Versatility of aqueous micellar solutions for self-assembled monolayers engineering

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Self-assembled monolayers (SAMs) are crucial for molecular electronics and surface functionalization.
• Traditional SAM formation often relies on organic solvents, posing environmental and processing challenges.
• Developing water-based methods for SAMs is essential for greener and more compatible fabrication processes.

Purpose of the Study:

• To investigate the self-assembly of thiol-terminated molecules onto gold surfaces using aqueous micellar solutions.
• To compare the density and quality of SAMs formed in aqueous micellar solutions versus traditional organic solvents.
• To explore the application of this aqueous method for fabricating molecular devices and functionalizing gold nanoparticles.

Main Methods:

• Utilized aqueous micellar solutions for the self-assembly of aliphatic and aromatic thiol-terminated molecules onto gold substrates.
• Employed Scanning Tunneling Microscopy (STM) to analyze the density and defect structure of the self-assembled monolayers (SAMs).
• Investigated ligand-exchange reactions on dodecanethiol (DT)-stabilized gold nanoparticles and SAM formation via micropatterned resist masks using aqueous solutions.

Main Results:

• Achieved higher density SAMs using aqueous micellar solutions compared to ethanol, primarily due to a significant reduction in defect density (etch pits, domain boundaries).
• Demonstrated the successful insertion of conjugated molecules into dodecanethiol (DT) SAMs from an aqueous solution.
• Showcased ligand-exchange on DT-stabilized gold nanoparticles and the preparation of DT SAMs on gold using micropatterning with aqueous solutions.

Conclusions:

• Aqueous micellar solutions provide an effective and environmentally friendly alternative to organic solvents for creating high-quality SAMs on gold.
• This water-based approach enhances SAM density by minimizing defects, not by increasing molecular packing.
• The findings enable the use of water for molecular device fabrication compatible with microelectronic lithography requirements.