Nature of Cu Interstitials in Al2O3 and the Implications for Filament Formation in Conductive Bridge Random Access Memory Devices

Resistive random access memory (RRAM) is a prime candidate to replace Flash memory. Of the two classes of RRAM, conductive bridge RAM (CBRAM) is favoured over that based on filaments of oxygen vacancies because of its larger on/off resistance ratio. The nature of the filament in Cu/Al₂O₃-based CBRAM is analysed using density functional theory. The defect and binding energies of Cu interstitials and clusters in Al₂O₃ are calculated. The binding energy per Cu interstitial is shown to significantly increase with increasing Cu coordination, whereas the binding per oxygen vacancy only slightly increases with vacancy concentration. This explains why metal filaments in CBRAM devices tend to be denser than oxygen vacancy filaments. Using three different filament models, we discover that the strong binding between Cu interstitials drives filament formation, resulting in Al ions being driven out of the Cu-rich environment. This leads to the formation of densely packed metallic Cu filaments with bonding similar to Cu metal, as confirmed by electronic structure calculations

Energetics of intrinsic defects in NiO and the consequences for its resistive random access memory performance

Energetics for a variety of intrinsic defects in NiO are calculated using state-of-the-art ab initio hybrid density functional theory calculations. At the O-rich limit, Ni vacancies are the lowest cost defect for all Fermi energies within the gap, in agreement with the well-known p-type behaviour of NiO. However, the ability of the metal electrode in a resistive random access memory metal-oxide-metal setup to shift the oxygen chemical potential towards the O-poor limit results in unusual NiO behaviour and O vacancies dominating at lower Fermi energy levels. Calculated band diagrams show that O vacancies in NiO are positively charged at the operating Fermi energy giving it the advantage of not requiring a scavenger metal layer to maximise drift. Ni and O interstitials are generally found to be higher in energy than the respective vacancies suggesting that significant recombination of O vacancies and interstitials does not take place as proposed in some models of switching behaviour.The authors thank the Engineering and Physical Sciences Research Council for funding from EPSRC Grant No. EP/M009297.This is the accepted manuscript. The final version is available at http://scitation.aip.org/content/aip/journal/apl/107/12/10.1063/1.4931751

Searching for help online: An analysis of peer-to-peer posts on a male-only infertility forum.

Men’s experiences of infertility help seeking are under-researched and thus less widely understood than women’s experiences, with men’s needs for support often missing from reproductive research knowledge. This article presents a thematic analysis of peer-to-peer posts within the context of a UK men-only online infertility forum. The key themes demonstrate that men value male support from those with experience, and that masculinity influences help-seeking requests and men’s accounts more broadly. We highlight the value of such online communities in offering support to men in need while recognising the importance of further research across other online settings in order to inform practice around supporting men in the reproductive realm

Improved Calculation of Li and Na Intercalation Properties in Anatase, Rutile, and TiO2(B)

In recent years, TiO2, as a potential electrode material in Li and Na batteries, has been the subject of considerable experimental and computational research. However, the typical density functional theory (DFT) functionals used (e.g., the generalized gradient (GGA)) for such calculations are not without their shortcomings. To avoid these well-known issues, we report the first use of hybrid DFT calculations to calculate the Li and Na intercalation properties for anatase, rutile, and TiO2(B). The magnitude of GGA intercalation voltage underestimation is shown to vary depending on the polymorphs. We find that Li intercalation is most energetically preferred in anatase, while Na intercalation is most feasible for TiO2(B). Using the screened exchange hybrid functional, all intercalation processes are shown to be thermodynamically favorable, with the exception of Na in rutile. The electronic structures of these intercalated materials are also calculated, and significant improvements, in terms of band gap prediction and charge localization, are presented in comparison with GGA. We hope that our results will encourage more use of hybrid density functionals in the modeling of fundamental battery material properties.We thank the Engineering and Physical Sciences Research Council for funding from EPSRC grant EP/M009297

Two total syntheses of trigoxyphins K and L

Two total syntheses are presented for trigoxyphins K and L, tricyclic terpenoids from Trigonostemon xyphophylloides. The first proceeds via electrophlic cyclization in A/C-ring substrates to close the B-ring at C4–C5 then 1 O2-mediated hydroxybutenolide formation to trigoxyphin L, with Luche reduction leading to trigoxyphin K. The second route develops from tetralone ring expansion to a B/C-ring intermediate that, by one-step O-demethylation-lactonization-isomerization, affords trigoxyphin K, then trigoxyphin L following enolate oxygenation

Wavelength dependent mechanism of phenolate photooxidation in aqueous solution

Phenolate photooxidation is integral to a range of biological processes, yet the mechanism of electron ejection has been disputed. Here, we combine femtosecond transient absorption spectroscopy, liquid-microjet photoelectron spectroscopy and high-level quantum chemistry calculations to investigate the photooxidation dynamics of aqueous phenolate following excitation at a range of wavelengths, from the onset of the S0-S1 absorption band to the peak of the S0-S2 band. We find that for λ ≥ 266 nm, electron ejection occurs from the S1 state into the continuum associated with the contact pair in which the PhO˙ radical is in its ground electronic state. In contrast, we find that for λ ≤ 257 nm, electron ejection also occurs into continua associated with contact pairs containing electronically excited PhO˙ radicals and that these contact pairs have faster recombination times than those containing PhO˙ radicals in their ground electronic state