The formation of Ni silicide alloyed with Pt has been analyzed by atom probe tomography. A 300
°C/1
h anneal results in simultaneous growth of the NiSi and Ni
2Si phases: the Ni
2Si phase is a ...continuous layer with columnar grains, while the NiSi phase forms a discontinuous layer. Direct evidence of Pt diffusion short-circuits via Ni
2Si grain boundaries is shown. The presence of Pt in the grains and interphase boundaries may explain the change in the Ni silicide formation for the Ni(5% Pt)/Si system.
The first stages of Ni silicides have been studied by laser assisted atom probe tomography. The observations were realized on a Ni alloyed with 5% of Pt film on (1
0
0)Si, at room temperature. ...Without any heating, it has been observed the formation of two phases with distinct compositions: a layer of relatively constant thickness about 2
nm, with a composition close to NiSi and a cluster of Ni
2Si. These observations are in accordance with the nucleation followed by lateral growth model deduced from calorimetric measurement of silicides and intermetallics growth. The redistribution of Pt during the first stage of formation of the silicides has also been measured.
The lattice and grain boundary diffusion coefficients of As in 260
nm-thick Ni
2Si films were measured. The Ni
2Si layers were prepared via the reaction between a Si layer deposited by low pressure ...chemical vapor deposition and a Ni layer deposited by magnetron sputtering on a Si substrate covered with a SiO
2 film. As was implanted in the silicide. Its concentration profiles were measured using secondary ion mass spectroscopy before and after annealing (550–700
°C). 2D finite element diffusion simulations taking into account lattice diffusion and grain boundary (GB) diffusion were performed based on the microstructure of the samples. They were found to fit accurately the measured profiles and allowed to measure the diffusion coefficients for each temperature. Lattice diffusion is characterized by a pre-exponential factor
D
0
v
∼
1.5
×
10
−1
cm
2
s
−1 and an activation energy
Qv
∼
2.72
eV. In the case of GB diffusion
P
0
=
sδD
0
gb
=
9.0
×
10
−3
cm
3
s
−1 and the activation energy was found to be higher than for lattice diffusion with
Qgb
∼
3.07
eV. Existing data concerning diffusion in silicides and other materials is used to discuss these results. The diffusion of As in Ni
2Si could be reduced due to impurity segregation in GBs.
Multiferroic particulate composites $(1-x)$
Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$-$(x)$CoFe$_2$O$_4$ with ($x$
= 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by mechanical mixing of the
...calcined and milled individual ferroic phases. X-ray diffraction and Raman
spectroscopy analysis confirmed the formation of both perovskite
Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ (BCTSn) and spinel
CoFe$_2$O$_4$ (CFO) phases without the presence of additional phases. The
morphological properties of the composites were provided by using Field
Emission Scanning Electron Microscopy. The BCTSn-CFO composites exhibit
multiferroic behavior at room temperature, as evidenced by ferroelectric and
ferromagnetic hysteresis loops. The magnetoelectric (ME) coupling was measured
under a magnetic field up to 10 kOe and the maximum ME response found to be 0.1
mV /cm/ Oe for the composition 0.7 BCTSn-0.3 CFO exhibiting a high degree of
pseudo-cubicity and large density.
Multiferroic CoFe2O4-Ba0.95Ca0.05Ti0.89Sn0.11O3 core-shell nanofibers (CFO@BCTSn NFs) were synthesized by a sol-gel co-axial electrospinning technique. The scanning electron microscope and ...transmission electron microscope were used to check nanofibers' core-shell structure/configuration. X-ray diffraction and a high-resolution transmission electron microscope were used to confirm the spinel structure of CFO and the perovskite structure of BCTSn. The magnetic character of the resultant CFO@BCTSn NFs was determined by SQUID magnetometry. The piezoelectricity was verified using piezo-response force microscopy, which revealed an entirely covered ferroelectric shell outline, in accordance with SEM and TEM observations. The magnetoelectric (ME) coefficient was measured as a function of the applied external DC magnetic field. The maximum ME coefficient obtained for the CFO@BCTSn NFs was 346 mV cm-1 Oe-1. The high magnetoelectric coupling suggests that CFO@BCTSn NFs could be a promising candidate for magnetic field sensor and magnetoelectric device applications.
Antiferroelectrics are promising materials for high energy density capacitors and the search for environmentally-friendly and efficient systems is actively pursued. An elegant strategy to create and ...design new (anti)ferroic system relies on the use of nanoscale superlattices. We report here the use of such strategy and the fabrication of nanoscale BiFeO3/NdFeO3 superlattices and in depth characterization using high resolution X-ray diffraction and Transmission Electron Microscopy. The structural analysis at atomic scale demonstrates that such superlattices host anti-polar ordering most likely described by an antiferroelectric-like Pbnm symmetry. Temperature dependence of anti-polar state and structural transition further hint that the stability of the anti-polar state is controlled by the BiFeO3 layer thickness within the stacking and, in a more moderate way, by interlayer strain. Discovery of such polar arrangement in superlattices and the possible generalization to the whole rare-earth family pave the way to new platforms for energy storage application as well as nano-electronic devices.
The electrocaloric (EC) effect and energy storage properties of eco-friendly ferroelectric Ba0.9Sr0.1Ti1-xSnxO3 (BSTS-x) ceramics prepared by the conventional solid-state reaction method were ...studied. Significant energy efficiency exceeding 80% was found in our samples. In particular, BSTS-5 and BSTS-10 samples exhibit 92% and 88% efficiency, respectively, over a wide temperature range around room temperature (RT). Direct EC measurement and an indirect method based on the thermodynamic approach were used to characterize the EC effect, and both yielded consistent results. The largest electrocaloric responsivity of 0.73 K mm/kV was obtained for BSTS-0 at 368 K with an adiabatic temperature change DT(EC) of 0.55 K at a low applied electric field of only 7.4 kV/cm. With increasing Sn-content, the EC response of BSTS-x ceramics decreases, while their diffuseness increases over an extensive temperature range, centered at RT. A significant coefficient of performance (COP > 26) was found for our samples. The obtained results demonstrate the possibility of designing eco-friendly materials with higher EC effect and energy efficiency for potential solid-state refrigeration and energy storage devices.
Strain engineering is a powerful mean for tuning the various functionalities of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials such as NdFeO3 (NFO) are of prime interest ...because of their intriguing magnetic properties as well as their technological potential applications especially as thin films. Here, using a large set of complementary and advanced techniques, we show that NFO epitaxial thin films, successfully grown by pulsed laser deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical thickness tc of 54 nm, associated with the occurrence of structural modifications related to symmetry and domain pattern changes. By varying the tensile misfit strain through the decrease of film thickness below tc, the amplitudes of in and out-of-plane magnetization can be continuously tuned while their ratio stays constant. Furthermore, different low-temperature magnetic behaviors are evidenced for strained and relaxed films, suggesting that the strain-induced structural state impacts the magnetic phase stability.
L'objectif de cette étude est de caractériser la redistribution d'éléments d'alliages et de dopants au cours des premiers stades de formation des siliciures de Ni. Pour cela, nous avons étudié la ...nature, la séquence et la cinétique des phases formées, dans un premier temps pour les systèmes binaires Pd/Si, Pt/Si et Ni/Si, puis pour les systèmes ternaires (Ni,Pt)/Si et Ni/(Si, As) présentant un intérêt technologique pour la nanoélectronique. Ainsi, nous avons couplé des techniques de caractérisation originales (calorimétrie différentielle à balayage sur films minces, sonde atomique tomographique, diffraction des rayons X in situ) pour mesurer la redistribution du Pt dans les phases formées et leurs cinétiques de croissance. Nous avons pu développer un modèle pour décrire les premiers stades de croissance de ces siliciures alliés et dégager les mécanismes mis en jeu ainsi que les facteurs limitant la redistribution des éléments d'alliage et des dopants.
