Bimodal distribution of neon nanobubbles in aluminum

Ne 1s core-level photoelectron spectra from Ne nanobubbles implanted in aluminum exhibit two peaks whose binding energies and relative intensities change with implantation energy, isochronal annealing, and sputtering. These changes in the core-level spectra are manifestations of the nanometer size of the bubbles since the screening of the photohole by the Al conduction electrons depends on the bubble size. Existence of a bimodal depth and size distribution of Ne nanobubbles is demonstrated in this work: smaller bubbles of about 4 in radius are formed close to the Al(111) surface while the larger sized bubbles of 20 in radius exist deeper below in the beneath subsurface region. A general relation between the radius of the rare-gas bubbles and their core-level binding energies is established.