ELECTRON-EMISSION FROM CONDUCTING SURFACES IMPACTED BY MULTIPLY-CHARGED POLYATOMIC IONS

In this paper, we present results on secondary electron emission from impacts of electrosprayed, multiply-charged, macromolecular ions on various conducting surfaces. The impact speeds are in the range v = 30 to 140 km/s and are above the threshold for kinetic electron emission. Below approximately 80 km/s, the yield is proportional to M(v(2) - v(t)(2)), a dependence which goes through a smooth transition to a (v - v(0))-dependence at higher impact speeds. Here v(0) and v(t) are the extrapolated threshold velocities. For a fixed mass and constant incident velocity, we observe an increase in the secondary electron yield as we increase the ion charge-state. This increase is explained by the acceleration of the incident ion by its image charge field. The measured electron yield is highly dependent on target material and on surface treatment prior to the experiment. A non-Poissonian behaviour is observed in the shape of the electron number distributions. We furthermore find the electron yield per unit mass from impacting macromolecular ions to be larger than from atomic ions.