High sensitivity sputter neutral mass spectrometry - Sputtering of neutral mixed clusters from gold-aluminum alloys

We have used the surface sensitivity of laser sputter neutral mass spectrometry to make measurements of clusters sputtered from AuAl alloys surfaces with high dynamic range. Polycrystalline AuAl4 and Au4Al were bombarded with 15 keV Ar+ at 60° incidence, and the resulting secondary neutral yield distributions were measured using laser postionization mass spectrometry. Neutral clusters containing up to 28 atoms were observed and exhibited an odd-even variation in signal dependent on the stability of the photoion. Clusters sputtered from Au4Al were gold rich compared to the substrate and the yield of neutral clusters containing n atoms, Yn, was found to follow a power in n, i.e. Yn ∝ n−δ, where the exponent δ was approximately 3.4.