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

Theroy of Photoelectron Emission From an X-Ray Interference Field

In this chapter, we will present the theory for the photoelectronemission from an X-ray interference field. The dipole approximationholds astonishingly well, even for hard X-rays, as far as the magnitudeof the transition matrix element is concerned. However, the forward–backward asymmetry caused already by higher order multipole termscannot be neglected when the photoelectron is emitted by the coherentaction of two X-ray waves travelling in different directions. We willexplicitly elaborate the underlying theory and how corresponding dataare analyzed. Furthermore, we will briefly describe the theory behind theX-ray standing wave excited photoemission of valence band electrons

X-ray standing wave analysis of highly perfect Cu crystals and electrodeposited submonolayers of Cd and Tl on Cu surfaces

Experimental requirements for measuring the structure and coverage of adsorbates in the monolayer regime on single crystals with x-ray standing wavefields are discussed in detail along with a thorough description of the theory. The near-surface region of Cu crystals was probed depth selectively by detecting K as well as L fluorescence as a function of fluorescence escape angle. The effects of crystalline imperfections and of dispersive crystal arrangements on the spatial resolution of standing wave measurements are described. Copper crystals with (111) and (100) surface orientation were used as substrates for electrodeposition of Cd and Tl from an aqueous electrolyte using cyclic voltammetry. Submonolayer amounts of Cd and Tl deposited in the underpotential range were investigated on the emerged electrodes with x-ray standing waves keeping the samples under atmospheric pressure, in air, or in inert atmosphere

Surfaçage manuel ou ultrasonique (définitions et comparaisons)

LILLE2-BU Santé-Recherche (593502101) / SudocPARIS-BIUM (751062103) / SudocLILLE2-UFR Odontologie (593502202) / SudocSudocFranceF

Studying the onset of galvanic steel corrosion in situ using thin films: film preparation, characterization and application to pitting

This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron x-radiation. Characterized by x-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈4 nm thickness were studied in situ in an electrochemical cell under potential control (−0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by x-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at a potential of about +0.8 V Cr-oxide was removed from the steel film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by x-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft x-ray scanning absorption microscopy at the Fe L$_{2,3}$-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies