UV to NIR photon conversion in Nd-doped rutile and anatase titanium dioxide films for silicon solar cell application

Undoped and Nd-doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 °C under 0.1 mbar O2. By selecting adequate substrates, TiO2 films doped with 1, 2 or 5 at.% Nd were grown and constituted with polycrystalline rutile, highly oriented (2 0 0) rutile film, or oriented (0 0 4) anatase. An UV to NIR photon conversion is evidenced in the films. Indeed, intense and well-resolved emission lines from Nd3+ have been observed upon excitation above the TiO2 bandgap at room temperature. The sensitised emission of Nd3+ is found to be much efficient in rutile than in anatase structure. Low temperature photoluminescence measurements lead to fine resolved peaks corresponding to the Nd3+ 4f transitions with different spectral characteristic according to the host matrix used. Photoluminescence dependence temperature evidences that the light emission from Nd3+ in anatase-based films is probably influenced by the presence of self-trapped excitons or by orbital interaction. Mechanisms of sensitisation host to Nd3+ are proposed for both matrixes. Finally, the Nd dopant concentration and the microstructure of TiO2 rutile films are found to affect the photoluminescence emission intensity. Rutile film (2 0 0) oriented is the most adapted host matrix to sensitise 1 at.% Nd3+ ions for an emission around 1064 nm making such Nd-doped layers interesting for photon conversion by down shifting process

UV to NIR photon conversion in Nd-doped rutile and anatase titanium dioxide films for silicon solar cell application

Undoped and Nd-doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 °C under 0.1 mbar O2. By selecting adequate substrates, TiO2 films doped with 1, 2 or 5 at.% Nd were grown and constituted with polycrystalline rutile, highly oriented (2 0 0) rutile film, or oriented (0 0 4) anatase. An UV to NIR photon conversion is evidenced in the films. Indeed, intense and well-resolved emission lines from Nd3+ have been observed upon excitation above the TiO2 bandgap at room temperature. The sensitised emission of Nd3+ is found to be much efficient in rutile than in anatase structure. Low temperature photoluminescence measurements lead to fine resolved peaks corresponding to the Nd3+ 4f transitions with different spectral characteristic according to the host matrix used. Photoluminescence dependence temperature evidences that the light emission from Nd3+ in anatase-based films is probably influenced by the presence of self-trapped excitons or by orbital interaction. Mechanisms of sensitisation host to Nd3+ are proposed for both matrixes. Finally, the Nd dopant concentration and the microstructure of TiO2 rutile films are found to affect the photoluminescence emission intensity. Rutile film (2 0 0) oriented is the most adapted host matrix to sensitise 1 at.% Nd3+ ions for an emission around 1064 nm making such Nd-doped layers interesting for photon conversion by down shifting process

Collisional radiative model of a helium capillary glow discharge including atomic collisions

A new collisional radiative model of helium capillary glow discharge has been developed that incorporates the l changing atomic collisions, the associative ionization and the n changing atomic collisions (for the states n ≥ 8). This model is used to determine the electron temperature of low density plasmas. The range of validity of the model is 0.3 ≤ PHe (torr) ≤ 5 for the helium pressure, 109 ≤ ne (cm -3) ≤ 2 × 101^3 for the electron density, 1 ≤ ⊘ (mm) ≤ 16 for the discharge diameter and the ionisation degree α ≤ 10^-3. The electron temperature is close to 45 000 K.Un nouveau modèle collisionnel radiatif est développé en tenant compte des transferts d'excitation entre sous-niveaux d'un même état par collisions atomiques, de l'ionisation associative et des transferts d'excitation entre états de n différents (n ≥ 8). Ce modèle est utilisé pour déterminer la température électronique des plasmas à basse densité. Le domaine de validité du modèle est 0,3 ≤ PHe (torr) ≤ 5 pour la pression d'hélium 109 ≤ ne (cm-3) ≤ 2 x 10^13 cm-3 pour la densité électronique, 1 ≤ ⊘ (mm) ≤ 16 pour le diamètre des décharges et le degré d'ionisation α ≤ 10^-3. La température électronique est de l'ordre de 45 000 K

Pulsed Laser Surface Treatment of multilayer Au/Ni/Cu coatings to Improve the corrosion Resistance of Componenents in electronics

International audienc

Metallic thin films heated by pulsed lasers. Numerical simulation of the thermal field and the melting kinetics

This modeling is especially applied to the pulsed laser induced heating and melting of a metallic film deposited on a substrate. Study of the thermal field over a surface is usually performed by considering the assumption of ‘semi-infinite medium’. However, a thin film deposited on a rough substrate surface induces bad thermal contacts commonly known as ‘thermal contact resistance’. This interfacial thermal resistance affects the melting kinetics mainly when the film thickness (Z) is small comparatively to the heat diffusion length (Z$_T$). In this work the heat conduction equation and related boundary conditions are resolved by using the implicit finite differences method. The heat source (i.e. the laser intensity) is treated as a surface boundary layer. The thermal contact resistance is introduced in the computation procedure when the heat wave propagation reaches the thin film/substrate interface. It is then possible to calculate the critical temperatures and the melting threshold fluence for high and low contact resistance values. Under these conditions, the temperature profile and melting depth are plotted considering different thickness.. Finally, for 750 mJ/cm² excimer laser fluence and 0.1 cm²/s thin film apparent diffusivity results show that for Z/Z$_T$ higher than 0.5, there is no sensitive effect of the thermal contact resistance on the melting kinetics

Nanoparticle Formation by Femtosecond Laser Ablation

International audienc

Direct synthesis of titanium nitride by laser-plasma

No abstract availabl

Nitruration d'alliages légers par laser à excimère

L'amélioration des propriétés tribologiques des alliages d'aluminium permettrait de substituer des pièces en acier ou en fonte dans les moteurs de voitures et donc d'alléger les véhicules et diminuer la consommation de carburant. Pour y parvenir il est nécessaire de renforcer la surface des alliages d'aluminium. Le procédé développé et utilisé dans cette étude est un procédé de nitruration par plasma produit par laser qui permet de synthétiser du nitrure d'aluminium en surface et jusqu'à une épaisseur de quelques microns. L'utilisation de plusieurs techniques d'analyse (analyses nucléaires, analyses cristallographiques, analyses par microscopie électronique) permet de décrire précisément la structure de la couche formée par ailleurs le rôle du plasma dans la formation de la couche a été étudié