Cover Illustration:The cover image presents the application of scanning-tunneling microscopy and spectroscopy (STM/STS) in exploring the surface properties of single atomic surface alloys. In article No.1911035, Wang et al. demonstrate that the singly dispersed Au atoms in the top and second layers of the Cu(111) substrate can present slight difference in the local density of states, which can be detected by STM observations and correlated with their different interactions with the adsorbed CO molecules.