Search results for "Mil"
showing 10 items of 29279 documents
Enhancing domain wall velocity through interface intermixing in W-CoFeB-MgO films with perpendicular anisotropy
2019
We study the influence of He+ irradiation induced interface intermixing on magnetic domain wall (DW) dynamics in W-CoFeB (0.6 nm)-MgO ultrathin films, which exhibit high perpendicular magnetic anisotropy and large Dzyaloshinskii-Moriya interaction (DMI) values. Whereas the pristine films exhibit strong DW pinning, we observe a large increase in the DW velocity in the creep regime upon He+ irradiation, which is attributed to the reduction of pinning centers induced by interface intermixing. Asymmetric in-plane field-driven domain expansion experiments show that the DMI value is slightly reduced upon irradiation, and a direct relationship between DMI and interface anisotropy is demonstrated. …
Reactive Sintering of molybdenum disilicide by Spark Plasma Sintering from mechanically activated powder mixtures: Processing parameters and properti…
2008
Abstract Dense molybdenum disilicide with a nano-organized microstructure was synthesized by mechanical activation, by producing nanostructured agglomerates of a 1:2 mixture of Mo and Si, followed by the synthesis/consolidation in one step using SPS technology. In order to synthesize a dense molybdenum disilicide with a perfectly controlled microstructure, an investigation of the influence of Spark Plasma Sintering processing parameters (temperature, heating rate, mechanical pressure and holding time) on the chemical composition and the microstructure characteristics has been performed. The present work shows also that the so-obtained materials present better oxidation resistance in compari…
Nucleation of GaN nanowires grown by plasma-assisted molecular beam epitaxy: The effect of temperature
2011
Abstract The growth of GaN nanowires by means of plasma assisted molecular beam epitaxy directly on Si(1 1 1) has been investigated as a function of temperature. Statistical analysis of scanning electron microscopy pictures taken for different growth temperatures has revealed that density, diameter, length and length dispersion of nanowires were strongly dependent on temperature. Length dispersion, in particular, was found to be significant at high temperature. These features have been assigned to the different duration of the nucleation process with temperature, namely to the dependence with temperature of the time necessary for the size increase of the three-dimensional precursors up to a…
The role of seed electrons on the plasma breakdown and preglow of electron cyclotron resonance ion source
2009
The 14 GHz Electron Cyclotron Resonance Ion Source at University of Jyväskylä, Department of Physics (JYFL) has been operated in pulsed mode in order to study the plasma breakdown and preglow effect. It was observed that the plasma breakdown time and preglow characteristics are affected by seed electrons provided by a continuous low power microwave signal at secondary frequency. Sustaining low density plasma during the off-period of high power microwave pulses at the primary frequency shifts the charge state distribution of the preglow transient toward higher charge states. This could be exploited for applications requiring fast and efficient ionization of radioactive elements as proposed f…
Hydrodynamic Modeling of Transport and Noise Phenomena in Bipolar Two-Terminal Silicon Structures
1998
International audience
Electromagnetically induced switching of ferroelectric thin films
2007
We analyze the interaction of an electromagnetic spike (one cycle) with a thin layer of ferroelectric medium with two equilibrium states. The model is the set of Maxwell equations coupled to the undamped Landau-Khalatnikov equation, where we do not assume slowly varying envelopes. From linear-scattering theory, we show that low-amplitude pulses can be completely reflected by the medium. Large-amplitude pulses can switch the ferroelectric. Using numerical simulations and analysis, we study this switching for long and short pulses, estimate the switching times, and provide useful information for experiments.
Reversed polarized emission in highly strained a-plane GaN/AlN multiple quantum wells
2010
The polarization of the emission from a set of highly strained $a$-plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite $c$ axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the $c$ axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been p…
Enhancement of the Multipactor Threshold Inside Nonrectangular Iris
2018
Multipactor breakdown is studied inside the capacitive iris of a rectangular waveguide with a skewed slot along its longitudinal cross section. Both the iris length and height are assumed to be small compared to the electromagnetic wavelength. Therefore, the quasi-static approximation is applied so as to describe the RF field distribution inside the iris gap, whereas a 2-D model is used to analyze the electron motion. The peculiarities of RF field structure are studied using the conformal mapping approach, which shows that the electric field lines can be approximated by circular arcs when the iris length is much larger than its height. The electron motion inside the iris gap is analyzed usi…
Accumulation of positrons from a LINAC based source
2020
International audience; The GBAR experiment aims to measure the gravitational acceleration of antihydrogen H̅. It will use H̅+ ions formed by the interaction of antiprotons with a dense positronium cloud, which will require about 1010 positrons to produce one H̅+. We present the first results on the positron accumulation, reaching 3.8±0.4×108 e+ collected in 560 s.
Topological two-dimensional Su–Schrieffer–Heeger analog acoustic networks: Total reflection at corners and corner induced modes
2021
In this work, we investigate some aspects of an acoustic analogue of the two-dimensional Su-Schrieffer-Heeger model. The system is composed of alternating cross-section tubes connected in a square network, which in the limit of narrow tubes is described by a discrete model coinciding with the two-dimensional Su-Schrieffer-Heeger model. This model is known to host topological edge waves, and we develop a scattering theory to analyze how these waves scatter on edge structure changes. We show that these edge waves undergo a perfect reflection when scattering on a corner, incidentally leading to a new way of constructing corner modes. It is shown that reflection is high for a broad class of edg…