High-resolution elastic strain measurement from electron backscatter diffraction patterns: new levels of sensitivity

In this paper, we demonstrate that the shift between similar features in two electron backscatter diffraction (EBSD) patterns can be measured using cross-correlation based methods to +/- 0.05 pixels. For a scintillator screen positioned to capture the usual large solid angle employed in EBSD orientation mapping this shift corresponds to only approximately 8.5 x 10(-5)rad at the pattern centre. For wide-angled EBSD patterns, the variation in the entire strain and rotation tensor can be determined from single patterns. Repeated measurements of small rotations applied to a single-crystal sample, determined using the shifts at four widely separated parts of the EBSD patterns, showed a standard deviation of 1.3 x 10(-4) averaged over components of the displacement gradient tensor. Variations in strains and rotations were measured across the interface in a cross-sectioned Si1-x Gex epilayer on a Si substrate. Expansion of the epilayer close to the section surface is accommodated by tensile strains and lattice curvature that extend a considerable distance into the substrate. Smaller and more localised shear strains are observed close to the substrate-layer interface. EBSD provides an impressive and unique combination of high strain sensitivity, high spatial resolution and ease of use.     

Mapping type III intragranular residual stress distributions in deformed copper polycrystals

Cross-correlation-based analysis of electron backscatter diffraction patterns has been used to map the intragranular residual stress variations in polycrystalline copper samples deformed to different plastic strain levels of 0%, 2%, 6% and 10%. We map the deviation from the mean stress within each grain and present histograms of stress levels mapped over many grains which show a central Gaussian-like peak with non-Gaussian tails at the higher stress magnitudes. The width of the peaks increased with increasing plastic deformation and the tails became more obvious. Plots correlating maximum in-plane shear stress and distance to the nearest grain boundary demonstrate that stress “hot spots” tend to accumulate near grain boundaries.     

Post‐construction liability and insurance

Angus Wilson, Director of the Special Services Division of Mott, Hay and Anderson, consulting engineers in the UK, discusses a form of 10‐year guarantee against latent defects which is now available in Britain and growing at rate of about 40% a year.     

In Pursuit of Zero 2.0: Recent Developments in Nonfouling Polymer Brushes for Immunoassays

“Nonfouling” polymer brush surfaces can greatly improve the performance of in vitro diagnostic (IVD) assays due to the reduction of nonspecific protein adsorption and consequent improvement of signal-to-noise ratios. The development of synthetic polymer brush architectures that suppress adventitious protein adsorption is reviewed, and their integration into surface plasmon resonance and fluorescent sandwich immunoassay formats is discussed. Also, highlighted is a novel, self-contained immunoassay platform (the D4 assay) that transforms time-consuming laboratory-based assays into a user-friendly and point-of-care format with a sensitivity and specificity comparable or better than standard enzyme-linked immunosorbent assay (ELISA) directly from unprocessed samples. These advancements clearly demonstrate the utility of nonfouling polymer brushes as a substrate for ultrasensitive and robust diagnostic assays that may be suitable for clinical testing, in field and laboratory settings.     

The origin of shallow n-type conductivity in boron-doped diamond with H or S co-doping: Density functional theory study

The ionization potentials and the electron affinities of doped diamond were calculated using B3LYP hybrid density functional theory and nanocrystalline cluster models, while taking into account the quantum confinement of the charge carriers. In many cases donor and acceptor levels were created in the middle of the gap between the conduction and valence bands. A possible explanation for the n-type behavior created by co-doping diamond films with boron and sulfur is given in terms of thermally activated electron donation from an SVS (V is vacancy) donor to a BB acceptor band. Both lie deep in the band gap. It is proposed that electrons in the BB acceptor band are mobile charge carriers. It is also proposed that the conversion of boron-doped diamond from p-type conductivity, with hole charge carriers in the top of the valence band, to n-type conductivity, following treatment in a deuterium plasma, may arise from formation of interstitial hydrogen donor levels and B_nH_m acceptor levels that create an acceptor band in which electrons are mobile. Again, both are deep in the band gap of pure diamond. In a prior attempt to explain this n-type behavior, BH_n defects with unrelaxed structures were proposed to be shallow donors to the diamond conduction band. This paper shows that these defects become deep donors when their structures are optimized. Finally, defects created from vacancies with 1 to 4 H in them are shown to be deep donors to the diamond conduction band.     

Slurry Consistency and In Situ Synchrotron X-Ray Diffraction During the Early Hydration of Portland Cements With Calcium Chloride

Class A and H oil well cements are compared at 25° and 50°C with 0%, 1%, 2%, and 4% CaCl₂. Up to 4% CaCl₂ accelerated Class A thickening, but 4% led to slower thickening than 2% for Class H. C₃S hydration in the two cements responded differently to CaCl₂. CaCl₂ always accelerated aluminate hydration. For Class A, CaCl₂ accelerated early Ca(OH)₂ precipitation, but sometimes reduced the amount at longer times. This may be coupled to C–S–H gel composition changes. For Class H, Ca(OH)₂ precipitation changes nonlinearly with CaCl₂ concentration. Ettringite to monosulfate conversion and Friedel's salt formation were sometimes seen.     

Further results on the in situ anaerobic corrosion of carbon steel and copper in compacted bentonite exposed to natural Opalinus Clay porewater containing native microbial populations

Since 2012, a long-term in situ corrosion experiment (IC-A) is being conducted in the Mont Terri Underground Research Laboratory in Switzerland to investigate the corrosion behaviour of candidate canister materials in conditions representative of the Swiss concept for the disposal of high-level waste and spent nuclear fuel. To date, carbon steel and various types of copper coatings have been retrieved after different exposure periods of up to 3 years, and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, the nature of the interaction between the metal and the surrounding bentonite, and the microbial populations in the bentonite and surrounding porewater. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Much less alteration on either the metal or the bentonite was observed in the case of copper samples. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials. This paper summarises the results of the experimental programme obtained to date and discusses the relationship observed between exposure time and the evolution of the metal–bentonite interface for both carbon steel and copper.     

Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO₂) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H₃PO₄) etching, nitrogen (N₂) gas anneal and forming gas (Ar: H₂) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.     

Computational insights into charge transfer across functionalized semiconductor surfaces

Abstract

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H₂ and O₂ gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes.