Low Temperature STM Studies of Single Rare-Earth Molecules on Surfaces*

Rare-earth metals are important for many technological applications from catalysis, emission, energy up-conversion to quantum information science. Local environment of rare-earth metals play vital role in their applications and engineering of electronic, and magnetic structures of rare-earth systems are of great interest. One of the best options to control the environment of rare-earth ions is to place them in molecular scaffolds where the ligands not only protect them but also can be used to modify their electronic and magnetic properties. Here, we have developed a variety of rare-earth based molecular systems that can be deposited onto materials surfaces intact under ultrahigh vacuum environment. Atomic level characterizations of structural and electronic properties of individual rare-earth molecular systems are performed with a low temperature ultrahigh vacuum scanning tunneling microscope (UHV-LT-STM) capable of single molecule tunneling spectroscopy and controlled manipulation of atoms/molecules on surfaces. dI/dV tunneling spectroscopy, and spectroscopic mapping of single molecules containing caged Eu, La, Lu, and Tb rare-earth metals adsorbed on metal surfaces such as Au(111) and Cu(111) reveal the energy gaps of highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO) as well as the spatial locations of electronic states within the molecules. The experimental measurements are corroborated by density functional theory calculations to understand their electronic states.