In our work we investigated (de)polarization effects in molecular monolayers. Our primary goal was to highlight the difference between two quantities that are often synonymously used as dielectric constant. One, εeff, is an effective quantity necessary to correctly describe depolarization phenomena, while the other, ε , is the “true” dielectric constant of the monolayer, which is relevant for capacitance measurements or estimation of tunnelling barriers.
ε relates the induced polarization of a medium to the total electric field E present inside the medium which, in our case, is given by the monolayer. Alternatively, one can also define an auxiliary dielectric constant, , which relates the polarization to the externally applied electric field, i.e., the field present outside of the monolayer. The difference between these two definitions has recently been elaborated by Natan et al.1
In our work, although denoted as ε, we actually calculated, plotted, and discussed . We note here that ε would have been the more appropriate choice, as outlined in Ref. 1. However, the conversion between the two quantities is straightforward, . This relationship reveals that ε is always bigger than . For the case of the biphenyl monolayers in particular, ε is also bigger than the depolarization factor εeff, while for longer or less polarizable molecules the differences between the two latter quantities are less pronounced