Growth Mechanism of Subsurface Argon Nanobubbles at Pd(111)

Strain on surfaces of heterogeneous catalysts has been attracting a keen attention due to its impact on catalytic activities. The surface strain can be induced by rare gas ion implantation on single crystal substrates. We investigated the growth of subsurface nanobubbles and the strain of the surface lattice induced by Ar ⁺ ion bombardment at a Pd(111) substrate by temperature-programmed desorption (TPD) and low energy electron diffraction (LEED). The TPD spectra of Ar emitted from nanobubbles showed multiple peaks indicating the existence of multiple domains with different depths. From the dependence of TPD spectra on the substrate temperature, ion acceleration energy, and ion incident angle, we proposed models of formation processes of Ar nanobubbles in terms of diffusive and ballistic transport of Ar atoms in the Pd lattice.