We assumed that the relative permittivity, dielectric constant ε S could be also used as a collective property , and the dependence ε S = F(L) could be compared with the function x = f(L). Therefore, Bockris, Devanathan, and Müller predicted, in the early 1960s, based on their (BDM) model of the EDL, the value of ε S ≈ 6 for the first molecular layer of water . This was indeed confirmed experimentally by AFM measurements, the change at the mica/water interface covers the region ε ≈ 4-80 in the 10-nm layer . Recently, using capacitive measurements with the modified AFM in boron nitride slit-like channels in a range of layer thicknesses 1 ÷ 300 nm, Fumagalli et al. found ε S ≈ 2 at the interfaces, for layer thicknesses of 2 to 3 water molecules (see also ). Thus, just as in the case of above viscosity measurements with EC-AFM, this technique allows the determination of ε S , the collect ive property of the medium X, s tar t ing a t s ubna no met er distances from the surface. The device would be desirable to complement with a potentiostat for potential-controlled measurements, similar to EC-AFM; it would give the opportunity to study the effect of the potential on the interfacial ε S .