Atomically-defined on-surface synthesis of multilayer metal-organic frameworks.

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• On-surface synthesis enables high-resolution material design but is typically restricted to monolayer materials.
• Metal-organic frameworks (MOFs) are crucial functional materials with diverse applications.

Purpose of the Study:

• To demonstrate the feasibility of on-surface synthesis for multilayer metal-organic frameworks (MOFs).
• To investigate the structural and electronic properties of multilayer Fe-TCNQ MOFs.
• To explore the influence of substrate on MOF growth modes.

Main Methods:

• On-surface synthesis of Fe-TCNQ multilayer MOFs.
• High-resolution Scanning Tunneling Microscopy (STM) for structural analysis.
• Density Functional Theory (DFT) computations for electronic structure and bonding.

Main Results:

• Successfully synthesized multilayer Fe-TCNQ MOFs with both in-plane and out-of-plane bonding.
• Observed distinct coordination geometry and electronic structures in multilayer MOFs due to interlayer interactions.
• Demonstrated substrate-dependent growth modes: Volmer-Weber on graphene/Ir(111) and Stranski-Krastanov on Au(111).

Conclusions:

• On-surface synthesis can overcome monolayer limitations for MOF construction.
• Interlayer chemical interactions significantly influence the properties of multilayer MOFs.
• Substrate choice is critical in controlling the growth mode of on-surface synthesized MOFs, opening avenues for 3D MOF fabrication.