Solutions Are the Problem: Ordered Two-Dimensional Covalent Organic Framework Films by Chemical Vapor Deposition

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Covalent organic frameworks (COFs) offer high porosity and tunable properties but conventional synthesis methods are slow and yield difficult-to-process powders.
• There is a need for efficient techniques to produce crystalline COF thin films for advanced applications.

Purpose of the Study:

• To develop a facile and rapid synthesis method for producing highly crystalline and ordered COF thin films.
• To demonstrate the versatility of the proposed method for various COF linkages and substrates.

Main Methods:

• Chemical vapor deposition (CVD) utilizing co-evaporation of monomers onto a heated substrate.
• Characterization using grazing-incidence wide-angle X-ray scattering (GIWAXS), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis, and atomic force microscopy (AFM).

Main Results:

• Highly crystalline, defect-free COF films (40 nm-1 μm thick) with hydrazone, imine, and ketoenamine linkages were synthesized in under 30 minutes.
• Crystallinity, alignment, and successful monomer conversion were confirmed by multiple spectroscopic and microscopic techniques.
• Atomic force microscopy revealed a growth mechanism involving the coalescence of triangular crystallites into smooth films.

Conclusions:

• The CVD co-evaporation method provides a rapid and efficient route to high-quality COF thin films.
• The synthesized COF films exhibit potential for applications in size exclusion membranes, catalysis, and organic electronics.