Measurement of Sputtered-Particle Velocity Spectra

Abstract

A time‐of‐flight technique was employed to determine the velocity distributions of particles sputtered from polycrystallinecopper targets by a 1‐ to 5‐keV pulsed Cs+‐ion beam. Velocityspectra were obtained for sputtered atoms having velocities greater than 2×106 cm/sec and for sputtered ions having velocities less than 3×106 cm/sec. In all cases, the target surface normal bisected the 64° angle between the detector and the incident ion beam, the target temperature was 20°C, and the flight path was 40 cm. Analytical models were fitted to the time‐of‐flight data. High‐velocity emission was found to be described best by binary collisions at the target surface and low‐velocity emission by Maxwellian distributions with temperatures predicted by C. H. Townes's theory of sputtering. It is proposed that the binary collisions (high‐velocity particles) are responsible for preferred angular emission along close‐packed crystallographic directions and that the low‐velocity particles are responsible for the cosinusoidal component of the angular distribution.