Role of the surface in writing, erasing and maintaining nanostructures at the LaAlO$_{3}$/SrTiO$_{3}$ interface*

Nanoscale control of the metal-insulator transition in LaAlO$_{3}$/SrTiO$_{3}$ heterostructures can be achieved using local voltages applied by a conducting AFM probe. The mechanism is believed to be governed by a ``water cycle'' in which the surface is locally charged via hydrogen passivation, resulting in high-resolution modulation doping of the LaAlO$_{3}$/SrTiO$_{3}$ interface.\footnote{F. Bi et al., Appl. Phys. Lett.97, 173110 (2010)} A Kelvin probe image method is applied to study how water content in the gas environment influences such charge writing. Persistence tests are performed, in which the long-term behavior is studied by keeping the AFM-written nanostructures (nanowire and sketch FET\footnote{C.Cen et al., Science, 323, 1026 (2009)}) in different ambient environments. The self-erasure process is particularly obvious in moisture environments, but is slowed greatly in dry inert gas and can be even halted under modest vacuum conditions ($\sim$10$^{-3}$ Torr).