Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 $$\upmu $$ μ J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences $$({F}_{\mathrm{th}})$$ ( F th ) and the incubation factor $$(\zeta )$$ ( ζ ) were also determined. Graphic abstract

Femtosecond-Laser-Ablation Dynamics in Silicon Revealed by Transient Reflectivity Change

The dynamics of ablation in monocrystalline silicon, from electron-hole plasma generation to material expansion, upon irradiation by a single femtosecond laser pulse (1030 nm, 300 fs pulse duration) at a wide range of fluences is investigated using a time-resolved microscopy technique. The reflectivity evolution obtained from dynamic images in combination with a theoretical Drude model and a Two-Temperature model provides new insights on material excitation and ablation process. For all fluences, the reflectivity increased to a temporary stable state after hundreds of femtoseconds. This behavior was predicted using a temperature-dependent refractive index in the Drude model. The increase in velocity of plasma generation with increasing fluence was theoretically predicted by the Two-Temperature model. Two ablation regimes at high fluences (>0.86 J/cm2) were identified through the measured transient reflectivity and ablation crater profile. The simulation shows that the fluence triggering the second ablation regime produces a boiling temperature (silicon, 2628 K).

Thermal Stability and Radiation Tolerance of Lanthanide-Doped Cerium Oxide Nanocubes

The thermal and radiation stability of free-standing ceramic nanoparticles that are under consideration as potential fillers for the improved thermal and radiation stability of polymeric matrices were investigated by a set of transmission electron microscopy (TEM) studies. A series of lanthanide-doped ceria (Ln:CeOx; Ln = Nd, Er, Eu, Lu) nanocubes/nanoparticles was characterized as synthesized prior to inclusion into the polymers. The Ln:CeOx were synthesized from different solution precipitation (oleylamine (ON), hexamethylenetetramine (HMTA) and solvothermal (t-butylamine (TBA)) routes. The dopants were selected to explore the impact that the cation has on the final properties of the resultant nanoparticles. The baseline CeOx and the subsequent Ln:CeOx particles were isolated as: (i) ON-Ce (not applicable), Nd (34.2 nm), Er (27.8 nm), Eu (42.4 nm), and Lu (287.4 nm); (ii) HMTA-Ce (5.8 nm), Nd (6.6 nm), Er (370.0 nm), Eu (340.6 nm), and Lu (287.4 nm); and (iii) TBA-Ce (4.1 nm), Nd (5.0 nm), Er (3.8 nm), Eu (7.3 nm), and Lu (3.8 nm). The resulting Ln:CeOx nanomaterials were characterized using a variety of analytical tools, including: X-ray fluorescence (XRF), powder X-ray diffraction (pXRD), TEM with selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS) for nanoscale elemental mapping. From these samples, the Eu:CeOx (ON, HMTA, and TBA) series were selected for stability studies due to the uniformity of the nanocubes. Through the focus on the nanoparticle properties, the thermal and radiation stability of these nanocubes were determined through in situ TEM heating and ex situ TEM irradiation. These results were coupled with data analysis to calculate the changes in size and aerial density. The particles were generally found to exhibit strong thermal stability but underwent amorphization as a result of heavy ion irradiation at high fluences.

Effects of 445 nm, 520 nm and 638 nm Laser Irradiation on the Dermal Cells

Background: The invention of non-ionizing emission devices revolutionized science, medicine, industry, and the military. Currently, different laser systems are commonly used, generating the potential threat of excessive radiation exposure, which can lead to adverse health effects. Skin is the organ most exposed to laser irradiation; therefore, this study aims to evaluate the effects of 445 nm, 520 nm, and 638 nm non-ionizing irradiation on keratinocytes and fibroblasts. Methods: Keratinocytes and fibroblasts were exposed to a different fluency of 445 nm, 520 nm, and 638 nm laser irradiation. In addition, viability, type of cell death, cell cycle distribution, and proliferation rates were investigated. Results: The 445 nm irradiation was cytotoxic to BJ-5ta (≥58.7 J/cm2) but not to Ker-CT cells. Exposure influenced the cell cycle distribution of Ker-CT (≥61.2 J/cm2) and BJ-5ta (≥27.6 J/cm2) cells, as well as the Bj-5ta proliferation rate (≥50.5 J/cm2). The 520 nm irradiation was cytotoxic to BJ-5ta (≥468.4 J/cm2) and Ker-CT (≥385.7 J/cm2) cells. Cell cycle distribution (≥27.6 J/cm2) of Ker-CT cells was also affected. The 638 nm irradiation was cytotoxic to BJ-5ta and Ker-CT cells (≥151.5 J/cm2). The proliferation rate and cell cycle distribution of BJ-5ta (≥192.9 J/cm2) and Ker-CT (13.8 and 41.3 J/cm2) cells were also affected. Conclusion: At high fluences, 455 nm, 520 nm, and 638 nm irradiation, representing blue, green, and red light spectra, are hazardous to keratinocytes and fibroblasts. However, laser irradiation may benefit the cells at low fluences by modulating the cell cycle and proliferation rate.

Unravelling the secrets of the resistance of GaN to strongly ionising radiation

GaN is the most promising upgrade to the traditional Si-based radiation-hard technologies. However, the underlying mechanisms driving its resistance are unclear, especially for strongly ionising radiation. Here, we use swift heavy ions to show that a strong recrystallisation effect induced by the ions is the key mechanism behind the observed resistance. We use atomistic simulations to examine and predict the damage evolution. These show that the recrystallisation lowers the expected damage levels significantly and has strong implications when studying high fluences for which numerous overlaps occur. Moreover, the simulations reveal structures such as point and extended defects, density gradients and voids with excellent agreement between simulation and experiment. We expect that the developed modelling scheme will contribute to improving the design and test of future radiation-resistant GaN-based devices.

The ordering effects of an n-Si defect structure, induced by high fluences of ions with MeV energies

The results of studies of the structural and optical properties of silicon irradiated with light ions of MeV energies with fluences exceeding 1016 cm–2 are generalized. The structure of silicon irradiated with ions is con ventionally divided into several regions (ion path, braking, and outside the braking region), the kind of which is determined by the type of ions, their mass, energy, and temperature during irradiation. It is established that the irradiation with high fluences of light ions of MeV energies causes the formation of ordered layers in the bulk of silicon at depths up to several hundred microns, associated with defects whose properties differ from those of the matrix. It is shown that, under such irradiation conditions, the nature of the defect formation (the number and width of the revealed ordered linear structures and their location relative to the braking region of ions) depends on the mass and energy of ions, the ion beam intensity, the irradiation temperature, and the crystal properties. The effect of the ordering of defects in the form of stress lines and their propagation outside the braking region was discovered, when silicon was irradiated with ions of both hydrogen and helium. It is found that this effect depends on the irradiation intensity and occurs, only when the beam current density is less than 0.45 μA/cm2. It is established that, for silicon irradiated with helium ions in the region of ion path, characteristic is not the monocrystalline, but fragmentary structure, which has an aggregate of ordered stress lines (associated with defects) located in parallel to the braking band of helium ions, and the braking band consists of voids etched as a continuous layer and in the form of separate clusters. It is revealed that the irradiation of dis location silicon with deuterium ions leads to the movement of dislocations during the irradiation and to their crossing of the deuteron braking line due to the formation of stacking faults.

InPAs Alloys Use for Electrical Engineering in Hard-radiation Environment

Effective functioning of electronics in high- radiation environment requires developing of novel semiconductor systems with radiation-tolerant properties. In given work, in search of semiconductor materials with immunity to radiation, investigations have been focused on InPxAs1-x alloys. Investigating of electrical and optical characteristics and physical processes, flowing in heavily irradiated InPxAs1-x alloys under high fluences of high-energy electrons and fast neutrons, let us create new generation of radiation-resistant semiconductor materials for electrical engineering application in hard-radiation environment.

Influence of 25 MeV Si ions and 25 MeV O ions on the chemical and structural properties of PEEK films

Poly (ether ether ketone) (PEEK) material can be used in a wide variety of fields, such as the aerospace, automotive, electronics, and nuclear industries. In this research, the irradiation effect of 25 MeV Si ions and 25 MeV O ions on the PEEK films was studied, focusing on the changes in chemical and structural properties. By analyzing surface morphology and microstructure evolution of the PEEK films after 25 MeV Si ion and 25 MeV O ion irradiation, particles were generated on surface of the PEEK after 25 MeV Si ion irradiation and black dots were generated on surface of the PEEK after 25 MeV O ion irradiation. The irradiation reduced the surface roughness of the PEEK films from the atomic force microscopy (AFM) results. The Fourier transform infrared (FTIR) results indicated that the groups and structure of the material were not changed by irradiation. The X-ray photoelectron spectroscopy (XPS) results showed that the contents of the chemical bonds C–C, C=O increased first and then decreased with the increasing of the fluences. The generated free radicals were observed by the electron paramagnetic resonance spectroscopy (EPR) at room temperature and the irradiation degradation mechanisms were analyzed. Thermal properties of the PEEK irradiated by 25 MeV O ions, indicating that a new secondary crystallization peak was found during the cooling stage. Consequently, the low fluences irradiation improves in the viscoelasticity and mechanical properties of PEEK films, while the high fluences irradiation reduces its performance.

Emergence of anomalous dynamics in soft matter probed at the European XFEL

Dynamics and kinetics in soft matter physics, biology, and nanoscience frequently occur on fast (sub)microsecond but not ultrafast timescales which are difficult to probe experimentally. The European X-ray Free-Electron Laser (European XFEL), a megahertz hard X-ray Free-Electron Laser source, enables such experiments via taking series of diffraction patterns at repetition rates of up to 4.5 MHz. Here, we demonstrate X-ray photon correlation spectroscopy (XPCS) with submicrosecond time resolution of soft matter samples at the European XFEL. We show that the XFEL driven by a superconducting accelerator provides unprecedented beam stability within a pulse train. We performed microsecond sequential XPCS experiments probing equilibrium and nonequilibrium diffusion dynamics in water. We find nonlinear heating on microsecond timescales with dynamics beyond hot Brownian motion and superheated water states persisting up to 100 μs at high fluences. At short times up to 20 μs we observe that the dynamics do not obey the Stokes–Einstein predictions.