Kondo effect in single cobalt phthalocyanine molecules adsorbed on Au(111) monoatomic steps.

The Kondo effect in single dehydrogenated cobalt phthalocyanine (CoPc) molecules adsorbed on Au(111) monoatomic steps was studied with a low temperature scanning tunneling microscope. The CoPc molecules adsorbed on Au(111) monoatomic steps show two typical configurations, which can be dehydrogenated to reveal Kondo effect. Moreover, the Kondo temperatures (T(K)) measured for different molecules vary in a large range from approximately 150 to approximately 550 K, increasing monotonically with decreasing Co-Au distance. A simple model consisting of a single Co 3d(z) (2) orbital and a Au 6s orbital is considered and gives a qualitative explanation to the dependence. The large variation of T(K) is attributed to the variation of the interaction between the magnetic-active cobalt ion and the Au substrate resulted from different Co-Au distances.