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Pulsed laser ablation appears as a promising technique for depositing thin films. A large variety of successful experimental results were obtained in this field, including the growth of high-temperature superconducting films, ferroelectric films, oxides, semiconductors, diamonds, etc. One of the main advantages of this technology is the relative simplicity of the experimental set-up and the possibility to get good homogeneity, complex stoichiometry materials and well adhesive dense layers. The main drawback seems to be the production of macroparticles, their transfer to the growing film inducing inhomogeneity and roughness onto the surface, lowering the properties of the thin films. In a common configuration, the laser-generated flux is collected on a planar substrate positioned parallel to the irradiated surface. In order to improve the stoichiometry and the quality of the films, several modifications, like simultaneous generation of two plumes from different targets with different targets with different laser beams, were proposed. In this paper, we present some results concerning the production of cryolite thin films using the conventional pulsed laser deposition technique and the dual crossed beams pulsed laser deposition technique. Plasma plumes expanding in vacuum and interacting together are visualized. The different species ejected in the plumes are detected through narrow-band filters in order to determine their kinetic energies. The morphology and the composition of the films are compared with the thermal evaporation technique.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pulsed laser ablation appears as a promising technique for depositing thin films. A large variety of successful experimental results were obtained in this field, including the growth of high- temperature superconducting films, ferroelectric films, oxides, semiconductors, diamonds, etc. One of the main advantages of this technology is the relative simplicity of the experimental set-up and the possibility to get good homogeneity, complex stoichiometry materials and well adhesive dense layers. The main drawback seems to be the production of macroparticles, their transfer to the growing film inducing inhomogeneity and roughness onto the surface, lowering the properties of the thin films. In a common configuration, the laser-generated flux is collected on a planar substrate positioned parallel to the irradiated surface. In order to improve the stoichiometry and the quality of the films (particle free) several modifications were proposed like simultaneous generation of two plumes from different targets (double ablation) with different laser beams. In this paper, we present some results concerning the production of cryolite thin films using the conventional pulsed laser deposition technique (C-PLD) and the dual crossed beam pulsed laser deposition technique DCB-PLD). Plasma plumes expanding in vacuum and interacting together are visualized. The different species ejected in the plumes are detected through narrow-band filters in order to determine their kinetic energies. The morphology and the composition of the films are compared with the thermal evaporation technique.

Pulsed laser ablation has attracted great attention over the past few years as promising technique for depositing thin films. A large variety of successful experimental results were obtained in this field, including the growth of high- temperature superconducting films, ferroelectric films, oxides, semiconductors, diamonds, etc. One of the main advantages of this technology is the simplicity of the experimental set-up. In a common configuration, the laser- generated flux of particles is collected on a planar substrate positioned parallel to the irradiated surface. Several modifications, like simultaneous generation of two plumes from different targets (double ablation), were proposed. Different lasers (e.g. KrF with (lambda) equals 248 nm, Nd-YAG with (lambda) equals 532 nm, etc.) with energy density 2 - 10 J/cm 2 were used in the ablation experiments both in vacuum and into diluted ambient gas (pressure up to 750 mTorr). Monte Carlo simulation was found to be a successful technique for theoretical investigations of the laser ablation processes. This method has allowed us to investigate the influence of elastic collisions and chemical reactions in the laser ablated plume on the angular characteristics of the flow. The results of the simulation show that elastic collisions give rise to focusing of particles towards the surface normal and to the redirection of the velocities of the more energetic particles in the direction close to the surface normal. The chemical reactions are found to influence the angular distributions in the way opposite to the one of elastic collisions. The reaction heat contributes to the energy of particles and the velocity distributions are affected by reactions. As result of these processes, the angular distributions are broadened from the surface normal. Additional collisions with the particles of the ambient gas were shown to influence the composition and uniformity of thin films. The study of these processes is of a particular interest for the developing of pulsed laser deposition (PLD) technique.

A large field of applications as microelectronics, micromechanics and optics needs to overcome the deposition of various materials showing dielectric, superconducting, piezoelecinc properties under thin film form. Numerous methods were developed as Chemical Vapour Deposition, Sputtering, Thermal Evaporation. Since the early 1980's, a new process based on laser ablation is developed.1 The Pulsed Laser Deposition (P.L.D) method is based on the laser evaporation of a target and the subsequent deposition of the ablation plume on a substrate (see fig. 1). A wide variety of materials was successfully deposited in thin film form by this method. Recently, Nb5Te4 thin films were realized for the first time by using P.L.D process.3 The Nb5Te4 compound presents strong anisotropic properties and finds applications in microelectronics (1D conductors) and micromechanics (solid lubricant). These first results3 shown the key roles played by the laser fluence and the substrate temperature on the film composition and crystallisation. For example, increasing the laser fluence decreases the interreticular distance observed by X-ray diffraction and increases the Te/Nb ratio. This shows the importance of kinetic parameters of the laser-induced plume on the crystallisation process. In order to understand the influence of the laser parameters on the film formation, it is necessary to study the ablation process and the expansion of the ablation cloud.