Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols

Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate

Exploration of alternative supply chains and distributed manufacturing in response to COVID-19; a case study of medical face shields - Express article

Quarantine conditions arising as a result of the coronavirus (COVID-19) have had a significant impact on global production-rates and supply chains. This has coincided with increased demands for medical and personal protective equipment such as face shields. Shortages have been particularly prevalent in western countries which typically rely upon global supply chains to obtain these types of device from low-cost economies. National calls for the repurposing of domestic mass-production facilities have the potential to meet medical requirements in coming weeks, however the immediate demand associated with the virus has led to the mobilisation of a diverse distributed workforce. Selection of appropriate manufacturing processes and underused supply chains is paramount to the success of these operations. A simplified medical face shield design is presented which repurposes an assortment of existing alternative supply chains. The device is easy to produce with minimal equipment and training. It is hoped that the methodology and approach presented is of use to the wider community at this critical time.</p

Byčkovljev psaltir

Byčkovljev psaltir Osim folija Byčkovljeva psaltira (Lenjingrad, Javna biblioteka) prijepis je iz 11. st., koji je dotjerivan u 12. st. Autor članka nazire da su u to doba učinjene i neke korekture, koje tekst približavaju tzv. ruskoj redakciji psaltira. Iz ortografije se ne vidi u koje se područje Kijevske Rusije može smjestiti. Međutim autor je otkrio da taj sveščić pripada gotovo kompletnom psaltiru koji se nalazi u manastiru Sv. Katarine na Sinaju: codex. slav. 6. Ostali psaltiri koji su sudjelovali u pisanju psaltira upotrebljavali su čak arhaičniju ortografiju, a jedan od njih miješao je č i c: to pokazuje da pisar nije bio iz Kijeva ili Galicije-Volinije. Mnogi dijelovi su dotjerivani (i možda korigirani) u 12. stoljeću, ali je jasno da su se mnoga čitanja tipično ruske redakcije nalazila u originalu 11. stoljeća. U postskriptumu autor zaključuje da je ruska redakcija zapravo bugarska iz Simeonova doba

Mechanical microscopy of the interface between yttria-partially-stabilised zirconia and porcelain in dental prostheses

In recent decades, the high strength, high toughness and appealing aesthetics of Yttria-Partially-Stabilised Zirconia (YPSZ) has made this ceramic the material of choice for dental prostheses. During manufacture YPSZ copings are veneered with porcelain to match the appearance of natural teeth and to reduce wear. However, near-interface chipping of the veneer is observed as a persistent primary failure mode. Recent studies suggest that failure is associated with the mechanical and microstructural state within a few microns of the interface. This insight has provided the motivating driver for this study: to develop and implement new characterisation techniques to improve the understanding of the YPSZ-porcelain interface and thereby reduce failure rates. Microscale characterisation of the interface was performed using energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray Diffraction (XRD) and transmission electron microscopy. These studies indicated that YPSZ phase variation, elemental composition gradients and distinct microstructural features are present within 10 μm of the interface. Porcelain nanoscale voiding was found at the interface, and small angle neutron scattering confirmed that this is induced by tensile creep. High resolution (microscale) residual stress analysis was performed in YPSZ using XRD and Raman spectroscopy, and in porcelain using a new pair distribution function analysis technique. Cross-validation of these results was performed using improved implementations of the ring-core focused ion beam milling and digital image correlation technique. The variation of Young's modulus, yield strength and fracture toughness were determined using spatially resolved micropillar compression and splitting. Improved evaluation of the single-crystal stiffness of YPSZ was also performed using a new neutron diffraction based technique. The results of this analysis indicate a complex interaction within the first 50 &mu;m of the YPSZ-porcelain interface which leads to a significant reduction in porcelain toughness and an increased propensity to fail at this location.</p