Multilayers that comprise thin films of heavy metals and ferromagnets have been shown to host Néel-type magnetic skyrmions at room temperature. Fresnel defocus imaging in Lorentz transmission electron microscopy is a widely used technique for recording magnetic information about skyrmions. However, the visibility of Néel-type skyrmions in Fresnel defocus images is typically low, both because only a small component of their magnetic field contributes to the signal and because of the presence of diffraction contrast from the polycrystalline multilayer structure. Here, we take advantage of the out-of-plane hysteresis in such samples to record background-subtracted Fresnel defocus images. We demonstrate an improvement in magnetic signal-to-noise ratio and spatial resolution by a factor of 3 for a (Pt/Co/NiFe)×5 multilayer. We also use simulated Fresnel defocus images of Néel-type magnetic skyrmions to understand the influence of defocus on apparent skyrmion size.

Accuracy of atom probe tomography measurements is strongly degraded by the presence of phases that have different evaporation fields. In particular, when there are perpendicular interfaces to the tip axis in the specimen, layers thicknesses are systematically biased and the resolution is degraded near the interfaces. Based on an analytical model of field evaporated emitter end-form, a new algorithm dedicated to the 3D reconstruction of multilayered samples was developed. Simulations of field evaporation of bilayer were performed to evaluate the effectiveness of the new algorithm. Compared to the standard state-of-the-art reconstruction methods, the present approach provides much more accurate analyzed volume, and the resolution is clearly improved near the interface. The ability of the algorithm to handle experimental data was also demonstrated. It is shown that the standard algorithm applied to the same data can commit an error on the layers thicknesses up to a factor 2. This new method is not constrained by the classical hemispherical specimen shape assumption.

Nanostructured Al1−xMnx/Al1−yMny multilayers were deposited from room temperature ionic liquid using galvanostatic control at various current densities and electrolyte compositions. By tuning the deposition parameters, multilayers with both micrometer and nanometer layer thicknesses were synthesized, with modulation of the elastic modulus and hardness between Mn-lean and Mn-rich layers. Surface morphology, composition, and microstructure of the films were characterized using x-ray diffraction and electron microanalysis tools. Nanoindentation and nanoscratch tests were performed to evaluate the mechanical and tribological properties of selected multilayers. Finally, the effects of deposition parameters on the microstructure evolution and mechanical properties of the multilayers were discussed.

Self-assembled nanostructures of α,ω-dihexylsexithiophene (DH6T) formed by spreading DH6T solutions onto freshly cleaved mica surface were studied by atomic force microscopy. The effects of solvent and concentration on the nanostructures of DH6T molecules were studied. Flat, well-ordered, and platelet-like domains were observed on mica surfaces after treatment with various polar solvent solutions of DH6T. These domains form a uniform film with height of 2.4 ± 0.2 nm, which is consistent with a 45° tilt in the molecular conformation of DH6T on mica surfaces. The formation mechanism of these multilayers is discussed in detail.

We study the homogenization process of ferromagnetic multilayers in the presence of surface energies:super-exchange, also called interlayer exchange coupling,and surface anisotropy. The two main difficulties are the non-linearity of the Landau-Lifshitz equation and the absence of a good sequenceof extension operators for the multilayer geometry.First, we consider the case when surface anisotropy is the dominant term, then the case when the magnitude of the super-exchange interaction is inversely proportional to the interlayer distance. We establishthe homogenized equation in these two situations.

The mechanixcal behavior of W/Cu multilayers with periods ranging from 24 down to 3 nm prepared by ion beam sputtering was analyzed using a method combining X-ray diffraction and tensile testing, and instrumented indentation. Cracks perpendicular to the tensile axis observed by optical microscopy were generated in the films under the largest applied tensile stresses. These cracks may appear in the multilayer while W layers are still in a compressive stress state. Elastic modulus and hardness values were extracted from nano-indentation data. Crack initiation and elastic constants were observed to depend on the period of these multilayers.

A numerical model has been developed to simulate images obtained from the three-dimensional atom probe. This model was used to simulate the artefacts commonly observed in two-phase materials. This model takes into account the dynamic evolution of the atomic-scale shape of the specimen during field evaporation. This article reviews the model and its applications to some specific cases. Local magnification effects were studied as a function of the size, the shape, and the orientation of precipitated phases embedded in the matrix. Small precipitates produce large aberrations in good agreement with experiments. The magnification from such precipitates, as measured from the simulation, is only found to match the theoretical value for mesoscopic scale precipitates (size similar to the specimen size). Orientation effects are also observed in excellent agreement with experiments. The measured thickness of a grain-boundary-segregated film in the simulation is found to decrease with the angle between the normal to the grain boundary and the tip axis. Depth scaling artefacts caused by variation in the evaporation field of atoms in multilayer structures were successfully simulated and again showed good agreement with effects observed experimentally.