J. Pacaud

Strains and stresses in an epitaxial Ni(111)/Mo(110) multilayer grown by direct ion beam sputtering

Abstract An epitaxial Ni(111)/Mo(110) multilayer was grown on a (1 1 2 0) oriented monocrystalline sapphire substrate in a high vacuum sputtering deposition system. The strain and stress state of the layers has been measured with X-ray diffraction in symmetric and asymmetric geometries. Non-equal biaxial coherency stresses due to the Nishiyama–Wassermann epitaxial relation between both lattices are clearly evidenced. The values of the stress-free lattice parameters of molybdenum and nickel sublayers, deduced from the global stress analysis, supports the hypothesis of an interfacial alloying effect between layers with diffusion of nickel in the Mo layers and, to a lesser degree, of molybdenum in Ni layers. On the other hand, the Ni layers appear nearly fully relaxed. A detailed analysis of the stresses in the film shows a strong contribution of a compressive stress field due to possible post-growth atomic rearrangements occurring inside the multilayered film.

Experimental and theoretical study of electron density and structure factors in CoSb3

We refine two low-order structure factors of the skutterudite CoSb₃ using convergent beam electron diffraction. The relatively large unit cell of this material causes the disks to overlap and introduces a series of challenges in the refinement procedure. These challenges and future work-arounds are discussed. The refined structure factors F₂₀₀ and F₆₀₀ are compared to X-ray diffraction and density functional calculated values, the latter calculated using two different functionals. Both relaxed and experimental lattice parameters are tested to explicitly highlight the impact of the lattice geometry and atomic position on the structure factors.

Experimental measurement of electron diffuse scattering in magnetite using energy-filter and imaging plates

We have measured the diffuse scattering in magnetite as a function of temperature using the LEO 912Ohms energy-filtering electron microscope and the imaging plates. This study takes the advantage of the Koehler illumination system, energy filtering and the imaging plates for recording electron diffraction pattern over a large dynamic range. The experiment clearly shows a quantitative change in diffuse scattering distribution, which has the characteristics of one-dimensional ordering. This study clearly demonstrates the possibility for the quantitative study of diffuse scattering using electron diffraction.

Anisotropic strain-stress state and intermixing in epitaxial Mo(110)/Ni(111) multilayers: An x-ray diffraction study

The present study deals with the analysis of elastic strains and stresses in high-quality heteroepitaxial Mo/Ni superlattices with periods Λ lying in the range 4.8–27.6 nm. The strain-stress state in this lattice-mismatched system grown under energetic deposition conditions (ion beam sputtering) is rather complex, resulting from three contributions: (i) intrinsic (growth) stress due to atomic peening, (ii) coherency stresses of opposite sign in the two elemental layers due to the observed Nishiyama–Wassermann epitaxial relationship Ni[11¯0](111)∥Mo[001](110), and (iii) interfacial mixing. The measurement of the lattice parameters of Mo and Ni sublayers in various crystallographic directions was performed by x-ray diffraction, using the sin2u2009ψ method adapted for epitaxial layers. A large anisotropy of elastic strain and associated in-plane coherency stresses is revealed in the Mo sublayers, while for Ni sublayers no such behavior could be detected due to the superimposition of growth variants with threefol...

Electron Diffuse Scattering Study of Perovskite Thin Films

The main requirement for many devices is the growth of a high purity and high structural quality thin film. The perovskite structure is extremely sensitive to the deposition condition and particularly to the temperature and the partial pressure of oxygen. Changes in deposition conditions may lead to a large deviation of the dielectric properties of thin films from those of bulk materials. The chemistry of defects is often proposed as an explanation of this deviation. Beside the oxygen deficiency, the cation stoichiometry seems to play a major role on the structure and properties of the grown film as it might induce the nucleation of structural defects (dislocation loops, stacking fault, RuddlesdenPopper faults...).

The Microstructure and Mechanical Behavior of Deformed Silicon

The microstructure and mechanical behavior of deformed silicon were characterized using transmission electron microscopy and nanoindentation. Structural defects such as stacking faults and dislocations were observed through the diffraction contrast in transmission electron microscopy. The mechanical properties of deformed Si and 111 Si wafer and mechanical behaviors during contact loading were also characterized using nanoindentation. The hardness values of silicon samples were ~10 ㎬ and the elastic modulus were varied with indentation conditions. Elbow or pop-out behaviors were found in load-displacement curves of silicon samples during nanoindentation. Deformed silicon showed ‘pop-out’ behavior more frequently under the load of 10 mN, which is attributed to the structural defects in deformed silicon.

Quantitative electron diffraction evidence for one-dimensional ordering in magnetite above the Verwey transition.

Energy-filtered electron diffraction and three-dimensional reciprocal lattice mapping was used to study the nature of diffuse scattering in magnetite above the Verwey transition temperature. Characteristic Huang scattering associated with a single molecular polaron is observed at room temperature. As the temperature is lowered, the experiment shows narrowing of diffuse scattering in the (001) directions and additional ringlike diffuse scattering at q approximately 0.8, which suggests the presence of one-dimensional structures above the Verwey transition. Experimental measurements of temperature-dependent correlation lengths and diffuse scattering intensity indicate an increase in the number and length of the one-dimensional structure as the temperature is cooled toward the transition. This study demonstrates the electron sensitivity to atomic displacement and the quality of electron diffraction data for studying phase transition in complex materials.