Study of Microscopic Residual Stresses in an Extruded Aluminium Alloy Sample after Thermal Treatment

Abstract: A method is proposed to calculate the microscopic residual stresses in extruded cylindrical samples of non-ageing aluminium alloy 5083 (Al–Mg), arising from quenching in fresh water from 530°C. We start from the premise that the alloy is single-phase and non-isotropic on a microscopic scale; it consists of many grains that exhibit different mechanical response depending on their crystallographic orientation and neighboring grains. Microscopic residual stresses depend on the applied heat treatment, microstructure and mechanical strength of the individual grains. The stresses were calculated from neutron diffraction data. Genetic programming algorithms were used to calculate microscopic residual stresses, considering that each diffraction peak describes the stress distribution of a group of grains having a certain orientation, size and environment. The algorithm assigns a stress value to each grain according to the distribution of the diffraction peaks and the microstructural parameters of these grains.This work was supported by the Madrid Regional Government-FEDER grant Y2018/NMT-4668 (Micro-Stress-MAP-CM) and the project MAT2017-83825-C4-1-R. We would also like to express our gratitude to FLNR-JINP for the beam time allocated on the FSD instrument, and to the HeuristicLab Software developers

Engineering a Spin-Orbit Bandgap in Graphene-Tellurium Heterostructures

Intensive research has focused on harnessing the potential of graphene for electronic, optoelectronic, and spintronic devices by generating a bandgap at the Dirac point and enhancing the spin-orbit interaction in the graphene layer. Proximity to heavy p elements is a promising approach; however, their interaction in graphene heterostructures has not been as intensively studied as that of ferromagnetic, noble, or heavy d metals, neither as interlayers nor as substrates. In this study, the effective intercalation of Te atoms in a graphene on Ir(111) heterostructure is achieved. Combining techniques such as low energy electron diffraction and scanning tunneling microscopy, the structural evolution of the system as a function of the Te coverage is elucidated, uncovering up to two distinct phases. The presented angle-resolved photoemission spectroscopy analysis reveals the emergence of a bandgap of about 240 meV in the Dirac cone at room temperature, which preserves its characteristic linear dispersion. Furthermore, a pronounced n-doping effect induced by Te in the heterostructure is also observed, and remarkably the possibility of tuning the Dirac point energy towards the Fermi level by reducing the Te coverage while maintaining the open bandgap is demonstrated. Spin-resolved measurements unveil a non-planar chiral spin texture with significant splitting values for both in-plane and out-of-plane spin components. These experimental findings are consistent with the development of a quantum spin Hall phase, where a Te-enhanced intrinsic spin orbit coupling in graphene surpasses the Rashba one and promotes the opening of the spin-orbit bandgap.Comment: 9 pages, 4 figure

Host preferences and differential contributions of deciduous tree species shape mycorrhizal species richness in a mixed Central European forest

Mycorrhizal species richness and host ranges were investigated in mixed deciduous stands composed of Fagus sylvatica, Tilia spp., Carpinus betulus, Acer spp., and Fraxinus excelsior. Acer and Fraxinus were colonized by arbuscular mycorrhizas and contributed 5% to total stand mycorrhizal fungal species richness. Tilia hosted similar and Carpinus half the number of ectomycorrhizal (EM) fungal taxa compared with Fagus (75 putative taxa). The relative abundance of the host tree the EM fungal richness decreased in the order Fagus > Tilia >> Carpinus. After correction for similar sampling intensities, EM fungal species richness of Carpinus was still about 30–40% lower than that of Fagus and Tilia. About 10% of the mycorrhizal species were shared among the EM forming trees; 29% were associated with two host tree species and 61% with only one of the hosts. The latter group consisted mainly of rare EM fungal species colonizing about 20% of the root tips and included known specialists but also putative non-host associations such as conifer or shrub mycorrhizas. Our data indicate that EM fungal species richness was associated with tree identity and suggest that Fagus secures EM fungal diversity in an ecosystem since it shared more common EM fungi with Tilia and Carpinus than the latter two among each other