Formation of STM images of Ni3Al (001) and (111) surfaces -: art. no. 115425

We present the results of scanning tunnel microscope (STM) measurements performed on a Ni3Al(111) surface, combined with a theoretical study of the formation of STM images of (001) and (111) surfaces of this alloy. The STM images of the Ni3Al(111) surface show a superstructure with the lattice constant corresponding to the size of the surface unit cell. An earlier interpretation of this result assumes that this superstructure represents the distribution of the surface Al atoms, while Ni atoms remain invisible in the STM images. This supposition is confirmed here by presented STM simulations. Moreover, numerical calculations show that a similar effect should also appear in the STM images of the Ni3Al(001) surface. A detailed theoretical analysis indicates that the domination of Al atoms in the STM images of both surfaces is mainly caused by the intra-atomic s-p(z) interference. This kind of intra-atomic interference reduces the s and p(z) current contributions tunneling through surface Ni atoms and increases considerably the corresponding contributions flowing through Al atoms. As a result, only the surface Al atoms appear in the STM images.