Non-thermal plasma etching of MOF thin films in high optical quality for interference sensing

Metal-organic frameworks (MOFs) in a thin film (TF) form have appeared recently as multifunctional elements for micro- and opto-electronic devices. However, achieving the roughness of MOF TF less than 10 nm is still a challenge, which limits their further integration with the corresponding devices. Here, we report on plasma etching (PE) approach allowing one to improve the quality of MOF TF surfaces. We demonstrate that PE of a spin-coated HKUST-1 TFs with a varied thickness (1.9 to 3 mu m) and roughness (more than 200 nm) decreases the film roughness by 100 times (up to 2 nm), while the chemical composition and the structure remain. As a result, an optical quality for the TF surface can be achieved resulting to a mirror like reflectivity as well as an optical sensitivity of water through the interference effect. The obtained results, thereby, pave the way to a universal post-processing of MOF TFs for diverse applications where their roughness plays a key role.