posted on 2021-12-02, 20:38authored byAshok Kumar Mahato, Saikat Bag, Himadri Sekhar Sasmal, Kaushik Dey, Indrajit Giri, Mercedes Linares-Moreau, Carlos Carbonell, Paolo Falcaro, E. Bhoje Gowd, Ratheesh K Vijayaraghavan, Rahul Banerjee
Synthesis of covalent organic framework
(COF) thin films on different
supports with high crystallinity and porosity is crucial for their
potential applications. We have designed a new synchronized methodology,
residual crystallization (RC), to synthesize sub 10 nm COF thin films.
These residual crystallized COF thin films showcase high surface area,
crystallinity, and conductivity at room temperature. We have used
interfacial crystallization (IC) as a rate-controlling tool for simultaneous
residual crystallization. We have also diversified the methodology
of residual crystallization by utilizing two different crystallization
pathways: fiber-to-film (F–F) and sphere-to-film (S–F).
In both cases, we could obtain continuous COF thin films with high
crystallinity and porosity grown on various substrates (the highest
surface area of a TpAzo COF thin film being 2093 m2 g–1). Precise control over the crystallization allows
the synthesis of macroscopic defect-free sub 10 nm COF thin films
with a minimum thickness of ∼1.8 nm. We have synthesized two
COF thin films (TpAzo and TpDPP) using F–F and S–F pathways
on different supports such as borosilicate glass, FTO, silicon, Cu,
metal, and ITO. Also, we have investigated the mechanism of the growth
of these thin films on various substrates with different wettability.
Further, a hydrophilic support (glass) was used to grow the thin films
in situ for four-probe system device fabrication. All residual crystallized
COF thin films exhibit outstanding conductivity values. We could obtain
a conductivity of 3.7 × 10–2 mS cm–1 for the TpAzo film synthesized by S–F residual crystallization.