Tuning Up or Down the Critical Thickness in LaAlO_3/SrTiO_3 through In-Situ Deposition of Metal Overlayers

摘要

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO_3 and SrTiO_3 has attractedmuch attention from the oxide electronics research field. One of its hallmark features is the existence of a criticalLaAlO_3 thickness of 4 unit-cells (u.c.) for interfacial conductivity to emerge. In this study, the chemical,electronic, and transport properties of LaAlO_3/SrTiO_3 samples capped with different metals grown in a systemcombining pulsed laser deposition, sputtering, and in situ X-ray photoemission spectroscopy are investigated.The results show in Fig. 1 that for metals with low work function a q2DES forms at 1 – 2 u.c. of LaAlO_3 and isaccompanied by a partial oxidation of the metal, a phenomenon that affects the q2DES properties and triggersthe formation of defects. In contrast, for noble metals, the critical thickness is increased above 4 u.c. The resultsare discussed in terms of a hybrid mechanism that incorporates electrostatic and chemical effects.