Physical vapor deposition of refractory oxides by laser ablation Available to Purchase

Background: The Department of Energy is interested in refractory oxide films for the protection of weapons components. Material compatibility and chemical resistance are the primary film properties that are of interest. The films must be thermally stable and be free of mechanical imperfections to satisfy the project requirements. Chemical deposition methods, while successful for some applications, are not useful for the deposition of such films on the insides of long, thin metallic tubes. The laser used for the vapor deposition will be arranged to propagate its beam inside the tube. This will be accomplished in two ways, in free space propagation TEM mode by conventional focusing or by insertion of an optical fiber of appropriate diameter into which the beam has already been launched. The target material will be moved inside the tube on the end of a probe which will be moved to asure that the entire inside of the tube is uniformly coated with the oxide material. We are structuring our program to ultimately address the application. Introduction: We have shown the practicality of using laser ablation physical vapor deposition for the deposition of films of highly refractory oxide materials on various substrates. In particular, we have concentrated our efforts on the oxides of aluminum and erbium. Other rare earth oxides are also being evaluated. We have measured film deposition rates as a function of laser energy and are in the process of optimizing the pulse format and other parameters. Experimental Apparatus: We have used an XeCl excimer laser operating at a wavelength of 308nm with a pulse energy of up to 350mJ and a KrF laser having an output of 600mJ at 248nm. The repetition rate was variable from 1 to 100 Hz. The refractory oxide target was located in a vacuum chamber equipped with transparent windows to allow the laser radiation to impinge on the target material. The substrate could be heated to a maximum temperature of 900C. The target and substrate can be continuously rotated during the irradiation procedure. Experimental Procedure: We investigated nine refractory oxides which were deposited on stainless steel coupon shaped substrates held at a temperature of 400C. The laser was focused onto the heated, rotating oxide target. The targets had various sizes but were generally the shape of pellets, 1.5cm dia × 3mm thick. The oxide targets were sintered to greater than 94% of theoretical density. The substrates were arranged as close as possible to the ablation targets to facilitate efficient deposition. Results and Analysis: The mass loss of the target was approximately 2μg per Joule of illuminating energy. In all cases the target interepted 4 to 5% of the ablated mass. Future Work: The experiments aimed at demonstrating deposition on the interior of tubes are in progress as are measurement of the adhesion of films