Cyclic loading for the characterisation of strain hardening during in situ microcompression experiments

Various parameters from fabrication and testing are known to influence the behaviour for microcompression experiments, especially the work-hardening behaviour. In this regard, the most important factor is found to be the availability of unconstrained slip planes. The second-most important factor is the lateral constraint acting on the sample, which usually arises from friction between indenter and pillar in a combination with a laterally stiff indenter setup, which can generate significant grain rotation and deviation from ideal single slip behaviour. The effect of lateral constraints on the strain-hardening rate is demonstrated on single crystals of gold and a novel solution by cyclic loading conditions is suggested, which could provide comparable conditions for different types of indenter hardware. In this work, the cyclic loading method is shown to minimise the influence of lateral constraints and provide more accurate measurements of strain-hardening behaviour than commonly applied microcompression methods by preventing grain rotation due to frictional constraint.     

Plastic shear response of a single asperity: a discrete dislocation plasticity analysis

We investigate the plastic shear response during static friction of an asperity protruding from a large FCC single crystal. The asperity is in perfectly adhesive contact with a rigid platen and is sheared by tangentially moving the platen. Using discrete dislocation plasticity simulations, we elucidate the plastic shear behaviour of single asperities of various size and shape, in search for the length scale that controls the plastic behaviour. Since plasticity can occur also in the crystal, identification of the length scale that controls a possible size-dependent plastic behaviour is far from being trivial. It is found that scaling down the dimensions of an asperity results in a higher contact shear strength. The contact area is dominant in controlling the plastic shear response, because it determines the size of the zone, in and below the asperity, where dislocation nucleation can occur. For a specific contact area, there is still a dependence on asperity volume and shape, but this is weaker than the dependence on contact area alone.     

The impact of various drug ferrying additives on phase transitions behavior of Calcite,Vaterite and Aragonite

The study aimed to explore the influence of eleven excipients (in three groups) on the phase transition of CaCO3. The groups were; Group 1: Ca-TEG (CaCO3- Tetraethylene Glycol), Ca-PVP (Polyvinylpyrollidone), Ca-LUT (Lutrol Micro 127 MP), Ca-HPMC (Hydroxypropylmethyl Cellulose) and Ca-Blank, Group 2: Ca-G44/14 (Gelucire 44/14), Ca-CRH40 (Cremophor RH40), Ca-SHS (Solutol HS15), Ca-LAB (Labrasol) and Group 3: Ca-GE (Garlic extract), Ca-CAS (Casein), Ca-TCT (Transcutol). Group 1 confers the characteristics of only Calcite, while, Group 2, gave the highest mole fraction of Vaterite. Group 3 gave the highest mole fraction of Vaterite followed by Calcite/Aragonite. FESEM of Ca-CRH40 illustrated numerous parallel stacks of nano-hexagonal vaterite columns building the inner structure of bacillus type Vaterite, while that of Ca-TCT suggested the presence of sunflower shaped Vaterite particles and rhombohedral calcite. The % dissolution efficiency was found maximum for Ca-TEG (90.65%) followed by Ca-PVP (86.13%), Ca-HPMC (76.25%), Ca-LUT (52.12%) and CaBlank (22.96%).     

Morphology and micromechanical behavior of blends of ethene/1-hexene copolymers

Using (Me₅Cp)₂ZrCl₂ and Et(Ind)₂ZrCl₂ activated by methylaluminoxane (MAO), ethene/1-hexene copolymers of markedly different densities were produced under the same conditions. Binary blends were produced by melt blending of a high-density ethene/1-hexene copolymer with an elastomeric ethene/1-hexene copolymer. Transmission electron microscope (TEM) investigations of ultrathin sections of samples stained with ruthenium tetroxide revealed the morphology of the different blends. Depending on the blend composition, the degrees of segregation differed. An analysis of the TEM micrographs shows that increasing the segregation of the elastomeric blend component seems to be accompanied by an increase of the mean thickness of the crystalline lamellae of the matrix. Corresponding to the TEM results, typical morphological structures were also revealed by scanning force microscope (SFM) investigations using the tapping mode and a force modulation mode. Furthermore, these SFM techniques were applied to study in situ local deformations and changes in the morphological structures in a certain specimen position while the external stress was successively increased. Results of these experiments, as well as those from additional TEM in situ tensile tests of thin sections, show that the deformation that appears homogeneously down to the micron range is strongly inhomogeneous in the submicron range.     

New insights into the regulation of synaptic transmission and plasticity by the endoplasmic reticulum and its membrane contacts

Mammalian neurons are highly compartmentalized yet very large cells. To provide each compartment with its distinct properties, metabolic homeostasis and molecular composition need to be precisely coordinated in a compartment-specific manner. Despite the importance of the endoplasmic reticulum (ER) as a platform for various biochemical reactions, such as protein synthesis, protein trafficking, and intracellular calcium control, the contribution of the ER to neuronal compartment-specific functions and plasticity remains elusive. Recent advances in the development of live imaging and serial scanning electron microscopy (sSEM) analysis have revealed that the neuronal ER is a highly dynamic organelle with compartment-specific structures. sSEM studies also revealed that the ER forms contacts with other membranes, such as the mitochondria and plasma membrane, although little is known about the functions of these ER-membrane contacts. In this review, we discuss the mechanisms and physiological roles of the ER structure and ER-mitochondria contacts in synaptic transmission and plasticity, thereby highlighting a potential link between organelle ultrastructure and neuronal functions.     

In situ TEM study of stability of TaRhx diffusion barriers using a novel sample preparation method

The atomic diffusion mechanisms associated with metallurgical failure of TaRh_x diffusion barriers for Cu metallizations were studied by in situ transmission electron microscopy (TEM). The issues related to in situ heating of focused ion beam (FIB) prepared cross-sectional TEM samples that contain Cu thin films are discussed. The Cu layer in Si/(13 nm)TaRh_x/Cu stacks showed grain growth and formation of voids at temperatures exceeding 550 °C. For Si/(43 nm)TaRh_x/Cu stacks, grain growth of Cu was delayed to higher temperatures, i.e., 700 °C, and void formation was not observed. Extensive surface diffusion of Cu, however, preceded bulk diffusion. Therefore, a 10 nm film of electron beam evaporated C was deposited on both sides of the TEM lamellae to limit surface diffusion. This processing technique allowed for direct observation of atomic diffusion and reaction mechanisms across the TaRh_x interface. Failure occurred by nucleation of orthorhombic RhSi particles at the Si/TaRh_x interface. Subsequently, the barrier at areas adjacent to RhSi particles was depleted in Rh. This created lower density areas in the barrier, which facilitated diffusion of Cu to the Si substrate to form Cu₃Si. The morphology of an in situ annealed lamella was compared with an ex situ bulk annealed sample, which showed similar reaction morphology. The sample preparation method developed in this study successfully prevented surface diffusion/delamination of the Cu layer and can be employed to understand the metallurgical failure of other potential diffusion barriers.     

Whereabouts of missing atoms in a laser-injected Si: Part 1

In a stealth dicing of Si wafers, voids are formed in laser-induced modified volumes (LIMVs). Most of the voids are free from apparent defects such as dislocations and cracks. Needless to say, in what will become a void (pre-void) upon laser injection, Si atoms are present prior to the laser injection. The critical issue is where these missing atoms are after the laser injection. Two obvious possibilities are that (1) they remain inside the Si wafer as interstitials (I’s) or (2) these I’s reach the surface of the wafer to disappear. If (1) is the case, I’s are to coagulate to form dislocation loops of I-type upon post laser-injection annealing. However, it has been shown that this is not the case. In order to see whether (2) is the case, surfaces of a laser-injected Si wafer were studied by a scanning electron microscope in detail. No evidence of I’s having reached the surfaces was obtained.     

Nitriding molybdenum: Effects of duration and fill gas pressure when using 100-Hz pulse DC discharge technique

Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry(XRD), scanning electron microscopy(SEM), and atomic force microscopy(AFM) are used for the structural and morphological analysis of the nitrided layers. Vickers’ microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar(1 bar = 105Pa). A considerable increase in surface microhardness(approximately by a factor of 2) is observed for longer duration(10 h) and 2-mbar pressure. Longer duration(10 h) and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.     

Filling carbon nanotubes with metals by the arc-discharge method: the key role of sulfur

Various filled carbon nanotubes have recently been successfully produced by the arc-discharge method by doping a 99.4% graphite anode with a transition metal like Cr, Ni, a rare earth like Yb, Dy, or a covalent element like S, Ge. In this work, the structural characteristics of these encapsulated nanowires were studied by High Resolution Transmission Electron Microscopy and their chemical composition was investigated using Electron Energy-Loss Spectroscopy with high spatial resolution: this analysis mode provides elemental concentration profiles across or along the filled nanotubes. Except in the case of Ge for which only pure Ge fillings were identified, surprising amounts of sulfur, which was present as an impurity ( 0.25%) in the graphite rods, were found within numerous filling materials. When using high purity carbon rods, no filled nanotube was obtained. We chose the case of Cr to clearly evidence that the addition of sulfur in catalytic quantity is responsible for the formation of filled nanotubes, including sulfur free encapsulated nanowires. A growth mechanism based on a catalytic process involving three elements, i.e. carbon, a metal and sulfur, and taking into account the experimental results is proposed. Received: 20 January 1998 / Received in final form and accepted: 9 April 1998     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

Thermal and Structural Behaviors of Polypropylene Nanocomposites Reinforced with Single-Walled Carbon Nanotubes by Melt Processing Method

In this work, polypropylene (PP) matrix reinforced with several single-walled carbon nanotubes (SWNTs) concentrations were prepared by a melt-mixing method. The effect of SWNTs on the thermal degradation behavior of polypropylene was studied by thermal gravimetric analysis. The results revealed that adding the SWNTs into the PP can increase the decomposition temperature. The results obtained from differential scanning calorimetry showed that incorporating SWNTs reduced the crystallinity but increased the crystallization temperature of the PP. The mechanical measurements showed that the tensile modulus of the nanocomposite was greatly enhanced to 882 MPa, compared to 485 MPa for pristine PP. For wide-angle X-ray diffraction tests, two cooling methods were used. The addition of SWNTs to the polymer in slow-cooled samples resulted in partial crystallization in the γ -form, while SWNTs had no effect in water-cooled samples, the sample crystallizing in the α -form. Scanning electron microscopy observations on the fracture surface of the nanocomposites showed the dispersion of the SWNTs in the nanocomposites.     

Imaging polycrystalline and smoke MgO surfaces with atomic force microscopy: a case study of high resolution image on a polycrystalline oxide

Atomic force microscopy in contact, non-contact and in high resolution modes have been used to image MgO powder samples, obtained at different degree of sintering, starting from Mg(OH)₂ decomposition or obtained in form of smoke. From high resolution AFM images of MgO smoke, the lattice periodicity on regular surfaces has been revealed for the first time, under ambient conditions. The high surface perfection of the microcrystals has been further confirmed by HRTEM analysis. To obtain more information on the local structure of the single faces, in terms of type and distribution of the surface active sites, the adsorption of a simple probe molecule (CO) on such surfaces has been investigated by means of FTIR spectroscopy.     

Adsorption geometry of glycine on Cu（001） determined with low—energy electron diffraction and scanning tunnelling microscopy

Using low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) it has been found that glycine molecules adsorbed on Cu(001) can form but only the (2×4) and c(2×4) superstructures. On the basis of the missing LEED spots of the surface, it has been concluded that: each (2×4) unit cell consists of two molecules, one being the mirror image of the other; the C－C axis of both molecules lies in the mirror plane of the Cu substrate without a significant shift and twist from the plane; and the two O atoms of the carboxylate group of both molecules locate at the same height level without significant buckling. According to these conclusions, a structural model has been proposed for the (2×4) superstructure (a model for the c(2×4) superstructure already exists). We argue that the (2×4) and c(2×4) superstructures must have similar specific surface free energy, that their hydrogen bonds must be of N-H-O_II type, and that their local adsorption geometry must be similar or even the same. The advantage of combining STM with LEED to determine surface structures is clearly demonstrated.     

SO2 adsorption capacity of K2CO3-impregnated activated carbon as a function of K2CO3 content loaded by soaking and incipient wetness

The SO₂ adsorption capacity of K₂CO₃-impregnated activated carbons, prepared by soaking carbon in large volumes of K₂CO₃ in solution of various concentrations, varies linearly with respect to the loading of K₂CO₃ on the carbon up to about 12% K₂CO₃ by weight. Above 12%, the capacity for SO₂ levels out and then decreases. This suggests that at high loadings the K₂CO₃ either aggregates and/or blocks pores of the activated carbon. In contrast, the adsorption capacity of carbons prepared by repeatedly (maximum of three times total) loading K₂CO₃ via incipient wetness is much larger than that of the soaked samples, up to 70% more, when the loading of K₂CO₃ is greater than 12%. Static and dynamic adsorption, DSC, SEM, EDX and incipient wetness studies of the samples show that the impregnant aggregates but does not block carbon pores.     

Correlating Raman peak shifts with phase transformation and defect densities: a comprehensive TEM and Raman study on silicon

Silicon is the most often used material in micro electromechanical systems (MEMS). Detailed understanding of its mechanical properties as well as the microstructure is crucial for the reliability of MEMS devices. In this paper, we investigate the microstructure changes upon indentation of single crystalline (100) oriented silicon by transmission electron microscopy (TEM) and Raman microscopy. TEM cross sections were prepared by focused ion beam (FIB) at the location of the indent. Raman microscopy and TEM revealed the occurrence of phase transformations and residual stresses upon deformation. Raman microscopy was also used directly on the cross‐sectional TEM lamella and thus microstructural details could be correlated to peak shape and peak position. The results show, however, that due to the implanted Ga⁺ ions in the lamella the silicon Raman peak is shifted significantly to lower wavenumbers. This hinders a quantitative analysis of residual stresses in the lamella. Furthermore, Raman microscopy also possesses the ability to map deformation structures with a lateral resolution in the submicron range. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of the immunogold labeling of single light chains and whole immunoglobulins with anti-kappa on LR-white and epoxy sections

The purpose of this study was to examine the intensity of the immunogold labeling of kappa light chains as single molecules and as parts of whole immunoglobulin molecules in LR-White sections and epoxy sections both practically and theoretically. Human renal tissues including deposits of kappa light chains and immune complex deposits of IgA were embedded in both LR-White resin and epoxy resin. Immunogold labeling was performed on unetched thin sections of both resins with anti-κ or anti-IgA. In all relevant cases the immunolabeling was intense on the LR-White sections. Single kappa light chains were intensely labeled also on the epoxy sections, although not as intensely as on LR-White sections. In contrast, the immunogold labeling of whole immunoglobulins with anti-κ and anti-IgA was weak and hardly positive on the epoxy sections. Consequently, the quotient labeling_lr-white/labeling_epoxy for anti-κ was significantly lower for labeling of single light chains (3.6) than for labeling of whole immunoglobulins (15.9). The corresponding quotient for labeling of whole immunoglobulins with anti-IgA was 17.0. Supported by theoretical considerations, it is believed that the copolymerization between the epoxy resin and the antigens allows the knife to cleave the large whole immunoglobulins more easily than the smaller single kappa chains. This prevents satisfactory immunolabeling of whole immunoglobulins on epoxy sections whether anti-κ or anti-IgA is used as antibodies, while single kappa chains are easily immunolabeled.     

Cesium doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and micro‐Raman investigation of optical phonons

Undoped and cesium‐doped zinc oxide (ZnO) thin films have been deposited on sapphire substrate (0001) using the sol–gel method. Films were preheated at 300 °C for 10 min and annealed at 600 and 800 °C for 1 h. The grown thin films were confirmed to be of wurtzite structure using X‐ray diffraction. Surface morphology of the films was analyzed using scanning electron microscopy. The photoluminescence (PL) spectra of ZnO showed a strong ultraviolet (UV) emission band located at 3.263 eV and a very weak visible emission associated with deep‐level defects. Cesium incorporation induced a blue shift of the optical band gap and quenching of the near‐band‐edge PL for nanocrystalline thin film at room temperatures because of the band‐filling effect of free carriers. A shift of about 10–15 cm⁻¹ is observed for the first‐order longitudinal‐optical (LO) phonon Raman peak of the nanocrystals when compared to the LO phonon peak of bulk ZnO. The UV resonant Raman excitation at RT shows multiphonon LO modes up to fifth order. Copyright © 2010 John Wiley & Sons, Ltd.