Shunta Iwamoto1,Ryo Nakayama2,Seoungmin Chon1,Ryota Shimizu2,Taro Hitosugi2
Tokyo Institute of Technology1,The University of Tokyo2
Shunta Iwamoto1,Ryo Nakayama2,Seoungmin Chon1,Ryota Shimizu2,Taro Hitosugi2
Tokyo Institute of Technology1,The University of Tokyo2
Metal–organic frameworks (MOFs) are crystalline porous materials composed of metal ions and organic ligands. Many reports have described the synthesis of oriented MOF films with high crystallinity and flatness by liquid-phase processes such as layer-by-layer method. Liquid-phase methods often require modification of the substrate surface with self-assembled monolayers, and there is a risk of corrosion and contamination of the interface by the solution. By contrast, synthesis by physical vapor deposition is suitable to prevent the degradation caused by solvents and is advantageous for the fabrication of well-defined interfaces and easy patterning for further device fabrication. Until now, oriented thin films of two-dimensional MOFs were fabricated on insulating substrates by physical vapor deposition<sup>1</sup>. However, the oriented three-dimensional MOF films have only been synthesized on metal surfaces<sup>2</sup>, and never on insulating substrates by physical vapor deposition.<br/> <br/>In this study, we report the fabrication of (111)-oriented thin films of a three-dimensional-MOF HKUST-1<sup>3</sup> ([Cu<sub>3</sub>(BTC)<sub>2</sub>], BTC = 1,3,5-benzenetricarboxylate) on insulating glass substrates by combining vacuum deposition and annealing in acetic acid vapor. HKUST-1 is expected for device applications because of the tunability in ionic and electronic conductivities by introducing molecules into the pores. We utilized two-step processes for the HKUST-1 thin film fabrication. First, trimesic acid and copper(II) acetate thin films were deposited on the glass substrates as a precursor. Second, post-deposition annealing was performed in air and an acetic acid atmosphere. While the thin film annealed in air showed no peaks corresponding to HKUST-1 in the out-of-plane X-ray diffraction (XRD) pattern, the thin film annealed in acetic acid vapor showed 111, 222, and 333 diffractions, indicating (111)-oriented HKUST-1 films were successfully synthesized on the glass substrate. These results suggest that annealing with the acetic acid vapor facilitates the precursor diffusion and the solid-phase reaction to form HKUST-1 crystals.<br/> <br/>References<br/>1. Chon et al., MRS Fall Meeting, 2022, NM06.05.23.<br/>2. Han et al., J. Mater. Chem. A, 2019, 7, 19396–19406.<br/>3. Chui et al., Science, 1999, 283, 1148–1150.