Mechanical properties of electrochemically synthesised metal-organic framework thin films

We investigated the mechanical properties of metal-organic framework thin-film coatings grown by an electrochemical method, which allows fast deposition in environmentally friendly solvents. For the first time, Cu(CHDA) and Cu(INA)(2) are electrochemically synthesised as dense coatings on Cu-electrodes, alongside the well-known Cu-3(BTC)(2) (CHDA = trans-cyclohexane-1,4-dicarboxylate; INA = isonicotinate; BTC benzene-1,3,5-tricarboxylate). In order to probe the mechanical behaviour of the MOF coatings, both nanoindentation and nanoscratch experiments are performed. The indentation of a polycrystalline film allows the determination of average Young's moduli and hardness of the coatings. Cu(CHDA) exhibits the highest stiffness and hardness, with values of 10.9 GPa and 0.46 GPa, respectively. Intermediate values are obtained for the well-known Cu-3(BTC)(2) and the smallest values for Cu(INA)(2). A close inspection of the crystal lattice of the MOF materials under investigation allows for correlating the mechanical properties and structural building units of these materials. Finally, the effect of the fundamental mechanical properties of MOF films on their scratch and wear resistance is illustrated.