Levantino, M.

Plech, A.

Reich, S.

Reichenberger, S.

Streubel, R.

Ziefuss, A. R.

English

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SCIENTIFIC HIGHLIGHTSCOMPLEX SYSTEMS AND BIOMEDICAL SCIENCES5 9  I  H I G H L I G H T S  2 0 2 2Finding the best e ciency for laser-machining of gold colloidsA detailed understanding of the heating e ciency and property change of colloidal gold nanoparticles during the fragmentation process was missing. Using  X-ray  scattering,  the  local  excitation e ciency of  gold nanoparticles  was  examined on ultrashort timescales. Although the absorption e ciency  is  higher,  the  heating  e ciency  at the plasmon resonance of gold nanoparticles is signi cantly  lower  compared  to  the  intraband excitation. The synthesis of quantum-sized metal particles without any organic impurities can be achieved by laser ablation and laser fragmentation of matter in an inorganic, liquid environment [1]. However, in order to enable  independent and  exible material design, which is  required  for  the  di erent  demands  of  technological applications such as catalysis, the mechanisms and processes that occur during laser excitation, heating and structure transformations of nanoparticles need to be understood [2]. In this work, the excitation (heating) e ciency  of  gold  colloids  by  laser  pulses  was  studied with picosecond time resolution, and was compared for 532 nm under plasmon excitation and 400 nm at interband excitation with 1 ps laser pulses. Plasmon excitation generally shows a higher ground state extinction and absorption (as seen in Figure 48), which is bene cial for resonant applications, where a very local strong electric  eld can be harnessed. The inset in Figure 48 additionally depicts an electron micrograph of the used nanoparticles with an impression of the near- eld that is excited by the incoming polarised laser. Fig. 48: Spectral extinction of a gold colloid of 53 nm particles in water from measurement (crosses) and calculation (line), together with the optical excitation wavelengths (arrows).  The inset depicts some gold nanospheres together with the excited near- eld distribution when illuminated by a linear polarised light source.It was found that the heating of the nanoparticles within several  hundred  picoseconds  a er  laser  excitation, despite  the  higher  absorption  e ciency  at  532  nm (optical plasmon excitation), is considerably lower compared to an interband excitation at 400 nm. Hereby, the particle heating and temperature change, as well as the subsequent structure and size change of the laser-excited nanoparticles, was measured with the help of wide-and small-angle X-ray scattering, respectively, using the laser-pump-X-ray-probe setup at beamline ID09.  At  this  setup,  the  transient  state  of  the  lattice expansion of colloidal gold nanoparticles can be caught with a 50 ps time resolution and be calorically (e.g., by the heating e ciency   compared  to  the  incoming  laser intensity. Figure 49 shows the measured lattice expansion (interpreted as nanoparticle heating) at the two wavelengths and a pump-probe delay of 55 ps, together with a theoretical prediction including the gold expansion coe cient  and  latent  heat.  The  lattice  expansion  is expected to stop at about 1.8 %, where the melting point of gold is reached, and the powder scattering should vanish. Indeed, the increase of the expansion follows the prediction with an onset of melting around 40 – 80 J/m2. Yet, the expansion for 532 nm  green line in Figure 49) shows a much smaller slope than predicted by the absorption coe cient, indicating a lower heating e ciency despite the higher absorptivity.The reason for this behaviour is currently hypothesised to originate from an ultrafast bleaching of the plasmon resonance due to non-equilibrium excitation, as well as yet-to-be-validated additional dissipation channels Fig. 49: Transient lattice expansion of the colloid as a function of applied laser  uence for 400 nm  blue symbols  and 532 nm (green symbols) laser pulses. The lines show the predicted expansion (dashed line for 532 nm) and the  tted expansion for both wavelengths.C O M P L E X  S Y S T E M S  A N D  B I O M E D I C A L  S C I E N C E SS C I E N T I F I C  H I G H L I G H T S6 0 H I G H L I G H T S  2 0 2 2  I PRINCIPAL PUBLICATION AND AUTHORSLow efficiency of laser heating of gold particles at the plasmon resonance - an X-ray calorimetry study, A. Plech (a), A.R. Ziefuss (b), M. Levantino (c), R. Streubel (b), S. Reich (a), S. Reichenberger (b), ACS Photon. 9, 2981-2990 (2022); https:/doi.org/10.1021/acsphotonics.2c00588In situ structural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres, A. Ziefuß (b), S. Reich (a), S. Reichenberger (b), M. Levantino (c), A. Plech (a), Phys. Chem. Chem. Phys. 22, 4993-5001 (2020); https:/doi.org/10.1039/C9CP05202J(a) Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology, Karlsruhe (Germany)(b) Technical Chemistry and CENIDE, University Duisburg-Essen (Germany)(c) ESRFREFERENCES[1] V. Amendola, M. Meneghetti, Phys. Chem. Chem. Phys. 15, 3027-3046 (2013). [2] A.R. Ziefuss et al., Adv. Mat. 2101549 (2021).due  to  the  interaction  of  the  near- eld  with  the nanoscale environment. The study will enhance general understanding of how ultra-short laser pulses and nanoparticles interact and how this interaction can be used to tune the properties of nanoparticles for future applications.The general excitement born out of the ability to access the ultrafast time scales has caused a rush of new ideas, new materials and new instruments. There is clear evidence now that materials can be directed between di erent macroscopic states by using electronic or phononic excitations. One feat in particular has attracted a lot of e ort, namely the control of materials with an ultrashort laser pulse, on pathways unattainable at thermodynamic equilibrium. Recent studies utilising time-resolved optical spectroscopy [1] revealed a size-dependent spin-state switching time and sparked the expectation that transition-metal compounds would obey the rule “the smaller the  aster”, owing to a positive elastic feedback from the expanding lattice on  the  volume-changing  molecules.  At  equilibrium, both the unit cell volume and the concentration of high spin molecules show correlated jumps upon the phase transition from low- to high-spin state at 165 K.In this work, 100-ps X-ray di raction was synchronised to a 1-ps pump laser exciting a charge transfer state to probe the photo-induced dynamics of an Fe(III) compound. The experiments were performed at beamline ID09  in quasi-grazing  re ection geometry at 0.2° incidence angle to enhance the signal from the thin  lm sample and reduce di use background from a bulky substrate (Figure 50). A quantitative  structural  analysis  [2,3] at several time delays allowed to establish a sequence of events in the non-equilibrium dynamics. Interestingly, this material exhibits  a  very  di erent  behaviour  from  the  insulator-to-metal transformation dynamics of an inorganic semiconductor upon propagation of laser-induced, long-range deformations [4]. In the latter case, the phase Temporal decoupling between lattice expansion and molecular spin transition observed with time-resolved X-ray di ractionTime-resolved  X-ray  di raction  was  used  to investigate the photo-induced dynamics in microcrystals of a spin crossover iron complex. By tracking the molecular spin state and the structure of the lattice a er laser photo-excitation, it is demonstrated that the volume expansion precedes the thermo-elastic spin transition in this prototypical system for molecular cooperativity. 

Finding the best efficiency for laser machining of gold colloids

https://publikationen.bibliothek.kit.edu/1000155924/150315047

Finding the best efficiency for laser machining of gold colloids

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