Mechanical and Electrical Studies of Two-dimensional Covalent Organic Frameworks

Two-dimensional (2D) covalent organic frameworks (COFs) are a promising new class of 2D materials with the potential for highly-tunable chemical, mechanical, electrical, and optical properties. As porous polymers, 2D COFs are predicted to have a combination of low mass density and high mechanical strength. Here we discuss mechanical and electrical measurements on COF thin films. For the mechanical measurements, we have developed a protocol for synthesizing COF films as thin as 1.5 nm at a liquid-liquid interface, lifting and drying them on a PDMS stamp, and then performing a dry transfer onto a prepatterned substrate to make suspended COF films. The transferred films exhibit excellent uniformity, smoothness, and cleanliness. We report results for the 2D Young's modulus and mechanical strength using nanoindentation measurements performed using an atomic force microscope. We will also discuss initial electrical measurements on COF films designed to have small energy gaps.

This work was supported by the Army Research Office (W911NF-15-1-0447).