Strength and fracture of Si micropillars: A new scanning electron microscopy-based micro-compression test

A novel method for in situ scanning electron microscope (SEM) micro-compression tests is presented. The direct SEM observation during the instrumented compression testing allows for very efficient positioning and assessment of the failure mechanism. Compression tests on micromachined Si pillars with volumes down to 2 μm3 are performed inside the SEM, and the results demonstrate the potential of the method. In situ observation shows that small diameter pillars tend to buckle while larger ones tend to crack before failure. Compressive strength increases with decreasing pillar diameter and reaches almost 9 GPa for submicrometer diameter pillars. This result is in agreement with earlier bending experiments on Si. Difficulties associated with precise strain measurements are discusse

In situ compression tests on micron-sized silicon pillars by Raman microscopy—Stress measurements and deformation analysis

Mechanical properties of silicon are of high interest to the microelectromechanical systems community as it is the most frequently used structural material. Compression tests on 8 μm diameter silicon pillars were performed under a micro-Raman setup. The uniaxial stress in the micropillars was derived from a load cell mounted on a microindenter and from the Raman peak shift. Stress measurements from the load cell and from the micro-Raman spectrum are in excellent agreement. The average compressive failure strength measured in the middle of the micropillars is 5.1 GPa. Transmission electron microscopy investigation of compressed micropillars showed cracks at the pillar surface or in the core. A correlation between crack formation and dislocation activity was observed. The authors strongly believe that the combination of nanoindentation and micro-Raman spectroscopy allowed detection of cracks prior to failure of the micropillar, which also allowed an estimation of the in-plane stress in the vicinity of the crack ti

Diamond wire-sawn silicon wafers - from the lab to the cell production

Wafers for the PV industry are mainly sawn with a multi-wire slurry saw. This process is slow (it takes almost half a day to complete a cut) and generates a lot of waste: around half the silicon is sawn away and contaminating the slurry, and the wire is worn and has lost strength. After each cut, the slurry has to be cleaned from the silicon debris and the wire has to be exchanged. In contrast, sawing the wafers with a diamond-plated wire is faster, requires only a cooling liquid that is easy to filter from silicon debris and uses a wire that can be kept for several cut. But this new sawing technique only has a chance to develop if the solar cell production lines developed for slurry sawn wafers is capable of processing these diamond-plated wire sawn wafers efficiently. This study focused on the differences of surface properties of wafers cut via a slurry wire-saw and via a diamond-plated wire-saw. From these surface differences, it is possible to explain the differences in cell processing behaviour and to update the cell production line. Finally, it is shown that wafers sawn with a diamond-plated wire can give cells that are as efficient as the slurry sawn wafers, which validates this new diamond-plated wire wafering method for the production of solar cells

Self-assembled amyloid fibrils with controllable conformational heterogeneity

Amyloid fibrils are a hallmark of neurodegenerative diseases and exhibit a conformational diversity that governs their pathological functions. Despite recent findings concerning the pathological role of their conformational diversity, the way in which the heterogeneous conformations of amyloid fibrils can be formed has remained elusive. Here, we show that microwave-assisted chemistry affects the self-assembly process of amyloid fibril formation, which results in their conformational heterogeneity. In particular, microwave-assisted chemistry allows for delicate control of the thermodynamics of the self-assembly process, which enabled us to tune the molecular structure of ??-lactoglobulin amyloid fibrils. The heterogeneous conformations of amyloid fibrils, which can be tuned with microwave-assisted chemistry, are attributed to the microwave-driven thermal energy affecting the electrostatic interaction during the self-assembly process. Our study demonstrates how microwave-assisted chemistry can be used to gain insight into the origin of conformational heterogeneity of amyloid fibrils as well as the design principles showing how the molecular structures of amyloid fibrils can be controlledopen0

Screening for Toxic Amyloid in Yeast Exemplifies the Role of Alternative Pathway Responsible for Cytotoxicity

The relationship between amyloid and toxic species is a central problem since the discovery of amyloid structures in different diseases. Despite intensive efforts in the field, the deleterious species remains unknown at the molecular level. This may reflect the lack of any structure-toxicity study based on a genetic approach. Here we show that a structure-toxicity study without any biochemical prerequisite can be successfully achieved in yeast. A PCR mutagenesis of the amyloid domain of HET-s leads to the identification of a mutant that might impair cellular viability. Cellular and biochemical analyses demonstrate that this toxic mutant forms GFP-amyloid aggregates that differ from the wild-type aggregates in their shape, size and molecular organization. The chaperone Hsp104 that helps to disassemble protein aggregates is strictly required for the cellular toxicity. Our structure-toxicity study suggests that the smallest aggregates are the most toxic, and opens a new way to analyze the relationship between structure and toxicity of amyloid species

Exploring Chromophore-Binding Pocket: High-Resolution Solid-State 1H–13C Interfacial Correlation NMR Spectra with Windowed PMLG Scheme

High-resolution two-dimensional (2D) 1H–13C heteronuclear correlation spectra are recorded for selective observation of interfacial 3–5.5 Å contacts of the uniformly 13C-labeled phycocyanobilin (PCB) chromophore with its unlabeled binding pocket. The experiment is based on a medium- and long-distance heteronuclear correlation (MELODI–HETCOR) method. For improving 1H spectral resolution, a windowed phase-modulated Lee–Goldburg (wPMLG) decoupling scheme is applied during the t1 evolution period. Our approach allows for identification of chromophore–protein interactions, in particular for elucidation of the hydrogen-bonding networks and charge distributions within the chromophore-binding pocket. The resulting pulse sequence is tested on the cyanobacterial (Cph1) phytochrome sensory module (residues 1–514, Cph1Δ2) containing uniformly 13C- and 15N-labeled PCB chromophore (u-[13C,15N]-PCB-Cph1Δ2) at 17.6 T