Elevation from Binary to Ternary Resistive Switching Behaviors in Cubane-like Copper Iodide Clusters by Ligand Engineering

Multilevel memory is a feasible solution for the explosive demand for data storage in the Big Data era. In this work, ligand engineering has been implemented in cubane-type Cu 4 I 4 L 4 clusters to obtain three complexes: Cu 4 I 4 L 4 (L = P(Ph- p -Cl) 3 ( 1 ), PPh 3 ( 2 ), P(Ph- p -OCH 3 ) 3 ( 3 )), in which the substitutes on the p -position of benzyl vary from electron-withdrawing (–Cl) to electron-donating (−OCH 3 ) groups. Interestingly, with enhancement of electron-donating ability, the trend of more distorted Cu 4 I 4 cores, enhanced Cu···Cu interactions, and higher structural dimensions can be achieved. Consequently, in FTO/Cu 4 I 4 L 4 /Ag memristors, the electron-withdrawing group (–Cl) and neutral group (–H) exhibit bistable resistive switching performances, and a strong electron-donating group (−OCH 3 ) can give ternary resistive switching behavior (OFF/ON1/ON2 current ratio: 1:10 2.74:10 3.73, V Set1 / V Set2: 1.09/1.48 V). The mechanism about the elevation from binary to ternary memory behavior in these cubane-like Cu 4 I 4 L 4 clusters has been clarified: the external voltage-induced I···Cl halogen bonding and C–H···π interaction contribute to the binary resistive switching performances in FTO/ 1 /Ag and FTO/ 2 /Ag, and the presence of the second conductive state in FTO/ 3 /Ag stems from the injected carrier delocalization on the Cu 4 I 4 core due to strong Cu···Cu interactions. The rules drawn in this work can provide a feasible strategy for the design of novel multilevel memories.