Showing papers by "Etienne Snoeck published in 2011"
TL;DR: This work has studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO(3), where the mismatch with the substrate is relaxed through the formation of domains (twins).
Abstract: Strain engineering enables modification of the properties of thin films using the stress from the substrates on which they are grown. Strain may be relaxed, however, and this can also modify the properties thanks to the coupling between strain gradient and polarization known as flexoelectricity. Here we have studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO3, where the mismatch with the substrate is relaxed through the formation of domains (twins). Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal an intricate strain distribution, with gradients in both the vertical and, unexpectedly, the horizontal direction. These gradients generate a horizontal flexoelectricity that forces the spontaneous polarization to rotate away from the normal. Polar rotations are a characteristic of compositionally engineered morphotropic phase boundary ferroelectrics with high piezoelectricity; flexoelectricity provides an alternative route for generating such rotations in standard ferroelectrics using purely physical means.
499 citations
TL;DR: The genesis, theoretical basis and practical application of the new electron holographic dark-field technique for mapping strain in nanostructures are presented and the development places geometric phase within a unified theoretical framework for phase measurements by electron holography.
62 citations
TL;DR: In this paper, the authors combine direct measurements of strain, electrical mobility measurements, and a rigorous modeling approach to provide insights about strain-induced mobility enhancement in FinFETs and guidelines for device optimization.
Abstract: This study combines direct measurements of strain, electrical mobility measurements, and a rigorous modeling approach to provide insights about strain-induced mobility enhancement in FinFETs and guidelines for device optimization. Good agreement between simulated and measured mobility is obtained using strain components measured directly at device level by a novel holographic technique. A large vertical compressive strain is observed in metal gate FinFETs, and the simulations show that this helps recover the electron mobility disadvantage of the (110) FinFET lateral interfaces with respect to (100) interfaces, with no degradation of the hole mobility. The model is then used to systematically explore the impact of stress components in the fin width, height, and length directions on the mobility of both n- and p-type FinFETs and to identify optimal stress configurations. Finally, self-consistent Monte Carlo simulations are used to investigate how the most favorable stress configurations can improve the on current of nanoscale MOSFETs.
35 citations
TL;DR: Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers and comparison of the simulations with experimental results shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.
Abstract: Magnetization dynamics and field dependent magnetization of different devices based on 25-30 nm thick Permalloy (Py) films: such as single Py layers (Py/MgO; Py/CoFeB/Al2O3) and Py inserted as a magnetic layer in magnetic tunnel junctions (Py/CoFe/Al2O3/CoFe; Py/CoFeB/Al2O3/CoFe; Py/MgO/Fe) have been extensively studied within a temperature range between 300 K down to 5 K. The dynamic response was investigated in the linear regime measuring the ferromagnetic resonance response of the Py layers using broadband vector network analyzer technique. Both the static and the dynamic properties suggest the possible presence of a thermally induced spin reorientation transition in the Py interface at temperatures around 60 K in all the samples investigated. It seems, however, that the details of the interface between Py and the hardening ferromagnet/insulator structure, the atomic structure of Py layers (amorphous vs. textured) as well as the presence of dipolar coupling through the insulating barrier in the magnetic tunnel junction structures could strongly influence this low temperature reorientation transition. Our conclusions are indirectly supported by structural characterization of the samples by means of X-Ray diffraction and high resolution transmission electron microscopy techniques. Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers. Comparison of the simulations with experimental results also shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.
15 citations
TL;DR: In this paper, the authors used lowvoltage transmission electron holography to probe surface electrostatic potentials in graphene membranes and carbon nanotubes, as the number of graphenes varies.
14 citations
TL;DR: In this article, the structural and magnetic properties of magnetically soft ternary Co80-xFexB20 alloys were investigated as a function of composition, thickness, and annealing temperature.
Abstract: We report on the change in the structural and magnetic properties of magnetically soft ternary Co80-xFexB20 alloys as a function of composition, thickness, and annealing temperature. Compositions high in cobalt show a significant change in coercivity after annealing. This is explained using the random anisotropy model by relating the magnetic exchange length to the grain size of the crystallites. The presented results are a systematic study explaining trends seen in the transition from soft to hard magnetic behavior, providing insight into why the soft CoFeB alloys have been so successful recently in spintronic devices.
13 citations
TL;DR: In this article, the early stages of Pt growth on Al 2 O 3 (0001) are investigated by means of electron microscopy and X-ray diffraction, and the growth is of Volmer-Weber type and epitaxy of islands could be reached at elevated temperature.
13 citations
Patent•
28 Jan 2011
TL;DR: In this paper, a method for manufacturing solid cobalt nanorods epitaxied on a solid substrate was proposed, in which at least one surface portion (8) of the solid substrate (5) is immersed in a metal solution including a precursor of cobalt with an initial concentration in a liquid solvent medium, said surface portion being made of crystalline solid platinum.
Abstract: The invention relates to a method for manufacturing solid cobalt nanorods (2) epitaxied on a solid substrate (5), in which: at least one surface portion (8) of the solid substrate (5) is immersed in a metal solution including at least one compound that is a precursor of cobalt with an initial concentration in a liquid solvent medium, said surface portion (8) being made of crystalline solid platinum; during a growing step, said metal solution is maintained with the substrate (5) resting in a pressurised reaction chamber and under conditions suitable for allowing spontaneous growth by epitaxy of cobalt nanorods (2) from said platinum-free surface portion(s) (8) of said substrate (5).
3 citations