Multilevel Resonant Tunneling through Purely Organic Radical Molecules in a Si-Based Double-Tunnel Junction

The use of purely organic radicals is promising, especially for future applications in molecular spintronics. However, the techniques used to form their molecular junctions, including break-junction and scanning tunneling microscopy techniques, are unsuitable for the integration of molecular devices in a large-scale setting. In this study, a Si-based double-tunnel junction with purely organic radicals, where adamantyl nitronyl nitroxide <i>p</i>-terphenyl (NN-TP) molecules are embedded as quantum dots in the oxide layer of a metal-oxide-semiconductor (MOS) structure, was demonstrated. Notably, this MOS structure functions as a tunnel junction, which has a high affinity for the current Si technology. In this study, multilevel resonant tunneling through the discrete energy levels of the NN-TP molecules at 7 K was achieved; moreover, the tunneling current was observed at 100 K. Furthermore, our device exhibited resonant tunneling through a singly occupied molecular orbital, indicating the survival of an unpaired electron in the radical molecules. Thus, our findings hold promise for incorporating the attractive functions of organic radicals into Si-based solid-state devices, thereby enabling the large-scale integration of molecular devices.