Morphological control of a metal−organic framework for single-crystal electronic device fabrication

Abstract

Single-crystal electronic devices of metal−organic frameworks (MOFs) unveil their intrinsic electrical conductivity values by eliminating the influence of grain boundaries. Their fabrication demands sophisticated control of crystal morphology: micro/nano fabrication requires crystals with hundred-nanometer thicknesses, whereas manual fabrication requests those with hundred-micrometer lengths. Herein, we report morphological control of an electrically conductive MOF, Zn2(TTFTB) (TTFTB4− = tetrathiafulvalene tetrabenzoate), by synthetically tuning nucleation and growth processes during crystallization. Whereas adjusting water content, organic solvent, solution pH, metal ion concentration, and reaction procedures including temperature, time, and heating and cooling rates did not produce crystals for either device fabrication method, increasing the concentration of H4TTFTB led to crystals exhibiting an average length of 450 μm with the longest above 800 μm. The growth of large Zn2(TTFTB) crystals is facilitated by self-assembly of the ligand in the reaction mixture before formation of the MOF. These large crystals enabled manual fabrication of single-crystal 2-contact probe devices, which displayed an average electrical conductivity of 3.84 × 10−6 S·cm−1 in ambient conditions.