A remarkable STM pattern has been obtained by Repp and Meyer . They have found FOs of Cu(111) to survive on a bilayer NaCl/Cu(111) surface (Fig. ). The surface state of the latter is a little different from the original Cu(111), which results in a slightly bigger oscillation period of 1.9 nm (vs 1.5 nm on the Cu(111) surface). Interestingly, the adsorption of neutral Au adatoms does not result in FOs for such NaCl surfaces. Such occurrence is apparently a result of neutral Au adatom showing close to no interaction with ionic lattice of the NaCl surface. On the other hand, applying pulse voltage and negatively charging such an Au adsorbate induces relaxation of the NaCl film and consequently allows for Au 6s electron state interaction with the surface state, resulting in an expected FOs STM pattern. Using such a modified surface, authors have managed to use STM to directly image electron states associated with HOMO and LUMO of the adsorbed pentacene molecules However, further discussion of this find is outside the scope of this review.