Laser ablation studies of palladium electrolytically loaded with hydrogen and deuterium.

Abstract

The kinetic-energy distributions (KED's) of ${\mathrm{Pd}}^{+}$, ${\mathrm{H}}_{\mathit{n}}^{+}$, ${\mathrm{D}}_{\mathit{n}}^{+}$ (n=1 to 3), and electrons created in a picosecond laser-produced plasma from palladium metal were studied using a spherical-sector electrostatic energy analyzer followed by a time-of-flight mass spectrometer. High-resolution, Fourier-transform mass spectroscopy showed no ${\mathrm{PdH}}_{\mathit{n}}^{+}$ or ${\mathrm{PdD}}_{\mathit{n}}^{+}$ ions. The total yield of ${\mathrm{Pd}}^{+}$ ions grew linearly with laser power, while the yields of ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ increased exponentially. The yields of ${\mathrm{H}}_{2}^{+}$ and ${\mathrm{H}}_{3}^{+}$ increased with laser power density slowly, comparable to the yields of ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ at low laser power density only. The average ion kinetic energy was a linear function of laser power for all species, but with a much higher average kinetic energy for ${\mathrm{Pd}}^{+}$ than for other species at a given laser power. The KED's for ${\mathrm{Pd}}^{+}$ were dominated by a plasma component with a Maxwellian shape, accompanied by a thermionic component with a kinetic energy in the range of 0--1 eV. The ${\mathrm{H}}^{+}$, ${\mathrm{H}}_{2}^{+}$, ${\mathrm{H}}_{3}^{+}$, and ${\mathrm{D}}^{+}$ KED's were basically Maxwellian, but the origins were offset to positive kinetic energies, with the offset energy increasing linearly with mass. There was no thermal component for the ${\mathrm{H}}_{\mathit{n}}^{+}$ or ${\mathrm{D}}^{+}$ ions.