物質科学セミナー
2019年５月2７日（月）午後XX時XX分–
3B213プレゼンテーションルーム

Synthesis of ultra-small gold nanoparticles by ns-pulsed laser fragmentationin liquids - Impact of laser intensity and electrolytes onparticle size
A. R. Ziefuß1, S. Reichenberger1, C. Rehbock1, I. Chakraborty2, W. J.
Parak2, S. Barcikowski1
1- Technical Chemistry I and Center for Nanointegration, Duisburg-Essen (CENIDE),
University of Duisburg-Essen, Universitaetsstrasse 7, 45141 Essen

2- Fachbereich Physik und Chemie, CHyN, Universität Hamburg, Luruper Chaussee 149,22607 Hamburg
Pulsed laser fragmentation in liquids (LFL) is a useful tool to tune the particle size of laser-fabricated nanoparticles(NP) [1], yielding ultra-small NP (USNP) with mean diameters < 3 nm. However, adequate process control requires
an understanding of the PLFL mechanisms, which could be affected by the laser parameters, the size of the educt
NP, and the composition of the medium. Typically, the pulse duration is discussed as a decisive criterion ruling thefragmentation process. Commonly, distinctions are made between electronically induced Coulomb explosion forhigh laser peak powers (ultrashort pulses) and thermally induced evaporation for low laser peak powers [2].
Immediately after the laser pulse, the USNPs must be stabilized to prevent coalescence processes. In case NP aresynthesized without organic ligands, electrostatic stabilization by ions, similar to that previously reported for laser
ablation in liquids [3], is anticipated.
In this work, we systematicallyexamined the LFL of AuNP with highintensity nanosecond pulses and aimed
to differentiate effects associated tophysical parameters (laser intensity)and chemical effectors (mediumcomposition). All experiments werecarried out in a liquid flow passage
reactor, which allows a precise controlof the energy input per volume(Figure 1A). In an initial study we
examined to what extent the laser
intensity and the educt particle size
affect the size distribution of theresulting USNP. These findings indicatethat the fragmentation process is a one
pulse and one step event, yielding
monomodal AuNPs in case a pulse
Figure 1: A) Illustration of the fragmentation process [1]. B) Plot of the resulting particle
peak power of 1.62 × 1012 W/m2 issizes after fragmentation with different laser intensities. Squares show the results after
exceeded and all educt particles arefragmentation with a 9 ns laser with 0.1 kHz (‘ns-low-RR’), circles show the result afterlarger than 13.4 ± 2.1 (Figure 1B). In
fragmentation with a 2 kHz, 7 ns laser (‘ns-high-RR’) and triangles the results after PLFL
with a 10 ps laser with 80 kHz (‘ps high-RR’) [1]. C) Mass yield of particles after LFLa second study we examined whether
withpHlaserand‘ns-low-RR’
and differentadditives.
theionic strengthof theaqueous fragmentation medium influences the resulting particle size distributions
and mass yield of NP < 3 nm. We could verify a significant synergism between pH and specific ion effects, yielding
the highest mass yield of USNPs at pH = 10 and at micromolar sodium chloride concentrations. Furthermore, ourfindings indicate that the influence is anion specific, following a direct Hofmeister series (HS) of anions at neutral
pH and an inverse HS in the alkaline regime (Figure 1C).
[1] A. R. Ziefuß, S. Reichenberger, C. Rehbock, I. Chakraborty, W. J. Parak, H. Huang, S. Barcikowski, Laser Fragmentation of Colloidal Gold
Nanoparticles with High-Intensity Nanosecond Pulses Driven by a Single-Step Fragmentation Mechanism with a Defined Educt Particle-SizeThreshold, JPCC, 122 (38), 22125-22136 (2018)[2] S. Hashimoto, D. Werner, T. Uwada, Studies on the interaction of pulsed lasers with plasmonic gold nanoparticles toward lightmanipulation, heat management, and nanofabrication, JPPC, 13, 28-54 (2012)[3] V. Merk, C. Rehbock, F. Becker, U. Hagemann, H. Nienhaus, S. Barcikowski, In situ non-DLVO stabilization of surfactant-free, plasmonic gold
nanoparticles: effect of Hofmeister's anions, Langmuir, 4213–4222 (2014)

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