Electronic switching in nanoscale titanium oxide devices

Titanium metal is widely used as a top metal contact for nanoscale molecular electronic devices, where it has been assumed to form a few-atom-thick Ti carbide overlayer. Using a vacuum delamination technique we expose and analyze chemically pristine buried titanium/organic monolayer interfaces from devices that have displayed `molecular electronic switching'. We establish that under many conditions the titanium instead forms a \textit{few-nanometer-thick Ti oxide} overlayer. Both TiO2 and reduced TiOx species exist -- this mixed stoichiometry Ti oxide is responsible for the electronic switching. In the separate field of `conventional' nano-electronics, oxide based electrical-resistance switches are pursued for next generation nonvolatile random access memories (R-RAMs). However, the metal/oxide/metal switching mechanism is poorly understood. We demonstrate in Pt/TiOx/Pt nanocrosspoint devices that the switching is channeling (on) and recovering (off) the Schottky barrier at the Pt/TiO2 interface due to the creation and drift of positively charged oxygen vacancies under electric field. Engineered oxygen vacancy profiles predictively control the switching polarity and conductance to support a general physics model of switching in these devices.