The lasers that we are exploiting in our research line are those known as pulsed laser sources; as the name indicates, vast amounts of energy are delivered in short windows of time, as short as the conventional electronic relaxation time (10-12 s). This gives us many possibilities for modifying materials; among the various options, we are especially interested in the synthesis of colloids, surface modification, and photoreduction.
Regarding the laser-mediated synthesis of colloids, we are working on three main approaches; laser ablation in liquids (LAL), laser melting in liquids (LML), and laser fragmentation in liquids (LFL). In the case of LAL, the nanomaterials are produced by the ablation of a solid target immersed in a liquid medium; since both elements can be almost anything, the possibilities for tailor designing new materials are virtually endless. Currently, we are especially interested in addressing one of the major challenges for the laser-mediated synthesis of materials; control the element composition of nanoalloys for their employment in catalysis.
Regarding LML, in our specific case, we are focussing on the irradiation of a liquid jet containing material in powder, and depending on the laser fluence used, we can heat the material, melt it, or completely evaporate it. When we melt the material, we can homogenize the size of nanoparticles or change their morphology. The process is simple; first, the solid material absorbs the incoming energy, and if the energy is enough to promote its melting, the melted material fuse and forms larger structures. When the incoming energy is enough to exceed the material’s melting temperature, it can reach its evaporation point leading to the detachment of its surface through its evaporation. The above-described phenomena occur when employing a “ns” pulsed laser source. However, when using a laser with a pulse duration shorter than “ps”, the size modification occurs by Coulomb explosion, which enables the fragmentation of the irradiated material, which is also known as LFL. In exceptional cases where the energy is too high, it is possible to fragment the material by near-field ablation.
Regarding the laser-mediated surface modification field, we irradiate the surface of almost any material, from metals to polymeric membranes, and take advantage of the multiphoton absorption phenomenon exerted by ultrafast laser radiation to induce element segregation or, in extreme cases, cold ablation. Such precise modification of the materials’ surfaces allows us to tailor design the morphology of the materials’ surfaces. Currently, we are using this technology to provide properties such as superhydrophilicity, superhydrophobicity, superamphiphilicity, crystal phase modification, or atomic cluster rearangement to different materials.
Regarding the laser-mediated photoreduction, what we do is basically irradiate nanoparticle-precursor molecules dissolved in various solvents to promote either their photolysis or their reduction/oxidation by the interaction with the radicals that come from the molecular dissociation of the corresponding solvents , which are conventionally reached at peak intensities of 1010-1012 W/cm2. This technique is mainly employed in our laboratory to get nanoalloys from immiscible elements, a practice that cannot be acheived by alternative laser-mediated methodologies.