The complete atomic structure of a five-monolayer film of LaAlO3 on SrTiO3 has been determined for the first time by surface x-ray diffraction in conjunction with the coherent Bragg rod analysis phase-retrieval method and further structural refinement. Cationic mixing at the interface results in dilatory distortions and the formation of metallic La(1-x)SrxTiO3. By invoking electrostatic potential minimization, the ratio of Ti{4+}/Ti{3+} across the interface was determined, from which the lattice dilation could be quantitatively explained using ionic radii considerations. The correctness of this model is supported by density functional theory calculations. Thus, the formation of a quasi-two-dimensional electron gas in this system is explained, based on structural considerations.

We report the first complete determination, using surface x-ray diffraction, of the surface structure of TiO2-terminated SrTiO3(001), both at room temperature in vacuum, and also hot, under typical conditions used for thin film growth. The cold structure consists of a mixture of a (1x1) relaxation and (2x1) and (2x2) reconstructions. The latter disappear over several minutes upon heating. The structures are best modeled by a TiO2-rich surface similar to that proposed by Erdman et al. [Nature (London) 419, 55 (2002).10.1038/nature01010]. Both reconstructions have been shown by density functional theory to be energetically favorable. The calculated (1x1) surface energy is higher, indicating that it may be a disordered mixture of the reconstructions. Atomic displacements are significant down to three unit cells, which may have important implications on possible surface ferroelectric phenomena in SrTiO3.

The use of an area detector in grazing-incidence X-ray experiments lends many advantages in terms of both speed and reliability. Here a discussion is given of the procedures established using the PILATUS pixel detector developed at the Swiss Light Source for optimizing data acquisition and analysis of surface diffraction data at the Materials Science beamline, especially with regard to reflectivity measurements, crystal truncation and fractional order rods, and grazing-incidence diffraction experiments.

Surface x-ray diffraction was used to determine the atomic structures of La 1−x Sr x MnO 3 thin films, grown monolayer by monolayer on SrTiO 3 by pulsed laser deposition. Structures for one-, two-, three-, four-, six-, and nine-monolayer-thick films were solved using the Coherent Bragg rod analysis phase-retrieval method and subsequent structural refinement. Four important results were found. First, the out-of-plane lattice constant is elongated across the substrate-film interface. Second, the transition from substrate to film is not abrupt, but proceeds gradually over approximately three unit cells. Third, Sr segregates towards the topmost monolayer of the film: we determined a Sr-segregation enthalpy of −15 kJ/ mol from the occupation parameters. Finally, the electronic bandwidth W was used to explain the onset of magnetoresistance for films of nine or more monolayers thickness. Resistivity measurements of the nine monolayer-thick film confirm magnetoresistance and the presence of a dead layer with mostly insulating properties.

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We report on the structural determination of the surface of TiO 2-terminated SrTiO 3 ͑001͒ using surface x-ray diffraction. The detailed analysis of two surface diffraction data sets are presented, one ͑cold͒ taken at room temperature in vacuum, and the other ͑hot͒ under typical conditions used for thin film growth. 49 different combinations of possible surface terminations are described for the cold structure, from which the final structure was chosen, consisting of a weighted mixture of a ͑1 ϫ 1͒ relaxation and ͑2 ϫ 1͒ and ͑2 ϫ 2͒ reconstructions, simultaneously present at the surface. The structures are best modeled by a TiO 2-rich surface similar to that proposed by Erdman et al. ͓Nature ͑London͒ 419, 55 ͑2002͔͒. The reconstructions are energetically favorable according to density functional theory. They disappear within several minutes upon heating to the hot conditions, forming a termination very similar to the cold ͑1 ϫ 1͒, but more puckered and higher in energy. Six additional models, suggested by direct methods and the literature, to describe the hot surface are also discussed. Direct methods confirm the TiO 2-rich termination and the atomic positions of the hot surface. The atomic coordinates for the two TiO 2-rich surfaces exhibit significant displacements down to three unit cells, which may have important implications on possible surface ferroelectric phenomena in SrTiO 3. Surface energy considerations suggest a temperature-induced order-disorder transition, produced by a mixing of the ͑2 ϫ 1͒ and ͑2 ϫ 2͒ reconstructions, to form the hot pseudo ͑1 ϫ 1͒ structure. Electrostatic stability arguments provide circumstantial support for the experimentally determined TiO 2-rich surfaces.

A novel energetic smoothing mechanism in the growth of complex metal-oxide thin films is reported from in situ kinetic studies of pulsed laser deposition of on , using x-ray reflectivity. Below 50% monolayer coverage, prompt insertion of energetic impinging species into small-diameter islands causes them to break up to form daughter islands. This smoothing mechanism therefore inhibits the formation of large-diameter 2D islands and the seeding of 3D growth. Above 50% coverage, islands begin to coalesce and their breakup is thereby suppressed. The energy of the incident flux is instead rechanneled into enhanced surface diffusion, which leads to an increase in the effective surface temperature of DeltaT approximately 500 K. These results have important implications on optimal conditions for nanoscale device fabrication using these materials.

We present the first angle-resolved photoemission spectroscopy (ARPES) results on three-dimensional manganese perovskite La 0.66 Sr 0.34 MnO 3. In contrast to ARPES results on layered manganites, a finite and k-dependent spectral weight at the Fermi level was observed. We propose a complex energy band to describe the low binding energy electronic states, which may result from the temporally dynamic orbital orientation distributions and/or nanoscale charge inhomogeneities, to account for the anomalously broad ARPES features observed in the measurements. Flat sections of the Fermi surface were determined. A density wave resulting from nesting instabilities induced by the flat Fermi surface sections is manifested by the energy band folding.