Nanoparticle Formation by Laser Ablation and by Spark Discharges — Properties, Mechanisms, and Control Possibilities

Laser ablation (LA) and spark discharge (SD) techniques are commonly used for nanoparticle (NP) formation. The produced NPs have found numerous applications in such areas as electronics, biomedicine, textile production, etc. Previous studies provide us information about the amount of NPs, their size distribution, and possible applications. On one hand, the main advantage of the LA method is in the possibilities of changing laser parameters and background conditions and to ablate materials with complicated stoichiometry. On the other hand, the major advantage of the SD technique is in the possibility of using several facilities in parallel to increase the yield of nanoparticles. To optimize these processes, we consider different stages involved and analyze the resulting plasma and nanoparticle (NP) parameters. Based on the performed calculations, we analyze nanoparticle properties, such as mean size and mean density. The performed analysis (shows how the experimental conditions are connected with the resulted nanoparticle characteristics in agreement with several previous experiments. Cylindrical plasma column expansion and return are shown to govern primary nanoparticle formation in spark discharge, whereas hemispherical shock describes quite well this process for nanosecond laser ablation at atmospheric pressure. In addition, spark discharge leads to the oscillations in plasma properties, whereas monotonous behavior is characteristic for nanosecond laser ablation. Despite the difference in plasma density and time evolutions calculated for both phenomena, after well-defined delays, similar critical nuclei have been shown to be formed by both techniques. This result is attributed to the fact that whereas larger evaporation rate is typical for nanosecond laser ablation, a mixture of vapor and background gas determines the supersaturation in the case of spark

Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes

The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between $0$ and $\sim 4$ ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay dependent decrease of the Low-Spatial-Frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination are quantified individually.Comment: 5 pages, 5 figures, Conference On Laser Ablation (COLA) 2013. The final publication is available at http://link.springer.com. Accepted for publication in Applied Physics

Possible surface plasmon polariton excitation under femtosecond laser irradiation of silicon

The mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated. We demonstrate the transient evolution of the density of the excited free-carriers. As a result, the experimental conditions required for the excitation of surface plasmon polaritons are revealed. The periods of the resulting structures are then investigated as a function of laser parameters, such as the angle of incidence, laser fluence, and polarization. The obtained dependencies provide a way of better control over the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material.Comment: 11 pages, 8 figures, accepted for publication in Journal of Applied Physic

Etude numérique de l'effet de l'oxydation précoce sur la mouillabilité des surfaces traitées au laser

International audienceSurface texturing by direct laser ablation creates micro-and nano-scale roughness on materials, resulting in increased surface area and improved surface energy. In particular, micro-and nanotextured surfaces find numerous applications in virus and bacterial repulsion, including the osseo-intergration process in biomedical implants. Laser treatment is one of the most efficient tools for surface texturing, but it can introduce surface oxidation or chemical modifications that cause changes in wettability over time. Despite the significance of these changes, the underlying reasons are not yet fully understood. To gain further insights into these effects, we performed reactive molecular dynamics (RMD) simulations to understand the effect of early oxidation on laser-treated titanium at different temperatures. The obtained results demonstrate that oxide thickness increases with time. Hence, the TiOx layer grows more quickly in the early stages (0-130 ps) than it does in the later stages (130-300 ps). This condition is brought on by an increase in the TiOx layer and a decrease in O2 diffusion. The obtained results are then used in a series of wetting simulations showing that the presence of oxide makes the droplet behavior less hydrophobic in agreement with experimental observations. Interestingly, because oxide layer thickness rises with time, the contact angle drops down with time, thus the calculated early dynamics of titanium surface oxidation correlates well with the early time-evolution of lasertreated surface wettability.La texturation de surface par ablation laser directe est capable de créer une rugosité à l'échelle micro et nanométrique sur les matériaux, ce qui se traduit par une surface accrue et une énergie de surface modifiée. En particulier, les surfaces micro- et nanotexturées trouvent de nombreuses applications dans la répulsion virale et bactérienne, mais sont également intéressantes pour promouvoir le processus d'ostéo-intégration dans les implants biomédicaux. Le traitement au laser est l'un des outils les plus efficaces pour la texturation de surface, mais il peut introduire une oxydation de surface ou des modifications chimiques qui entraînent des changements de mouillabilité au fil du temps. Malgré l'importance de ces changements, les raisons sous-jacentes ne sont pas encore pleinement comprises. Pour mieux comprendre ces effets, nous avons effectué des simulations de dynamique moléculaire réactive (RMD) pour comprendre l'effet de l'oxydation précoce sur le titane traité au laser à différentes températures. Les résultats obtenus démontrent que l'épaisseur d'oxyde augmente avec le temps. Par conséquent, la couche de TiOx croît plus rapidement dans les premiers stades (0–130 ps) que dans les derniers stades (130–300 ps). Cette condition est provoquée par une augmentation de la couche de TiOx et une diminution de la diffusion d'O2. Les résultats obtenus sont ensuite utilisés dans une série de simulations de mouillage montrant que la présence d'oxyde rend le comportement des gouttelettes moins hydrophobe en accord avec les observations expérimentales. Fait intéressant, parce que l'épaisseur de la couche d'oxyde augmente avec le temps, l'angle de contact diminue avec le temps, ainsi la dynamique précoce calculée de l'oxydation de la surface du titane est bien corrélée avec l'évolution précoce de la mouillabilité de la surface traitée au laser

Laser Ablation - From Fundamentals to Applications

Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser-matter interactions. Many experiments were undertaken to clarify the major ablation mechanisms. At the same time, numerous theoretical studies, both analytical and numerical, were proposed to describe these interactions. These studies paved the ways toward the development of numerous laser applications, ranging from laser micro- and nanomachining to material analysis, nanoparticle and nanostructure formation, thin-film deposition, etc. Recently, more and more promising novel fields of laser applications have appeared, including biomedicine, catalysis, photovoltaic cells, etc. This book intends to provide the reader with a comprehensive overview of the current state of the art in laser ablation, from its fundamental mechanisms to novel applications

Mechanisms of laser-based synthesis and modifications of nanomaterials

International audienceLasers are known to be extremely versatile tools suitable both for the synthesis and modifications of numerous nanomaterials with unique and extremely interesting optical properties suitable for a wide range of applications in various fields ranging from optics and photonics to medical applications. Efficient control over these processes is still challenging and often requires numerical simulations because of the complex interplay of many physical and chemical processes involved that depend on the combination of both material properties and laser parameters. To simulate these processes, multi-physical modeling should be used including electromagnetic, thermal, mechanical, and chemical effects taking place at several time and space scales. Depending on the experimental conditions, nanoparticles can be formed, grow, aggregate, or on the contrary decay, so that a set of transient variations often take place, particularly when multipulse laser irradiation is applied. In the case of short and ultra-short laser pulses, strongly non-linear and time-dependent processes play a role involving not only ionization but also phase transitions, acoustic vibrations, shock waves, as well as void formation, and cavitation. If a considerable energy is released in a very short time, firstly aggregates decay, then nanoparticles are fragmented. Here, based on numerical calculations, the roles of several above-mentioned effects are analyzed. The performed simulations can be used for a better understanding of laser interactions with nanoobjects

Smart Nanohybrids and Multi-Material Nanoparticles: Synthesis, Properties, Modeling and Applications

International audienceMany applications of modern nanotechnology take advantage of various properties of smart nanomaterials, such as optical, thermo-, mecha-no-, magneto-plasmonics, etc., where one property is enhanced or modified due to another [1-3]. Thus, nanoparticle aggregation and fragmentation, formation of bi-metallic, multi-material, alloy, Janus, and/or multi-component nanoparticles pave the way toward extremely wide modification possibilities of their absorption spectra, but also of their physical properties and potential functions in various fields including medicine, solar energy, catalysis, etc. Ultra-short laser pulses are, furthermore, ex-tremely versatile tools well-suitable for nano-particle generation and for the following modi-fications of their sizes, shape, composition, and morphology [2]. Laser absorption and scattering effects rely on their plasmonic properties, but also on their band structure, size, composition, shape, and concentration as well as on the main laser parameters, such as wavelength, intensity, and pulse duration. The following laser-induced phenomena include electronic processes, fast heating, chemical reorganizations, various phase transitions, sintering and/or decomposition, as well as longer relaxation and cooling. Atomistic approaches, such as all-atom molecular dynamics simulations are particularly advantageous for numerical modeling of such systems. In this study, several examples of laser-induced modifications of smart nano-hybrids, nano-alloys, and multi-material nanoparticles will be presented. Firstly, attention is focused on the initial heating stage accompanied by melting, sintering, and/or fragmentation. Then, the cooling is addressed, where phase and species segregation and annealing take place. Size- and composition-dependent particle modifications are thus examined. The obtained results are of interest for the analysis of pulsed laser-induced nanoparticle formation in liquids (PLAL) [1-3], nanoparticle aggregation-fragmentation experiments, sintering, 3D manufacturing, etc.Particularly, bimetallic nanoparticles, such as AgAu, AlAu, CoAu, and FeAu, CoNi are to be considered. Then, attention is focused on more complex nanoformulations, such as raspberry or core-shell Ni@Au, Au@Ni, Co@Au and Au@Co, Fe@Au and their oxides, their structure, optical, magnetic, and chemical properties, as well as their interests for applications such as cancer theranostics and photocatalysis.Keywords: femtosecond laser, molecular dynamics, smart nanohybrids, alloys, catalysis, cancer theranostics, solar cells. Figure 1: Calculated extinction spectra of bare Au NPs (red line), Fe oxide NPs (black line), and core-satellite Au-Fe NPs (green line) and image of nanostructures formed from laser-ablated Au NPs and Fe NPs in liquids. Figure 2: MD simulations of Ni@Au and Au@Ni nanoformulations after laser heating in different regimes.References: [1] Coviello, V., Forrer, D. and Amendola, V., ChemPhysChem 23, no. 21 (2022): e202200136.[2] Popov, A.A., Swiatkowska-Warkocka, Z., Marszalek, M., Tselikov, G., Zelepukin, I.V., Al-Kattan, A., Deyev, S.M., Klimentov, S.M., Itina, T.E. and Kabashin, A.V., Nanomateri-als 12, no. 4 (2022): 649.[3] Swiatkowska-Warkocka, Z. Applied Scienc-es 11, no. 5 (2021): 1978

Multiscale modeling of ultra-short pulsed laser-induced phenomena in transparent solids.

International audienceUltra-short laser pulses provide unique possibilities not only for precise laser treatment of optical materials but also for the fabrication of sub-wavelength structures both on the surface and in the volume of transparent materials. These structures have numerous applications in optics, photonics, telecommunications, medicine, and many other fields. The mechanisms involved are based on material ionization, light propagation, scattering, and absorption. In a multipulse regime, femtosecond laser pulses can induce a set of distributed defects and/or inhomogeneities leading to an additional local field enhancement or to several localized hot spots, accompanied by an additional electronic excitation, nanopore formation, densification, etc. These processes are investigated by using the developed multi-scale modeling that allows explanations of several fascinating effects, such as volume nanogratings and other periodic structure formation. In this talk, modeling details and several simulation results will be presented providing insights into the effects induced by multi-pulse ultrashort laser interactions with initially transparent solid materials. It will be shown how based on the presented analysis, it is possible not only to determine optimal laser parameters but also to predict structure properties