When applying mechanical stress to a bulk metallic glass it responds with elastic and/or plastic deformations. A comprehensive microscopic theory for the plasticity of amorphous solids remains an open task. Shear transformation zones consisting of dozens of atoms have been identified as smallest units of deformation. The connexion between local formation of shear transformations zones and the creation of macroscopic shear bands can be made using statistical analysis of stress/energy drops or strain slips during mechanical loading. Numerical work has proposed a power law dependence of those energy drops. Here we present an approach to circumvent the experimental resolution problem using a waiting time analysis. We report on the power law-distributed deformation behaviour and the observation of a crossover in the waiting times statistics. This crossover indicates a transition in the plastic deformation behaviour from three-dimensional random activity to a two-dimensional nano shear band sliding.

We report the local-conductivity properties of a La 0.8 Ca 0.2 MnO 3 thin film, studied by conductive atomic force microscopy. Nonvolatile and bipolar reversible switching of nanometer-sized regions was observed. A threshold voltage, U c Ϸ 3 V, and a logarithmic pulse-width dependence compatible with domain-wall creep were revealed. The results are difficult to explain in terms of an ionic drift scenario but rather indicate a switching mechanism based on orbital and accompanying structural changes. A phenomenological model of an electric field-induced structural transition is proposed.

Cerium oxide is often applied in today's catalysts due to its remarkable oxygen storage capacity. The changes in stoichiometry during reaction are linked to structural modifications, which in turn affect its catalytic activity. We present a real-time in situ study of the structural transformations of cerium oxide particles on ruthenium(0001) at high temperatures of 700 °C in ultra-high vacuum. Our results demonstrate that the reduction from CeO to cubic CeO proceeds via ordered intermediary phases. The final reduction step from cubic to hexagonal CeO is accompanied by a lattice expansion, the formation of two new surface terminations, a partial dissolution of the cerium oxide particles, and a massive mass transport of cerium from the particles to the substrate. The conclusions allow for new insights into the structure, stability, and dynamics of cerium oxide nanoparticles in strongly reducing environments.

We report active control of the friction force at the contact between a nanoscale asperity and a La0.55Ca0.45MnO3 (LCMO) thin film using electric fields. We use friction force microscopy under ultrahigh vacuum conditions to measure the friction force as we change the film resistive state by electric field-induced resistive switching. Friction forces are high in the insulating state and clearly change to lower values when the probed local region is switched to the conducting state. Upon switching back to an insulating state, the friction forces increase again. Thus, we demonstrate active control of friction without having to change the contact temperature or pressure. By comparing with measurements of friction at the metal-to-insulator transition and with the effect of applied voltage on adhesion, we rule out electronic excitations, electrostatic forces and changes in contact area as the reasons for the effect of resistive switching on friction. Instead, we argue that friction is limited by phonon relaxation times which are strongly coupled to the electronic degrees of freedom through distortions of the MnO6 octahedra. The concept of controlling friction forces by electric fields should be applicable to any materials where the field produces strong changes in phonon lifetimes.Friction is a complex phenomenon that occurs between two bodies at a sliding contact.Despite the fact that it often can be described by straight-forward empirical relations, its fundamental cause is by no means simple. With the advent of the atomic force microscope (AFM), understanding and controlling nanoscale friction has become one of the major interests in modern tribology. A promising direction is reported in several literature studies [1-8] which show a clear change in measured nanoscale friction force when the electronic state of the material is altered. Abrupt increases are observed in the non-contact dissipation of Nb [5] and the contact friction of YBCO [6] and Pb [1,8] as the materials are heated through their superconducting transitions. Contact friction measurements on Si [4] and GaAs [2] semiconductors demonstrate a strong dependence on the charge carrier density, while the contact friction of VO2 is strongly increased on heating through the metal-to-insulator transition (MIT) from the insulating to the metallic state [3,7].