Rémi Torres

Possible surface plasmon polariton excitation under femtosecond laser irradiation of silicon

The mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated. We demonstrate the transient evolution of the density of the excited free-carriers. As a result, the experimental conditions required for the excitation of surface plasmon polaritons are revealed. The periods of the resulting structures are then investigated as a function of laser parameters, such as the angle of incidence, laser fluence, and polarization. The obtained dependencies provide a way of better control over the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material.

Formation of femtosecond laser induced surface structures on silicon: Insights from numerical modeling and single pulse experiments

Abstract Laser induced periodic surface structures (LIPSS) are formed by multiple irradiation of femtosecond laser on a silicon target. In this paper, we focus and discuss the surface plasmon polariton mechanism by an analysis of transient phase-matching conditions in Si on the basis of a single pulse experiment and numerical simulations. Two regimes of ripple formation mechanisms at low number of shots are identified and detailed. Correlation of numerical and experimental results is good.

Study on laser-induced periodic structures and photovoltaic application

We have irradiated silicon with a series of femtosecond laser pulses to improve light absorption at the silicon surface. The laser treated surface namely black silicon shows excellent optical properties on mono and multicrystalline silicon wafers with a reflectivity reduction down to 3%, without crystal orientation dependence. After the laser process, the front side of samples has been boron‐implanted by Plasma Immersion Ion Implantation to create the 3D p+ junction. Improved electrical performances have also been demonstrated with a 57% increase in the photocurrent, compared to non‐texturized surface.

Laser Textured Black Silicon Solar Cells with Improved Efficiencies

Femtosecond laser irradiation of silicon has been used for improving light absorption at its surface. In this work we demonstrate the successful implementation of femtosecond laser texturisation to enhance light absorption at Si solar cell surface. In order to adapt this technology into solar industry, the texturisation process is carried out in air ambient. The microstructure similar to what has been produced in vacuum can be made in air by using appropriate laser conditions. The texturised surface shows excellent optical properties with a reflectivity down to 7% without crystalline orientation dependence. Junction formation and metallisation proceeded after texturisation. Suns-Voc measurements are performed to evaluate the cell performance and decent electrical characteristics have been achieved.

Laser Applications for Nanotechnology : Insights From Numerical Modeling

Laser‐produced nanoparticles have found many applications in bio‐photonics, medicine and in the development of photovolvatic cells. Many experiments have been performed demonstrating the formation of these particles from solid targets in vacuum, in the presence of a gas or a liquid. However, it is still difficult to predict the size distribution of these particles. Therefore, we have performed an extensive numerical modeling of the involved physical processes. The developed models allow us to compare the relative contribution of several processes involved in the cluster production by laser ablation: (i) direct cluster ejection from a target under rapid laser interaction, (ii) condensation/evaporation; (iii) fragmentation/aggregation processes during cluster diffusion; and (iv) diffusion and coalescence if nanoparticles are deposited on a substrate. The calculation results of both hydrodynamic and molecular dynamics simulations demonstrate that an exposure of a target to a short or ultra‐short laser pulse ...

Nanofabrication with pulsed lasers

The employment of pulsed lasers offers a novel unique tool for nanofabrication [1]. When focused on the surface of a solid target, pulsed laser radiation causes a variety of phenomena, including heating, melting, and finally ablation of the target, and such processes can lead to an efficient material nanostructuring. First, the laser-assisted removal of material from the irradiated spot can result in a spontaneous formation of variety of periodic nanoarchitectures within this spot. Second, laser ablation of material from a solid target leads to the production of nanoclusters, which can then be either deposited on a substrate to form a nanostructured film or released into a liquid environment to form a colloidal nanoparticle solution. Our on-going projects on laser nanofabrication include the following activities: 1. Laser-assisted self-structuring to form nanoscale features on the surface. In this case, we consider spontaneously formed architectures on the surface under laser-matter interactions. In the first method, fs laser ablation in residual gas leads to a formation of micro-scale spikes on Si surface, which condition a drastic increase of the absorption of the treated surface (“black silicon”) that is important for photovoltaic applications [2]. In the second method, we create hot, highly absorbing laser plasma by a phenomenon of laser-induced gas breakdown and use it to treat surfaces and thus form unique “photon crystal-like” structures, which are of importance for optoelectronics applications [3,4]. 2. Pulsed Laser ablation in liquids. In this method, fs laser radiation is used to ablate a solid target in liquid ambience (aqueous solutions of biopolymers etc) to form colloidal nanoparticles [5–7]. Nanomaterials synthesized by this method exhibit unique proper-ties, which can not be reproduced by conventional chemical routes, including small size (down to 1 nm) and size dispersion, unique surface chemistry, and the absence of toxic contaminants on nanoparticle surface. Such properties give a promise for successful “in vivo” applications of nanoparticles. In particular, we showed that Si nanoparticles pre-pared by laser ablation are fluorescent and capable of exhibiting singlet oxygen under photoexcitation, making them excellent candidates for PDT of cancer [8]. 3. Near-field nanoparticle-assisted nanostructuring of surfaces: fabrication of patterned nanoarrays. In these methods, laser ablation through glass nanoparticles dispersed on the surface is used in combination with photolithography to form nanoplasmonics arrays for biosensing applications [9].