Data from: Dynamics of contact electrification

Although the electrical charging of objects brought into contact has been
observed for at least two thousand years, the details of the underlying
mechanism are still not yet fully understood. The present paper deals with
the very basic process of contact electrification between two metals. We
have developed an experimental method to follow the charge of a small
sphere bouncing on a grounded planar electrode on a time scale down to 1
µs. It reveals that the sphere is discharged in the moment of contact
which lasts about 6-8 µs. However, at the very moment of disruption of the
electrical contact it regains charge far beyond the expectation according
to the contact potential difference. The excess charge rises with
increasing contact area.