Modulation of Heteroepitaxial Metal Organic Framework Crystallization by Local Chemical Environment via Organic-Step Interaction*

Heterogeneous nucleation mitigates uncontrolled bulk nucleation by reducing the interfacial energy of the new nucleus, leading to smaller nucleation barriers and reducing the supersaturations required for nucleation. This approach has the benefit of controlling over crystal number, location, and orientation by manipulating the degree of chemical and/or structural match between the substrate and new phase. To understand the formation of hybrid MOF-semiconductor materials, we used in situ AFM to study the nucleation of ZIF-8 on ZnO faces. The results show that on ZnO (001) methylimidazole molecules poison the terrace regions preventing ZIF formation except along the step edge, the ZIF-8 exhibits large percentage of (111) face on ZnO (001) face due to symmetry match. In contrast, on (100) the linker configuration support ZIF-8 nucleation and epitaxial film form due to lattice match. However, the ZIF-8 crystal on step edge shows no orientation control. The control of MOF nucleation on substrate with different nutrient ions symmetry provide a general way to synthesize MOF film with uniform orientation.