![]() ![]() Subsequently it was shown that for the non-conducting interfaces grown by sputtering in high pressure oxygen the ratio was about 1.1. In a study using molecular beam epitaxy (MBE) as growth technique, it was shown that interfaces can be tuned from conducting to insulating by varying the La and Al ratio in the films, 10,11 with conducting interfaces forming only for a ratio slightly below 1. 8,9 One facet of the problem which only recently entered the discussion is the importance of the stoichiometry of the LAO layer, more in particular the La:Al ratio. 4 When grown by PLD, different conductivity regimes are found for different amount of background oxygen pressure 5–7 around 10 −6 mbar the conducting layer extends into the STO bulk, interface conductance is found around 10 −3 mbar, and insulating interfaces are produced above 10 −2 mbar. 2 Conductance requires a TiO 2-terminated STO surface to furnish the correct surface charge state as well as the required Ti 3 d orbitals 1,3 and a critical thickness of 4 unit cells of LAO. Most of the work is done using the technique of pulsed laser deposition (PLD) and by now it is clear that the occurrence of conductance is a complicated interplay between self-doping of the interface to avoid divergence of the electric potential, the production of oxygen defects in the deposition process, and the stoichiometry of the growing film. Ever since the pioneering work by Ohtomo & Hwang 1 in 2004 there has been interest in studying the properties of the interface between band insulators such as LaAlO 3 (LAO) and SrTiO 3 (STO), which yield conducting interfaces and a two-dimensional electron gas. ![]()
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