Silicon dominates the electronics industry, yet creating amorphous silicon layers on crystalline silicon substrates typically relies on ion implantation or plasma‐based methods. Ultrafast laser pulses offer a promising alternative for localized amorphization, but achieving uniform transformations on large areas by consecutive pulses remains challenging, particularly at near‐infrared wavelengths where the fluence window for amorphization before material damage is relatively narrow. In this work, we investigate the use of deep‐ultraviolet (DUV, 258 nm) femtosecond pulses for producing continuous, uniform amorphous layers on Si(100) and Si(111). Single‐ and multi‐pulse threshold analyses reveal that DUV provides a fluence window for amorphization up to six times larger than at 1030 nm, enabling over 30 successive shots per site without the occurrence of ablation by incubation effects. Using appropriate fluence and overlap conditions, we achieve uniform amorphous lines and areas with thickness of 20–45 nm. Electron microcopy analyses confirm high uniformity and sharp amorphous/crystalline interfaces (<1.5 nm). Time‐resolved reflectivity measurements reveal melting and resolidification dynamics, with melt durations up to 2.5 ns without evidence of a counter‐propagating solidification front. These results establish DUV femtosecond processing as a scalable route for direct writing of ultra‐thin amorphous structures, advancing fabrication techniques for microelectronics and silicon photonics.

Nanoalloys occupy a focal point of research across many fields as, for instance, catalysis, optics, magnetism, quantum technologies and biomedical materials. This special collection provides a panorama of the research ongoing about their synthesis, modelling and applications.

Nanoparticles are widely regarded as optimal for catalytic reactions; however, larger particles with highly active surfaces may offer an intriguing alternative for advancing catalytic technologies. This study employs pulsed laser melting to transform colloidal copper/magnetite nanoparticles into surface-active submicron CuxFe3-xO4-CuyO-CuzFe1-z composite particles, tailored for ethanol oxidation fuel cells. The findings reveal that colloidal particles tend to cluster into either homogeneous or heterogeneous aggregates, mediated by the surrounding liquid. This clustering aids the formation of desired phases during pulsed laser processing. Temperature-dependent thermodynamic phase transitions, combined with pulse-driven heating-cooling dynamics, promote copper oxidation and magnetite reduction, achieving both compositional control and microstructural surface activation. The synthesized heterostructures demonstrated excellent performance in ethanol oxidation, both as primary catalytic materials and as activity-enhancing supports for platinum. Oxidation state analysis post electrocatalysis indicated a reduction in graphite bonds and an increase in oxygen bonds, attributed to the high oxygen content of the catalysts' surface. The electrocatalysis ethanol oxidation process generated potent oxidizing agents, including ozone, oxygen and hydroxyl radicals, with the ability of degrading the sp2 hybrid structure of graphite. Despite their submicron size, the kinetically activated composite particles exhibited exceptional surface activity, positioning them as cost-effective alternatives to the conventional catalysts for fuel cell technologies.

The development of high-performance biomedical implants requires a deep understanding of the molecular interactions between water molecules and titanium (Ti) surfaces. In this study, fully atomistic molecular dynamics simulations were used to study the static and dynamic wetting behavior of water nanodroplets on both flat and femtosecond laser-induced nanotextured Ti surfaces. Our findings reveal a clear transition from Wenzel to Cassie-Baxter wetting states as surface roughness increases, significantly affecting droplet spreading. We also observe the damping of nanodroplet vibrations and a roughness-dependent shift toward hydrophobicity, driven by stronger atomic interactions between water molecules and surface atoms. Furthermore, the interaction energy between water droplets and nanotextured Ti surfaces decreases with increasing roughness, reinforcing the observed changes in wettability. The discrepancies observed between classical wetting models and nanoscale behavior emphasize the limitations of current theoretical approaches and the importance of developing more advanced models. This study provides valuable insights into optimizing Ti surface properties for improved implant performance through controlled wettability.

Nanoparticle assembly, alloying and fragmentation are fundamental processes with significant implications in various fields such as catalysis, materials science, and nanotechnology. Understanding these processes under fast heating conditions is crucial for tailoring nanoparticle properties and optimizing their applications. For this, we employ molecular dynamics simulations to obtain atomic-level insights into nanoparticle behavior. The performed simulations reveal intricate details of sintering, alloying and fragmentation mechanisms shedding light on the underlying physical phenomena governing these processes. The calculation results help to visualize nanoparticle evolution upon undercritical and supercritical heating elucidating not only the role of temperature, but also of nanoparticle sizes and composition. In particular, it is shown that surface tension and surface energy play important roles not only in nanoparticle melting but also in its fragmentation. When the added energy exceeds a critical threshold, the nanoparticle begins to experience alternating compression and expansion. If the tensile stress surpasses the material's strength limit, fragmentation becomes prominent. For very small particles (with radius smaller than ∼10 nm), this occurs more rapidly, whereas sub-nano-cavitation precedes the final fragmentation in larger particles, which behave more like droplets. Interestingly, this effect depends on composition in the case of AuNi alloy nanoparticles, as expected from the phase diagrams and excess energy. The heating level required to overcome the mixing barrier is also determined and is shown to play an important role in the evolution of AuNi nanoparticles, in addition to their size. Furthermore, our findings provide insights into controlling nanoparticle synthesis for various applications in numerous nanotechnological domains, such as catalysis, sensors, material analysis, as well as deseas diagnostics and treatment. This study bridges the gap between experimental observations and theoretical predictions paving the way for designing advanced nanomaterials with enhanced functionalities.

Femtosecond laser allows the production of THz radiation that is very promising for the imaging of various tissues and, namely, for in vivo cancer detection. Despite numerous very convincing experimental demonstrations, the mechanisms involved in image formation are still under discussion. In this paper, based on modeling, we analyze the major physical processes involved in THz laser interactions with tissues, namely with skin. Particular attention is given to the mechanisms involved in integrated THz imaging with NIR femtosecond laser illumination. An effective medium approach is found to be helpful. The difference in water fraction, pores, and additional nanoparticles and nanorods are shown to play a role in the considered non-invasive optical imaging of skin cancer.

Lasers 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 multi-pulse 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.

Phase formation by pulsed laser irradiation of suspended nanoparticles has recently been introduced as a promising synthesis technique for heterostructures. The main challenge still lingers regarding the exact mechanism of particle formation due to the non-equilibrium kinetic by-products resulting from the localized alternative, fast, high-temperature nature of the process. Here, the authors analyze the bond breaking/formation of copper or copper (II) interfaces with ethanol during the absorption of pulses for Cu-CuO-Cu2O formation applicable as an electrocatalyst in ethanol oxidation fuel cells. This study includes but is not limited to, a comprehensive discussion of the interaction between nano-laser pulses and suspension for practical control of the synthesis process. The observed exponential and logarithmic changes in the content of heterostructures for the CuO-ethanol and Cu-ethanol samples irradiated with different fluences are interpreted as the dominant role of physical and chemical reactions, respectively, during the pulsed laser irradiation of suspensions synthesis. It is also shown that the local interface between dissociated ethanol and the molten sphere is responsible for the oxidative/reductive interactions resulting in the formation of catalytic-augmented Cu3+ by-product, thanks to the reactive bond force field molecular dynamics studies confirmed by ab-initio calculations and experimental observations.

The classical wetting models, such as the Wenzel and Cassie-Baxter have been extensively used to quantify the wettability of laser-textured surfaces. However, these models do not provide any description of the corresponding droplet dynamics. In this work, we propose a detailed continuum-level modelling to study the wetting dynamics of a water droplet on Ti-6Al-4V alloy. The calculations are performed for flat surfaces and surfaces with various reliefs. The calculated evolutions of the droplet spreading parameter for flat surfaces, surfaces with triangular reliefs and one with two different periods and heights not only provide explanations of several experimental results but also underline the perspectives of using complex reliefs for efficient wettability control. Thus, such simulations are shown to be useful in relief design and laser texturing for a wide range of applications, for example, laser treatment of artificial implants and prostheses.

The combination of magnetic and plasmonic properties at the nanoscale promises the development of novel synergetic image-guided therapy strategies for the treatment of cancer and other diseases, but the fabrication of non-contaminated magneto-plasmonic nanocomposites suitable for biological applications is difficult within traditional chemical methods. Here, we describe a methodology based on laser ablation from Fe target in the presence of preliminarily ablated water-dispersed Au nanoparticles (NPs) to synthesize ultrapure bare (ligand-free) core-satellite nanostructures, consisting of large (several tens of nm) Fe-based core decorated by small (mean size 7.5 nm) Au NPs. The presence of the Fe-based core conditions a relatively strong magnetic response of the nanostructures (magnetization of >12.6 emu/g), while the Au NPs-based satellite shell provides a broad extinction peak centered at 550 nm with a long tale in the near-infrared to overlap with the region of relative tissue transparency (650–950 nm). We also discuss possible mechanisms responsible for the formation of the magnetic-plasmonic nanocomposites. We finally demonstrate a protocol to enhance colloidal stability of the core-satellites in biological environment by their coating with different polymers. Exempt of toxic impurities and combining strong magnetic and plasmonic responses, the formed core-satellite nanocomposites can be used in biomedical applications, including photo- and magneto-induced therapies, magnetic resonance imaging or photoacoustic imaging.

The paper presents precise modifications of ZnO:Al thin films with silver nanoparticles by CW laser leading to the improvement of the composite structure and optical properties. The violet laser wavelength (405 nm) was chosen to be far from the plasmon resonance wavelength. The morphology of the obtained ZnO:Al thin films with silver nanoparticles was investigated. It was detected that under an exposure by laser power densities I0 = 0.89 MW/ cm2 and I0 = 1.07 MW/cm2 and scanning velocities Vsc = 100 mu m/s and Vsc = 50 mu m/s, the film structure became denser, the size of ZnO:Al crystallites increased, and the size of silver nanoparticles decreased. The effects of laser radiation on the optical characteristics of the samples were then investigated. Particularly, a blue shift of the plasmon resonance peak and an increase in the bandgap from 3.27 eV to 3.36 eV were obtained. Additionally, numerical modeling was performed based on a photothermal film processing mechanism and clearly explained the observed effects.

Structuring below diffraction limit is key to developing new laser processing technologies as well as to understanding light‐induced processes on mesoscopic scales, notably self‐organization. Here, an advanced numerical perspective on the generation of embedded self‐arranged sub‐wavelength periodic patterns is developed, describing multipulse ultrafast laser interaction with bulk silica glass. Combining light and material dynamics, the approach couples self‐consistently nonlinear propagation, electronic excitation, and fluid dynamics resulting in irreversible phase transitions and localized damage. With increasing the number of applied pulses, the modification changes from localized nanovoids and elongated random nanopatterns toward regular void nanogratings dominantly covering the spot of the focused laser beam. Driven by local and collective scattering events, the order imposed by electric field patterns is then amplified and stabilized by the material response. The model predicts the gradual evolution of the optical properties considering the complex interplay between material arrangement and the electromagnetic field distribution. It allows thus to define light transport optical functions optimizing losses and anisotropic effects.

High-index dielectric metasurfaces can support sharp optical resonances enabled by the physics of bound states in the continuum (BICs) often manifested in experiments as quasi-BIC resonances. They provide a way to enhance light-matter interaction at the subwavelength scale bringing novel opportunities for nonlinear nanophotonics. Strong narrow-band field enhancement in quasi-BIC metasurfaces leads to an extreme sensitivity to a change of the refractive index that may limit nonlinear functionalities for the pump intensities beyond the perturbative regime. Here we study ultrafast self-action effects observed in quasi-BIC silicon metasurfaces and demonstrate how they alter the power dependence of the third-harmonic generation efficiency. We study experimentally a transition from the subcubic to supercubic regimes for the generated third-harmonic power driven by a blue-shift of the quasi-BIC in the multiphoton absorption regime. Our results suggest a way to implement ultrafast nonlinear dynamics in high-index resonant dielectric metasurfaces for nonlinear meta-optics beyond the perturbative regime.

The paper investigates how the surface relief of an implant affects cell behavior. Currently, most implant manufacturers claim the key impact biocompatibility factor to be surface micro-roughness. We suppose that the interaction between cells and implants also depends on such relief peculiarities as continuous or discontinuous topography, subcellular distance between peaks and presence of porous oxide layer. We have developed the laser processing conditions that provide three different reliefs: "open grooves", "grid" and "close grooves". Along with the micro-roughness characteristics the reliefs differ with their deepness and period of grooves. The surface composition analysis results have shown a sandwich structure consisting of Ti -> TiO -> Ti2O3Nx -> TiO2 (anatase) -> TiO2 (rutile). The wettability study has demonstrated superhydmphilicity (CA is 0 degrees) for all reliefs. The quantitative and qualitative analysis of hMSCs proliferation and osteogenic differentiation was performed for 20 days. In vitro study has revealed the topography affects the spatial orientation of cells. The shape and size of the cell nuclei vary with different topographies. We have found continuous "open grooves"structures with the subcellular to cellular period are beneficial for cells' life-sustaining activity. Discontinuous "grid" structures with individual slots might not provide cells with mobility with the least external mechanical effect compared to "open grooves".

We observe a blueshift of the generated third-harmonic signal on subpicosec-ond timescales enabled by multiphoton absorption in resonant silicon metasurfaces. We demonstrate a transition from a super-cubic to sub-cubic regime for the third-harmonic generation efficiency.

Femtosecond laser texturing is a promising surface functionalization technology to improve the integration and durability of dental and orthopedic implants. Four different surface topographies were obtained on titanium-6aluminum-4vanadium plates by varying laser processing parameters and strategies: surfaces presenting nanostructures such as laser-induced periodic surface structures (LIPSS) and ‘spikes’, associated or not with more complex multiscale geometries combining micro-pits, nanostructures and stretches of polished areas. After sterilization by heat treatment, LIPSS and spikes were characterized to be highly hydrophobic, whereas the original polished surfaces remained hydrophilic. Human mesenchymal stem cells (hMSCs) grown on simple nanostructured surfaces were found to spread less with an increased motility (velocity, acceleration, tortuosity), while on the complex surfaces, hMSCs decreased their migration when approaching the micro-pits and preferentially positioned their nucleus inside them. Moreover, focal adhesions of hMSCs were notably located on polished zones rather than on neighboring nanostructured areas where the protein adsorption was lower. All these observations indicated that hMSCs were spatially controlled and mechanically strained by the laser-induced topographies. The nanoscale structures influence surface wettability and protein adsorption and thus influence focal adhesions formation and finally induce shape-based mechanical constraints on cells, known to promote osteogenic differentiation.