LaAlO$_3$/SrTiO$_3$ field-effect nanodevices using in-situ-grown Au top gates*

Conductive-atomic force microscope (c-AFM) lithography can create a wide range of nanostructures based on the LaAlO$_3$/SrTiO$_3$ system, including field effect transistors\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} , single-electron transistors\footnote{G. L. Cheng, \textit{et al.}, Nature Nanotechnology \textbf{6}, 343 (2011).} and superconducting nanoelectronics\footnote{J. P. Veazey, \textit{et al.}, Nanotechnology \textbf{24}, 375201 (2013).}. However, the operating range of gated devices is often limited by tunneling through insulating barriers. Using in-situ Au deposited on top of LaAlO$_3$, we create vertical field-effect devices with significantly lower leakage due to the large bandgap of LaAlO$_3$. We describe the fabrication process for vertical field-effect nanodevices and show representative transport measurements both at room temperature and low temperatures.