Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa2_2Cu3_3O7−δ_{7-\delta} thin films

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La$_{2/3}$Ca$_{1/3}$MnO$_3$ (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO$_2$ planes, resulting in non-stoichiometric layer sequences that could directly impact the high-$T_c$ superconductivity

Atomic resolution mapping of phonon excitations in STEM-EELS experiments

Atomically resolved electron energy-loss spectroscopy experiments are commonplace in modern aberrationcorrected transmission electron microscopes. Energy resolution has also been increasing steadily with the continuous improvement of electron monochromators. Electronic excitations however are known to be delocalised due to the long range interaction of the charged accelerated electrons with the electrons in a sample. This has made several scientists question the value of combined high spatial and energy resolution for mapping interband transitions and possibly phonon excitation in crystals. In this paper we demonstrate experimentally that atomic resolution information is indeed available at very low energy losses around 100 meV expressed as a modulation of the broadening of the zero loss peak. Careful data analysis allows us to get a glimpse of what are likely phonon excitations with both an energy loss and gain part. These experiments confirm recent theoretical predictions on the strong localisation of phonon excitations as opposed to electronic excitations and show that a combination of atomic resolution and recent developments in increased energy resolution will offer great benefit for mapping phonon modes in real space

Stabilization of the perovskite phase in the Y-Bi-O system by using a BaBiO3_{3} buffer layer

A topological insulating phase has theoretically been predicted for the thermodynamically unstable perovskite phase of YBiO$_{3}$. Here, it is shown that the crystal structure of the Y-Bi-O system can be controlled by using a BaBiO$_{3}$ buffer layer. The BaBiO$_{3}$ film overcomes the large lattice mismatch of 12% with the SrTiO$_{3}$ substrate by forming a rocksalt structure in between the two perovskite structures. Depositing an YBiO$_{3}$ film directly on a SrTiO$_{3}$ substrate gives a fluorite structure. However, when the Y-Bi-O system is deposited on top of the buffer layer with the correct crystal phase and comparable lattice constant, a single oriented perovskite structure with the expected lattice constants is observed.Comment: 8 pages, 7 figures + 4 pages supporting informatio

Altered density of glomerular binding sites for atrial natriuretic factor in bile duct-ligated rats with ascites

The renal response to atrial natriuretic factor is blunted in cirrhosis with ascites. This might be due to alterations of renal receptors for atrial natriuretic factor. Therefore density and affinity of glomerular atrial natriuretic factor binding sites of bile duct-ligated rats with ascites (n = 10) and of sham-operated controls (n = 10) were determined. Glomerular atrial natriuretic factor binding sites were identified to be of the B-(biologically active) and C-(clearance) receptor type. Discrimination and quantitative determination of B and C receptors for atrial natriuretic factor were achieved by displacement experiments with atrial natriuretic factor(99-126) or des(18-22)atrial natriuretic factor(4-23), an analogue binding to C receptors only. Density of total glomerular atrial natriuretic factor binding sites was significantly increased in bile duct-ligated rats (3,518 ± 864 vs. 1,648 ± 358 fmol/mg protein; p < 0.05). This was due to a significant increase of C-receptor density (3,460 ± 866 vs. 1,486 ± 363 fmol/mg protein; p < 0.05), whereas density of B receptors was not significantly different in bile duct-ligated rats (58 ± 11 vs. 162 ± 63 fmol/mg protein). Affinity of atrial natriuretic factor to its glomerular binding sites did not differ significantly between both groups. These data suggest that an altered glomerular atrial natriuretic factor receptor density could be involved in the renal resistance to atrial natriuretic factor in cirrhosis with ascites

Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films

It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of $\rm{YBa_2Cu_3O_{7-\delta}}$ grown by pulsed laser deposition are annealed at up to 700 atm O$_2$ and 900$^\circ$C, in conjunction with Cu enrichment by solid-state diffusion. The films show clear formation of $\rm{Y_2Ba_4Cu_7O_{15-\delta}}$ and $\rm{Y_2Ba_4Cu_8O_{16}}$ as well as regions of $\rm{YBa_2Cu_5O_{9-\delta}}$ and YBa$_2$Cu$_6$O$_{10-\delta}$ phases, according to scanning transmission electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. Similarly annealed $\rm{YBa_2Cu_3O_{7-\delta}}$ powders show no phase conversion. Our results demonstrate a novel route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.Comment: Accepted for publication in Physical Review Material

De la Bible aux jouets de Noël chez les Moundang du Tchad

L'étude des premières stratégies missionnaires évangéliques chez les Moundang du Tchad, avec pour technique centrale, la traduction des Évangiles et l'introduction de l'écriture, révèle une forme de continuité, mais aussi de rupture. En effet, si l'évangélisation s'accompagne de la « raison graphique » au début du XXe siècle, un siècle plus tard, les Églises évangéliques nord-américaines proposent un échange inédit, associant conversion religieuse et consumérisme. Avec l'analyse ethnographique de l'opération « Christmas Child » proposée par the Samaritan's Purse, une ong évangélique, cet article montre comment l'évangélisation en Afrique, où la figure de Jésus est placée au centre, remet en cause les structures sociales et politiques locales. Comme un bain révélateur, cette opération donne aussi l'occasion de questionner les notions de société de consommation et de loisir en Occident, mettant en lumière un lien particulier entre christianisme et marché.The study of the first evangelical missionary strategies among the Mundang in Chad reveals continuity as well as rupture.  Indeed, if the Bible's translation and the introduction of the logic of writing were central to the strategy of evangelical missionaries in the early twentieth century, a century later, North American evangelical churches have embraced a new partnership that combines religious conversion and consumerism.  This article takes an ethnographic approach to study Operation Christmas Child conducted by the Samaritan's Purse, an evangelical NGO.  It points up how evangelism in Africa, with its strong emphasis on the role of Jesus, challenges local social and political structures.  Like a gradual unveiling, this operation also provides an opportunity to question the Western concepts of leisure and consumer society, highlighting a special connection between Christianity and market consumerism

Controlling the interfacial conductance in LaAlO₃/SrTiO₃ in 90∘ off-axis sputter deposition

We report on the fabrication of conducting interfaces between LaAlO 3 and SrTiO 3 by 90 ∘ off-axis sputtering in an Ar atmosphere. At a growth pressure of 0.04 mbar the interface is metallic, with a carrier density of the order of 1 × 10 13 cm − 2 at 3 K. By increasing the growth pressure, we observe an increase of the out-of-plane lattice constants of the LaAlO 3 films while the in-plane lattice constants do not change. Also, the low-temperature sheet resistance increases with increasing growth pressure, leading to an insulating interface when the growth pressure reaches 0.10 mbar. We attribute the structural variations to an increase of the La/Al ratio, which also explains the transition from metallic behavior to insulating behavior of the interfaces. Our research shows that the control which is furnished by the Ar pressure makes sputtering as versatile a process as pulsed laser deposition, and emphasizes the key role of the cation stoichiometry of LaAlO 3 in the formation of the conducting interface