Abstract: An overview is given of different modeling work that has been carried out, and is currently going on in our research group, in the field of modeling for laser ablation (LA). Most emphasis will be put on nanosecond (ns) LA, more specifically describing the laser-solid interaction, leading to heating, melting and vaporization of the target, by a heat conduction model, the expansion of the evaporated plume in vacuum or in a background gas by a set of conservation equations, and the plasma formation in the plume, assuming local thermal equilibrium. Some first results for nanoparticle formation in the expanding plume will be presented as well. Also, the process of target heating in the case of femtosecond (fs) LA will be described by means of a two-temperature model, and phase transitions, more specifically evaporation, will be illustrated by means of molecular dynamics simulations.
Abstract: Light scattering techniques provide powerful methods to investigate a variety of different materials properties. Brillouin scattering is used to the study the elastic properties of bulk solids and thin supported films at ambient and high temperatures. Work on iron pyrite and tungsten carbide films are described as illustrations with theoretical methods using surface Green’s functions being used in the analysis. Raman scattering is used to study corrosion and passivation of iron in an alkaline solution and stress patterns in diamond plastically deformed at high temperature.
Abstract: A 3-D transient modelling based on the numerical resolution of the fluid flow ant the heat transfer equations is developed for butt welding using the cladding process. The physical mechanisms included in our model concern the matter melting, and the re-solidification. The implementation of developed procedures called User Defined Functions (UDFs) working interactively with Fluent CFD code, and a dynamic mesh method, allows to treat the problem with its specific and complex boundary conditions. The fusion, resolidification, and the temperature dependence of the physical properties are taken into account. As results, clad formation and information on the temperature field are obtained.
Abstract: Al/TiB2 metal matrix composite (MMCs) was fabricated on aluminium AA1200 with the aim of improving the wear resistance property of the substrate. The characterization of the MMCs was carried out by Optical Microscopy (OM), Scanning Electron Microscopy (SEM/EDS) and X-ray Diffraction (XRD). The microhardness and wear resistance tests were achieved. Results showed that the microhardness property of the AA1200 was increased by three times the original value and the wear resistance was also significantly improved.
Abstract: Laser forming is a technique consisting in the design and the construction of complex metallic work pieces with special shapes difficult to achieve with the conventional techniques. By using lasers, the main advantage of the process is that it is contactless and does not require any external force. It offers also more flexibility for a lower price. This kind of processing interests the industries that use the stamping or other costly ways for prototypes such as in the aero-spatial, automotive, naval and microelectronics industries. The analytical modeling of laser forming process is often complex or impossible to achieve, since the dimensions and the mechanical properties change with the time and in the space. Therefore, the numerical approach is more suitable for laser forming modeling. Our numerical study is divided into two models, the first one is a purely thermal treatment which allows the determination of the temperature field produced by a laser pass, and the second one consists in the thermo-mechanical coupling treatment. The temperature field resulting from the first stage is used to calculate the stress field, the deformations and the bending angle of the plate.
Abstract: The growth of thin films by laser ablation involves very complex physical processes. The quality of the layer and stoechiometry of the deposits depend on key parameters like the ion energy and their angular distribution. The evolution of ions number and energy, and the angular distributions in regards to the incident laser energy, have been studied by the mean of a charges collector. We present the polar diagrams of energy and number of ions collected by irradiating a silicon target using an excimer laser at different energies.
Abstract: A new class of low-k materials thin films, deposited from a DiPhenyleMethylSilane (DPMS) vapors was prepared using PECVD technique. These films are elaborated in microwave excited DECR plasma reactor (Distributed Electron Cyclotron Resonance) from pure DiPhenylMethylSilane (DPMS) using various plasma discharge power (100-400 W) or mixed with 50% of oxygen (O2).The improvements of film properties were investigated by capacitance–frequency (C–f), current–voltage (I–V) techniques and Fourier transform infrared spectroscopy (FTIR). The obtained results show that an increase in plasma discharges power from 100 to 400 watts leads to the decrease in dielectric constant value from 4.4 to 3.7 (measured at 10 kHz). The incorporation of oxygen improves the dielectric properties of the films; the dielectric constant value was reduced to 2.9.
Abstract: In this work, we have employed chemical bath deposition (CBD) method to obtain nanocrystalline PbS thin films in the presence of polyethylene oxide (PEO). The spectral response of Au/PbS-pSi(100)/Al Schottky photodiodes at different PEO amount were studied. The response exhibits a combined effect of photogeneration in the heterojunction (HJ) Si side and PbS. Spectral response were observed progressively at shorter wavelength due to the surface absorption. The peak centered at 410 nm properly corresponds to photo-exited holes being injected from PbS to the Si substrate. The intensity of the peak of R(λ) increases with PEO amount, this increasing was attributed to the decreasing of band gap (Eg).
Abstract: Amorphous Se100-x (Sn Sb)x glasses with (0 ≤ x ≤ 20 at. %) were prepared by the usual melt quench technique. Thin films for these compositions were prepared by thermal evaporation onto ultrasonically cleaned glass substrates kept at room temperature. From the spectral dependence of the absorption coefficient, a direct electronic transition was mainly responsible for the photon absorption inside these films. The effects of composition on the optical properties of Se100-x(Sn Sb) x thin films was investigated. The refractive index, n, for the as-prepared and annealed films has been analyzed according to the Wwmple–DiDominico single oscillator model. The effect of addition (Sn Sb) on the nature and degree of crystallization has been investigated by studying the structure using transmission electron microscope, X-ray diffraction and scanning electron microscope.