The paper by Hasegawa and Avouris has also presented experimental evidence in the form of the periodic charge density waves in the STM image of the Friedel oscillations. Similar to the paper of Crommie et al. , they have worked on Au(111) surfaces and observed a wave-like pattern arising from steps on the surface. They have further confirmed these findings using Cu(111) and Ag(111) surfaces. Avouris with colleagues have proved that STM reflects the electronic structure of the adsorbate and, therefore, can and should be used to study Friedel oscillations. The importance of this paper can hardly be overestimated because, nowadays, most experimental studies of FOs are done using STM. These early works have started a new twist in studying Friedel's waves. From then on, experimental STM observations have become an important tool in FO research.