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18 This technique is based on the injection of small droplets of a liquid precursor in a low-pressure vaporizer ( T ϭ 250 ☌), where the liquid immediately vaporizes and forms a stable gas phase. The layers are grown by pulsed liquid injection metalorganic chemical vapor deposition ͑ MOCVD ͒. The deposition technique has been described in detail by Dubourdieu et al. Heterostructures of La 0.7 Sr 0.3 MnO 3 and SrTiO 3 were grown on a SrTiO 3 (001) substrate to obtain a sequence of 15 bilayers described as ͓ (La 0.7 Sr 0.3 MnO 3 ) m (SrTiO 3 ) n ͔ 15 with varying LSMO ( m ϭ 5, 8, 12, 16, 32, where m is the number of LSMO monolayers ͒ and constant STO thickness ( n ϭ 8, where n is the number of STO monolayers ͒. The LSMO layer is under tensile stress while the STO layer is under compressive stress. This small lattice mismatch causes the epitaxial film to be strained. The misfit along the interface is defined as ␦ ϭ 2( a STO Ϫ a p -LSMO )/( a STO ϩ a p -LSMO ) ͑ where a STO and a p -LSMO are the lattice parameters ͒. Since these different structures are all present in the superlattice films, misfit stress will result along the interfaces. The room temperature structure of the SrTiO 3 substrate is well established it is a cubic perovskite ( Pm 3 m ) with lattice parameter a STO ϭ 0.390 50 nm. For simplicity, and for comparing film and substrate, the indexing will be referred to the cubic perovskite structure with lattice parameter a p ϭ 0.3875 nm. Under the growth conditions prevailing in our experiment and for a composition x ϭ 0.33, it is to be expected 16 that bulk LSMO will have a rhombohedral pseudocubic symmetry ( R ̄ 3 c ) with hexagonal lattice parameters a Ϸ 0.552 nm and c Ϸ 1.336 nm. All three phases have slightly deformed perovskite structures due to a distortion of the MnO 6 octahedra. 16 Three phase fields were distinguished: a rhombohedral phase with space group symmetry R ̄ 3 c, an orthorhombic phase ( Pnma ), and a monoclinic phase ( P 2 1 / c ). The structural phase diagram of La 1 Ϫ x Sr x MnO 3 as a function of Sr doping and oxygen partial pressure during the synthesis was described by Mitchell et al. Both of these processes are likely to be present in Mn-based heterostructures as well. relaxation and diffusion/segregation processes occur- ring during epitaxial growth of the heterostructure.