[en] Recently proposed novel neural network hardware designs imply the use of memristors as electronic synapses in 3D cross-bar architecture. Atomic layer deposition (ALD) is the most feasible technique to fabricate such arrays. In this work, we present the results of the detailed investigation of the gradual resistive switching (memristive) effect in nanometer thick fully ALD grown TiN/HfO₂/TiN stacks. The modelling of the I-V curves confirms interface limited trap-assisted-tunneling mechanism along the oxygen vacancies in HfO₂ in all conduction states. The resistivity of the stack is found to critically depend upon the distance from the interface to the first trap in HfO₂. The memristive properties of ALD grown TiN/HfO₂/TiN devices are correlated with the demonstrated neuromorphic functionalities, such as long-term potentiation/depression and spike-timing dependent plasticity, thus indicating their potential as electronic synapses in neuromorphic hardware

[en] Hard x-ray photoelectron diffraction (hXPD) patterns recorded with a momentum microscope with high k-resolution (0.025 Å⁻¹ equivalent to an angular resolution of 0.034° at 7 keV) reveal unprecedented rich fine structure. We have studied hXPD of the C 1s core level in the prototypical low-Z material Graphite at 20 photon energies between 2.8 and 7.3 keV. Sharp bright and dark lines shift with energy; regions of Kikuchi band crossings near zone axis exhibit a filigree structure which varies rapidly with energy. Calculations based on the Bloch wave approach to electron diffraction from lattice planes show excellent agreement with the experimental results throughout the entire energy range. The main Kikuchi bands in the [001] zone axis appear fixed on the momentum scale with a width of the corresponding reciprocal lattice vector, allowing to reconstruct the size of the projected Brillouin zone. The newly developed high-energy k-microscope allows full-field imaging of (k _x, k _y)-distributions in large k-fields (up to >22 Å⁻¹ dia.) and time-of-flight energy recording. (paper)

[en] The heavy-fermion behavior in intermetallic compounds manifests itself in a quenching of local magnetic moments by developing Kondo spin-singlet many-body states combined with a drastic increase of the effective mass of conduction electrons, which occurs below the lattice Kondo temperature T _K. This behavior is caused by interactions between the strongly localized 4f electrons and itinerant electrons. A controversially discussed question in this context is how the localized electronic states contribute to the Fermi surface upon changing the temperature. One expects that hybridization between the local moments and the itinerant electrons leads to a transition from a small Fermi surface in a non-coherent regime at high temperatures to a large Fermi surface once the coherent Kondo lattice regime is realized below T _K. We demonstrate, using hard x-ray angle-resolved photoemission spectroscopy that the electronic structure of the prototypical heavy fermion compound YbRh₂Si₂ changes with temperature between 100 and 200 K, i.e. far above the Kondo temperature, T _K = 25 K, of this system. Our results suggest a transition from a small to a large Fermi surface with decreasing temperature. This result is inconsistent with the prediction of the dynamical mean-field periodic Anderson model and supports the idea of an independent energy scale governing the change of band dispersion. (paper)

[en] We have studied the influence of corrosive environment on the mechanism of changes in fatigue resistance of automotive structural steels. Analysis of the experimental data has shown that the fatigue resistance of metal materials in corrosive environments is reduced significantly with the increased time of testing. This, in turn, causes a continuous decrease in fatigue curves in the multi-cycle area without reaching the endurance limit. We have identified the factors affecting the resistance to fatigue failure: the medium and its aggressiveness; stress cycle frequency, shape and asymmetry. The presence of a corrosive environment makes it problematic to determine the moment of origin of a macro crack, necessary for the analytical assessment of the time before its appearance. The proposed use of the current sag curves under the sample cyclic loading will allow to fix the moment of the crack origin and to determine the speed of its subsequent propagation. This allows to optimize the choice of structural materials for machines taking into account the operating conditions and to justify the technological manufacturing process in order to reduce material consumption, increase durability and maintainability. (paper)

[en] Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO₃(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO₃/Pt junctions with a sub-μm Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ∼30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO₃/Pt (Cr/BaTiO₃) interface +0.42(−0.03) eV following downward to upward polarization reversal.