P. Parreira

Stability, bistability and instability of amorphous ZrO2 resistive memory devices

Amorphous zirconium oxide thin films deposited at room temperature, sandwiched between Pt and Ti electrodes, show resistive bipolar resistive switching with good overall performance figures (retention, ON/OFF ratio and durability). A variability observed during electrical characterisation is consistent with the coexistence of two different resistive switching mechanisms within the ZrO2 layer. Electron energy loss spectroscopy is used to map chemical variations across the device on the nanoscale. Partial oxidation of the Ti electrode creates an ohmic contact with zirconia and injects positively charged oxygen vacancies into the zirconia layer that are then responsible for resistive switching at the Pt / zirconia interface.

Dynamical Torque in CoxFe3-xO4 Nanocube Thin Films Characterized by Femtosecond Magneto-Optics: A π-Shift Control of the Magnetization Precession.

For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles.

Resistive switching in ZrO2 films: physical mechanism for filament formation and dissolution

Resistive switching devices, also called memristors, have attracted much attention due to their potential memory, logic and even neuromorphic applications. Multiple physical mechanisms underpin the non-volatile switching process and are ultimately believed to give rise to the formation and dissolution of a discrete conductive filament within the active layer. However, a detailed nanoscopic analysis that fully explains all the contributory events remains to be presented. Here, we present aspects of the switching events that are correlated back to tunable details of the device fabrication process. Transmission electron microscopy and atomically resolved electron energy loss spectroscopy (EELS) studies of electrically stressed devices will then be presented, with a view to understanding the driving forces behind filament formation and dissolution.

Explicit design of transfer functions for volume-rendered images by combining histograms, thumbnails, and sketch-based interaction

Visual quality of volume rendering for medical imagery strongly depends on the underlying transfer function. Conventional Windows–Icons–Menus–Pointer interfaces typically refer the user to browse a lengthy catalog of predefined transfer functions or to pain-staking refine the transfer function by clicking and dragging several independent handles. To turn the standard design process less difficult and tedious, this paper proposes novel interactions on a sketch-based interface that supports the design of 1D transfer functions via touch gestures to directly control voxel opacity and easily assign colors. User can select different types of transfer function shapes including ramp function, free hand curve drawing, and slider bars similar to those of a mixing table. An assorted array of thumbnails provides an overview of the data when editing the transfer function. User performance is evaluated by comparing the time and effort necessary to complete a number of tests with sketch-based and conventional interfaces. Users were able to more rapidly explore and understand volume data using the sketch-based interface, as the number of design iterations necessary to obtain a desirable transfer function was reduced. In addition, informal evaluation sessions carried out with professionals (two senior radiologists, a general surgeon and two scientific illustrators) provided valuable feedback on how suitable the sketch-based interface is for illustration, patient communication and medical education.