Figure 7.

SAW microcentrifugation synthesis of MOFs. The top shows the experimental setup in which two opposing asymmetric SAWs, generated by offset interdigitated transducers at each end, drive an azimuthal microcentrifugation flow within a sessile drop consisting of the MOF precursor solution comprising 1,3,5‐benzenetricarboxylic acid (BTC; C₆H₃(CO₂H)₃) and copper(II) nitrate hemi(pentahydrate) (Cu(NO₃)₂ · 2.5 H₂O). As illustrated in the inset, the MOF powder that crystallizes on the substrate after 5 min of SAW excitation appears to possess out‐of‐plane (in the direction transverse to the substrate) orientation. This is evident in the experimental results below, which show that the crystals not only progressively decrease in size from i) the atomic force microscopy (AFM) images and ii) the particle size distributions, but are also increasingly oriented from iii) the x‐ray diffraction (XRD) spectra as the input voltage and hence the SAW power is increased from a) 0 V (i.e., control experiment without SAW excitation), b) 1.5 V, c) 4.5 V, d) 7.5 V, and e) 9 V. Scale bars denote a length scale of 50 µm. Also shown in the XRD results are the Pawley fits (calc) to the experimental (obs) data, as well as the difference between them (diff). Adapted with permission under a CC‐BY 4.0 license.^{[ 115 ]} Published by Springer Nature.