The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory. The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.

Tunnel devices based on ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) barriers hold great promises for emerging data storage and computing technologies. The resistance state of the device can be changed by a suitable writing voltage. However, the microscopic mechanisms leading to the resistance change are an intricate interplay between ferroelectric polarization controlled barrier properties and defect-related transport mechanisms. Here is shown the fundamental role of the microstructure of HZO films setting the balance between those contributions. The oxide film presents coherent or incoherent grain boundaries, associated to the existence of monoclinic and orthorhombic phases in HZO films, which are dictated by the mismatch with the substrates for epitaxial growth. These grain boundaries are the toggle that allows to obtain either large (up to ≈ 450 %) and fully reversible genuine polarization controlled electroresistance when only the orthorhombic phase is present or an irreversible and extremely large (≈ 10 3 -10 5 %) electroresistance when both phases coexist.are the resistances after polarizing the junction with writing voltages V W + or V W and R min (V W +,-) is the minimum resistance among these states. Accordingly, binary high (OFF) and low resistance (ON) states can be written in a ferroelectric memory cell and read by probing its resistance. It has also been shown that by performing minor polarization loops, ferroelectric tunnel devices can store information in different resistive states, mimicking the functioning of a memristive element. [4,5] This approach has been successfully achieved by using ferroelectric perovskites such as BaTiO 3 , [6][7][8][9] Pb(Zr 0.2

Mechanical effects on cells have received more and more attention in the studies of tissue engineering, cellular pathogenesis, and biomedical device design. Anisotropic biaxial cyclic stress, reminiscent of the in vivo cellular mechanical environment, may promise significant implications for biotechnology and human health. We have designed, fabricated and characterized a microdevice that imparts a variety of anisotropic biaxial cyclic strain gradients upon cells. The device is composed of an elastic membrane with microgroove patterns designed to associate cell orientation axes with biaxial strain vectors on the membrane and a Flexcell stretcher with timely controlled vacuum pressure. The stretcher generates strain profile of anisotropic biaxial microgradients on the membrane. Cell axes determined by the microgrooves are associated with the membrane strain profile to impose proper biaxial strains on cells. Using vascular smooth muscle cells as a cell model, we demonstrated that the strain anisotropy index of a cell was likely one of the determinant mechanical factors in cell structural and functional adaptations. The nuclear shape and cytoskeleton structure of smooth muscle cells were influenced by mechanical loading, but were not significantly affected by the strain anisotropy. However, cell proliferation has profound responses to strain anisotropy.

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Ab initio calculations based on density functional theory have been performed to determine the properties of self-interstitial atoms (SIAs), vacancies, and single H and He atoms in hcp-Er. The results show that the most stable configuration for a SIA is a basal octahedral configuration, while the octahedral (O), basal split, and crowdion (C) interstitial configurations are less stable, followed by the split ⟨0001⟩ dumbbell and tetrahedral configurations. For both H and He defects, the formation energy of an interstitial atom is less than that of a substitutional atom in hcp-Er. Furthermore, the tetrahedral interstitial position is more stable than an octahedral position for both He and H interstitials. The hybridization of the He and H defects with Er atoms has been used to explain the relative stabilities of these defects in hcp-Er.

In the quest for energy efficient and fast memory elements, optically controlled ferroelectric memories are promising candidates. Here, we show that, by taking advantage of the imprint electric field existing in the nanometric BaTiO3 films and their photovoltaic response at visible light, the polarization of suitably written domains can be reversed under illumination. We exploit this effect to trigger and measure the associate change of resistance in tunnel devices. We show that engineering the device structure by inserting an auxiliary dielectric layer, the electroresistance increases by a factor near 2 × 103%, and a robust electric and optic cycling of the device can be obtained mimicking the operation of a memory device under dual control of light and electric fields.

Interatomic potentials for an ErÀH system are derived based on an analytical bond-order scheme. The model potentials provide a good description of the bulk properties and defect properties of hcp-Er, including lattice parameters, cohesive energy, elastic constants, point defect formation energies, and surface and stacking fault energies. In addition to experimental data, an ab initio method is used to construct the necessary database of different phases. We demonstrate that such potentials can reproduce the hydrogen behavior in an α-phase ErÀH system for a low hydrogen/metal ratio. Especially, the present potentials can be employed for modeling the energetics and structural properties of fcc ErH 2 , including lattice parameters, elastic constants, bulk modulus, Young's modulus, shear modulus, as well as the formation energies and migration barriers of point defects in ErH 2 .

No abstract