This study introduces a novel approach to enhance the photocatalytic activity of ZnO films. By using single-pulsed nanosecond laser irradiation on Au/Pd/ZnO and Pd/Au/ZnO trilayer stacks, deposited by magnetron sputtering, we synthesized well-mixed Au–Pd alloyed nanoparticles (NPs) on a ZnO thin film. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of the bimetallic NPs, and adjusting the layer thickness and stacking order allowed us to control the relative Au and Pd content. Under solar simulated light, we assessed the photocatalytic activity for indigo carmine (IC) dye degradation and found that ZnO films decorated with monometallic Au–Pd NPs exhibited superior performance compared to pristine ZnO and ZnO films with monometallic NPs. The photocatalytic activity was assessed for indigo carmine dye degradation. The optimum bimetallic composition (0.8 Pd, 0.2 of Au) showed a 13.8-fold increase in dye degradation compared to the pristine ZnO film and up to a 7.6-fold improvement over ZnO films decorated with monometallic nanoparticles. This study offers a facile and scalable method for preparing bimetallic NPs on semiconductor films for enhanced photocatalytic applications.

We report the fabrication of metal alloy Au–Pd nanoparticles on semiconductor thin film substrates (ZnO) by laser-induced dewetting. Employing a UV excimer laser, a single pulse was directed onto a three-layer film stack on a glass substrate: glass/ZnO/Au/Pd and glass/ZnO/Pd/Au. We simulated the temperature attained by the thin films enabling the prediction of energy thresholds required for melting the metal films but avoiding modifying the ZnO film. A specific range is reported of the pulse energy conducive to nanoparticle formation and the energy threshold required to modify the ZnO film beneath them. Depending on the pulse energy applied, the mean diameter of the nanoparticles varied from approximately 150 to around 70 nm. Notably, higher fluences resulted in smaller particles but also induced surface cracks in the ZnO film. Additionally, we observed a reduction in nanoparticle size with increased Pd content. Our results show that laser-induced dewetting can produce bimetallic alloy nanoparticles and, at the same time, ensure the preservation of the optical properties of the ZnO film. This approach opens avenues for tailoring material characteristics and expanding the range of applications of metal nanoparticles on semiconductor-based systems.

We present, for the first time, the use of graphene layers on the surface of transparent samples (glass) to improve laser-induced breakdown spectroscopy (LIBS) performance. Our results show that the presence of few-layer graphene allows the optical emission of glass to be observed at lower irradiance than conventional LIBS. This effect is discussed in the frame of the absorption of the laser pulse by the graphene and the heat transfer to the beneath the sample. It is reported that the LIBS intensity increases with the number of graphene layers when it ranges from 6 to 15 layers. The surface of the sample after LIBS revealed that the graphene was almost completely removed after one pulse without causing apparent visible damage to the sample. The proposed method to improve LIBS in order to obtain a compelling characterization of transparent samples is both easy and cheap to implement.

Growing ultrathin nanogranular (NG) metallic films with continuously varying thickness is of great interest for studying regions of criticality and scaling behaviors in the vicinity of quantum phase transitions. In the present work, an ultrathin gold plasmonic NG film was grown on a sapphire substrate by RF magnetron sputtering with an intentional deposition gradient to create a linearly variable thickness ranging from 5 to 13 nm. The aim is to accurately study the electronic phase transition from the quantum tunneling regime to the metallic conduction one. The film structural characterization was performed by means of high-resolution transmission electron microscopy, atomic force microscopy, as well as x-ray diffraction and reflectivity techniques, which indicate the Volmer-Weber film growth mode. The optical and electrical measurements show a transition from dielectric-isolated gold NPs towards a continuous metallic network whentbecomes larger than a critical value oft(M)=7.8 nm. Our results show that the onset of the percolation region occurs when a localized surface plasma resonance transforms to display a Drude component, indicative of free charge carriers. We demonstrate that, by using a continuously varying thickness, criteria for metallicity can be unambiguously identified. The onset of metallicity is clearly distinguished by the Drude damping factor and by discontinuities in the plasma frequencies as functions of thickness.

Spring Meeting 2019. International Conference on Advanced Materials, Acropolis Congress Centre, Nice, France, May 27-31 2019

We evaluate the performance of an adhesion buffer layer between ordered metal nanoparticle arrays and dielectric substrates on the particles' morphological manipulation by pulsed laser irradiation. The experiments are performed irradiating with only one nanosecond pulse at 355 nm, triangular nanoprism arrays fabricated by nanosphere lithography (polystyrene spheres with 1030 nm in diameter), followed by film deposition by magnetron sputtering. The reshaping of the nanoprisms into spheres as result of laser-induced melting is investigated for three different materials: prisms made of Cr, Au and Au with a buffer layer made of Cr (Au/Cr). These elements are chosen because their interfacial interaction with the substrates (soda-lime glass and fused silica) is quite different. Our results show that single pulse irradiation at fluences above the metal melting threshold allows the formation of disorder spheres for the case of Au, but ordered spheres for the cases of Cr and Cr/Au. Therefore, the function of the buffer layer is to improve the adhesion between the prisms and the substrate, thus allowing their reshaping by laser-induced melting but preserving their position. The strong interaction between Cr and the substrate is also exploited for the nanostructuration of the substrate by the formation of ordered holes with sub-micrometer dimensions. These findings reboot laser postprocessing of ordered structures fabricated by nanosphere lithography exploit to explore new capacities of nanostructuration.

Manganese-doped zinc oxide thin films (ZnO:Mn) were grown on silicon and corning glass using double beam pulsed laser deposition. In this configuration, two synchronized pulsed-laser beams were employed to ablate independently ZnO and Mn targets. The presence of the zinc blende phase was investigated by means of X-ray diffraction, pulsed laser photoacoustic analysis and the calculation of the lattice parameter a. The crystallography plane (110) of the cubic zinc blende was found in all the films. Energy dispersive X-ray spectroscopy and different statistical analysis were employed to analyze the effect of the relative delay between plasma plumes on the average incorporation of Manganese. The minimum content of Mn—0.176 at%—was found for a relative delay of 10 µs, this result suggest that this delay is the inflection point to be considered in relation to a significant decrease in the incorporation of the dopant element. A significant positive Correlation analysis—r (4) = 0.98, p < 0.05—between the thickness and the average Mn incorporation was found, this means that as the percentage of manganese in the structure increases the thickness also increases.

Mercury is a chemical element used in multiple applications; it is non-degradable and has bioaccumulation potential. Among toxic metals, mercury gets attention for its high toxic capacity. There is, therefore, great interest in developing analytical techniques for detection and real-time monitoring of mercury, to obtain reliable data for fundamental and applied studies, aimed to a rational and responsible use of this material, and to minimize its impact on the environment. In this work, the Laser-Induced Breakdown Spectroscopy (LIES) technique is applied to the analysis of dental amalgams with varying mercury concentrations in an Ag-Cu-Sn matrix. For each multi-elemental sample, we observed and recorded the spectra of laser-plasmas at delay times after the laser pulse between 1 and 5 mu s. Calibration curves were built to determine the concentration of mercury in the amalgams, using suitable corrections to compensate for the changes in electron number density and temperature associated to the large changes in the samples' matrix occurring at the different Hg concentration. The accuracy of the calibration curves at different delay times was estimated and discussed.

A Nd:YAG ns-pulsed laser was used to ablate Al, Cd and Zn targets, which were placed between the plates of a planar charged capacitor. The plasma generates a transient redistribution of the electrical charges on the plates that can be measured as a voltage drop across a resistor connected to the ground plate. This signal is proportional to the capacitor applied voltage, the distance between the plates and the total number of ions produced in the ablation process which in turn is related to the laser energy and the ablated mass. After a series of pulses, the targets were weighed on a thermogravimetric balance to measure the ablated mass. Our results show that the electrical signal measured on the resistor is univocally related to the ablated mass from the target. Therefore, after a proper calibration depending on the material and the experimental geometry, the electrical signal can be used for real time quantitative measurement of the ablated mass in pulsed laser generated plasma experiments. The experiments were repeated on an aluminum target, with and without the presence of the external electric field in order to determine the possible influence of the applied electric field on the ablated mass.

We investigate the features of Au nanoparticles (NPs) formation by laser irradiation of thin films and its application in Nanoparticle Enhancement Laser Induced Breakdown Spectroscopy (NELIBS). Ns laser pulsed irradiation of Au thin films previously deposited on glass, allowed simultaneously the modification of the surface morphology of the metal film and the enhancement of the LIBS signal of the glass. Our results demonstrate that the presence of Au either as thin film or NPs favors the formation of a plasma composed by Au and the elements of underlying substrate. Thus, it is possible observing the optical emission of the glass at much lower irradiance than in conventional LIBS. The effect of the thickness of the starting film, laser fluence and number of pulses on the nanostructuration of the surface and the enhancement of the emission signal were analyzed. Under the studied conditions, the first pulse produces the formation of Au NPs and a LIBS spectrum with dominant emission of Au lines over the lines from the substrate. The subsequent pulses modify the NPs morphology and decrease the amount of Au on the substrate, thus the emission of the glass elements dominates the spectrum. After a certain number of pulses, the NPs are removed leaving an apparently clean surface after the analysis.

Au thin films with tens of nm in thickness deposited on glass substrates were irradiated with nanosecond UV (355 nm) laser pulses at atmospheric pressure and in vacuum conditions (similar to 600 and 10(-5) Torr). We studied the effect of the laser fluence (200-400 mJ/cm(2)), thickness of the starting film (similar to 40-80 nm) and surrounding pressure on the partial ablation/evaporation of the films and the morphology of the produced nanoparticles (NPs). The dynamics of NPs formation was studied by measuring in real time the transmission of the samples upon continuous-wave laser exposure, and by means of probe beam deflection technique. The ejection of material from the film as a result of the irradiation was confirmed by time-resolved shadowgraphy technique. Experiments show that the NPs diameter and their size distribution are smaller when the irradiation is performed in vacuum regardless the laser fluence and thickness of the started film. It is also shown that the plasmon band shifts to higher frequencies with. lower background pressure. The optical measurements show that the films melt and ablate during the laser pulse, but the transmission of the irradiated areas continues changing during tens of microseconds due to ejection of material and solidification of the remaining gold. Our results indicate that partial ablation cannot be neglected in nanostructuration by ns-pulsed irradiation of thin films when their thickness is in the studied range. (C) 2017 Elsevier B.V. All rights reserved.

In this paper we present the application of Independent Component Analysis to a set of time-resolved LIBS spectra, acquired on a brass sample at different delay times. The decomposition of the LIBS spectra in few Independent Components with a given temporal evolution is then exploited for obtaining the temporal evolution of the plasma electron temperature, through the application of the three-dimensional Boltzmann plot method recently proposed by the authors. This method allows the determination of the electron temperature temporal evolution without any knowledge of the spectral parameters (transition probability, degeneracy of the levels, etc.…) of the emitting lines. Only the knowledge of the energy of the upper level of the transition is required. The reduction of the LIBS spectral dataset to few Independent Components and associated proportions, further simplifies the determination of the plasma electron temperature temporal evolution, since the intensity of the emission lines does not need to be calculated. The results obtained are compared with the ones obtained using classical two-dimensional Boltzmann plot approach.

We report on the optical properties in the dielectric regime of gold nanostructured granular thin films fabricated through sputter deposition with a composite target at room temperature and over a wide photon energy range (0.62-4.13 eV) by means of Spectroscopic Ellipsometry. The thickness and the films effective optical constants are successfully determined using an approach based on multiple Gaussian oscillators. In the quasi-static regime, i.e., 2R << lambda, and in the dipole approximation, examining the real and imaginary parts, epsilon(1), epsilon(2), of the dielectric function, it is shown that the dc optical conductivity is almost negligible (sigma = omega epsilon(0)epsilon(2) <<10(-5) Omega cm(-1)) and only the capacitive contribution holds for the electron-phonon relaxation in localized surface plasmon of the gold particles. Furthermore, we find that the resonant frequencies omega(p) becomes red-shifted when the particles are electromagnetically coupled to each other or when the surrounding medium dielectric constant, epsilon(m) , increases, thus exhibiting a wide spectral tuning range of 1.95-2.24 eV. (C) 2017 Elsevier B.V. All rights reserved.

We studied the effect of the repetition rate of laser pulses (RRLP) in the range from 1–10 Hz in the production of silver nanoparticles (Ag-NPs) by laser ablation in ethanol. Laser pulses with a duration of 7 ns, a wavelength of 1064 nm and an energy of 60 mJ were used to ablate a 99.99% pure silver target immersed in 10 ml of ethanol. Transmittance analysis and atomic absorption spectroscopy were used to study the silver concentration in the colloidal solutions. The ablation process was studied by measuring the transmission of the laser pulses through the colloid. It is shown that for a fixed number of laser pulses (NLP) the ablation efficiency, in terms of the ablated silver mass per laser pulse, increases with the RRLP. This result contradicts what had previously been established in the literature.

The pulsed photoacoustic (PA) technique was used to study the synthesis by laser ablation of silver nanoparticles (Ag-NPs) in ethanol. PA technique allowed to determine the production rate per laser pulse and concentration of synthesized Ag-NPs. The samples were produced by using a pulsed Nd:YAG laser with 1064 nm of wavelength and 7 ns of pulse duration. The laser pulse energy varied from 10 to 100 mJ. Transmission electron microscopy micrographs demonstrated that the obtained nanoparticles were spherical with an average size close to 10 nm. The absorption spectra of the colloids showed a plasmon absorption peak around 400 nm. The PA analyses showed a significant reduction of the production rate of Ag-NPs during the first hundreds of laser pulses. For a higher number of pulses this rate was kept almost constant. Finally, we found that the root mean square (RMS) value of the PA signal was proportional to the laser pulse fluence on the target surface. Thus PA technique was useful to monitor the ablation process. (c) 2015 Elsevier B.V. All rights reserved.

In this work, we propose an extended Boltzmann plot method to determine the usefulness of spectral lines for plasma parameter calculations. Based on the assumption that transient plasmas are under ideal conditions during an specific interval of time Δt, (i.e. thin, homogeneous and in local thermodynamic equilibrium (LTE)), the associated Boltzmann plots describe a surface in the space defined by the coordinates X=Energy, Y=Time and Z=ln (λjlIj/gjAjl), where Ij is the integrated intensity of the spectral line, gj is the statistical weight of the level j, λjl is the wavelength of the considered line and Ajl is its transition rate. In order to express the Boltzmann plot surface in terms of a reduced set of constants Bi, and δi, we developed as a power series of time, the logarithm of In(t)/In(t0), where In(t) is the integrated intensity of any spectral line at time t, and In(t0) at initial time. Moreover, the temporal evolution of the intensity of any spectral line and consequently the temperature of the plasma can be also expressed with these constants. The comparison of the temporal evolution of the line intensity calculated using these constants with their experimental values, can be used as a criterion for selecting useful lines in plasma analysis. Furthermore, this method can also be applied to determine self-absorption or enhancement of the spectral lines, to evaluate a possible departure of LTE, and to check or estimate the upper level energy value of any spectral line. An advantage of this method is that the value of these constants does not depend on the spectral response of the detection system, the uncertainty of the transition rates belonging to the analyzed spectral lines or any other time-independent parameters. In order to prove our method, we determined the constants Bi and δi and therefore the Boltzmann plot surface from the temporal evolution of carbon lines obtained from a plasma generated by a Nd:YAG laser. The plasma was produced in vacuum and was observed at different distances from the target. A good agreement between the temperature calculated by the traditional Boltzmann plot and by this method was obtained.

The self-generated electric and magnetic fields in laser induced plasmas (LIPs) in air during the first 40 ns are experimentally investigated using different electric, magnetic and optical techniques. To produce LIPs we used the second and third harmonics (532 and 355 nm) of a Nd:YAG nanosecond pulsed laser with a range of irradiance from 10(11) to 10(12) W cm(-2). The variation in time of the electric field was detected using the tip of a coaxial cable, and the spontaneous magnetic field (SMF) was measured using a (B) over dot probe. The spatial and temporal evolution of the plasma was studied using shadowgraphy and fast photography. It was observed that produced LIPs using pulses of 532 and 355 nm, generate plasmas of double core over the laser axis, while we observed that produced LIPs by pulses of 1064 nm are composed of a single core plasma. We found that the double-core plasmas have a quadrupole distribution of the charge, consisting of two oppositely directed dipoles which in turn correspond to each plasma core. The magnetic diagnostic showed an oscillating magnetic field azimuthal to the main axis of the double-plasma.

Expanded use of fast photography is proposed to characterize laser ablation plasma plumes by the analysis of a set of photographs by means of appropriate mathematical algorithms. The laser ablation plasma plumes studied were generated by ablation of both a multicomponent target of the nominal composition Ni50Mn37Sn13 and a highly pure Cu target (Cu) using a Q-switched Nd-YAG laser system. The experiments were conducted under different background argon pressures. Several photograph parameters such as intensity per unit time of exposure for a pixel, mean intensity per pixel per unit time of exposure, integrated intensity and cross correlation were studied. The intensity per unit time of exposure allowed for identification of the fast component of the, triple structure of the expanding plasma into the background gas (that. travels at a speed close to the one measured in vacuum). This parameter together with the use of cross correlation enabled the identification of regions of the expanded plasma plume with higher and lower similarities in their optical emission behavior. The mean intensity per pixel per unit time of exposure can be used as a measurement of the amount of light emitted by the plume as a function of time.