X. F. Zhu

Structure and mechanical properties of Saxidomus purpuratus biological shells.

The strength and fracture behavior of Saxidomus purpuratus shells were investigated and correlated with the structure. The shells show a crossed lamellar structure in the inner and middle layers and a fibrous/blocky and porous structure composed of nanoscaled particulates (~100 nm diameter) in the outer layer. It was found that the flexure strength and fracture mode are a function of lamellar organization and orientation. The crossed lamellar structure of this shell is composed of domains of parallel lamellae with approximate thickness of 200-600 nm. These domains have approximate lateral dimensions of 10-70 μm with a minimum of two orientations of lamellae in the inner and middle layers. Neighboring domains are oriented at specific angles and thus the structure forms a crossed lamellar pattern. The microhardness across the thickness was lower in the outer layer because of the porosity and the absence of lamellae. The tensile (from flexure tests) and compressive strengths were analyzed by means of Weibull statistics. The mean tensile (flexure) strength at probability of 50%, 80-105 MPa, is on the same order as the compressive strength (~50-150 MPa) and the Weibull moduli vary from 3.0 to 7.6. These values are significantly lower than abalone nacre, in spite of having the same aragonite structure. The lower strength can be attributed to a smaller fraction of the organic interlayer. The fracture path in the specimens is dominated by the orientation of the domains and proceeds preferentially along lamella boundaries. It also correlates with the color changes in the cross section of the shell. The cracks tend to undergo a considerable change in orientation when the color changes abruptly. The distributions of strengths, cracking paths, and fracture surfaces indicate that the mechanical properties of the shell are anisotropic with a hierarchical nature.

Comparative investigation of fracture behaviour of aluminium-doped ZnO films on a flexible substrate

The differences in the fracture behaviour of aluminium-doped ZnO (AZO) films on a flexible substrate subjected to tensile and compressive strains were investigated by using a simple-support bending method. It is found that the crack density and the crack spacing of the AZO films become saturated both in the face-out (FO) and in the face-in (FI) bending tests when the applied strain reaches a certain value. The saturated crack density of the AZO film in the FO bending is higher than that of the film in the FI bending. Crack-initiation strain of the film in the FO bending is smaller than that of the film in the FI bending. The fracture energy of the AZO films is also analyszed. Failure behaviours of the films are examined and exhibit different failure mechanisms for the films subjected to tensile and compressive strains.

Investigation of deformation instability of Au/Cu multilayers by indentation

Plastic deformation behavior of Au/Cu multilayers with individual layer thicknesses of 25–250 nm was investigated via microindentation experiments. It was found that plastic instability of the Au/Cu multilayer exhibits strong length scale (individual layer thickness and grain size) dependence. The smaller the length scale, the easier shear bands form. In other words, plastic deformation becomes unstable with decreasing length scale. Cross-sectional observation along with plan-view indicates that the occurrence of plastic deformation instability corresponds to transformation of the deformation mechanism associated with geometrical configuration and length scale of the material. At nanometer scale, buckling-assisted interface crossing of dislocations results in local shear band, while, at submicron scale or above, local dislocation pileup-induced interface offset leads to plastic instability. Theoretical analysis is conducted to understand the length scale-dependent plastic deformation behavior of the multilayer.

Understanding nanoscale damage at a crack tip of multilayered metallic composites

Through quantitative focused ion beam cross-sectional characterization technique, we directly observed shear displacement in a range from several nanometers to a few tens of nanometers occurring in the plastic deformation zone ahead of a crack tip in nanolayered Cu/Ta composite subjected to tensile load. As a result, shear-mode fracture of the Cu/Ta laminate composite was eventually caused. A theoretical analysis of the interface barrier strength of nanolayered metallic composites here and reported in literature finds a critical individual layer thickness below which the nature of fracture of the nanolayered composites tends to be shearing failure. (c) 2008 American Institute of Physics.

Two different types of shear-deformation behaviour in Au-Cu multilayers

Localised shear deformation of a material is usually identified as a particular feature of deformation inhomogeneity. Here, we show two different types of shear deformation-behaviour that occurred in Au–Cu multilayers subjected to microindentation load, namely, a cooperative-layer-buckling-induced shear banding in a nanoscale multilayer and a direct localised shearing across a layer interface along a shear plane in a submicron-scale multilayer. Theoretical analysis indicates that the formation of the two different types of shear deformation in the multilayers depends on a competition between the dislocation-pile-up-induced stress concentration at the layer interface and the barrier strength of the layer interface for glissile dislocation transmission.

Tensile and fatigue properties of ultrafine Cu-Ni multilayers

Tensile and fatigue properties of Cu–Ni multilayers with different nominal individual layer thicknesses (λ) (10–100u2009nm) on a polyimide substrate were investigated. The nominal yield strength and fatigue strength of the multilayer/polyimide composite as a function of λ were determined. The experimental results indicate that both yield and fatigue strengths increase as λ decreases until λ is less than 20u2009nm. Tensile and fatigue cracking behaviour were examined to understand the damage mechanism of the ultrafine metallic multilayers.

Microstructures and strengthening mechanisms of Cu/Ni/W nanolayered composites

Cu/Ni/W nanolayered composites with individual layer thickness ranging from 5u2009nm to 300u2009nm were prepared by a magnetron sputtering system. Microstructures and strength of the nanolayered composites were investigated by using the nanoindentation method combined with theoretical analysis. Microstructure characterization revealed that the Cu/Ni/W composite consists of a typical Cu/Ni coherent interface and Cu/W and Ni/W incoherent interfaces. Cu/Ni/W composites have an ultrahigh strength and a large strengthening ability compared with bi-constituent Cu–X (Xu2009=u2009Ni, W, Au, Ag, Cr, Nb, etc.) nanolayered composites. Summarizing the present results and those reported in the literature, we systematically analyze the origin of the ultrahigh strength and its length scale dependence by taking into account the constituent layer properties, layer scales and heterogeneous layer/layer interface characteristics, including lattice and modulus mismatch as well as interface structure.

Origin of cracking in nanoscale Cu/Ta multilayers

Cracking behaviors in nanoscale Cu/Ta multilayers bonded to polyimide substrates have been investigated by uniaxial tensile tests. Experimental results show that cracks originate from the localized deformation regions associated with aligned grain boundaries. Microscopical observations suggest that the alignment of the grain boundaries is caused by local grain boundary sliding and grain rotation, which resulted in the in-plane and out-of-plane cooperative movements of the grains in the multilayers. From the localized damage regions, shear fracture in the through-thickness direction occurred in the nanoscale Cu/Ta multilayer.

Ataxin-3 promotes genome integrity by stabilizing Chk1

Abstract The Chk1 protein is essential for genome integrity maintenance and cell survival in eukaryotic cells. After prolonged replication stress, Chk1 can be targeted for proteasomal degradation to terminate checkpoint signaling after DNA repair finishes. To ensure proper activation of DNA damage checkpoint and DNA repair signaling, a steady-state level of Chk1 needs to be retained under physiological conditions. Here, we report a dynamic signaling pathway that tightly regulates Chk1 stability. Under unperturbed conditions and upon DNA damage, ataxin-3 (ATX3) interacts with Chk1 and protects it from DDB1/CUL4A- and FBXO6/CUL1-mediated polyubiquitination and subsequent degradation, thereby promoting DNA repair and checkpoint signaling. Under prolonged replication stress, ATX3 dissociates from Chk1, concomitant with a stronger binding between Chk1 and its E3 ligase, which causes Chk1 proteasomal degradation. ATX3 deficiency results in pronounced reduction of Chk1 abundance, compromised DNA damage response, G2/M checkpoint defect and decreased cell survival after replication stress, which can all be rescued by ectopic expression of ATX3. Taken together, these findings reveal ATX3 to be a novel deubiquitinase of Chk1, providing a new mechanism of Chk1 stabilization in genome integrity maintenance.

High Q factor propagating plasmon modes based on low-cost metals

A hybrid plasmonic–photonic crystal consisting of a low-cost metal (Al or Cu) covered by self-assembly polystyrene sub-micro sphere arrays is fabricated. The angle-resolved reflection spectra show the existence of propagating optical surface modes in the structure. Especially, under normal incidence, five surface modes can be observed clearly. With the help of theoretical calculation, the origin of surface resonance modes is confirmed. From both the experiment and simulation, the surface plasmon modes supported by this structure possess high Q factors, which are comparable with those of the modes based on noble metals. Moreover, with a dielectric layer deposited on the top of the structure, its potential application for surface plasma polariton sensors is proposed.