Estimation of the Young’s Modulus of Nanometer-Thick Films Using Residual Stress-Driven Bilayer Cantilevers

Precise prediction of mechanical behavior of thin films at the nanoscale requires techniques that consider size effects and fabrication-related issues. Here, we propose a test methodology to estimate the Young’s modulus of nanometer-thick films using micromachined bilayer cantilevers. The bilayer cantilevers which comprise a well-known reference layer and a tested film deflect due to the relief of the residual stresses generated during the fabrication process. The mechanical relationship between the measured residual stresses and the corresponding deflections was used to characterize the tested film. Residual stresses and deflections were related using analytical and finite element models that consider intrinsic stress gradients and the use of adherence layers. The proposed methodology was applied to low pressure chemical vapor deposited silicon nitride tested films with thicknesses ranging from 46 nm to 288 nm. The estimated Young’s modulus values varying between 213.9 GPa and 288.3 GPa were consistent with nanoindentation and alternative residual stress-driven techniques. In addition, the dependence of the results on the thickness and the intrinsic stress gradient of the materials was confirmed. The proposed methodology is simple and can be used to characterize diverse materials deposited under different fabrication conditions.

A cell-based drug discovery assay identifies inhibition of cell stress responses as a new approach to treatment of epidermolysis bullosa simplex

ABSTRACT In the skin fragility disorder epidermolysis bullosa simplex (EBS), mutations in keratin 14 (K14, also known as KRT14) or keratin 5 (K5, also known as KRT5) lead to keratinocyte rupture and skin blistering. Severe forms of EBS are associated with cytoplasmic protein aggregates, with elevated kinase activation of ERK1 and ERK2 (ERK1/2; also known as MAPK3 and MAPK1, respectively), suggesting intrinsic stress caused by misfolded keratin protein. Human keratinocyte EBS reporter cells stably expressing GFP-tagged EBS-mimetic mutant K14 were used to optimize a semi-automated system to quantify the effects of test compounds on keratin aggregates. Screening of a protein kinase inhibitor library identified several candidates that reduced aggregates and impacted on epidermal growth factor receptor (EGFR) signalling. EGF ligand exposure induced keratin aggregates in EBS reporter keratinocytes, which was reversible by EGFR inhibition. EBS keratinocytes treated with a known EGFR inhibitor, afatinib, were driven out of activation and towards quiescence with minimal cell death. Aggregate reduction was accompanied by denser keratin filament networks with enhanced intercellular cohesion and resilience, which when extrapolated to a whole tissue context would predict reduced epidermal fragility in EBS patients. This assay system provides a powerful tool for discovery and development of new pathway intervention therapeutic avenues for EBS.

Nanomechanical spectroscopy of ultrathin silicon nitride suspended membranes

Mechanical properties of a nanomechanical resonator significantly impact the performance of a resonant Nano-electromechanical system (NEMS) device. We study the mechanical properties of suspended membranes fabricated out of low-pressure chemical vapor deposited silicon nitride thin films. We fabricated doubly-clamped membranes of silicon nitride with thickness less than 50 nm and length varying from 5 to 60 μm. The elastic modulus and stress in the suspended membranes were measured using Atomic Force Microscope (AFM)-based nanomechanical spectroscopy. The elastic moduli of the suspended membranes are significantly higher than those of corresponding on-substrate thin films. We observed a reduction in net stress after the fabrication of suspended membrane, which is explained by estimating the thermal stress and intrinsic stress. We also use a mathematical model to study the stress and thickness-dependent elastic modulus of the ultrathin membranes. Lastly, we study the capillary force-gradient between the SiNx suspended membrane-Si substrate that could collapse the suspended membrane.

Study on controllable thickness and flatness of wafer-scale nickel shim in precision electroforming process: simulation and validation

A new approach to precision electroforming of a wafer-scale nickel shim with rotating cathode using an auxiliary cathode mask is developed to improve thickness uniformity and flatness. The effects of critical process parameters, including cathode rotating speed, cathode mask size, and current density, on the thickness uniformity and flatness of electroformed nickel shim are systematically studied based on experiments and numerical simulations. The results show that the thickness uniformity of deposits is highly dependent on the current density distribution, where a cathode mask can effectively tune electrical field lines and induce a more uniform current density distribution. The simulations and experimental results consistently agree that a minimum thickness nonuniformity of 8% and below 1% on the wafer with a diameter of 80 mm and 40 mm, respectively, can be achieved using a mask with a 70 mm opening size. However, for flatness, cathode rotating speed influences the surface warpage due to the intrinsic stress, which results from the electrocrystallization process and uneven thickness caused by the edge effect. It is also found that the gradient current density can significantly reduce the intrinsic stress with better flatness. The best flatness is controlled below 47 µm and 32 µm on the wafer with diameters of 80 mm and 40 mm, respectively, under the synergistic effect of optimal cathode rotating speed (30 rpm) and gradient current density.

Finite Element Analysis of the Parthenon marble block- steel clamp system response under acceleration

<p class="Abstract">Finite element analysis is employed to investigate the mechanical behaviour and failure scenarios of the marble block–steel clamp ancient masonry system utilised in the Parthenon (Athens Acropolis) under static loading analysis. The input data for the model are acquired by the laboratory testing of early 20th century restoration steel clamps, such as through tensile strength measurements and metallography, as well as bibliographic sources from various scientific fields (i.e. material properties, archaeometry, restoration, structural engineering and geology). Two different embedding materials (Portland cement mortar and lead), used for the nesting of the clamps, are examined under bending or stretching, induced by acceleration forces. The conservation status of the materials is taken into account by employing an intrinsic stress, as is the case when corrosion products build up in a confined space. The aim of this work is to provide a tool for the assessment of the conservation potential of the marble blocks in parts of the monument that require specific attention. Simulation results indicate the resilience of the Parthenon’s structural system under most examined scenarios and highlight the importance of intrinsic stresses, the existence of which may lead to the fracture of the marble blocks under otherwise harmless loading conditions.</p>

Comparing the Influence of Residual Stress on Composite Materials Made of Polyhydroxybutyrate (PHB) and Amorphous Hydrogenated Carbon (a-C:H) Layers: Differences Caused by Single Side and Full Substrate Film Attachment during Plasma Coating

Polyhydroxybutyrate (PHB) is a bio-based, biodegradable and commercially used polymer, which in its native form is unfortunately not generally applicable. A widely used technique to adapt polymers to a wider range of applications is the surface modification with amorphous hydrogenated carbon (a-C:H) layers, realized by plasma-enhanced chemical vapor deposition (PE-CVD). However, this process creates intrinsic stress in the layer–polymer system which can even lead to full layer failure. The aim of this study was to investigate how the carbon layer is affected when the basic polymer film to be coated can follow the stress and bend (single side attachment) and when it cannot do so because it is firmly clamped (full attachment). For both attachment methods, the a-C:H layers were simultaneously deposited on PHB samples. Ex-situ characterization was performed using a scanning electron microscope (SEM) for surface morphology and contact angle (CA) measurements for wettability. In addition, the stress prevailing in the layer was calculated using the Stoney equation. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) measurements were used to investigate the chemical composition of the coating surface.

Emergency Medicine Shift Factors Causing the Most Stress Among Emergency Medicine Residents

Introduction: Past studies demonstrate that stress and anxiety affect emergency medicine physicians, but the causal factors identified are usually from sources outside the work shift. We attempt to show the relationship between intrinsic factors of a work shift and anxiety perceived by residents, while also examining differing gender responses. Methods: In 2018, a cross-sectional survey of emergency medicine residents in the United States was distributed anonymously through the Emergency Medicine Residents Association. The survey consisted of demographic questions, novel questions identifying intrinsic factors, and the Generalized Anxiety Disorder 7-item (GAD-7) scale. Spearman correlation, independent t-test, and multivariate analysis of variance were performed. Results: Data from 573 residents found several stressful factors: working with a nurse perceived to be inefficient, working with no inpatient beds available, and working with a colleague perceived to be inefficient. The majority of respondents reported some general anxiety on the GAD-7 assessment. There was no difference on anxiety level as a function of year of residency (p > .05). There was a significant gender difference on anxiety level, t(571) = -4.8689, p < .05, where male residents reported lower anxiety levels (mean=5.15) as compared to female residents (mean=7.02). Lastly, post-hoc analyses revealed that male and female respondents reported differing levels of stress in response to several intrinsic stress factors. Conclusion: We identified several intrinsic factors during a shift that contribute to resident anxiety and analyzed differing gender responses to these factors; this may provide a framework for residency programs to minimize stressors in the future.

Deformation Mediated by Grain Rotation in Superhard Nanocrystalline cBN

Superhard materials such as diamond and cubic boron nitride (cBN) are becoming ever more scientifically and technologically important, and critical and fundamental knowledge about their constitutive properties and deformational mechanisms is in increasingly high demand. Although it has long been suggested by theoretical modeling that deformation of face-centered cubic superhard materials is dominated by Shockley partial dislocations and screw dislocations, there has been a glaring lack of experimental evidence. Here, we report in situ deformation experiments of nanocrystalline cBN (nc-cBN) samples at high pressures and temperatures using a deformation-DIA (D-DIA) apparatus coupled with synchrotron X-ray diffraction techniques. Intrinsic stress-strain relations have been obtained for nc-cBN for the first time, and only elastic deformation occurred up to a strain of at least 14% at room temperature (RT), demonstrating its remarkable strength, which was undoubtedly enhanced by observed microscopic features such as the Lomer-Cottrell (L-C) locks and high-angle GBs. While deformation at RT is dominated by brittle fractures and mechanic crushing induced by grain boundary twisting mediated by full dislocations, plasticity of nc-CBN at higher temperatures is controlled by grain rotation and twinning mediated by Shockley partial dislocations. At 4.0 GPa and 1200 °C, accumulated shear strain resulted in the conversion of cBN to hBN at or near twisting GBs, releasing stress and mediating deformation in the process. We demonstrate the apparent agreement between the differential micro-stress derived from peak broadening analysis and differential macro-stress deduced from lattice strain analysis.