Pulsed laser ablation in a cooled liquid environment

Pulsed laser ablation (PLA) is a unique method used to obtainatoms, ions, and small molecules from solid targets because ofits high-energy output, the ability to adjust the power of thelaser, and the purity of the final product.1,2 Most experiments onpulsed laser-solid interaction have been carried out in vacuum(10−4 Pa)3 or in a low pressure background gas,4 aiming at thin film fabrication and cluster formation.1 One of the advantages ofthe PLA method is that stoichiometric thin films can be preparedwith the same composition as the target materials. In addition,metals, semiconductors, and ceramics with high melting point canbe obtained at lower temperatures. However, this method has somedisadvantages, such as the size of the granules on the surface ofthin films is not even, big particles exist in the surface, and ahigh vacuum environment raises the preparation cost. Also, it isdifficult to obtain a thin film with big area using the PLA method.Some researchers have attempted to produce new materials by PLAin a static liquid medium. Figure 11.1 shows a typical schematicdiagram of the experimental apparatus of PLA in static liquid.5Mafune´ and coworkers prepared small silver, gold, and platinumclusters by laser ablation of ametal plate in the aqueous solution of asurfactant, where the clusters are encapsulated by the surfactant. Atthe same time, they also researched the influence of the preparationconditions, such as the concentration of the surfactant and thepower of laser ablation, on the stability of the nanoparticles in thesolution.5−8 Yang and coworkers prepared nanocrystalline diamond and cubic C3N4 by laser ablation of a graphite target in acetonesolution and ammonia solution, respectively.9,10,11 Iwabuchi et al.12prepared nanosized titania particles by PLA of a rutile single-crystaltarget in water. Compagnini et al.13 reported PLA of gold andsilver in several liquids (mainly water, ethanol, and chloroform).They observed the formation of metal sols by laser ablation inwater and ethanol and the formation of chloride compound solsby laser ablation in chloroform. This revealed that the chemicalstate of the formed nanoparticles depends mainly on the chemicalreactivity of the liquid. Liang et al.14 synthesized ultrafine SnO2−x nanocrystals by PLA of a tin metal plate in aqueous solutions ofsodium dodecyl sulfate and in pure water. Yeh and coworkers15also prepared aluminum hydroxides by laser ablation of an Al rodimmersed in water solvent. During aging, bayerite, gibbsite, andboehmite particles were formed simultaneously.

We report the preparation of silicon nanocrystals with efficient ultraviolet luminescence by nanosecond pulsed laser ablation in de-ionized water at a high laser fluence condition. Atomic force microscopy results show that nano-grains form in the process of laser ablation. Fourier transform infrared spectroscopy analyses indicate that silicon nanocrystals are formed and partially oxidized during synthesis. The photoluminescence measurement and the ultraviolet-visible transmittance spectroscopy of the samples prepared at various fluences reveal that all the prepared samples present an efficient ultraviolet emission at room temperature and it can be attributed to the quantum confinement effect and surface defect states. The emission wavelength of silicon nanocrystals is far shorter than visible light, which means potential applications in optoelectronic devices.

Pulsed laser ablation in liquid (PLAL) was used to synthesise indium oxide (In2O3) nanocolloidal suspension. Colloidal In2O3 nanoparticles (NPs) are synthesised by pulsed laser ablation of high-purity indium target in distilled water with various laser fluences at room temperature. UV–vis absorption and transmission electron microscopy were conducted to determine the bandgap, size, distribution and shape of the NPs. The optical properties, size and the morphology of the synthesised In2O3 were influenced strongly by laser fluence and wavelength. Laser ablation of indium in water produced spherical In2O3 NPs with an average size of 30 nm and their distribution was nearly Gaussian type.

In this paper, we propose a simple two-step method for the synthesis of Ag, Au, and Pt-doped ZnO nanoparticles. The method is based on the fabrication of targets using the pulsed laser deposition (PLD) technique where thin layers of metals (Ag, Pt, Au) have been deposited on a metal-oxide bulk substrate (ZnO). Such formed structures were used as a target for the production of doped nanoparticles (ZnO: Ag, ZnO: Au, and ZnO: Pt) by laser ablation in water. The influence of Ag, Au, and Pt doping on the optical properties, structure and composition, sizing, and morphology was studied using UV-Visible (UV-Vis) and photoluminescence (PL) spectroscopies, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The band-gap energy decreased to 3.06, 3.08, and 3.15 for silver, gold, and platinum-doped ZnO compared to the pure ZnO (3.2 eV). PL spectra showed a decrease in the recombination rate of the electrons and holes in the case of doped ZnO. SEM, TEM, and AFM images showed spherical-shaped nanoparticles with a relatively smooth surface. The XRD patterns confirm that Ag, Au, and Pt were well incorporated inside the ZnO lattice and maintained a hexagonal wurtzite structure. This work could provide a new way for synthesizing various doped materials.

Boron nanoparticles (BNPs) are attractive nanomaterials for their employment in many applications, such as neutron detection, boron neutron capture therapy, proton boron capture therapy and nuclear fusion. Depending on the specific application, 10B or 11B isotopes can be used.Nevertheless, there are significant challenges in developing suitable BNPs using both conventional chemical synthesis routes and dry fabrication techniques. In this study we report BNPs directly synthetised in water by pulsed Laser Ablation in Liquid (PLAL). Nanoparticles of elemental boron have been generated by laser ablation of a sintered 10B target in MilliQ water by employing ns laser pulse. The ablation resulted in BNPs and boron target micro-fragments with hydrogen gas and boric acid as by-products. Simple washing steps were used to obtain clean BNPs in water. The BNPs showed a narrow size distribution between 3 and 4 nm and their stability in water was induced by a thin layer of boron oxide surrounds BNPs. The BNPs were fully characterized by the chemical and structural point of view employing several techniques. A discussion on boron chemical reactions during laser ablation in water and after the NPs were released in solution was done.

Pulsed Laser Ablation in liquid (PLAL) is considered as a robust and simple technique for producing nanoparticles (NPs) using lasers. The carbon-based nanoparticles were fabricated via the PLAL approach by irradiating a graphite target with a pulsed Nd:YAG laser of wavelength 532 nm. The graphite target was immersed in distilled water and irradiated for 10 min. The pulse length, reputation rate, and fluence were 6 ns, 10 Hz, and 0.4 J cm−2, respectively. The structural and physical properties of the synthesized NPs were investigated and analyzed using different characterization methods. For example, Transmission Electron Microscopy (TEM) images revealed diverse carbon nanostructures such as graphene nanosheets, nanospheres, nanospheres in the shape of a necklace, and nanotubes. The spectrum of Energy Dispersive X-Ray spectroscopy (EDX) confirmed successful synthesis of high purity carbon nanostructures. Moreover, the result of X-Ray Diffraction (XRD) Spectroscopy indicated the presence of reduced Graphene Oxide (rGO) with a (002) plane and the absence of Graphene Oxide (GO). The transmission spectrum from Ultraviolet-Visible (UV–vis) analysis showed a strong trough at 266 nm which is attributed to the presence of carbon nanostructures. Furthermore, Fourier-Transform Infrared Spectroscopy (FTIR) analysis demonstrated the vibration bonds related to carbon. The nanostructures produced were semi-stable with little agglomeration as was inferred from the results of the Zeta Potential. Finally, the Dynamic Light Scattering (DLS) analysis supported the TEM results. PLAL technique is proved to be a simple method for producing carbon-based nanomaterials. Moreover, the laser fluence was found to be an important factor which affects greatly the type of nanostructures that could be synthesized during laser ablation.

The solution of the conventional Rayleigh–Plesset equation did not agree with the experimental results on the temporal variations of the sizes of cavitation bubbles produced by laser ablation in water. In this work, we modified the conventional Rayleigh–Plesset theory in the following two points to reproduce the experimental observation theoretically. One was to introduce the effect of the contact angle among the water, the cavitation bubble, and the ablation target. The other was to treat the surface tension and the kinematic viscosity coefficient of water as additional adjusting parameters to fit the theoretical result with the experimental observation. The latter modification was effective especially for laser ablation in the pressurized water. Better agreement between the theoretical and the experimental results was realized with the help of these modifications, but anomalous thermodynamic parameters were necessary to obtain the best fitting. We evaluated the pressures and the temperatures inside the cavitation bubbles.

In this paper, we prepared ZnO nano-particles by using pulsed laser ablation in water. ZnO particles are dispersed in pure water as a target material of laser ablation. We irradiated the ZnO particles in water with YAG laser with different wavelengths to investigate the effects of photon energy on the nano-particle formation. We measured both atomic composition of ZnO and crystallinity of the fabricated nano-particles by EDX and XRD. We also observed ZnO nano-particles by TEM. The averaged diameter of ZnO nano-particles was 6 nm.

Ag@Au core–shell nanoparticles synthesized by pulsed laser ablation in water: Effect of plasmon coupling and their SERS performance

Spray of gelled propellants from an impinging-jet injector under different temperatures

A simple and green strategy is presented to decorate ZnO nanorod array, based on electrophoresis deposition in the Au colloidal solution prepared by laser ablation in water and subsequent further laser irradiation. The surface of nanorods is homogeneously decorated with Au nanoparticles. The Au nanoparticles have good interfacial connection and strong binding with ZnO nanorods. The decoration morphology can be easily controlled by the size of Au colloids. Further experiments have revealed that suitable electrophoretic potential, small Au colloid's size, and enough inter-nanorod's spacing are crucial to formation of a homogeneous and strong surface decoration. Such Au nanoparticle-decorated ZnO nanorod array is functionalized and exhibits excellent surface-enhanced Raman scattering performance and shows the possibility of molecule-level detection. This study provides a new opportunity for the controllable surface modification of 1D semiconductor nanostructures and deepens the understanding of the physical mechanism of electrophoretic deposition.

Magnetite (Fe3O4) nanoparticles of 1–10 nm (with the maximum at 2 nm) were obtained via pulsed laser ablation of iron target in water in form of a stable dispersion without addition of surfactants and stabilizers. The structure of the material obtained was investigated using transmission electron microscopy, scanning electron microscopy, and Brunauer–Emmett–Teller methods. To investigate the composition of the particles in the sample, such methods as Fourier transform infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, and X-ray diffraction, were applied. Magnetite phase was found to be sufficiently pure, it was not contaminated by other iron oxide phases and contained not more than 0.5% of metallic iron in form of large particles. The study of the magnetic properties of the magnetite nanoparticles obtained has shown that they exhibit ferrimagnetic behavior at room temperature with the paramagnetic contribution explained by the presence of fine superparamagnetic particles.

Study of the influence of interfacial waves on heat transfer in turbulent falling films

One of the problems in the storage of cryogenic liquids is the increase in pressure in the closed container, A considerable quantity of heat may be transferred into the container because of the large temperature difference between the ambient temperature outside the container and the temperature of the cryogenic liquid. The increase in pressure in a closed container due to this heat leak may be calculated from the increase in liquid temperature, obtained from the heat-leak rate, and the vapor pressure-temperature equilibrium relation. Experience has shown, however, that the container pressure may be considerably greater than the calculated pressure based on an average liquid temperature. The difference between the actual pressure and that calculated from an average liquid temperature has been attributed to the development of temperature gradients in the liquid, O. A, Hansen,1 Linde Air Products, Inc., and M. D. Andonian,2 Cambridge Corporation, referred to the presence of liquid-temperature strata in their papers presented at the 1956 Cryogenic Engineering Conference.

In the deep geological situation, the gypsum is almost always associated with high temperature and the other mineral substances such as sodium chloride. And, hot saline brine will greatly affect the strength and deformability of gypsum by influencing the petrographic characteristics such as microstructure, granular minerals, composition content and morphology. To quantify the effect of brine temperature and concentration on fracture toughness and fracture characteristics of gypsum, a serious of tests, including cracked straight through Brazilian disc (CSTBD) tests and scanning electron microscopy (SEM), were carried out. The results demonstrated that, when at a given crack inclination angle, the fracture peak of gypsum decreases with the increase of liquid temperature. When at a given liquid temperature, due to common-ion effect, the fracture peak first decrease then increase with the increase of brine concentration. In all these cases, due to the effect of friction coefficient, the fracture peak first decreases then increases with the increase of prefabricated crack angle. From SEM morphology results, the microcrack density increases with liquid temperature increasing, whereas first increase then decrease with brine concentration increasing. Subsequently, by adopting the approach of back-propagation neural network, the effective FPZ at different conditions were obtained. It was found that the size of effective FPZ is closely dependent on brine temperature and concentration.