Abstract
Direct growth of metal-organic frameworks (MOFs) on substrates is a prerequisite to incorporating them into functional platforms and microdevices. Nevertheless, available reports mostly rely on the solvent-based routes, typically altered from processes for powder synthesis which are obstacles to the nanofabrication. Besides, although few vapor-phase growth approaches were presented, the proposed procedures required multiple steps, such as matrix deposition and post-conversion, to obtain desired MOF films on substrates. Here, we demonstrate a steam-assisted chemical vapor deposition (CVD) method to directly synthesize highly crystalline ZIF-67 thin films at the temperature <125 degrees C. With a slow deposition rate, the ZIF-67 forms a highly oriented thin film on a c-plane sapphire substrate, indicating the growth is epitaxial. Furthermore, we demonstrate the integration of directly grown CVD ZIF-67 as the active material of chemiresistors onto microelectronic chips. The ZIF-67 chemiresistors exhibit responses to the gas molecules, which are capable of diffusing into the cage of ZIF-67 at room temperature. The proposed synthesis method of ZIF-67 thin films is simple, scalable, cost-effective, and promising for numerous applications.