Nonintuitive Surface Self-Assembly of Functionalized Molecules on Ag(111).

Area of Science:

• Surface science
• Nanomaterials science
• Physical chemistry

Background:

• Molecular self-ordering on inorganic surfaces is key for nanomaterial fabrication.
• Functional groups are commonly used to control molecular arrangements, but this is insufficient for complex interfaces.
• Self-ordering processes at interfaces are intricate, influenced by various physical and chemical effects, often yielding unpredictable structures.

Purpose of the Study:

• To investigate the self-ordering behavior of a homologous series of quinones on a silver surface (Ag(111)).
• To elucidate the driving forces behind the formation of unexpected molecular structures at organic/inorganic interfaces.
• To develop a design principle for the self-assembly of functionalized molecules based on a comprehensive understanding of interaction mechanisms.

Main Methods:

• Utilized a combination of theoretical modeling and experimental characterization.
• Employed a machine-learning-based structure search algorithm to identify potential molecular arrangements.
• Performed experimental characterizations to validate theoretical predictions of interface structures.

Main Results:

• Demonstrated that quinones with identical functionalization form profoundly different structures on Ag(111).
• Identified a delicate balance between adsorbate-substrate interactions, adsorbate-adsorbate interactions, and steric hindrance as the cause of structural diversity.
• Achieved excellent agreement between theoretical models and experimental data regarding unit cell dimensions and molecular orientations.

Conclusions:

• The self-assembly of functionalized molecules at interfaces is governed by a complex interplay of multiple driving forces, not solely by functional groups.
• A machine-learning approach combined with experimental validation can uncover nonintuitive self-ordering mechanisms.
• A new design principle for molecular self-assembly has been devised, enabling better control over functional interface fabrication.