A more complex structure of ad-atoms has been observed by Silly et al., . The authors have reported the formation of hexagonal Ce superlattice on Ag(111) surface. The periodicity of FOs generated by Ce atoms corresponds with the Ce-Ce distances, being 32 Å (Fig. ). Similar FOs have also been imaged from lone Ce pair (Fig. ). The fitting of FOs, generated by lone Ce pairs, that are also present on the surface, using equations used by Crommie et al., has yielded the same phase shift (δ0 = 0.37 π) as fitting with theory by Hyldgaard and Persson 49 (see section 3.7 of this review) for the surface-mediated interactions, further proving the FOs nature of the Ce-Ce interactions. Interestingly, no such superstructures have been found for Ce deposited on Ag(100) surface due to the lack of electron surface state in the latter. The use of FOs also allows us to understand an unexpectedly higher stability of the superlattice at 4.8 K in comparison to a lower temperature. It appears that thermal energy at this temperature is sufficient to overcome a first potential energy maximum from the Ce-induced FOs. Lukas et al. have studied pentacene adsorbed on Cu(110). They have determined that pentacene arranges into long-ranged structures of parallel molecules. The propagation of the observed oscillations, however, is different from the one expected for the bare Cu(110). Thus, it originates from a different electronic state that is most likely a result of electron interaction (donation/backdonation) between the pentacene and the surface. This has been further confirmed with the CO desorption experiment from a Cu(110) surface. It appeared that in the presence of ordered pentacene, CO desorbs at 16 K less than for a surface covered with disordered pentacene. Interestingly, the spacing between the pentacene molecules is about 12 Å 19 similar to 12.5 Å found for Cu/Cu(111) adsorbates. This distance approximately corresponds to the period of FOs produced by a single adsorbed pentacene molecule (9.5 Å, giving kF of 0.66 Å -1 ). Small dif-ferences might be attributed to repulsion between the molecules. The previously discussed Repp et al. paper also mentions the presence of repulsive interaction for individual Cu atoms at distances below 10 Å.