A simple and fundamental design rule for resisting delamination in bimaterial structures

The determination of the peeling stress in the interface between the two layers of a bimaterial structure has long been of particular interest in the microelectronic industry. This is because peeling of deposited layers on silicon wafers, and delamination of encapsulated integrated circuits continue to be of great concern. Until now beam theory has not delivered a simple method of determining the direction of the peeling stress at the free edge of the structure, although a recent paper has proposed a formulation which approximates to the reality.Past studies have focused on determining the stresses in the interface. In this paper a different approach is taken. A fundamental formulation is derived for the moment that arises in the interface as a result of the naturally occurring reversal in sign of the peeling stress. It is shown that this peeling moment M_p completely generates the additional bending needed to ensure that the radius of curvature of each layer at the interface is identical, even when they have differing flexural rigidities.The direction and magnitude of the peeling moment M_p is determined in this paper, and its value is confirmed by finite element analysis for seven test cases representing a wide range of bimaterial structures. The expression for M_p is simple and easily computed, and it provides a fundamental design rule for resisting delamination in bimaterial structures.     

Exploiting Covalency to Enhance Metal–Oxide and Oxide–Oxide Adhesion at Heterogeneous Interfaces

We employ first-principles density functional calculations to explore atomic-level interactions and predict the ideal work of adhesion at the SiO₂/nickel and ZrO₂/SiO₂ interfaces. We find that chemical bonding at the interface serves to strengthen significantly interfaces formed with SiO₂, which exhibits significant covalent bonding character, relative to those formed using more ionic oxides, such as Al₂O₃, in place of SiO₂. The improved strength of these interfaces due to local bonding interactions may hold materials design implications for practical applications that require optimal adhesion between metal-ceramic layered structures, including thermal barrier coatings.     

A review of esthetic alternatives for the restoration of anterior teeth

Helicobacter pylori infection is an important cause of peptic ulcer disease and chronic gastritis. Infection with this bacterium stimulates the production of immunoglobulin (Ig) G antibody. Salivary IgG antibody tests to detect H pylori infection offer a convenient and noninvasive method of diagnosis. To evaluate an IgG salivary antibody kit, saliva was collected from 157 out-patients with dyspepsia referred for endoscopy to a tertiary centre. A salivary IgG ELISA antibody assay was performed using the Helisal Helicobacter pylori (IgG) assay kit, and at least four gastric biopsies were obtained. H pylori infection was confirmed by demonstration of the organism on Warthin-Starry silver stain (sensitivity 85%, specificity 55%). The prevalence of infection with H pylori was 30%. When the analysis was redone, excluding those treated with eradication therapy, the results were similar (sensitivity 86%, specificity 58%). The positive predictive value of the assay was 45% and the negative predictive value was 90%. Despite the ease of sampling, the assay used has limited diagnostic utility, lacking the predictive value to indicate which patients referred with dyspeptic symptoms to a tertiary care setting are infected with H pylori.     

The electrochromic properties of sputtered nickel oxide films

Electrochromic nickel oxide films were prepared by reactive RF sputtering from a nickel target in an oxygen atmosphere. The films were deposited as a compact 40 nm layer of trivalent nickel oxide, Ni₂O₃. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Voltammetry indicated that the eventual electrochromic reaction involved the β-Ni(OH)₂/β-NiOOH couple. In situ visible spectra showed electrochromic modulation of the transmittance throughout the visible range with a peak change in transmittance of about 60% at a wavelength of 500 nm. In situ spectra in the near-infrared region indicated improved electrochromic switching in this region; the sputtered nickel oxide film exhibited about a 30% change in transmittance in comparison to less than 10% for a similar electroprecipitated nickel hydroxide film. The sputtered nickel oxide films exhibited durable electrochromic switching for over 2500 coloration/bleaching cycles, a significant improvement over the less than 500 switching cycles exhibited by electroprecipitated nickel hydroxide films.