Two-Dimensional Metal-Organic Frameworks of Rare-Earth Molecular Systems on Surfaces

Metal organic frameworks (MOF) involving rare-earth ions may play important roles in potential applications. Both molecular scaffold and ordered arrangement of rare-earth atoms can contribute to the electronic and magnetic properties of the MOF. Here, we form two-dimensional MOFs of rare-earth based molecular systems on Au(111) surface and their electronic and structural properties are investigated with scanning tunneling microscopy (STM) and tunneling spectroscopy methods in ultrahigh vacuum environment at low temperatures. STM images reveal that both Eu and Tb based molecules form an ordered arrangement of ring like structures composed of 12 molecules each. These molecular rings then form a hexagonal lattice on Au(111) surface. A careful analysis reveals that the molecules are arranged in either left or right-handed stacking and thus the 2-D MOF structure as a whole is chiral. Single point tunneling spectroscopy and spectroscopic mapping of the MOFs are performed at sub-molecular resolution and reveal spatially varying electronic structure within the MOFs. The formation of chiral 2-D MOFs using rare-earth based molecular systems on materials surfaces may pave the way to incorporate them for solid state applications.