Effects of Te- and Fe-doping on the superconducting properties in FeySe1−xTex thin films

High quality FeySe1−xTex epitaxial thin films have been fabricated on TiO2-buffered SrTiO3 substrates by pulsed laser deposition technology. There is a significant composition deviation between the nominal target and the thin film. Te doping can affect the Se/Te ratio and Fe content in chemical composition. The superconducting transition temperature Tc is closely related to the chemical composition. Fe vacancies are beneficial for the FeySe1−xTex films to exhibit the higher Tc. A 3D phase diagram is given that the optimize range is x = 0.13–0.15 and y = 0.73–0.78 for FeySe1−xTex films. The anisotropic, effective pining energy, and critical current density for the Fe0.72Se0.94Te0.06, Fe0.76Se0.87Te0.13 and Fe0.91Se0.77Te0.23 films were studied in detail. The scanning transmission electron microscopy images display a regular atomic arrangement at the interfacial structure.

Effect of Water and Salt on the Colloidal Stability of Latex Particles in Ionic Liquid Solutions

The colloidal stability of sulfate (SL) and polyimidazolium-modified sulfate (SL-IP-2) latex particles was studied in an ionic liquid (IL) of ethylammonium nitrate (EAN) and its water mixtures. Aggregation rates were found to vary systematically as a function of the IL-to-water ratio. Repulsive electrostatic interactions between particles dominated at low IL concentrations, while they were significantly screened at intermediate IL concentrations, leading to destabilization of the dispersions. When the IL concentration was further increased, the aggregation of latex particles slowed down due to the increased viscosity and finally, a striking stabilization was observed in the IL-rich regime close to the pure IL solvent. The latter stabilization is due to the formation of IL layers at the interface between particles and IL, which induce repulsive oscillatory forces. The presence of the added salt in the system affected differently the structure of the interfaces around SL and SL-IP-2 particles. The sign of the charge and the composition of the particle surfaces were found to be the most important parameters affecting the colloidal stability. The nature of the counterions also plays an important role in the interfacial properties due to their influence on the structure of the IL surface layers. No evidence was observed for the presence of long-range electrostatic interactions between the particles in pure ILs. The results indicate that the presence of even low concentrations of water and salt in the system (as undesirable impurities) can strongly alter the interfacial structure and thus, the aggregation mechanism in particle IL dispersions.

Density Functional Theory Study on Anisotropic Arrangement of Interstitial Oxygen Atoms at (001) Interface of Oxide Precipitates in Si Crystal

The stability of the anisotropic oxygen (O) arrangement at the (001) interface of oxide precipitate (OP) in a Si crystal was analyzed by the density functional theory to understand the OP/Si interfacial structure and the gettering mechanism at the interface at an atomic level. In contrast to the case of the Si bulk, the O atoms align in one Si-Si zig-zag bond to some extent, then start to occupy other Si-Si bonds. After the O atoms are arranged in multiple series in the first interface layer to some extent, those in the second layer become more stable. This trend was confirmed for the second and third layers. The results support the existence of an experimentally observed transition layer with a composition of SiOx (x < 2) at the interface [Kissinger et al., ECS J. Solid State Sci. Technol., 9, 064002 (2020)]. Furthermore, several O alignments at the interface drastically reduce the formation energy of Si vacancies. The vacancies at the OP/Si interface were found to be effective gettering sites for Cu while the dangling bond was found to be an effective gettering site for Ni with a binding energy exceeding 1 eV.