Mehlhorn et al., and Knorr et. al., have also obtained similar interaction energies for CO on Cu(111) (Fig. ) as well as Cu and Co adatoms on Cu(111) and Ag(111) surfaces, respec- and Xue et al. , respectively. tively. According to the latter's STM results, the decay rate for each of the systems agrees with theoretical decay for 2D electron gas (1/r 2 ). The periodicity of FOs detected on Ag(111) surface is 38 Å, in perfect agreement with its theoretical kF value of 0.083 nm -1 94 (Please refer to section 1.4.2 for more details on parameters that govern FOs).