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Extended colloidal stability and high dispersion degree of nanolubricants are required to avoid nanoparticle deposition in combustion engines and to reduce friction and wear. In this study, the simple and rapid one-step technique of pulsed laser ablation in liquids is employed to synthesize precursor-free and highly-dispersed gold nanoparticles while the colloidal stability is measured by optical spectroscopy and transmission electron microscopy. We determine a remarkable colloidal stability at engine-like (2 h circulation, 150 °C, 6 bar) and ambient conditions for 9 months in terms of constant primary particle size. In contrast to additive-free oils, almost no agglomeration is observed, which might be attributed to the attachment of engine oil additives or pyrolyzed/oxidized molecules to the nanoparticles preventing attractive nanoparticle interactions.

The distinctive feature of upconverting compounds to absorb and emit light in the near-infrared region has made upconverting nanoparticles of great interest in various application fields. Nevertheless, these colloids show a highly hydrophobic behavior, and therefore, the use of a proper stabilizing agent is necessary in most cases. Although few chemical techniques for colloid stabilization are available, it is still difficult to achieve a fully reproducible synthesis method for stable upconverting nanoparticle colloids. In this work, upconversion 18 %Yb:1 %Er:NaYF4 nanoparticles were produced by ultrafast pulsed laser ablation in a water and 2-[2-(2-methoxyethoxy)- ethoxy]acetic acid (MEEAA) environment to assess the stabilization effect of the surfactant on the nanoparticle colloid properties. The effects of the laser fluence and MEEAA concentration on the nanoparticles′ properties were investigated by TEM, EDS, and emission spectra analyses. The results show that ultrashort pulsed laser ablation in liquid allows generating highly spherical nanoparticles with conserved stoichiometry and optical properties. Moreover, it is possible to obtain colloids with significantly higher stability and preserved optical properties by one-step PLAL processes directly in the MEEAA environment.

This review article highlights the recent advances of the synthesis and application of metal nanoparticles (NPs) fabricated via pulsed laser ablation in liquid (PLAL) phase and also introduces relevant NP formation mechanisms. Although wet-chemical approaches have been well established to synthesize colloidal metal NPs with various components and structures, some inherent drawbacks, such as reaction residuals and/or contaminations, largely limit some of their applications. The PLAL method has recently been developed as an alternative approach and received increasing attention for colloidal NP preparation, without involving complicated chemical reactions. In certain cases, by using PLAL, ligand-free and surface-clean NPs can be obtained and well dispersed in liquid, leading to the formation of a "surface-clean" NP dispersion. This unique feature renders PLAL-synthesised metal NPs attractive candidates for many interesting applications in catalysis, biology, sensing, and clean energy generation and storage. We conclude this review by proposing several interesting research directions and future challenges, from PLAL fabrication to applications. We hope this review can serve as a good reference and help with the further development of PLAL-NPs and their diverse applications.

Methods for the rapid construction of new chemical motifs have the potential to accelerate the development of nanoscience. The synthesis of new chemical entities by laser ablation has been systematically demonstrated by using mixtures of gold and selenium. The compounds generated are detected by time-of-flight mass spectrometry and, for selected compounds, the structure is investigated by using density functional theory optimization. In total, 67 new gold selenide clusters have been synthesized, demonstrating an unsuspected richness in gold chemistry. Chemical species generated in the gas phase might inspire new routes for the synthesis of novel compounds in the solid state.

Hercynite nanoparticles were obtained by pulsed laser ablation of hercynite in liquid media technique. Colloidal solutions of hercynite nanoparticles were synthesized in three different liquids by ablation using 532-nm output of a pulsed Nd:YAG laser with three laser fluencies. Transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used for the characterization of these nanoparticles. The nanoparticles obtained were of spherical shapes with cubic crystalline structure. It was observed that the laser fluence and liquid media could affect the morphology and size of hercynite nanoparticles.

A method is reported that uses visible continuous-wave laser to directly fabricate micropatterns in glasses containing silver (Ag) nanoparticles. Ag nanoparticles were formed in the glass using thermal treatment. Upon laser irradiation, Ag nanoparticles with their surface plasmon in resonance with the laser beam were partially melted and decreased in size due to the temperature increase induced by the excited Ag nanoparticles. Three-dimensional patterns were achieved by scanning the laser beam through the thickness of the glass.

Liquid-phase pulsed laser ablation (LP-PLA) is a promising technique for the fabrication of various nanomaterials because this technique is very simple and it is easy to control the experimental parameters. This paper demonstrates the synthesis of phase-controlled iron oxide magnetic nanoparticles by laser ablation of a bulk α-Fe2O3 target in the following liquid media: ethanol, D.I. water and acetone. Absorption spectra of the nanocolloidal solutions are measured by UV–Vis spectrophotometer. As-synthesized nanoparticles, extracted from the colloidal solutions, are characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM) equipped with X-ray energy dispersive spectrometry (EDX) and a vibrating sample magnetometer (VSM) to discover crystallinity, phase structure, morphology, elemental compositions and magnetic properties in detail. The experimental results showed that the type of target and the magnitude of laser power play important roles in controlling the uniformity of iron oxide phase in the final product nanoparticles. Laser ablation of the iron oxide target in ethanol and acetone yields crystalline maghemite (γ-Fe2O3) nanoparticles, while that in D.I. water yields amorphous hematite (α-Fe2O3). Use of an iron oxide (α-Fe2O3) target for PLA in all three solvents is able to prevent the formation of metal iron and wustite phases in the final product nanoparticles. Moreover, our nanoparticles obtained in all three solvents possess magnetic behaviour, particularly that obtained in acetone, which has better saturation magnetization than those in ethanol and D.I. water.

The development of a general method to fabricate spherical semiconductor and metal particles advances their promising electrical, optical, magnetic, plasmonic, thermoelectric, and optoelectric applications. Herein, by using CuO as an example, we systematically demonstrate a general bottom-up laser processing technique for the synthesis of submicrometer semiconductor and metal colloidal spheres, in which the unique selective pulsed heating assures the formation of spherical particles. Importantly, we can easily control the size and phase of resultant colloidal spheres by simply tuning the input laser fluence. The heating-melting-fusion mechanism is proposed to be responsible for the size evolution of the spherical particles. We have systematically investigated the influence of experimental parameters, including laser fluence, laser wavelength, laser irradiation time, dispersing liquid, and starting material concentration on the formation of colloidal spheres. We believe that this facile laser irradiation approach represents a major step not only for the fabrication of colloidal spheres but also in the practical application of laser processing for micro- and nanomaterial synthesis.

This article reports the target and liquid media influences on the microstructures and optical properties of ZnO nanoparticles synthesized using pulsed laser ablation (PLA) method. Zinc and ZnO target were ablated with laser in pure water and surfactant solution, respectively. The obtained nanoparticles were characterized using X-ray diffraction spectrometer, transmission electron microscopy, X-ray photoelectron spectroscopy, optical absorption spectrum, and photoluminescence spectrum. The nanoparticles synthesized in surfactant solution were of spherical shapes, but with different microstructures and optical properties. The nanoparticles synthesized in water using zinc target showed rod shapes and both UV and visible emissions. When ZnO target was ablated in water, flake-shaped nanoparticles were synthesized and strong UV, but weak violet emissions were observed. At last, the influences of PLA growth condition on the nanoparticles microstructures and the relationship between the optical properties and their stoichiometries were discussed.

Summary: This work reviews the interaction of photons with polymers with an emphasis on UV laser ablation and surface modification using VUV lamps. Laser ablation of polymers is an established process in industrial applications, but the mechanisms of ablation are still controversial. Different polymers, such as poly(methyl methacrylate), polyimides and specially designed polymers are used as examples to show that the mechanism is a mixture of photochemical and photothermal features which are closely related to the polymer structure and properties. Different approaches to probe the ablation mechanisms and to improve ablation are discussed. Photoactive groups have been introduced into the polymer structure to improve the quality of ablation and to elucidate the ablation mechanisms. The experimental techniques to probe the ablation mechanism range from time-resolved measurements, such as shadowgraphy, ToF-MS, and ns-surface interferometry to variations of the irradiation wavelengths and pulse lengths. The necessity for a critical evaluation of the experimental procedures and analysis is discussed exemplary for polyimides. The data for different types of polyimides are mixed up and some experimental procedures are possibly causing problems for the data evaluation. Various recent trends for laser ablation, such as ultrafast ablation or VUV ablation are also discussed. Surface modifications of polymers using VUV photons from lamps are discussed for oxidation and nitriding of poly dimethylsiloxane (PDMS) and polyolefines. The mechanism of the PDMS surface oxidation is presented in detail. Ablation pattern in TP1 created by 308 nm irradiation using a gray tone phase mask.

The laser ablation technique has been employed to study silver colloidal formation. Laser intensities, irradiation wavelengths (1064 nm and 532 nm), and solvents (water, methanol, and isopropanol) were all considered. Changes of the maximum UV-Visible absorbance of the solutions with laser intensities exhibited nonlinear behavior for 1064 nm and 532 nm and displayed better ablation efficiency at 532 nm. Larger mean sizes were observed at 532 nm or at higher pulse energy. For solvent effect, the bigger particle sizes were generated in H2O. As to colloidal stability, isopropanol, which has a lower dielectric constant than water, was found to stabilize Ag nanoparticles without protecting reagents over six months. Preliminary results in 2-butanol suggested that the viscosity of solvent may need to be considered in addition to the dielectric constant.

This paper presents the results of carbon nanoparticles (CNPs) production by infrared laser ablation of a graphite or a polycrystalline diamond target, submerged in one of two solvents, water or isopropanol. The targets were irradiated using a SPI fibre laser with a wavelength of 1064nm being operated at different average powers. After laser-assisted synthesis of CNPs, the resulting colloids, i.e particles in a liquid medium, were examined using the analytical techniques of dynamic light scattering, UV-Vis, Raman spectroscopy and fluorescence spectroscopy. The results show that the properties of CNPs strongly depend on processing conditions of the liquid phase-pulsed laser ablation (LP-PLA) process. In particular, the size of nanoparticles produced are affected by the processing parameters of the laser ablation. The results show that the laser processing of a graphite target in deionised water and in isopropanol produces carbon nanoparticles with properties that are beneficial for various biochemical and biomedical applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The technique of frozen matrix-assisted laser ablation coupled with resonance-enhanced multiphoton ionization and reflectron time-of-flight mass spectrometry was used to detect intact organic molecules directly from solutions. When frozen at the temperature of liquid nitrogen, the matrices of interest were ablated by a pulsed CO2 single-mode laser. The analyte molecules emerging from the ablated plume were then ionized by a tunable XeCl excimer laser-pumped dye laser and analysed with a gridless reflectron time-of-flight mass spectrometer. The ablation process from an ice matrix was studied with the amino acids tryptophan and tyrosine dissolved in an aqueous ethanol solution to a concentration level of 5 × 10−4 M. It was found that fragmentation of the analyte molecules is strongly dependent on the ablating laser fluence and that there is a laser fluence range just above the ablation threshold where the decomposition is negligible. The different fragmentation mechanisms are discussed and a cavitation under the liquid surface, causing the sonoluminescence signal from an ice matrix, was shown to be responsible for the decomposition of the analyte molecules ablated by a low photon energy IR laser. Under the appropriate conditions, the analyte molecules were found to have a low rotational temperature of about 150 K resulting from the jet-like cooling in multiple collisions with matrix molecules.

Here an alternative preparation route, pulsed laser ablation in liquid (LAL) of FeCl3 solution, is reported to facilely synthesize crystalline iron oxychloride (FeOCl) nanosheets at ambient conditions. Well-dispersed spherical gold (Au) nanoparticles (NPs) are simultaneously decorated on surface of the FeOCl nanosheets, which possess (010) preferred orientations with microsized dimensions in planar and tens of nanometers in thickness. The crystalline size and composition of the Au/FeOCl can be effectively modulated by simply changing FeCl3 concentrations. Technical observations illustrate that the nanocomposites possess good thermal stability and surface of which adsorbs abundant H2O molecularly and oxygen species chemically. The FeOCl nanosheets are formed through chemical side hydrolysis reaction in the localized liquid region with gradient temperature, which is derived from thermal transfer of LAL-induced plasma plume. The Au/FeOCl nanocomposites, as chemiresistors, show exceptionally high sensing response and perfect selectivity to HCl gas at room temperature. The excellent sensing behavior is ascribed to the Au-NP-enhanced surface chemisorption of oxygen species and selective adsorption of HCl for FeOCl nanosheets. The synthesized Au/FeOCl nanocomposites provide a new candidate for exclusive HCl detection. And the proposed LAL-assisted fabrication routes might open new perspectives for formation of other metal oxychloride compounds.