  The interface between polar LaAlO3 and non-polar SrTiO3 exhibits a remarkable
variety of electronic behavior associated with the formation of an interfacial
quasi-two-dimensional electron gas (q-2DEG). By "sketching" patterns of charge
on the top LaAlO3 surface, the LaAlO3/SrTiO3 interface conductance can be
controlled with near-atomic spatial resolution. Using this technique, a
sketch-based oxide nanotransistor (SketchFET) was demonstrated with a minimum
feature size of just two nanometers. Here we report direct measurements of the
potential barriers and electronic coupling between nanowire segments within a
SketchFET device. Near room temperature, switching is governed by thermally
activated field emission from the nanowire gate. Below T=150 K, a crossover to
quantum field emission is observed that is sensitive to structural phase
transitions in the SrTiO3 layer. This direct measurement of the source-drain
and gate-drain energy barriers is crucial for the development of
room-temperature logic and memory elements and low-temperature quantum devices.
