The exact perovskite structure has simple cubic symmetry and composition ABO 3 , where A is a relatively large cation and B a smaller one. The choices of A and B cations and the substitutions possible on either site generate a large variety of materials sharing the same base, with relatively small distortions of the size and shape of the cube. As in addition, these oxides often admit oxygen non stoichiometry with or without order to the amount of several per cent, they finally form a vast set

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... technologically relevant materials: conducting, insulating, ferroelectric, magnetic, superconducting,.... Heteroepitaxy of perovskite oxides allows one to construct atomically sharp interfaces between these materials and therefore to envisage a set of useful heterojunctions. The epitaxy has side effects that may also prove useful: (1) it forces a chemical neighbouring that would not occur naturally, creating a two-dimensional third material, and (2) it imposes a lateral strain. Both of these effects allow one to explore novel, sometimes unforeseen, properties with a strong two-dimensional character. This paper first reviews some of the knowledge that has been accumulated on {100} surfaces and interfaces of perovskites, with an emphasis on properties that could be used in future all-oxide microelectronics. It then exposes the case of the interface between the half-metal La 2/3 Sr 1/3 MnO 3 and the insulator SrTiO 3 , which plays a key role in the magnetoresistance of magnetic tunnel junctions. It particularly presents thorough electron energy loss spectroscopy measurements that uncover the atomic scale structural and electronic properties of these objects. 1