Interface structure of SrTiO3-LaAlO3 at elevated temperatures studied in-situ by synchroton x-rays

The atomic interface structure between SrTiO3 and LaAlO3 was studied at elevated temperatures employing in situ surface x-ray diffraction. The results at 473 K indicate that the lattice distorts significantly in two ways. First, the interatomic distances between the cations across the interface become as large as 4.03(2) Å. Second, the TiO6 octahedra at the interface contract their principal axis along the surface normal considerably and the Ti displaces off center. These distortions can be ascribed to the charge inbalance introduced by the change in atomic species across the interface and to a Jahn-Teller effect. The latter distortion suggests the presence of extra electrons at the interface, which is important for understanding the electronic properties of this system

Initial Structure and Growth Dynamics of YBa2Cu3O7-d during Pulsed Laser Deposition

The initial heteroepitaxial growth of YBa2Cu3O7-delta films on SrTiO3(001) substrates during pulsed laser deposition shows a growth-mode transition and a change of growth unit. The growth starts with two blocks, each two-thirds the size of the complete unit cell. The first of these blocks grows in a step-flow fashion, whereas the second grows in the layer-by-layer mode. Subsequent deposition occurs layer-by-layer of complete unit cells. These results suggest that the surface diffusion in the heteroepitaxial case is strongly influenced by the competition with formation energies, which is important for the fabrication of heteroepitaxial devices on the unit cell scale

Intensity interferometry of single x-ray pulses from a synchrotron storage ring

We report on measurements of second-order intensity correlations at the high brilliance storage ring PETRA III using a prototype of the newly developed Adaptive Gain Integrating Pixel Detector (AGIPD). The detector recorded individual synchrotron radiation pulses with an x-ray photon energy of 14.4 keV and repetition rate of about 5 MHz. The second-order intensity correlation function was measured simultaneously at different spatial separations that allowed to determine the transverse coherence length at these x-ray energies. The measured values are in a good agreement with theoretical simulations based on the Gaussian Schell-model.Comment: 16 pages, 6 figures, 42 reference

The atomic surface structure of SrTiO3 (001) studied with synchrotron X-rays

The atomic surface structure of single terminated SrTiO3(0 0 1) (1 × 1) is investigated employing surface X-ray diffraction. In order to obtain these surfaces a special treatment is needed consisting of chemical etching and annealing. Since this is done in an aqueous and subsequently oxygen environment, after which the crystals are kept at ambient conditions, the surface is studied in air. Crystal truncation rods are measured and several models that are proposed in literature in recent years are tested against the experimental data. These models include surface rumpling, low temperature-like distortions, strontium adatom and lateral displacement distortions for both TiO2 and SrO-terminated surfaces. None of these models represents the data very accurately. A much better fit to the experimental results is obtained by using a model in which a TiO2-terminated crystal is covered by an oxygen layer

Performance tests of an AGIPD 0.4 assembly at the beamline P10 of PETRA III

The Adaptive Gain Integrating Pixel Detector (AGIPD) is a novel detector system, currently under development by a collaboration of DESY, the Paul Scherrer Institute in Switzerland, the University of Hamburg and the University of Bonn, and is primarily designed for use at the European XFEL. To verify key features of this detector, an AGIPD 0.4 test chip assembly was tested at the P10 beamline of the PETRA III synchrotron at DESY. The test chip successfully imaged both the direct synchrotron beam and single 7.05 keV photons at the same time, demonstrating the large dynamic range required for XFEL experiments. X-ray scattering measurements from a test sample agree with standard measurements and show the chip's capability of observing dynamics at the microsecond time scale.Comment: revised version after peer revie