Solid-State Electrochemistry in Molecule/TiO[sub 2] Molecular Heterojunctions as the Basis of the TiO[sub 2] “Memristor”

Thin-layer carbon/molecule/ electronic junctions with thick molecular layers exhibit voltage-induced conductance switching, which may be repeated for at least hundreds of read/set/read/erase cycles. A fluorene(Fl)/ junction can be switched to a higher conductance "set" state by a positive voltage pulse and brought back to the lower conductance "erased" state by a negative pulse. Similar conductance changes occurred following exposure to or UV radiation, and the conductance change is completely inhibited in a dry atmosphere. The bias-induced conductance switching of junctions is consistent with electrochemical reduction of oxide to the much more conductive oxide, analogous to a solid-state redox reaction. The observations are consistent with reduction of hydroxylated sites to a much more conductive oxide by the electrons injected into the during a positive voltage pulse. If Fl is replaced by aminodecane or nitroazobenzene, the conductance switching is modified slightly, consistent with being the active switching component. The results bear directly on the origin of the hysteresis observed in -based junctions and also on their suitability as examples of recently reported "memristors" [ J. J. Yang , M. D. Pickett , X. Li , D. Ohlberg , D. Stewart , and R. S. Williams , Nat. Nanotechnol. , 3 , 429 (2008) ].