An instrument for measuring angular distribution of sputtered neutral atoms

An apparatus utilizing laser‐induced fluorescence (LIF) has been developed to measure high‐resolution angular distributions of sputtered neutral atoms. LIF provides sensitive detection, a feature necessary to monitor the low atomic fluxes inherent to angularly resolved sputtering measurements in the static sputtering regime. The apparatus incorporates a detector assembly which rotates about the sample in an ultrahigh vacuum (UHV) chamber, allowing a large range of angular measurements at different ion beam incidence angles. Laser light is brought to the detector in the UHV chamber via a single optical fiber and fluorescence photons exit the chamber via a fiber bundle. The optical fiber and fiber bundle are mounted in a fixed orientation on the detector, maintaining constant alignment as the assembly rotates. Angular resolution in the polar plane containing the incident ion beam and the surface normal is better than 3°. Angular resolution in the direction perpendicular to the polar plane is governed by the Doppler shift and is 0.028° for 3.2 eV atoms. Overall detection efficiency is estimated to be 5×10−9 counts per sputtered atom and 2×10−3 counts per atom entering the detection volume. Initial experiments using polycrystalline Zr to characterize the device are described.