing these processes in more detail, the structural dynamics during pulsed laser heating, melting and resolidification of Au nanoparticles have been measured with time-resolved x-ray scattering experiments [13][14][15], but the direct structural dynamics of a solid-solid phase transition has to our knowledge not been reported.…”