Laser Ablation Of Metal Targets Research Articles

Ionization of Helium Atoms by Triply Charged Metal Atoms during Laser Ablation of Metals in Superfluid Helium

The applicability of laser ablation of metal targets for obtaining triply charged ions of metal atoms, including low-melting metals, has been experimentally demonstrated. By analyzing the luminescence spectra of a plasma plume during laser ablation of a metal target immersed in superfluid helium, the main channel for the formation of helium ions in plasma at a laser beam power density below the breakdown threshold of the helium medium has been determined. It has been shown that the ionization of helium atoms occurs in two steps, the formation of the HeM3+ ionic complex and the dissociation of the complex via its interaction with a metal atom.

Laser Ablation of Metal Targets in a Liquid by Trains of Nanosecond Pulses

Laser Ablation of Metal Targets in a Liquid by Trains of Nanosecond Pulses

Numerical simulation of magnetizing processes of nickel nanowires and nanoballs grown in superfluid helium

The present work is dedicated to numerical modeling of magnetization processes of Ni nanoparticles ensembles acquired by pulsed laser ablation of metallic target in He II. The characteristic feature of the systems under study is their heterogeneous composition. One fraction of particles is represented by thin nanowires (with diameters of 4 nm strictly) meanwhile the other corresponds to a ball-shaped particles that can obtain diameters from 8 to 500 nm. The model was verified by comparing its calculation results with SQUID-magnetometry data.

Femtosecond laser ablation of metal targets: The physical origin of the power law size distribution of nanoparticles

Near-infrared femtosecond laser is employed to ablate the copper target in vacuum (10−4 Pa). The ejected nanoparticles are collected by a silicon substrate. The 3D profiles of the deposited nanoparticles indicate before resolidification on the substrate they are nanodroplets generated by some phase separation process, such as phase explosion or cavitation. To study the nanoparticles’ generation dynamics and size distribution, the commonly used methods are the molecular dynamics simulation and the Monte Carlo method. However, the former cannot predict the particle size distribution at the final state and the latter cannot provide a clear physical picture. In this paper, taking both the nanoparticles’ generation and ejection into account, an analytical thermodynamic model based on the nanodroplets’ evaporation is proposed. In this model, the nanoparticles’ sizes are redistributed due to the nanodroplets’ evaporation during the flight from the target to the substrate, which provides a clear physical picture and successfully explains the physical origin of the final power law particle size distribution on the substrate. The model bridges the gap between the final size distribution and the thermodynamic generation process of nanoparticles, which will benefit the size control of the ablation-generated nanoparticles.

Laser ablation of metals in salts melts

Laser ablation of metallic targets (Au, Cu, Al) in salts melts (NaNO3, NaNO2, LiNO3) at temperature 300–350 °C is experimentally realized. Laser ablation is accompanied by plasma formation on the target surface. Solid nanocomposites of salts with metallic nanoparticles are characterized with the help of optical spectroscopy and X-ray diffractometry. Extinction spectra of nanocomposites reveal the presence of elongated Au nanoparticles. XRD analysis confirms the presence of metallic Au in nanocomposites.

Synthesis of Ag-loaded TiO<sub>2</sub> multiscale structure by coupling underwater laser ablation with hydrothermal treatment

<p indent=0mm>Due to highly rigid demanding for various functional photocatalysts in energy conversion and environmental applications, TiO₂ stands as one of the most widely studied semiconductors and highlighted for heterogeneous photocatalysts. By splitting water in solar energy conversion cells, it also serves as the promising candidate for photoanode material. The distinguished popularity of TiO₂ is attributed to many advantages, such as relatively high quantum efficiency, low cost, biocompatibility, and high optical and chemical stability. In recent years, controlling the structural parameters of TiO₂ is of particular importance which determines the efficiency and physicochemical properties of the resultant photocatalysts. However, two obvious shortcomings restrict the wide applications of TiO₂. On the one hand, the rapid electron-hole recombination results in low quantum yield, which makes it more difficult to efficiently purify sewage in large scale and concentrated pollutants. On the other hand, due to its wide band gap <sc>(~3.2 eV),</sc> TiO₂ can only take effect in the UV region of the solar spectrum (~5% of the solar energy), while the energy absorption in the range of visible light containing about 45% of the solar energy cannot be captured. In order to extend the spectral range of the TiO₂ response, deposition of noble metals, such as Ag, on TiO₂ serves as one of the effective methods to reduce the chance of electron-hole recombination in photocatalytic process by coupling with the versatile properties of photocatalytic and antibactericidal activities. Ag could contribute to the formation of Schottky barriers at Ag/TiO₂ interfacial contact area, resulting in the reduction of electron-hole recombination in the photocatalytic process. Meanwhile, Ag brings in extra absorption bands at visible light spectra due to surface plasmon resonance (SPR) effect. The spectral range of the response of TiO₂ could be further extended to a much longer wavelength. However, it is found that the controllability of deposition of Ag on TiO₂ surface is weak in the process in regular methods, such as photodeposition, chemical reduction, and thermal impregnation, which usually require complicated equipment or toxic nitrogen for modification of TiO₂ with Ag. Hence, it is desired to explore a simple and nontoxic method to fabricate Ag/TiO₂ composite nanoparticles. Laser ablation is considered as a flexible method to synthesize nanoparticles, offering an alternative green route to well-separated nanoparticles. In this study, a simple, direct and flexible method by coupling pulsed laser ablation with hydrothermal treatment was used to obtain multiscale structured Ag/TiO₂ nanocomposites. Underwater laser ablation of metal targets has the characteristics of instantaneous high temperature and high pressure in heat affected zone due to confinement effect in aqueous condition, while the generated plasma quenched rapidly and formed rich nanostructures. Meanwhile, hydrothermal method shows great convenience for regulating the morphology of nanoparticles, smaller crystal thermal stress, smaller macro defects as well as higher uniformity. By optimizing the sequence of hybrid processing and hydrothermal reaction time, sea urchin structures and dendritic structures of TiO₂ were successfully prepared, enhancing the ultraviolet light absorption by scattering effect in the multiscale structures. Ag nanoparticles were further loaded on TiO₂, avoiding the aggregation and obtaining Ag/TiO₂ composite materials with excellent optical properties. Spherical Ag particles around <sc>20 nm</sc> were dispersedly deposited on the burrs of sea urchin structured TiO₂. Meanwhile, the secondary laser processing provides extra activation energy to further regulate TiO₂ morphology, leading to the formation of dendritic structures. Similar Ag nanoparticles were also successfully deposited or embedded on the surface of TiO₂ dendritic structures in the range of <sc>20–60 nm</sc> width. The crystallinity of as-prepared Ag-loaded TiO₂ is significantly improved by combing the rutile phase of TiO₂ with face-centered cubic structured Ag nanoparticles. The peak of TiO₂ light absorption will be red-shifted in the ultraviolet region and loaded Ag nanoparticles broadens the absorption band in the visible region. Wider absorption spectral band was achieved by Ag/TiO₂ composite with excellent optical properties, which can perform more application prospects in photocatalytic degradation of organic pollutants.

Acoustical monitoring of laser-matter interaction using nanosecond radiation pulses with periodically modulated intensity

Nanosecond laser ablation of metal target under the action of radiation pulses with periodically modulated intensity is investigated. Generated pressure pulses are detected by piezo-transducer (lithium niobate) on the back target side. Such approach permits to measure simultaneously recoil pressure behavior and calculate the irradiated surface displacement during laser action by comparison modulated parts of laser and acoustic signals. Nanosecond laser pulses contain 10–15 short peaks of 60 ps duration (1.08 μm wavelength) which provide fluence values up to 30 J cm−2 in the pulse. Plasma light emission is also registered with the help of photodiode. At the considered fluences surface displacement during the pulse turns out to be considerably smaller than theoretical estimation for free vacuum vaporization and measured experimental displacement which follows from the arrival time delay of another pressure signals generated with subsequent laser pulse directed to the same spot. Such behavior can be evidence that crater formation in the considered irradiation regime occurs after the pulse end.

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

Cold, dense, atomic ion clouds produced by cryogenic buffer-gas cooling

We produce cold and dense clouds of atomic ions (Ca$^+$, Dy$^+$) by laser ablation of metal targets and cryogenic buffer gas cooling of the resulting plasma. We measure the temperature and density of the ion clouds using laser absorption spectroscopy. We find that large ion densities can be obtained at temperatures as low as 6 K. Our method opens up new ways to study cold neutral plasmas, and to perform survey spectroscopy of ions that cannot be laser-cooled easily.

Synthesis and Characterization of Gold-Silver Nanoparticles in Deionized Water by Pulsed Laser Ablation (PLAL) Technique at Different Laser Parameter

Gold and silver nanoparticles (NPs) are physically synthesized using Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG)-pulsed laser ablation in liquid (PLAL) technique which is a rapid, simple and efficient one-step synthesis. The gold and silver colloidal solutions are separately prepared by 1064[Formula: see text]nm of pulsed laser ablation of metallic target (gold and silver) which is immersed in deionized water. Ultraviolet–visible spectroscopy (UV–Vis) analysis shows the absorption band of gold and silver NPs at [Formula: see text][Formula: see text]nm and [Formula: see text][Formula: see text]nm, respectively. The absorption spectra and color variations of gold and silver NPs at three different laser parameters (output laser energies, target distances from focal point and laser time exposures). High-resolution transmission electron microscopy shows the spherical shape of gold and silver NPs with 34[Formula: see text]nm and 33[Formula: see text]nm diameter of size, respectively, are reported. The aggregation and particle sizes of gold and silver NPs due to minimum energy (75[Formula: see text]mJ) and maximum energy (311[Formula: see text]mJ) are observed.

Effect of dual ultrashort laser pulses on metal ablation for efficient micromachining

The properties of laser ablation of metallic targets with ultrashort single and double pulses with a similar total energy were investigated for two target materials: silver and copper. The numerical analysis was performed using the developed femto-2d computer package developed by the authors based on the solution of a two-temperature model. The thermal dependence of the target optical and thermodynamic processes and their role in the overall target response to dual pulse laser irradiation were carefully considered. The ablation rate for a dual pulse laser machining at the optimal pulse separation time was found to be similar (for silver) or above (for copper) the ablation rate for a single pulse machining for the same total fluence. The advantages of using dual pulse laser micromachining are reduced maximum electron temperature and increased lattice temperature in the ablated region predicted by the model developed by the authors.

Analysis of plasma enhanced pulsed laser deposition of transition metal oxide thin films using medium energy ion scattering

In this study, plasma-enhanced pulsed laser deposition (PE-PLD), which is a novel variant of pulsed laser deposition that combines laser ablation of metal targets with an electrically-produced oxygen plasma background, has been used for the fabrication of ZnO and Cu2O thin films. Samples prepared using the PE-PLD process, with the aim of generating desirable properties for a range of electrical and optical applications, have been analysed using medium energy ion scattering. Using a 100 keV He+ ion beam, high resolution depth profiling of the films was performed with an analysis of the stoichiometry and interface abruptness of these novel materials. It was found that the PE-PLD process can create stoichiometric thin films, the uniformity of which can be controlled by varying the power of the inductively coupled plasma. This technique showed a high deposition rate of ∼0.1 nm s−1.

Synthesis of Au-Ag Alloy Nanoparticles in Deionized Water by Pulsed Laser Ablation Technique.

Au-Ag alloy nanoparticles are physically synthesized using rapid, simple and efficient Q-switched Nd:YAG pulsed laser ablation in liquid technique (PLAL). Au and Ag colloidal solutions are separately prepared by 1064 nm laser ablation of metallic target (gold and silver) which is immersed in deionized water. Au-Ag alloy nanoparticles are prepared by irradiating the mixture of Au and Ag colloidal solutions with 532 nm of second harmonic wavelength of Nd:YAG laser at three different ratio, 3:1, 1:1 and 1:3 within different exposure times. The three of plasmon absorption bands of Au-Ag nanoparticles are shifted linearly to the lower wavelength [499.67 nm (3:1), 481.25 nm (1:1), 467.91 nm (1:3)], as compared to plasmon absorption spectra of pure Au (520 nm) and Ag (400 nm). Moreover, the change in colors are also observed from red (Au) and yellow (Ag) to orange, brown and green color due to the Au-Ag alloy formations, respectively. Transmission electron microscopy shows the Ag shell around the inner core of Au spherical metal with broad size distribution due to the three different volume ratio, respectively (1.7 nm, 0.7 nm, 1.4 nm). Energy-dispersive X-ray spectroscopy analysis confirms the presence of Au and Ag elements in Au-Ag alloy nanoparticles without any contaminations. Attenuated total reflectance fourier transform infrared spectroscopy analysis also confirms the homogenous Au-Ag alloys chemical bonding.

Computer simulation and experimental benchmarking of ultrashort pulse laser ablation of metallic targets

AbstractIntegrated simulation results of femtosecond laser ablation of copper were compared with new experimental data. The numerical analysis was performed using our newly developed FEMTO-2D computer package based on the solution of the two-temperature model. Thermal dependence of target optical and thermodynamic processes was carefully considered. The experimental work was conducted with our 40 fs 800 nm Ti:sapphire laser in the energy range from 0.14 mJ to 0.77 mJ. Comparison of measured ablation profiles with simulation predictions based on phase explosion criterion has demonstrated that more than one ablation mechanisms contribute to the total material removal even in the laser intensity range where explosive boiling is dominating. Good correlation between experimental and simulation results was observed for skin depth and hot electron diffusion depth – two parameters commonly considered to identify two ablation regimes in metal. Analysis of the development dynamics for electron–lattice coupling and electron thermal conduction allowed explaining different ablation regimes because of the interplay of the two parameters.

Coagulation of Metals in Superfluid and Normal Liquid Helium.

The thermal emission study in this work has shown that coagulation of metals in liquid helium is accompanied by enormous local overheating of several thousand degrees. Direct experiments demonstrated, for the first time, that condensation of metals in superfluid helium occurs via the specific mechanism which is substantially faster than that in normal liquid helium. It has been stated that coagulation of metals in superfluid helium indeed occurs in two stages, a "hot" one of nanoparticles coalescence with the formation of molten nanospheres and the subsequent stage of their sticking together into nanowires. It turned out that if a laser ablation of metal targets immersed in superfluid helium was used for introducing a metal into liquid, the formation of nanowires occurs at distances of only about 1 mm from the laser focus. This leads to the presence of a considerable number of spherical inclusions in nanowires grown in such a way.

Experimental and computational study of the effect of 1 atm background gas on nanoparticle generation in femtosecond laser ablation of metals

Laser ablation of metal targets is actively used for generation of chemically clean nanoparticles for a broad range of practical applications. The processes involved in the nanoparticle formation at all relevant spatial and temporal scales are still not fully understood, making the precise control of the size and shape of the nanoparticles challenging. In this paper, a combination of molecular dynamics simulations and experiments is applied to investigate femtosecond laser ablation of aluminum targets in vacuum and in 1 atm argon background gas. The results of the simulations reveal a strong effect of the background gas environment on the initial plume expansion and evolution of the nanoparticle size distribution. The suppression of the generation of small/medium-size Al clusters and formation of a dense layer at the front of the expanding ablation plume, observed during the first nanosecond of the plume expansion in a simulation performed in the gas environment, have important implications on the characteristics of the nanoparticles deposited on a substrate and characterized in the experiments. The nanoparticles deposited in the gas environment are found to be more round-shaped and less flattened as compared to those deposited in vacuum. The nanoparticle size distributions exhibit power-law dependences with similar values of exponents obtained from fitting experimental and simulated data. Taken together, the results of this study suggest that the gas environment may be effectively used to control size and shape of nanoparticles generated by laser ablation.

Evolution of the composition of nanoparticles formed by the nanosecond Nd:YAG laser irradiation of an aluminium target in N2–O2 gas mixtures

Laser ablation of metallic targets in gas atmospheres gives rise to the formation of nanoparticle (NP) powders when high laser irradiances (i.e., > 1 GW/cm² for aluminium targets) are used. The properties of the NPs so formed vary as a function of the laser irradiation parameters and the pressure and composition of the ambient gas. Here, we studied the composition and structure of NPs formed by laser ablation of Al targets with a nanosecond Nd:YAG laser emitting at 1064 nm. The laser irradiance was 2.5 GW/cm2. N2–O2 gas mixtures containing different amounts of nitrogen (100–80 vol% N2) were used as ambient gas at atmospheric pressure. The influence of the ambient gas composition on the morphology and the structure of the NPs was studied ex-situ by scanning and transmission electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Their composition of light elements was determined by ion beam analysis. It was shown that together with metallic aluminium, different amounts of aluminium nitride and aluminium oxynitride were formed in the NPs as a function of the nitrogen concentration in the ambient gas. Below 95 vol% N2, the concentration of nitride phases decreases strongly. However, the formation of aluminium oxide (Al2O3) was not observed, whereas it was detected in NPs formed in air. A discussion of these results that takes into account the dynamics of the plasma plume is proposed.

Isotopic enrichment of Zn particles by laser ablation

The use of Zn in nuclear reactors reduces the amount of 60Co generated as a consequence of the natural activation of Co. On the other hand, isotopically enriched Zn can be used as a tracer in biological systems. At the present, the enrichment of Zn is obtained using gaseous compounds of the metal by centrifugal force. In this paper, we present a method based on laser ablation of metallic targets of Zn with a Nd–YAG nanosecond laser to produce isotopically enriched Zn particles. Also, the effect of the wavelength irradiation laser on the enrichment factor was studied and a procedure is proposed to collect the different enrichment fractions yield.

Some physical properties of zirconium and molybdenum oxide nanostructures produced by metal laser ablation in water

A number of results of experimental studies of physical properties of nanostructures of oxides of transition metals, i.e., zirconium (Zr) and molybdenum (Mo), obtained by laser ablation of metal targets in water are presented. The structure, morphology, and some optical characteristics are studied. It is shown that Zr and Mo oxides are synthesized under these conditions mostly as amorphous masses containing particles less than 1–2 nm in size, of which large nanostructures and hollow quasi-spheres are formed.

Piezoelectric electrospun nanocomposite comprising Au NPs/PVDF for nerve tissue engineering.

In this study, gold nanoparticles/Polyvinylidenefluoride (PVDF) composite electrospun mat with enhanced piezoelectricity were fabricated and characterized. Gold colloidal nanoparticles (Au NPs) were prepared via laser ablation of metallic targets in liquid media. The active Q-switched Nd:YAG laser was used as an irradiation source. Then, PVDF was dissolved in Au NPs colloidal solution at 30% wt for the synthesis of Au NPs/PVDF composite nanofibers by electrospinning. The optical absorbance spectra of Au NPS and the polymeric solutions were obtained by the UV-Visible spectroscopy. Moreover, the morphology of Au NPS, nanostructures of fibers and diameter size distribution of nanofibers were analyzed by Scanning Electron Microscopy, Field Emission Scanning Electron Microscopy, and Transmitted Electron Microscopy methods. The crystallinity and piezoelectricity of PVDF and Au NPs/PVDF composite nanofibers mats were measured by X-Ray Diffraction and Fourier Transform Infrared methods. Subsequently, in vitro cytocompatibility was evaluated by MTT assay and the attachment and morphology of PC-12 cells cultured on scaffolds were studied. It was found that laser ablated Au NPs can be used in electrospun nanofibers of PVDF with adequate structural properties and increase piezoelectricity of nanofibers which might be suitable for applying as nerve tissue engineering scaffolds. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1984-1993, 2017.