Electrical and Mechanical Controllability of Rotor Dynamics in MOF Thin Films Revealed by AFM-IR

Understanding the rotor dynamics within metal–organic frameworks (MOFs) is fundamental to the desired amphidynamic application. However, in-depth investigation has been hindered due to the inadequacy of current characterization tools. In this paper, a technique based on infrared-combined atomic force microscopy (AFM-IR) was developed, in which the infrared spectrum can be obtained under tip bias and tip force with nanometer resolution. The tip bias induced variation in infrared spectra of the Cu2(fbdc)2(dabco) film demonstrates that full width at half-maximum of the vibration–rotation coupling mode is competent for rotor speed characterization. Stalling of dipolar rotor speed in the Cu2(fbdc)2(dabco) film is observed under both tip bias and tip force, which indicates the electrical and mechanical controllability of MOF rotor dynamics. On this basis, the rotor behavior of few-layer MOF films is investigated to reveal the influence of self-assembled molecule stress on rotor dynamics. It is found that the rotor rotation is activated progressively as the film grows and self-assembled molecule stress releases. Our results pave the avenue for direct study of rotor dynamics within MOF films at the nanoscale.