  We investigate the behavior of mixed 3He-4He droplets on alkali surfaces at
zero temperature, within the frame of Finite Range Density Functional theory.
The properties of one single 3He atom on 4He_N4 droplets on different alkali
surfaces are addressed, and the energetics and structure of 4He_N4+3He_N3
systems on Cs surfaces, for nanoscopic 4He drops, are analyzed through the
solutions of the mean field equations for varying number N3 of 3He atoms. We
discuss the size effects on the single particle spectrum of 3He atoms and on
the shapes of both helium distributions.
