Enhanced and Selective Absorption of Molybdenum Nanostructured Surfaces for Concentrated Solar Energy Applications.

Surfaces of commercial molybdenum (Mo) plates have been textured by fs-laser treatments with the aim to form low-cost and efficient solar absorbers and substrates for thermionic cathodes in Concentrated Solar Power conversion devices. Morphological (SEM and AFM), optical (spectrophotometry), and structural (Raman spectroscopy) properties of the samples treated at different laser fluences (from 1.8 to 14 J/cm2) have been characterized after the laser treatments and also following long thermal annealing for simulating the operating conditions of thermionic converters. A significant improvement of the solar absorptance and selectivity, with a maximum value of about four times higher than the pristine sample at a temperature of 800 K, has been detected for sample surfaces treated at intermediate fluences. The effects observed have been related to the light trapping capability of the laser-induced nanotexturing, whereas a low selectivity, together with a high absorptance, could be revealed when the highest laser fluence was employed due to a significant presence of oxide species. The ageing process confirms the performance improvement shown when treated samples are used as solar absorbers, even though, due to chemical modification occurring at the surface, a decrease of the solar absorptance takes place. Interestingly, the sample showing the highest quantity of oxides preserves more efficiently the laser texturing. The observation of this behaviour allows to extend the applicability of the laser treatments since, by further nanostructuring of the Mo oxides, it could be beneficial also for sensing applications.

LIPSS Applied to Wide Bandgap Semiconductors and Dielectrics: Assessment and Future Perspectives.

With the aim of presenting the processes governing the Laser-Induced Periodic Surface Structures (LIPSS), its main theoretical models have been reported. More emphasis is given to those suitable for clarifying the experimental structures observed on the surface of wide bandgap semiconductors (WBS) and dielectric materials. The role played by radiation surface electromagnetic waves as well as Surface Plasmon Polaritons in determining both Low and High Spatial Frequency LIPSS is briefly discussed, together with some experimental evidence. Non-conventional techniques for LIPSS formation are concisely introduced to point out the high technical possibility of enhancing the homogeneity of surface structures as well as tuning the electronic properties driven by point defects induced in WBS. Among these, double- or multiple-fs-pulse irradiations are shown to be suitable for providing further insight into the LIPSS process together with fine control on the formed surface structures. Modifications occurring by LIPSS on surfaces of WBS and dielectrics display high potentialities for their cross-cutting technological features and wide applications in which the main surface and electronic properties can be engineered. By these assessments, the employment of such nanostructured materials in innovative devices could be envisaged.

Deep-Subwavelength 2D Periodic Surface Nanostructures on Diamond by Double-Pulse Femtosecond Laser Irradiation.

Two-dimensional laser-induced periodic surface structures with a deep-subwavelength periodicity (80 nm ≈ λ/10) are obtained for the first time on diamond surfaces. The distinctive surface nanotexturing is achieved by employing a single step technique that relies on irradiation with two temporally delayed and cross-polarized femtosecond-laser pulses (100 fs duration, 800 nm wavelength, 1 kHz repetition rate) generated with a Michelson-like interferometer configuration, followed by chemical etching of surface debris. In this Letter, we demonstrate that, if the delay between two consecutive pulses is ≤2 ps, the 2D periodicity of nanostructures can be tuned by controlling the number of pulses irradiating the surface. Under scanning mode, the method is effective in treating uniformly large areas of diamond, so to induce remarkable antireflection properties able to enhance the absorptance in the visible up to 50 times and to pave the route toward the creation of metasurfaces for future diamond-based optoelectronic devices.

Transition Metal Carbide Core/Shell Nanoparticles by Ultra-Short Laser Ablation in Liquid.

Transition metal carbide nanoparticles are a class of technological interesting materials with a wide range of applications. Among metal carbides, tantalum carbides have good compatibility with the biological environment while molybdenum carbides are used as catalyst in electrochemical reactions. Laser ablation of bulk transition metal targets in some liquids is here reported and laser ablation in organic solvents is used as simple synthetic strategy for the production of carbide nanostructures. Herein, the nanoparticles produced by ultra-short laser ablation of tantalum and molybdenum in water, acetone, ethanol and toluene have been characterized by TEM, XRD and XPS analysis. The combined effect of metal and solvent chemical and physical properties on the composition of the nanomaterials obtained has been pointed out. In particular, the different reactivity of Ta and Mo with respect to oxidizing species determines the composition of particles obtained in water, on the other hand the organic solvents decomposition allows to obtain transition metal carbide (TMC) nanoparticles. The observed carbonaceous shell formed on TMC allows to protect the particle's carbidic core and to improve and tailor the applications of these nanomaterials.

Sport injury prevention in individuals with chronic ankle instability: Fascial Manipulation® versus control group: A randomized controlled trial.

Chronic ankle instability (CAI) is one of the most common syndromes that occurs following an initial ankle sprain. Sprains are often correlated with recurrent sprains, loss of range of motion (ROM) and deficits in proprioception and postural control. The objectives were to evaluate the effectiveness of Fascial Manipulation® (FM) as a preventative measure in semi-professional athletes with CAI, and to monitor the symptomatology, equilibrium and ROM of the injured ankle. A single-blinded randomized controlled trial was conducted in the rehabilitation department of a medical centre. Twenty-nine semi-professional male footballers were recruited. Nine subjects with no previous symptomatology, were assigned to a baseline group, twenty symptomatic subjects were randomized into either the study or the control group. All three groups followed a specific training program. The control group followed normal training protocols and received standard medical care. The study group received an additional three FM treatment sessions. Symptomatology and ROM outcomes were recorded for all players at baseline, before each treatment for the treatment group, and at 1-, 3-, and 6-month follow-ups. At one year, an additional follow-up on was performed via phone. Four severe ankle traumas and one mild ankle trauma were reported in the control group during the trial period. The 6-month outcomes in the study group showed statistically significant improvements. The 1-year follow-up reported the absence of any reported trauma in the study group. FM was effective in improving ROM and symptomatology in footballers with CAI. FM intervention was effective in preventing injury in the study sample.

Silica Xerogel Obtained by Ultrashort Laser Irradiation of Tetraethyl Orthosilicate.

The formation of an opaque solid foam was induced by the direct interaction between tetraethyl orthosilicate (TEOS) and an ultrashort femtosecond laser source(Nd:glass, 527 nm, 10 Hz, 250 fs). The product, which resulted to be a silica xerogel, was characterized by different techniques. In particular, information about the morphology was obtained by scanning and transmission electron microscopy (SEM and TEM), while the presence of different functional groups was studied through IR measurements. Since the properties of this kind of material can be improved by functionalizing it with metal nanoparticles, a palladium metal target was ablated in liquid TEOS. TEM images show that palladium was present in the form of nanoparticles and EDX measurements confirm the presence of the metal inside the silica network.

Study of the Effect of Water Pressure on Plasma and Cavitation Bubble Induced by Pulsed Laser Ablation in Liquid of Silver and Missed Variations of Observable Nanoparticle Features.

In this work the effects of the pressure between 1-150 Bar on pulsed laser ablation in liquids (PLAL) during the production of silver nanoparticles (AgNPs) in water was investigated. The produced NPs are the results of two different well-known stages which are the plasma and the bubble evolution occurring until the generated material is released into the solution. The main aim of this work is to show which roles is played by the variation of water pressure on the laser induced plasma and the cavitation bubble dynamics during the NPs formation. Their implication on the comprehension of the as-produced NPs formation mechanisms is treated. The typical timescales of the different stages occurring in water at different pressures have been studied by optical emission spectroscopy (OES), imaging and shadowgraph experiments. Finally surface plasmon resonance (SPR) spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and scanning electron microscopy (SEM) for characterization of the material released in solution, have been used.

Formation of Titanium Carbide (TiC) and TiC@C core-shell nanostructures by ultra-short laser ablation of titanium carbide and metallic titanium in liquid.

Laser ablation of bulk target in liquid allows to obtain stable nanoparticles and nanostructures, also in metastable phases, limiting the use of hazardous reagents and extreme reaction conditions. Titanium carbide (TiC) is a ceramic compound with several technological applications ranging from biocompatible materials to wear resistant coatings. The possibility to obtain core/shell structures expands its range of application due to the ability of modify the surface properties of the core ceramic material. TiC and metallic titanium targets have been ablated by means of an ultra-short laser source in different liquid media (water, acetone, n-hexane and toluene). The obtained colloidal solutions have been characterized by TEM, XRD and micro-Raman analysis. In all the used experimental conditions TiC nanoparticles have been produced. During water and acetone mediated ablations, the oxidation of titanium has been observed, whereas by using oxygen free solvents, such as n-hexane and toluene, core/shell TiC nanoparticles embedded in amorphous and graphitic carbon shell, respectively, have been obtained.

Pulsed laser ablation of a continuously-fed wire in liquid flow for high-yield production of silver nanoparticles.

Using wires of defined diameters instead of a planar target for pulsed laser ablation in liquid results in significant increase of ablation efficiency and nanoparticle productivity up to a factor of 15. We identified several competitive phenomena based on thermal conductivity, reflectivity and cavitation bubble shape that affect the ablation efficiency when the geometry of the target is changed. On the basis of the obtained results, this work represents an intriguing starting point for further developments related to the up-scaling of pulsed laser ablation in liquid environments at the industrial level.

Nanoparticles and thin film formation in ultrashort pulsed laser deposition of vanadium oxide.

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.

Theoretical modeling of laser ablation of quaternary bronze alloys: case studies comparing femtosecond and nanosecond LIBS experimental data.

A model, formerly proposed and utilized to understand the formation of laser induced breakdown spectroscopy (LIBS) plasma upon irradiation with nanosecond laser pulses at different fluences and wavelengths, has been extended to the irradiation with femtosecond laser pulses in order to control the fractionation mechanisms which heavily affect the application of laser-ablation-based microanalytical techniques. The model takes into account the different chemico-physical processes occurring during the interaction of an ultrashort laser pulse with a metallic surface. In particular, a two-temperature description, relevant to the electrons and lattice of the substrate, respectively, has been introduced and applied to different ternary and quaternary copper-based alloys subjected to fs and ns ablation both in the visible (527 nm) and in the UV (248 nm). The model has been found able to reproduce the shorter plasma duration experimentally found upon fs laser ablation. Kinetic decay times of several copper (major element) emission lines have been examined together with those relevant to the main plasma parameters. The plasma experimental temperature, derived assuming a Boltzmann distribution, and the electron density following the Saha equation have been compared with the corresponding theoretical data. A satisfactory description of plasma parameters and main matrix constituent composition has been obtained in the time window where local thermal equilibrium was assumed for LIBS data analysis. Improved analytical capabilities are predicted upon delayed detection of plasma emission in femtosecond LIBS, in relation to the better LOD achieved and to the improved data reproducibility expected. Results support the utilization of ultrafast laser sources for trace detection, despite the residual fractionation occurring in the examined range of fluences which affects the linearity of experimental calibration curves built for tin and lead after internal standardization on copper. The validation of model results by experimental data allowed highlighting, from first principles, of the ablation mechanisms for the two temporal regimes and information on how this affects the accurate microanalysis of Cu-based alloys.