Orientation Control of a Two-Dimensional Conductive Metal-Organic Framework Thin Film by a Pyridine Vapor-Assisted Dry Process.

Metal-organic frameworks (MOFs) are attractive materials with periodic pore structures constructed by coordinating metal ions and organic ligands. Recently, Cu 3 (HHTP) 2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), a two-dimensional conductive MOF, has attracted attention as a promising device material. Owing to the anisotropy of Cu 3 (HHTP) 2 properties, oriented thin films of this MOF are desired for evaluating its physical properties and device integration. To date, wet processes have been used to fabricate Cu 3 (HHTP) 2 films, whereas dry processes are essential for high-quality devices. However, oriented Cu 3 (HHTP) 2 thin films have not yet been fabricated by using dry processes. In this study, we succeed in fabricating an orientation-controlled Cu 3 (HHTP) 2 film on Al 2 O 3 (001) by using a two-step dry process involving (1) the multilayer deposition of copper acetate and HHTP using a vapor deposition system and (2) pyridine vapor-assisted annealing. In-plane and out-of-plane X-ray diffraction patterns confirm the successful fabrication of the (001)-oriented Cu 3 (HHTP) 2 films. The conductivity evaluated by four-probe measurements is 2.6 × 10 -2 S cm -1 , comparable to that of films fabricated by wet processes. This study provides a novel guideline for the orientation control of two-dimensional conductive MOF thin films via a dry process.