Laser-induced Structural Modifications Research Articles

Evaluation of microscale crystallinity modification induced by laser writing on Mn3O4 thin films

Defining microstructures and managing local crystallinity allow the implementation of several functionalities in thin film technology. The use of ultrashort Bessel beams for bulk crystallinity modification has garnered considerable attention as a versatile technique for semiconductor materials, dielectrics, or metal oxide substrates. The aim of this work is the quantitative evaluation of the crystalline changes induced by ultrafast laser micromachining on manganese oxide thin films using micro-Raman spectroscopy. Pulsed Bessel beams featured by a 1 μm-sized central core are used to define structures with high spatial precision. The dispersion relation of Mn3O4 optical phonons is determined by considering the conjunction between X-ray diffraction characterization and the phonon localization model. The asymmetries in Raman spectra indicate phonon localization and enable a quantitative tool to determine the crystallite size at micrometer resolution. The results indicate that laser-writing is effective in modifying the low-crystallinity films locally, increasing crystallite sizes from ∼8 nm up to 12 nm, and thus highlighting an interesting approach to evaluate laser-induced structural modifications on metal oxide thin films.

Electrical and Optical Properties of Laser-Induced Structural Modifications in PbSe Films

PbSe chalcogenide films are widely used as photosensitive elements in gas analysis devices. High absorption in the IR spectrum region and low electrical resistance are important characteristics. Continuous laser radiation exposure of films in the near UV range makes it possible to achieve the desired characteristics, replacing oven heat treatment in the technological process. In the considered laser technology, PbSe films are subjected to photothermal action by a spot of focused radiation in the progressive scanning mode. In this work, changes in the optical and electrical film properties were studied, and the mechanism of structural laser modification was also considered.

High-Density Nanowells Formation in Ultrafast Laser-Irradiated Thin Film Metallic Glass

HighlightsUltrafast laser-induced nano-topography modifications: generation of highly concentrated 20 nm diameter nanowells on the surface with expected applications for storage of chemical and biological active species and for blocking crack propagation.Ultrafast laser-induced structural modifications: turning of a metallic glass to a composite material of monoclinic zirconia crystallites embedded inside amorphous metallic glass.A flexible one-step laser irradiation process without direct mechanical contact for thin film metallic glasses surface functionalization.

Ultrafast Laser Processing of Diamond Materials: A Review

Diamond laser engineering is of great importance for designing devices, which find applications in radiation sensing and quantum technologies. A review of the present state of the art of experimental and theoretical studies on ultrashort laser irradiation of diamond is presented. For a wide range of laser parameters, the optimization of laser-induced electronic, optical and structural modifications of diamond requires quantitative understanding of the microscopic processes underlying the high electronic excitation in the material.

Laser-induced structural modifications of differently aged soot investigated by HRTEM

Laser heating was applied to soot probed in the first inception region (nascent soot) and downstream (mature soot) of premixed methane and ethylene flames, burning in similar temperature and equivalence ratio conditions. Different properties of nascent and mature soot were investigated by TEM/HRTEM and EELS along with elemental analysis, UV–visible and Raman spectroscopy. Structural modifications were followed by HRTEM imaging applied to the soot before and after laser heating. Laser heating produced varied modifications of the lamellae organization dependent upon the morphology of pristine soot, in turn dependent on soot aging and fuel type (ethylene and methane). Specifically, structures in form of void shells versus multifaceted rosette structures were observed in the case of young nascent and mature soot, respectively, showing a relationship with their different nanostructures, namely amorphous versus disordered turbostratic structures. Additionally, the differentiation between void shells or multifaceted rosette structures can be used as signature for the occurrence of laser heating effects, which have to be avoided when the laser is instead employed for diagnostic purposes.

Ionization behavior and dynamics of picosecond laser filamentation in sapphire

Currently, laser-induced structural modifications in optical materials have been an active field of research. In this paper, we reported structural modifications in the bulk of sapphire due to picosecond (ps) laser filamentation and analyzed the ionization dynamics of the filamentation. Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material. The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track. By increasing laser energy, the length of the damage and filamentary track appeared to increase. In addition, the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations, but no increase in the filamentary zone diameter was observed with increasing laser energy.

Laser induced surface and structural modification of germanium in liquid environments

Laser-induced surface and structural modifications of germanium (Ge) in liquid environments of deionized water and ethanol have been investigated. Single crystal Ge (100) has been exposed by KrF excimer laser at four different fluences. Scanning electron microscope analysis reveals the formation of cavities, cracks, and ripples in case of ablation in deionized water, whereas the formation of cavities, ridges, and pores is observed in case of ablation in ethanol. The distinctness, density, and size of cavities are significantly larger in deionized water as compared to ethanol. It is attributed to lower absorption coefficient of deionized water (0.2 × 10−2/mm) as compared to ethanol (1.2 × 10−2/mm) for 248 nm, and consequently, more energy deposition to Ge takes place in the case of ablation in deionized water as compared to ethanol. Fourier transform infrared spectroscopy shows the formation of C-H stretching vibration band in case of ethanol at two moderate fluences. Raman spectroscopy reveals that only G...

Thermo-elasto-plastic simulations of femtosecond laser-induced structural modifications: Application to cavity formation in fused silica

The absorbed laser energy of a femtosecond laser pulse in a transparent material induces a warm dense matter region relaxation of which may lead to structural modifications in the surrounding cold matter. The modeling of the thermo-elasto-plastic material response is addressed to predict such modifications. It has been developed in a 2D plane geometry and implemented in a hydrodynamic Lagrangian code. The particular case of a tightly focused laser beam in the bulk of fused silica is considered as a first application of the proposed general model. It is shown that the warm dense matter relaxation, influenced by the elasto-plastic behavior of the surrounding cold matter, generates both strong shock and rarefaction waves. Permanent deformations appear in the surrounding solid matter if the induced stress becomes larger than the yield strength. This interaction results in the formation of a sub-micrometric cavity surrounded by an overdense area. This approach also allows one to predict regions where cracks may form. The present modeling can be used to design nanostructures induced by short laser pulses.

Laser-induced Structural Modifications inside Glass Using a Femtosecond Laser and a CO₂ Laser

Laser-induced Structural Modifications inside Glass Using a Femtosecond Laser and a CO₂ Laser

Thermal response and optical absorptance of metals under femtosecond laser irradiation

A detailed study on correlation between residual thermal response of a sample and its optical absorptance change due to laser-induced sur-face structural modifications in multi-shot fem-tosecond laser irradiation is performed. Ex-periments reveal an overall enhancement for residual thermal coupling and absorptance in air. Surprisingly, residual thermal coupling in air shows a non-monotonic dependence on pulse number and reaches a minimum value after a certain number of pulses, while these behaviors are not seen in absorptance. In vacuum, how-ever, both suppression and enhancement are seen in residual energy coupling although ab-sorptance is always enhanced. From these ob-servations, it appears that air plasma plays a dominant role in thermal coupling at a relatively low number of applied pulses, while the forma-tion of craters plays a dominant role at a high number of pulses.

Shot-to-shot correlation of residual energy and optical absorptance in femtosecond laser ablation

In this paper, we perform a shot-to-shot detailed study of how residual thermal energy correlates to the optical absorptance change due to laser-induced surface structural modifications in multi-shot femtosecond laser ablation. We observe an overall enhancement for residual thermal coupling and absorptance in air. Surprisingly, residual thermal coupling in air shows a non-monotonic dependence on pulse number and reaches a minimum value after a certain number of pulses, while these behaviors are not seen in absorptance. In vacuum, however, both suppression and enhancement are seen in residual energy coupling although absorptance is always enhanced. To explain these observations, we suggest that air plasma plays a dominant role in thermal coupling at a relatively low number of applied pulses, while the formation of a cavity plays a dominant role at a high number of pulses.

Laser-induced structural modifications in nanocrystalline silicon/amorphous silicon dioxide superlattices

We calculate and experimentally detect the laser melting threshold in nanocrystalline Si/amorphous SiO2 superlattices. Using laser energy density slightly above the melting threshold, we observe two types of laser-induced structural modifications: (i) disappearance of nanocrystalline Si phase in the samples with thin (∼2nm) SiO2 layers and (ii) amorphization of Si nanocrystals in the samples with thicker (⩾5nm) SiO2 layers. The observed Si nanocrystal amorphization increases optical absorption and intensity of visible photoluminescence in nanocrystalline Si/amorphous SiO2 superlattices.

Laser-induced structural modifications ofFeMoCuB metallic glasses before and after transformation into ananocrystalline state

The effects of laser treatments on the structural and magneticproperties of metallic ribbons have been studied using the melt-spunFe76Mo8Cu1B15 alloy in as-quenched andnanocrystalline states. 57Fe Mössbauer effect techniques,comprising transmission geometry measurements (TM) and detection ofconversion electrons (CEMS), have been employed in addition tomagnetization measurements, differential scanning calorimetry andx-ray diffraction. The Curie temperature of the as-quenched alloy wasabout 70 °C. The distributions of hyperfine magnetic fields aswell as quadrupole splitting obtained from TM and CEM spectra haverevealed the possibility of observing laser-induced structuralmodifications even at room temperature when the system is only weaklymagnetic. Consequently, both types of hyperfine interactions havebeen detected and they are nearly in equilibrium (having the samestrength or occurring to the same extent). After treatments with apulsed XeCl excimer laser (with a homogeneous beam of 5×5 mm2, 308 nm, 55 ns, 1 Hz), the significance of magneticdipole interactions rises as a function of the number of laser pulses(up to 64) and the laser beam fluence (up to 3 J cm-2). Notraces of laser-induced crystallization have been found. In thenanocrystalline Fe76Mo8Cu1B15 alloy, surfacecrystallization was already completely removed after the first pulseof 1 J cm-2.

Characterization of diamond-like carbon films before and after pulsed laser irradiation

In this work, we correlate the structural properties of DLC films with their photoelectric properties. DLC layers are deposited on silicon wafers by RF plasma-assisted chemical vapor deposition (RF PACVD). The films are irradiated with picosecond Nd 3+-YAG laser pulses at different wavelengths (213 and 266 nm) and energies (few μJ to mJ). Photoelectric sensitivity values are reported and compared with those of metals. The DLC coatings are characterized before and after irradiation by IR spectroscopy, micro-Raman spectroscopy and ellipsometry in order to observe laser-induced structural modifications of the layers. In situ measurements of work function variations at the surface induced by laser pulses are also reported.

Laser-induced structural modifications of glassy carbon surfaces

Structural modifications induced by pulsed laser irradiations in the surface layers of glassy carbon have been monitored by reflection high energy electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy. The glassy carbon samples were irradiated by 30 superimposed laser pulses (λ́=6.943 nm). The energy density (100–500 mJ/cm2 per pulse) delivered to the material and the repetition rate of the laser (0.05 Hz) have been chosen so that the temperature increase of the irradiated surface layers was below the melting point of the glassy carbon. The combined use of the analysis techniques indicated that the beginning of the solid state processes, leading to microstructural modifications of the surface layers, occurs at energy density of 300 mJ/cm2. An increase of the average crystalline size of graphitic clusters occurs upon radiation performed at fluences of 300 and 400 mJ/cm2, whereas at higher energy density the material undergoes complete amorphization. The analysis of chemical state and microstructure of the irradiated samples clearly demonstrates that graphitization or, conversely amorphization of glassy carbon surface layers can be achieved by a proper choice of the laser irradiation conditions.