Substrate effect on supramolecular self-assembly: from semiconductors to metals.

Area of Science:

• Surface Science
• Supramolecular Chemistry
• Materials Science

Background:

• Understanding supramolecular self-assembly on different substrates is crucial for designing functional organic materials.
• Semiconductor surfaces, particularly silicon, present unique challenges for molecular adsorption due to strong interactions.

Purpose of the Study:

• To investigate the influence of substrate type on the self-assembly of terephthalic acid (TPA).
• To compare supramolecular formation on pristine silicon, silver-coated silicon, and silver surfaces.
• To explore the potential for 2D metal-organic framework (MOF) formation on these surfaces.

Main Methods:

• Scanning tunneling microscopy (STM) was employed to visualize molecular arrangements.
• Terephthalic acid (TPA) was deposited onto Si(111)-7x7, Si(111)-√3x√3-Ag, and Ag(111) substrates.
• Iron (Fe) deposition was performed on TPA layers to study MOF formation.

Main Results:

• TPA did not form ordered structures on pristine Si(111)-7x7 due to strong molecule-substrate interactions.
• Ordered TPA supramolecular layers, stabilized by hydrogen bonds, formed on Si(111)-√3x√3-Ag, similar to Ag(111).
• Fe deposition induced 2D MOF formation on TPA/Ag(111) but not on TPA/Si(111)-√3x√3-Ag.

Conclusions:

• Passivated semiconductor surfaces (Si(111)-√3x√3-Ag) can support ordered supramolecular assembly similar to metal surfaces (Ag(111)).
• The ability to form 2D MOFs differs between TPA layers on silver and silver-coated silicon, suggesting substrate-specific electronic or chemical properties influence subsequent reactions.