Metal–organic coordination structures are materials comprising reticular metal centers and
organic linkers in which the two constituents bind with each other via metal–ligand coordination
interaction. 2D metal-organic (or porous coordination) frameworks have attracted tremendous
attention in the last two decades owing to their unique electronic, topological, magnetic properties.
These properties of 2D metal-organic frameworks suggest many potential applications of the
materials, for instance, they might be promising candidates to build functional molecular devices.
However, the fabrication of single layers of 2D metal-organic frameworks remains a great
challenge. In this regard, synthesizing conjugated organic monolayer with unique properties is
highly desirable. This thesis focuses on the fabrication of 2D metal–organic coordination structures
through on-surface synthesis on Au(111), Cu(111) and Ag(111) substrates. We used scanning
tunneling microscopy (STM) as an experimental tool and density-functional theory (DFT) as a
theoretical tool to characterize the electronic, topological, magnetic properties of the networks at a
This thesis consists of four projects as below:
In the first project, we synthesize single-layer Ni3
on a Au(111) substrate. We resolve
its structure at sub-molecular resolution using STM. The DFT calculations show that upon
adsorption on Au(111), the single-layer Ni3
interacts weakly with the substrate and retains
its planar structure. Interestingly, the non-trivial topological gap of the free-standing layer is
preserved in the surface-adsorbed layer. These results demonstrate that on-surface self-assembly is
a viable route to realize 2D-MOFs exhibiting exotic quantum phases.
In the second project, we design and synthesize a two-dimensional metal-organic network
], which comprises a Kagome lattice of Fe atoms. DFT calculation indicates that there
is a ferromagnetic ground state and a non-trivial 15 meV gap between the Dirac bands and the flat
band. Experimentally, we synthesize this structure on a Au(111) surface. We study this structure
at a single-molecule resolution and confirm that the on-surface structure is nearly identical to the
free-standing framework. We also use scanning tunneling spectroscopy (STS) to reveal the
presence of a magnetic moment on Fe atoms in the framework.
In the third project, we study the coordination behavior of Ni, Pt, Pd metal with 2,3,6,7,10,11-Hexaaminotriphenylene (HATP) molecules on a Ag(111) surface. We confirm that the
coordination reaction can happen with all three metals and also resolve the metal-organic
coordination structures at an atomic resolution.
In the last project, we synthesize single-layer 2D-MOF structures of Ni3
networks on a Ag(111) surface, and Cu3
networks on a Cu(111) surface. The
high resolution STM images show that the Ni3
networks are not flat but
titled out of plane on the Ag(111) surface, while the Cu3
network can grow into larger and
flat networks on the Cu(111) surface. Moreover, we use STS to study the coordinated Fe in
coordination network. The double-step structure in the STS spectra indicates that the
coordinated Fe atoms undergo spin-flip processs.
In summary, we design and synthesize five 2D metal-organic frameworks which comprises a
Kagome lattice of coordinated metal atoms. These studies may contribute to the development of
low-dimensional conjugated metal-organic materials.
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