  In geometrically symmetric capacitive radio-frequency plasmas driven by two
consecutive harmonics a dc self-bias can be generated as a function of the
phase shift between the driving frequencies via the Electrical Asymmetry Effect
(EAE). Recently the Secondary Electron Asymmetry Effect (SEAE) was discovered
(T. Lafleur, P. Chabert and J.P. Booth, J. Phys. D: Appl. Phys. 46 135201
(2013)): unequal secondary electron emission coefficients at both electrodes
were found to induce an asymmetry in single frequency capacitive plasmas. Here,
we investigate the simultaneous presence of both effects, i.e. a dual-frequency
plasma driven by two consecutive harmonics with different electrode materials.
We find, that the superposition of the EAE and the SEAE is non-linear, i.e. the
asymmetries generated by each individual effect do not simply add up. The
control ranges of the dc self-bias and the mean ion energy can be enlarged, if
both effects are combined.
