Before discussing the possible anisotropic character of FOs on some surfaces, we should first delve into how the Fermi surface of the material is able to affect the FOs. The smaller Fermi contour of the Fermi surface present in the reciprocal space of the metal means that one has fewer states per point of space. Therefore in real space, one would expect electrons to delocalize over farther distance, resulting in a bigger wavelength of the Friedel oscillations (Fig. ) Since in real materials, the Fermi surface is not perfectly isotropic, the Fermi wavevector kF -the radius of the Fermi surface -is dependent on the direction. Therefore, the decay rate of Friedel oscillations may differ from what is predicted only from the dimensionality of the electron gas. Its connection with the oscillation period has been shown in the subsection 1.4.2. On the other hand, as noted by Xue et al., , the chirality of the Dirac electrons may result in faster LDOS oscillations decay -i.e., instead of 1/ √ r for noble metals, for graphene, there is 1/ √ r 3 . Anisotropy allows for much further propagation of FOs and, therefore, as noted by Weismann et al. , should play an important role in surface phenomena. Anisotropic oscillations have also been directly observed in other studies . Weismann and co-workers have recorded cross-shaped FOs stemming from Co atoms below Cu(111) surface (Fig. ). Interestingly, for Cu(100) surface, the anisotropy has only become visible at a very low bias voltage (10 mV).