Pulsed Excimer Laser Ablation Research Articles

Surface and shape unification of excimer pulse irradiated Ag nanoparticles and associated surface-enhanced Raman scattering properties

Uniform, spherical Ag nanoparticles (NPs) were produced using nanosecond excimer pulsed laser ablation of a colloid target, which had been previously prepared using silver nitrate reduction. After the irradiation experiment, the surface condition and morphology of the samples were revealed by transmission electron microscopy, and the changes in the NPs characteristics caused by different laser fluences were confirmed using optical transmission measurements with an ultraviolet–visible-infrared spectrophotometer. A considerable narrowing of the surface plasmon extinction band was achieved at 300–450 mJ laser irradiation condition, and a quantitative concept of “circularity” was put forward to estimate the degree of optimization. In addition, the effect of light-pressure explains the cause of slight collision and fusion among the nanoparticles. An analysis of these characteristics offers direct evidence of good dispersion and a change in surface shape from irregular to an ideal spherical form. A surface-enhanced Raman scattering (SERS) experiment was proposed, based on the substrate of an irradiated Ag nanoparticle, and this showed new optimized properties for SERS detection. It also involves using a heat-melting mechanism to effect change, which assumes a solid–liquid–solid phase change chain and can be explained simply by triggering the photon absorption of electrons and their coupling to the Ag lattice, which is then terminated by a heat release to the solvent.

Synthesis and properties of Ag/ZnO core/shell nanostructures prepared by excimer laser ablation in liquid

Ag/ZnO core/shell nanostructure was synthesised by a 248-nm KrF excimer pulsed laser ablation in a liquid solution for the first time. It was found that the surface plasma resonance absorption of the Ag/ZnO core/shell nanostructures can be tuned by the thickness of the ZnO shell, which is in agreement with the finite difference in the time domain simulation. Furthermore, the ultraviolet emission spectrum of the Ag/ZnO core/shell nanostructures was stronger and blue-shifted compared with that of pure ZnO nanoparticles. This interesting photoluminescent phenomenon is analysed in detail and a possible explanation is proposed.

Green synthesis of selenium nanoparticles by excimer pulsed laser ablation in water

Pure selenium nanoparticles were successfully synthesized by Liquid Phase - Pulsed Laser Ablation (LP-PLA) in de-ionized water. Excimer laser (248 nm) operating at low fluence (F ∼ 1 J/cm2) was used to generate colloidal solutions of selenium nanoparticles. The obtained selenium nanoparticles were characterized by UV-visible spectroscopy, Raman spectroscopy, Dynamic Light Scattering, and Transmission Electron Microscopy. We describe the multi-modal size distributions generated and use the centrifugation method to isolate the smallest nanoparticles (∼60 nm in diameter).

Generation of Ag–Ag2O complex nanostructures by excimer laser ablation of Ag in water

Pulsed laser ablation in liquid (PLAL) has been well established as a facile method to produce nanoparticles from bulk materials, but it is still insufficient for fabricating anisotropic and complex nanostructures, especially without the use of surfactants. Here, we demonstrate that silver (Ag) nanosheets can be produced by pulsed excimer laser ablation of bulk Ag in water via laser re-processing of the laser-produced primary clusters. We also show that by combining PLAL and drop evaporation, rice-shaped Ag-Ag(2)O particles and their assemblies can be generated on Si substrates, because the interior flow of an evaporating colloidal drop could redistribute the laser-produced primary clusters, which results in the formation of complex nanostructures. These results show that PLAL is able to fabricate novel micro-/nanostructures while keeping its merit of "clean" fabrication.

Nanosecond Excimer Laser Ablation (W,Ti)C-Co Cemented Carbide

In order to increase the serving life of the cemented carbide, high energy pulsed excimer laser ablation was conducted on the surface of (W,Ti)C-Co cemented carbide cutting tool, and the processing parameters were optimized. The morphology of ablation surface was observed by SEM, composition analysis was applied by EDS. The results showed that with the increase of laser pulse number, the Cobalt binder content in cemented carbide decreased, while the micro-cracks increased. The average microhardness of laser irradiation region increased with increasing pulse number.

Influence of process conditions on chemical composition and electronic properties of AlN thin films prepared by ArF reactive pulsed laser deposition

AbstractAluminium nitride (AlN) thin films were deposited using a reactive ArF excimer pulsed laser ablation (PLD) of a pure Al target in a N2 plasma atmosphere, generated by a RF source, onto p‐Si <100> substrates, at increasing substrate temperatures. A radio‐frequency (13.56 MHz RF) apparatus was introduced with the specific aim of increasing the fraction of excited and/or ionized nitrogen species and, ultimately, to increase its reactivity toward the aluminum atoms, expanding in the plume, and the formation of AlN. We studied the dependence and correlation of structural, compositional and electric properties with the specific experimental conditions. The chemical composition of films, determined by XPS spectroscopy, revealed a trend of increased N2 reactivity, uptake and nitride formation, with deposition temperature. Electrical resistivity, measured by the four‐point‐probe method, has been found to be also strongly dependent on the substrate temperature and nitrogen incorporation. A possible explanation of the correlation of surface conductivity with chemical composition is suggested and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Generation of Ag2O Micro-/Nanostructures by Pulsed Excimer Laser Ablation of Ag in Aqueous Solutions of Polysorbate 80

A new route to synthesis of Ag(2)O micro-/nanostructures, including a mixture of cubes, pyramids, triangular plates, pentagonal rods, and bars, has been developed by pulsed excimer laser ablation of bulk silver in water using polysorbate 80 as surfactant. The polysorbate 80 played an important role in the formation of the Ag(2)O structures, and similar structures could be obtained in polysorbates 20 and 40 aqueous solutions. We have proposed a mechanism to explain the formation of Ag(2)O structures. This laser ablation method provides a unique approach to discover and fabricate new Ag(2)O morphologies.

Effect of hydrogen plasma treatment on the field emission of diamond-like films deposited by high power excimer laser ablation

The effect of hydrogen plasma treatment on the electron field emission of diamondlike carbon films (DLCs) deposited by high frequency and high power pulsed XeCl excimer laser ablation of pyrolytic graphite targets at room temperature was studied. Results indicated that the films exhibited improved electron emission, with the threshold field of the films decreased from 26 to 19 V/μm. Meanwhile, the current density increased considerably after the treatment. Two factors were responsible for the results. One was that the graphiterich DLC film surface formed with low energy carbon atoms or clusters during growth process was removed by the hydrogen plasma with the formation of a new surface comprised of high density sp3 bonded carbons, which exhibited a low electron affinity and good field emission . The other was that the dangling bonds of the carbon atoms on the film surface were saturated with Hatoms after the treatment, which further decreased the electron affinity.

Hollow Particles Formed on Laser-Induced Bubbles by Excimer Laser Ablation of Al in Liquid

Herein we show how the unique temporal and thermal events occurring during the pulsed excimer laser ablation of an Al target in water result in hollow Al2O3 micro/nanoparticles with smooth surfaces and an amorphous structure. We demonstrate that the hollow particles are formed on laser-induced bubbles from laser ionized/evaporated liquid during the ablation. The fabrication of hollow particles can be improved by the addition of ethanol to the water, and the particles contain crystalline Al. Our work and the associated mechanism represent a new paradigm to fabricate hollow particles directly from bulk material; that is, the excimer laser ablation produces nanoclusters from the target and bubbles from the liquid, and the bubble interfaces trap the nanoclusters, resulting in the formation of hollow particles.

Excimer Laser Production, Assembly, Sintering, and Fragmentation of Novel Fullerene-like Permalloy Particles in Liquid

We report the fabrication of permalloy nanoparticles by pulsed excimer laser ablation of a permalloy (Fe19Ni81) target in sodium dodecyl sulfate aqueous solution and the subsequent laser-induced assembly, sintering, and fragmentation of the nanoparticles. Specifically, permalloy nanoparticles with diameters of 400−600 nm were observed to assemble into fullerene-like hollow microparticles. Laser irradiation caused sintering of the assembled particles, which showed Wulff construction and ledge growth behavior and finally resulted in smooth shells. Laser−particle interactions also caused fragmentation of the micro/nanoparticles. When the particle concentration is high, laser fragmentation rather than laser ablation dominates due to enhanced light absorption and scattering. The experiments reveal the dynamic process of the nano- and microparticle formation, demonstrating the rich processing environment of laser ablation in liquid.

Fabrication of Permalloy Particles by Pulsed Laser Ablation in Water and Tween 80 Aqueous Solution

AbstractPermalloy particles were fabricated by pulsed excimer laser ablation in distilled water and Tween 80 aqueous solution with the same laser parameters. Nearly spherical particles and irregular and porous fragments were obtained in water due to rapid condensation and growth of the laser ablated clusters. The products obtained in Tween 80 aqueous solution contained well-shaped spheres but some were laser sintered together via laser-particle interactions. Holes or pits were observed on the surface of some particles, which we consider were caused by laser induced bubbles in the liquid. Our results demonstrate the rich environment ablation in liquids can be for novel particle formation.

Pulsed laser ablated off-stoichiometric thin films of the Heusler alloy Co 2TiSn on Si (100) substrate

We report the growth of thin films of ferromagnetic Heusler alloy Co 2TiSn on Si (100) substrate using KrF excimer pulsed laser ablation. Films of thicknesses ranging from 8 to 220 nm were deposited on Si (100) substrate heated up to 200 ± 10 °C, with an aim to study the structural, morphological and magnetic properties. The grown films are off-stoichiometric, polycrystalline, having single-phase with high degree of (220) texturing. Angle dependent fluorescence measurements suggest no segregation of alloying elements as a function of depth. X-ray reflectivity measurements indicate that all the films are having low density layer at the top as well as at the film-substrate interface. Magneto optical Kerr effect measurements at room temperature reveal clear hysteresis loops suggesting ferromagnetic behavior of the films. Thermal annealing at temperature ≥ 220 °C suggest transformation of Co 2TiSn phase into cobalt silicide phase, which confirms the necessity of low substrate temperature (< 220 °C) to produce such single-phase Co 2TiSn films.

Synthesis and control of size and structure of porous carbon films

Nanoporous carbon films are directly synthesized using a pulsed KrF excimer laser ablation deposition technique. Variations of the laser power density, substrate temperature, angle and distance between the substrate and target yield different sizes (0.2–2 μm) of porous structures of carbon films. Optical microscope was used to examine the surfaces of the samples. Raman scattering was used to characterize the samples, and the typical G- and D-bands have been identified. Intensities and profiles of the G- and D-bands strongly depend on the angle of deposition. The relationship between the deposition rate and the power density was also studied.

Preparation of TiO2 thin films by laser ablation for photocatalytic applications

Thin titanium dioxide (TiO2) films were deposited by pulsed KrF excimer laser ablation deposition system using a titanium oxide target. The effects of substrate temperature and oxygen partial pressure on the phase formations of various microstructures were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman scattering spectroscopy, and UV-Vis spectrophotometer. The film structures range from amorphous to mixed phase of anatase and rutile to pure anatase. Increasing the substrate temperature improves the quality of anatase phase of crystalline TiO2 films. The oxygen pressure in the range between 15 and 60 mTorr shows a single anatase phase in TiO2 films while the rutile and anatase mixed phases were observed elsewhere. The band gap of TiO2 films varied from 2.72 to 3.27 eV with increasing oxygen partial pressure while the film structures changed from rutile phase to anatase phase. The surface area of TiO2 films increased as oxygen partial pressure in film deposition. The photocatalytic performance evaluated by degradation of methylene blue in UV light was distinguishable in the TiO2 films with high anatase phase and surface area.

Radiation mechanism of pulsed laser ablation of metal Al

Time-resolved measurement of plasma emission spectra by pulsed XeCl excimer laser ablation of Al under different conditions is reported. The experimental results show that plasma emission spectra are composed of atomic spectrum, univalent ion spectrum and continuous radiation. The atomic spectrum intensity and duration is most significant, the next is the univalent ion spectrum, the continuous radiation is weakest. The detailed mechanism of species excitation is discussed. The continuum radiation comes from electron bremsstrahlung and recombination of electron and ion, the primary atomic and univalent ion excitation originate from recombination of ion and electron. The experimental results are qualitatively explained with the mechanism.

Laser irradiation of oligosiloxane copolymer thin films functionalized with side chain bulky carbosilane moieties

Linear oligosiloxanes functionalized with bulky side chain tris(trimethylsilyl)hexyl (TTSH) substituents were transformed into cross-linked materials by UV 193nm excimer pulsed laser ablation. The process occurred without any catalyst, by reactions of radicals formed in UV laser induced photolysis of side tris(trimethylsilyl)hexyl groups. Chemical changes were monitored by FTIR, LC/UV, GC/MS and solubility tests.

Ultrafast laser micromachining of 3C-SiC thin films for MEMS device fabrication

Femtosecond pulsed laser (800 nm, 120 fs) micromachining of thin films of 3C-SiC (β-SiC) semiconductor deposited on silicon substrate was investigated as a function of pulse energy (0.5 μJ to 750 μJ). The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, Coulomb explosion and photomechanical fragmentation, were correlated with the effects of pulse energy. The results show that the etch rate is higher and the ablation threshold is lower than those obtained with nanosecond pulsed excimer laser ablation, suggesting femtosecond laser’s potential for rapid manufacturing. In addition, the etch rates were substantially higher than those achievable in various reactive ion and electrochemical etching methods. Excellent quality of machined features with little collateral thermal damage was obtained in the pulse energy range (1–10 μJ). The leading material removal mechanisms under these conditions were photomechanical fragmentation, ultrafast melting and vaporization. At very low pulse energies (<1 μJ), nanoscale material removal has occurred with the formation of nanoparticles that is attributed to Coulomb explosion mechanism. The effect of assist gas on the process performance at low and high energy fluences is also presented.

Studies on strontium titanate/barium zirconate superlattices

Artificial superlattices of SrTiO 3 and BaZrO 3 were grown epitaxially with different periodicities on SrRuO 3 coated (001) SrTiO 3 substrates by pulsed excimer laser ablation. Superlattices were structurally characterized by X-Ray θ – 2 θ diffraction data. Electrical characterization was done in metal–insulation–metal configuration. Capacitance–voltage measurements showed limited amount of tunability. The DC field induced tunability has been observed to be sensitive to the periodicity of the superlattices, hence the effective strain present in the layers. Hysteretic behaviour in capacitance–voltage ( C – V ) and polarization versus electric field ( P – E ) results from the superlattices also indicate the sensitivity of the interfaces. Interfacial strain is supposed to be the most probable cause for such a behaviour which is also manifested in the variation of dielectric constant with individual layer thicknesses.

Dielectric, impedance and ferroelectric characteristics of c-oriented bismuth vanadate films grown by pulsed laser deposition

Ferroelectric bismuth vandante, Bi 2VO 5.5 (BVO) thin films with layered perovskite structure were deposited by pulsed excimer laser ablation technique on (1 1 1) Pt/TiO 2/SiO 2/Si substrates. The polarization hysteresis ( P versus E) studies on the BVO thin films at 300 K confirmed the remnant polarization ( P r) and coercive field ( E c) to be 5.6 μC/cm 2 and 113 kV/cm, respectively. The same was corroborated via the capacitance–voltage measurements. The dielectric response and conduction mechanism of BVO thin films under small ac fields were analyzed using impendence spectroscopy. A strong low frequency dielectric dispersion (LFDD) was found to exist in these films, which was ascribed to the presence of the ionized space charge carriers such as oxygen ion vacancies and interfacial polarization. The room temperature dielectric constant and the loss ( D) at 100 kHz were 233 and 0.07, respectively. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.85 eV. The frequency characteristics of BVO thin films under study showed universal dynamic response that was proposed by Jonscher for the systems associated with quasi-free charges.

Structural properties and impedance spectroscopy of excimer laser ablated Zr substituted BaTiO3 thin films

BaZr0.15Ti0.85O3 thin films were deposited on Pt-coated Si substrates using the pulsed excimer laser ablation technique. X-ray diffraction and atomic force microscope techniques were used to study the structural characteristics of the films. Films with good crystalline quality, with an average grain size of 0.5 µm were obtained, under various oxygen background pressures. Ferroelectric hysteresis loops recorded on the films deposited at 26.66 Pa oxygen pressure showed the best properties. To gain a further understanding of the electrical properties of these films, impedance spectroscopy was used and data acquired at several different temperatures. AC conductivity plots showed the presence of space charge conduction at low frequencies; however, at high frequencies, all the curves merged and expectedly showed an almost dc conduction behaviour. The activation energy obtained from ac conductivity data may be attributed to oxygen vacancy motion.