Scattering of low‐energy electrons on micron‐size pinholes

In exploring forces between charged particles and surfaces, we have sent a beam of low‐energy (0.5–40 eV) electrons through two (laser drilled) micron‐size pinholes in thin films of gold spaced 10 cm apart. Image forces associated with the solid around the second pinhole cause the beam to diverge into an angular distribution which is scanned with a movable slit and Channeltron detector. Distributions have widths which depend inversely on electron energy as expected from transit time considerations. The paraxial portion of the distribution appears to diverge as though from a weak negative electron lens. The impulse approximation for the radial component of the electron motion is used to derive a radial potential averaged along a line parallel to the pinhole axis. This potential approximately equals the expected value e/4x at x=10 A from the pinhole edge but deviates from this function at greater distances. This deviation may be due to geometric effects, to the impulse collision model employed, or to geometric irregularities at the edge. The results are useful in estimating efficiencies of filters for charged aerosol collection.