Crystalline Orientation–Dependent Spin Hall Effect in Epitaxial Platinum

We report on the spin Hall effect in epitaxial Pt films with well-defined crystalline (200), (220), and (111) orientations and smooth surfaces. The magnitude of the spin Hall effect has been determined by spin–torque ferromagnetic resonance measurements on epitaxial Pt/Py heterostructures. We observed a 54% enhancement of the charge-to-spin conversion efficiency of the epitaxial Pt when currents are applied along the in-plane <002> direction. Temperature-dependent harmonic measurements on epitaxial Pt/Co/Ni heterostructures compared to a polycrystalline Pt/Co/Ni suggest the extrinsic mechanism underlying spin Hall effect in epitaxial Pt. Our work contributes to the development of energy-efficient spintronic devices by engineering the crystalline anisotropy of non-magnetic metals.

Micro Electrical Discharge Machining Thermal Effect on Micro-Cracks Generation on Silicon Material

Various novel 3D micro machining technologies were researched and developed for silicon micro mechanical system fabrication. Micro EDM is one of them. The material removal mechanism is thermal sparking erosion and is completely independent with regards to the crystalline orientation of silicon, therefore there is no orientation constraint in processing the complex 3D geometry of silicon wafers. As thermal sparking implied, the process features local area high temperature melting and evaporating, and this characteristic has an adverse side-effect on the sparked surface integrity. One important concern is the generation of micro cracks, which would provide an adverse effect on the fatigue life of the micro feature element made of silicon. For this consideration, in this paper, with the experiment and SEM picture analysis approach, the author explored the micro crack generation characteristics on mono crystalline silicon wafers under micro EDM with available sparking energies and on the different crystal orientation surface machining. The generation of micro cracking is not only related with the sparking energy but also related with the crystalline orientation. The {100} orientation is the strongest surface to resist crack generation. For a strong-doped P type silicon wafer, there exists a maximum crack energy threshold. If single sparking energy is over this threshold, micro cracks unavoidably would be generated on any orientation surface. Two types of chemical etching post processes that can remove cracks on sparked surfaces are also tested and discussed.

Orientation selective grain sublimation–deposition in snow under temperature gradient metamorphism observed with diffraction contrast tomography

In this study on temperature gradient metamorphism in snow, we investigate the hypothesis that there exists a favourable crystalline orientation relative to the temperature gradient, giving rise to a faster formation of crystallographic facets. We applied in situ time-lapse diffraction contrast tomography on a snow sample with a density of 476 kg m−3 subject to a temperature gradient of 52 ∘Cm-1 at mean temperatures in the range between −4.1 and −2.1 ∘C for 3 d. The orientations of about 900 grains along with their microstructural evolution are followed over time. Faceted crystals appear during the evolution, and from the analysis of the material fluxes, we observe higher sublimation–deposition rates for grains with their c axis in the horizontal plane at the beginning of the metamorphism. This remains the case up to the end of the experiment for what concerns sublimation while the differences vanish for deposition. The latter observation is explained in terms of geometrical interactions between grains.