  The two-dimensional electron gas (2DEG) at the non-isostructural interface
between spinel gamma-Al2O3 and perovskite SrTiO3 is featured by a record
electron mobility among complex oxide interfaces in addition to a high carrier
density up to the order of 1E15 cm-2. Herein, we report on the patterning of
2DEG at the gamma-Al2O3/SrTiO3 interface grown at 650 {\deg}C by pulsed laser
deposition using a hard mask of LaMnO3. The patterned 2DEG exhibits a critical
thickness of 2 unit cells of gamma-Al2O3 for the occurrence of interface
conductivity, similar to the unpatterned sample. However, its maximum carrier
density is found to be approximately 3E13 cm-2, much lower than that of the
unpatterned sample (1E15 cm-2). Remarkably, a high electron mobility of
approximately 3,600 cm2V-1s-1 was obtained at low temperatures for the
patterned 2DEG at a carrier density of 7E12 cm-2, which exhibits clear
Shubnikov-de Hass quantum oscillations. The patterned high-mobility 2DEG at the
gamma-Al2O3/SrTiO3 interface paves the way for the design and application of
spinel/perovskite interfaces for high-mobility all-oxide electronic devices.
