Compositional Changes of Palladium Immersed in Deuterium under Laser Irradiation

Previous experiments by Nassisi and Biberian exploring the properties and behavior of palladium under local optical excitation in hydrogen and deuterium atmospheres have reported the unexpected emergence of lighter elements such as nickel and silicon on the Pd substrate. While morphological and phase changes of Pd bathed in hydrogen have been studied extensively due to the remarkable ability of Pd to absorb hydrogen into the metal matrix, the effect on Pd from local excitation by laser irradiation under these conditions is less well understood. We investigate the origin and mechanism surrounding the emergence of these lighter elements from this relatively simple experiment. We submerged three separate Pd bars in hydrogen and deuterium while simultaneously exposing them to optical stimulation at three different wavelengths and intensities. We acquired optical images of each roughly 1 cm² Pd bar at 1.2 µm resolution as well as acquired SEM/EDS elemental information at several points and over the entire bar before evacuating a chamber to 10 mTorr for one minute, then submerged the bar in the hydrogen/deuterium atmosphere at roughly 3 bar absolute. Under these conditions, we irradiated the Pd with different lasers (640nm at 5mW (pulsed), 532nm at 200mW, and 405nm at 20mW) in order to study before and after potential elemental changes to/on the Pd lattice. After several days under these conditions, the Pd bar was removed and again subject to optical and SEM/EDS microscopy. Whereas little to no elemental changes were observed under locations not irradiated, we found significant elemental differences under the locations of laser irradiation including the unexpected emergence of two separate 1 mm² patches of silicon under location irradiated with the green 200 mW laser and the 3mW red laser. We report on our methods and findings and recommend further investigation to explain the phenomena associated with these elemental changes.