Interface reconstruction in superconducting CaCuO2/SrTiO3 superlattices: A hard x-ray photoelectron spectroscopy study

Here we report about the interface reconstruction in the recently discovered superconducting artificial superlattices based on insulating CaCuO2 and SrTiO3 blocks. Hard x-ray photoelectron spectroscopy shows that the valence bands alignment prevents any electronic reconstruction by direct charge transfer between the two blocks. We demonstrate that the electrostatic built-in potential is suppressed by oxygen redistribution in the alkaline earth interface planes. By using highly oxidizing growth conditions, the oxygen coordination in the reconstructed interfaces may be increased, resulting in the hole doping of the cuprate block and thus in the appearance of superconductivity.Comment: 9 pages, 6 figure

Die Rolle von Interferon regulierenden Faktoren bei LGTV Infektionen

The activation of the innate immune response protects the host against viral infections. Innate recognition of viral signatures by pattern recognition receptors (PRRs) triggers the induction of type I Interferons (IFN) and results in a broad antiviral response. Here we show that various signaling components of the type I IFN pathway play a role in host defense against Langat virus (LGTV), a Flavivirus of the tick borne encephalitis virus (TBEV) serocomplex. IFN-beta promoter stimulator-1 (IPS-1) and myeloid differentiation primary response 88 (Myd88) which are adaptor molecules for PRRs like retinoic acid induced gene-I (RIG-I), melanoma differentiation-associated gene 5 (MDA5) and Toll like receptors (TLRs) promote survival in systemic LGTV infection. Further regulatory elements of the type I IFN pathway such as IFN- regulatory factor (IRF) -3 and IRF-7 mediate local protection against viral replication and dissemination, even though they are dispensable for survival. Especially IRF-7 limits replication and spread of LGTV in the periphery and plays a protective role in the central nervous system (CNS). The absence of IRF-7 in the brain was associated with higher local inflammation and a shift in tissue tropism. Neurons are already known to be highly susceptible to LGTV infection, but here it was shown that especially astrocytes rely on IRF-7 for protection against LGTV infection and propagation. IRF-7 normally provides a positive feedback loop to amplify the type I IFN response. The lack of IRF-7 was to date associated with decreased type I IFN production. Here it was shown that astrocytes are able to provide a potent local type I IFN response by an IRF-7 independent mechanism. This thesis provides new insights in antiviral defenses in the absence of IRF-7, specifically in the CNS.Die Aktivierung des angeborenen Immunsystems schützt den Wirt vor viralen Infektionen. Durch die Erkennung von viralen Bestandteilen mittels PRRs (Pattern recognition receptors) wird Typ I Interferon induziert, was zu einer breiten antiviralen Antwort führt. Diese Arbeit zeigt, dass unterschiedliche Komponenten des Typ I IFN Signalweges eine wichtige Rolle in der Abwehr von LGTV (Langat virus) spielen, einem Flavivirus, der dem TBEV (Tick-borne Encephalitis Virus) Serokomplex zugeordnet ist. IPS-1 (IFN-beta promoter stimulator-1) und Myd88 (myeloid differentiation primary response 88) sind Adapter-Moleküle für PRRs wie RIG-I (retinoic acid induced gene-I), MDA5 (melanoma differentiation-associated gene 5) und TLRs (Toll like receptors), die eine wichtige Rolle für das Überleben von LGTV Infektionen spielen. Weitere regulatorische Elemente des Typ I Interferon Signalweges wie IRF-3 (Interferon regulatory factor-3) und IRF-7 vermindern vor allem lokale Virusreplikation und dessen Verbreitung. Besonders IRF-7 vermittelt regionalen Schutz als restriktiver Faktor bei der Generierung von Viruspartikeln. So wird ein Befall von Organen in der Peripherie, sowie des zentralen Nervensystem limitiert. Die Abwesenheit von IRF-7 im Gehirn führt nicht nur zu erhöhter Virusreplikation, sondern auch zu stärkeren lokalen Entzündungsreaktionen und einer Veränderung im Zelltropismus. Während normalerweise vor allem Neuronen sensitiv gegenüber LGTV sind, konnte hier gezeigt werden, dass insbesondere Astrozyten auf die Funktionalität von IRF-7 angewiesen sind, um sich vor der Infektion und Replikation mit LGTV zu schützen. Die Induktion von IRF-7 führt in der Regel zu einer Amplifizierung der protektiven Interferon Antwort. Der Verlust von IRF-7 wurde daher bisher mit einer Verminderung der Typ I Interferon Produktion assoziiert. Astrozyten sind bei systemischer LGTV Infektion jedoch in der Lage, in einem IRF-7 unabhängigen Mechanismus hohe lokale Typ I Interferon Mengen zur Verfügung zu stellen. Diese Arbeit gibt neue Einblicke in die Wirkungsweise der antiviralen Abwehr mit einem besonderen Fokus auf Mechanismen im zentralen Nervensystem

Experimental investigation of a liquid desiccant system for air dehumidification working with ionic liquids

Electrically-driven compression chillers are the commonly used technology for cooling and dehumidifying air. Open sorption systems driven by solar heat are an alternative to conventional air dehumidification technology and may reduce primary energy consumption. For air dehumidification, liquid desiccant systems may exhibit some process engineering and thermodynamic advantages in comparison to solid desiccant systems. The liquid desiccant must exhibit low equilibrium water vapour pressures at the available heat rejection temperature level to achieve low air dew point temperatures and thus a strong air dehumidification with comparably low driving temperatures. Desiccant mass fractions should be as low as possible, but in order to achieve low vapour pressures required desiccant mass fractions may surpass the solubility limit. In the paper at hand, first experimental results of an internally cooled and heated, open liquid desiccant system working with an ionic liquid designed for air dehumidification are presented. It is demonstrated that ionic liquids designed according to the boundary conditions of the respective application may be a promising alternative to commonly used desiccants such as lithium chloride for solar air dehumidification with comparably high heat rejection and low driving temperatures

Surface energy and stability of stress-driven discommensurate surface structures

A method is presented to obtain {\it ab initio} upper and lower bounds to surface energies of stress-driven discommensurate surface structures, possibly non-periodic or exhibiting very large unit cells. The instability of the stressed, commensurate parent of the discommensurate structure sets an upper bound to its surface energy; a lower bound is defined by the surface energy of an ideally commensurate but laterally strained hypothetical surface system. The surface energies of the phases of the Si(111):Ga and Ge(111):Ga systems and the energies of the discommensurations are determined within $\pm 0.2$ eV.Comment: 4 pages RevTeX. 2 Figures not included. Ask for a hard copy (through regular mail) to [email protected]

Atomic-scale structure of the SrTiO3(001)-c(6x2) reconstruction: Experiments and first-principles calculations

The c(6x2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050-1100oC in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images

Structure determination of PF3 adsorption on Cu(100) using X-ray standing waves

The local structure of the Cu(100)c(4x2)-PF3 adsorption phase has been investigated through the use of normal-incidence X-ray standing waves (NIXSW), monitored by P 1s and F 1s photoemission, together with P K-edge near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows the molecule to be oriented with its C3v symmetry axis essentially perpendicular to the surface, while the P NIXSW data show the molecule to be adsorbed in atop sites 2.37±0.04 Å above the surface, this distance corresponding to the Cu-P nearest-neighbour distance in the absence of any surface relaxation. F NIXSW indicates a surprisingly small height difference of the P and F atoms above the surface 0.44±0.06 Å, compared with the value expected for an undistorted gas-phase geometry of 0.77 Å, implying significant increases in the F-P-F bond angles. In addition, however, the F NIXSW data indicate that the molecules have a well-defined azimuthal orientation with a molecular mirror plane aligned in a substrate mirror plane, and with a small (5-10°) tilt of the molecule in this plane such that the two symmetrically-equivalent F atoms in each molecule are tilted down towards the surface

Structure of a model TiO2 photocatalytic interface

The interaction of water with TiO2 is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there have been numerous studies of the rutile single-crystal TiO2(110) interface with water. This has provided an atomic-level understanding of the water-TiO2 interaction. However, nearly all of the previous studies of water/TiO2 interfaces involve water in the vapour phase. Here, we explore the interfacial structure between liquid water and a rutile TiO2(110) surface pre-characterized at the atomic level. Scanning tunnelling microscopy and surface X-ray diffraction are used to determine the structure, which is comprised of an ordered array of hydroxyl molecules with molecular water in the second layer. Static and dynamic density functional theory calculations suggest that a possible mechanism for formation of the hydroxyl overlayer involves the mixed adsorption of O2 and H2O on a partially defected surface. The quantitative structural properties derived here provide a basis with which to explore the atomistic properties and hence mechanisms involved in TiO2 photocatalysis