  We report a direct detection of time correlated single-electron tunneling
oscillations in a series array of small tunnel junctions. Here the current, I,
is made up of a lattice of charge solitons moving throughout the array by time
correlated tunneling with the frequency f=I/e, where e is the electron charge.
To detect the single charges, we have integrated the array with a
radio-frequency single-electron transistor (RF-SET) and employed two different
methods to couple the array to the SET input: by direct injection through a
tunnel junction, and by capacitive coupling. In this paper we report the
results from the latter type of charge input, where we have observed the
oscillations in the frequency domain and measured currents from 50 to 250 fA by
means of electron counting.
