Reaction of europium and some transition metals deposited as ultrathin films

Formation of rare earth (RE) and transition metal (TM) binary compounds, RExTMy, with different stoichiometry is well known [1]. Such compounds have been extensively studied during the last two or three decades, especially their magnetic properties. These compounds are interesting not only from a basic physics point of view but also from an applications standpoint. Certain important features occur in RExTMy thin films, such as large perpendicular magnetic anisotropy, a high Curie temperature, and a high coercive field makes these materials a promising candidate for potential applications in magneto-optical recording and/or permanent magnets used in on-wafer actuators and sensors. The aim of our work was to examine, over a wide range of Eu-TM (TM = Mn, Fe, Cr) concentrations, formation of ordered compounds or alloys in the form of thin films, and to determine their basic physical properties. A Molecular Beam Epitaxy systems equipped with XPS and RHEED, were used to prepare Eu-TM films. A series of 2-30nm thick Eu-TM films have been grown at room temperature by co-deposition or in multilayers form on MgO, GaAs or Si substrates with a 50 nm thick Mo buffer layer. We carried out electronic and crystallographic characterization of their properties using X-ray photoemission spectroscopy (XPS) and diffraction measurements. The magnetic and transport properties were investigated with the help of a SQUID magnetometer and a 4-point probe over a wide temperature range. Relative changes in the Eu 4rf/(Mn, Fe, Cr) 2p photoemission line area ratio, as well as chemical shifts of core levels monitored during the annealing process indicate mixing between europium and transition metals. The intermixing of the layers was also confirmed by the XRR measurements, where a formation of the uniform film from the point of view of electronic density was observed. The diffraction measurements indicate that the mixing of Eu-TM layers was the most efficient for the Eu/Mn system where a new Eu-Mn compound has been formed - EuMn2 exhibiting magnetic ordering at temperatures below 40K. Indication of formation of additional two intermetallic phases was found in the Eu-Mn system. The magnetic properties of Eu-Mn and Eu-Cr systems result mainly from the occurrence of divalent europium in samples, whereas in the case of the Eu-Fe system they are dominated by the presence of iron aggregated probably in nanoparticles

The composition induced crossover in nonlinear dielectric response in (1-x) Pb(Zr0.70Ti0.30)O-3-x BiMn2O5 (x=0, 0.02, 0.055, 0.11, 0.15, 0.22, and 1) ceramics

Ceramics based on lead zirconate-titanate Pb(Zr0.70Ti0.30)O-3 (PZT), bismuth manganite (BM) and the composite (1 - x) PZT-x BM were obtained. A systematic study of linear and nonlinear dielectric susceptibilities temperature and frequency dependences was conducted. A composition-induced crossover in nonlinear dielectric susceptibility was detected. The so-called scaled nonlinear susceptibility, a(3), was obtained from experimental values of the real part of the linear and third-order nonlinear dielectric susceptibilities. The value for a(3) was negative for low BM content in the whole temperature range specific to discontinuous ferroelectric phase transitions and relaxor behavior. In contradiction, a(3) was positive for BM and for the composite with sufficiently high BM content. The positive a(3) was attributed to a subsystem of dipoles created by trapped charges. Hopping charge transfer, which is a dominant mechanism for conduction in manganites, is responsible for the positive a(3) and for the colossal magnitude of the imaginary part of the linear dielectric susceptibility. The concentration of the ions was determined using scanning electron microscopy. The chemical disorder and the precipitation of ions determined using time of flight-secondary ion mass spectrometry correspond to a crossover in the electrical features

Physicochemical analysis of Bi2Te3 - (Fe, Eu) - Bi2Te3 junctions grown by molecular beam epitaxy method

Topological insulators (TI) are a class of materials gaining in importance due to their unique spin/electronic properties, which may allow for the generation of quasiparticles and electronic states which are not accessible in classical condensed-matter systems. Not surprisingly, TI are considered as promising materials for multiple applications in next generation electronic or spintronic devices, as well as for applications in energy conversion, such as thermo-electrics. In this study, we examined the practical challenges associated with the formation of a well-defined junction between a model 3D topological insulator, Bi2Te3, and a metal, Fe or Eu, from which spin injection could potentially be realized. The properties of multilayer systems grown by molecular beam epitaxy (MBE), with Fe or Eu thin films sandwiched between two Bi2Te3 layers, were studied in-situ using electron diffraction and photoelectron spectroscopy. Their magnetic properties were measured using a SQUID magnetometer, while the in-depth chemical structure was assessed using secondary ion mass spectroscopy. An examination of impact of Bi2Te3 structure on chemical stability of the junction area has been realized. For Fe, we found that despite room temperature growth, a reaction between the Fe film and Bi2Te3 takes place, leading to the formation of FeTe and also the precipitation of metallic Bi. For the Eu tri-layer, a reaction also occurs, but the Te chemical state remains intact

Semi-Conducting Properties of Titanium Dioxide Layer on Surface of Ti-15Mo Implant Alloy in Biological Milieu

The object of this work was to investigate structure, electrochemical behavior and semiconducting properties of the TiO2 oxide layer on the Ti–15Mo implant alloy surface in normal and inflammatory conditions of physiological saline solution. X-ray photoelectron spectroscopy measurements confirm the presence of the oxide layer on the Ti– 15Mo alloy surface. Electrochemical studies indicate excellent corrosion resistance of Ti–15Mo alloy in physiological saline solution. It was found that the investigated material under normal and inflammatory conditions behave like an insulator and n-type semiconductor, respectively

Inhomogeneity and Segregation Effect in the Surface Layer of Fe-Doped SrTiO3 Single Crystals

The e ect of Fe doping on SrTiO3 single crystals was investigated in terms of crystal and electronic structure over a wide temperature range in both oxidizing and reducing conditions. The electrical properties were thoroughly studied with a special focus on the resistive switching phenomenon. Contrary to the undoped SrTiO3 crystals, where isolated filaments are responsible for resistive switching, the iron-doped crystals showed stripe-like conducting regions at the nanoscale. The results showed a non-uniform Fe distribution of as-received crystals and the formation of new phases in the surface layer of reduced/oxidized samples. The oxidation procedure led to a separation of Ti(Fe) and Sr, while the reduction resulted in the tendency of Fe to agglomerate and migrate away from the surface as seen from the time of flight mass spectroscopy measurements. Moreover, a clear presence of Fe-rich nano-filament in the reduced sample was found

Spectroscopic Studies on Organic Matter from Triassic Reptile Bones, Upper Silesia

Fossil biomolecules from an endogenous source were previously identified in Cretaceous to Pleistocene fossilized bones, the evidence coming from molecular analyses. These findings, however, were called into question and an alternative hypothesis of the invasion of the bone by bacterial biofilm was proposed. Herewith we report a new finding of morphologically preserved blood-vessel-like structures enclosing organic molecules preserved in ironoxide-mineralized vessel walls from the cortical region of nothosaurid and tanystropheid (aquatic and terrestrial diapsid reptiles) bones. These findings are from the Early/Middle Triassic boundary (Upper Roetian/Lowermost Muschelkalk) strata of Upper Silesia, Poland. Multiple spectroscopic analyses (FTIR, To F-SIMS, and XPS) of the extracted "blood vessels" showed the presence of organic compounds, including fragments of various amino acids such as hydroxyproline and hydroxylysine as well as amides, that may suggest the presence of collagen protein residues. Because these amino acids are absent from most proteins other than collagen, we infer that the proteinaceous molecules may originate from endogenous collagen. The preservation of molecular signals of proteins within the "blood vessels" was most likely made possible through the process of early diagenetic iron oxide mineralization. This discovery provides the oldest evidence of in situ preservation of complex organic molecules in vertebrate remains in a marine environment

Physicochemical analysis of sediments formed on the surface of hydrophilic intraocular lens after Descemet’s stripping endothelial keratoplasty

An intraocular lens (IOL) is a synthetic, artificial lens placed inside the eye that replaces a natural lens that is surgically removed, usually as part of cataract surgery. The opacification of the artificial lens can be related to the formation of the sediments on its surface and could seriously impair vision. The physicochemical analysis was performed on an explanted hydrophilic IOL and compared to the unused one, considered as a reference IOL. The studies were carried out using surface sensitive techniques, which can contribute to a better understanding of the sedimentation process on hydrophilic IOLs’ surfaces. The microscopic studies allowed us to determine the morphology of sediments observed on explanted IOL. The photoelectron spectroscopy measurements revealed the presence of organic and inorganic compounds at the lens surface. Mass spectroscopy measurements confirmed the chemical composition of deposits and allowed for chemical imaging of the IOL surface. Applied techniques allowed to obtain a new set of information approximating the origin of the sediments’ formation on the surface of the hydrophilic IOLs after Descemet’s stripping endothelial keratoplasty

Coherent acoustic phonons generated by ultrashort terahertz pulses in nanofilms of metals and topological insulators

We report the generation of coherent acoustic phonons in materials with terahertz ultrashort pulses. This is demonstrated in metals and topological insulators by exciting an acoustic eigenmode in nanometric-sized thin films. The efficiency of the coupling is quadratic in the terahertz electric field strength within the range of investigation. Owing to a quantitative comparison between terahertz and near-infrared ultrashort pulse excitations, we show that the process of acoustic phonon generation by terahertz radiation is mainly driven by thermoelastic stress. While for the near-infrared light excitation the lattice temperature increase comes from a rapid energy transfer from the hot carriers to the phonon bath during carrier intraband relaxation, the thermoelastic stress induced by the terahertz electric field is linked to the scattering of the accelerated electrons leading to an ultrafast Joule effect

Quantum size effect on charges and phonons ultrafast dynamics in atomically controlled nanolayers of topological insulators Bi2Te3

This work was supported by the French Ministry of Education and Research, the CNRS, Region Pays de la Loire (CPER Femtosecond Spectroscopy equipment program) and the LIA-CNRS (Laboratoire International Associé) IM-LED. The partial financial support from National Science Center under project 2016/21/B/ST5/02531 is acknowledged. R. Rapacz was supported by FORSZT PhD fellowship.Heralded as one of the key elements for next generation spintronics devices, topological insulators (TIs) are now step by step envisioned as nanodevices like charge-to-spin current conversion or as Dirac fermions based nanometer Schottky diode for example. However, reduced to few nanometers, TIs layers exhibit a profound modification of the electronic structure and the consequence of this quantum size effect on the fundamental carriers and phonons ultrafast dynamics has been poorly investigated so far. Here, thanks to a complete study of a set of high quality molecular beam epitaxy grown nanolayers, we report the existence of a critical thickness of around ~6 nm, below which a spectacular reduction of the carrier relaxation time by a factor of ten is found in comparison to bulk Bi2 Te3 In addition, we also evidence an A1g optical phonon mode softening together with the appearance of a thickness dependence of the photoinduced coherent acoustic phonons signals. This drastic evolution of the carriers and phonons dynamics might be due an important electron-phonon coupling evolution due to the quantum confinement. These properties have to be taken into account for future TIs-based spintronic devices.Centre National de la Recherche Scientifiqu

Unique properties of silver and copper silica-based nanocomposites as antimicrobial agents

The paper reports a new route for the fabrication and determination of physicochemical properties and biological activity, of metallic silica-based nanostructure (Ag/SiO2, Cu/SiO2). A research studies shows mono-dispersed nanoparticles in silica matrix with an average size of 12 nm for silver, as well as 12 nm and 4 nm, respectively for copper in hydrophobic and hydrophilic silica composites. The chemical analysis highlights metallic silver and copper ions heterogeneously distributed in the composite as well as metallic oxides such as Ag2O, Cu2O and CuO in hydrophobic system, and CuO in hydrophilic one. Structural research evidences the presence of amorphous, stoichiometric and non-stoichiometric crystalline phase of silica. Biological studies reveal potentially inhibition of growth gram-positive and gram-negative bacteria as well as microscopic fungi. The size of metal nanoparticles and level of silica hydrophobicity show the highest inhibition bacterial growth for hydrophilic system with embedding inside them, 4 nm in size copper nanoparticles. Finally, cytotoxic interaction against human cells with respect to silver and copper silica-based nanocomposites was not found