Controlling Molecular Growth between Fractals and Crystals on Surfaces.

Area of Science:

• Surface science
• Supramolecular chemistry
• Materials science

Background:

• Functional molecules typically form 2D crystals on substrates.
• These molecules can also self-assemble into ordered fractal aggregates.
• Controlling the coexistence of fractal and crystalline patterns is crucial.

Purpose of the Study:

• Investigate conditions for coexisting Sierpiński triangle fractals and 2D molecular crystals.
• Explore growth competition between fractal and crystalline structures.
• Understand how to steer surface self-assembly for desired patterns.

Main Methods:

• Studied 4,4″-dihydroxy-1,1':3',1″-terphenyl molecules on Au(111) in ultrahigh vacuum.
• Tuned substrate and molecular surface coverage.
• Modified molecular functional groups.
• Employed Density Functional Theory (DFT) calculations and Monte Carlo simulations.

Main Results:

• Demonstrated the coexistence of Sierpiński triangle fractals and 2D molecular crystals.
• Identified tuning substrate coverage and molecular functional groups as key control parameters.
• Showcased the ability to generate both fractal and nonfractal structures from the same molecular building block.

Conclusions:

• Surface self-assembly can be steered to produce diverse structures, including fractals and crystals.
• The study provides insights into controlling molecular self-assembly for generating complex patterns.
• This work highlights the potential for designing materials with tailored fractal and crystalline architectures.