Detailed Scanning Electron Microscopy Observations Research Articles

New Procedure to Obtain Specific and High Absorbent Silicon Nanotextures: Inverted Pyramids, Cubic Nano-Microholes, Spiroconical Nano-Microholes and Rhombohedral-Stared Nanosheet Bouquets (Nanobuckets)

The present work relates to a process for silicon surface texturing for preparing large-area, silicon nanotextures on silicon substrates at ambient temperature by assisted chemical etching. A novel strategy comprises of two fundamental steps (metal-assisted chemical etching (MACE) and solution post-treatment) of using the silver catalyst to obtain specific nano- or micro-textures. The strategy is based on metal-induced (Ag) local oxidation and dissolution of a silicon substrate in three different concentrations of aqueous fluoride solution with the post-treatment solution. The etching technique is dependent on the etching time and concentration of aqueous fluoride solution. Therefore, detailed scanning electron microscopy observations reveal specifics shapes as inverted pyramids, cubic nano-microholes, spiroconical nano-microholes and rhombohedral-stared nanosheet bouquets (called Nanobukets), obtained for the first time on a (100) silicon surface by this new variant of the MACE method named Double Etching Method (DEM). Silicon nanostructures are used in many nanotechnology applications such as nano-microelectronics, optoelectronics or biomedical applications. UV-Visible spectrometry measurements carried out made it possible to obtain the lowest reflectance and highest absorbance values who are 3% and 97%, respectively for the rhomboedral-stared nanosheet bouquets on (100) crystalline silicon substrates in the UV-visible-NIR wavelength range from 300 to 1200 nm.

Lower Cretaceous Crato clay samples revisited: some new results from scanning electron microscope investigations of Afropollis pollen

This article presents re-investigated Crato Formation sample material from David J. Batten’s palynological legacy using a combination of light microscopy (LM) and scanning electron microscopy (SEM). The investigation shows that Afropollis jardinus specimens from Crato clay have central bodies that are either smaller (36%) or larger (42%) than half the diameter of the entire body or are lost (22%), probably due to preservational reasons. All grains display the same grading of the reticulum, in which the size of the brochi decreases from the proximal to the distal pole. This observation only was possible because no cover slips were used during LM observation and therefore the individual grains could be turned and moved with a micro-manipulator. Detailed SEM observations revealed that the height of the muri and the height of the always present granular infrastructure of the reticulate sexine generally increase from the distal to the proximal pole. On five of 19 specimens (plus a lump of four) investigated with SEM an ulcerate aperture can be observed on the distal pole, located within the smallest brochi of the reticulum, and three other specimens show a faint ulcerate aperture in the same location. The area with small the smallest brochi and the ulcus are restricted to the distal pole. This ulcerate aperture cannot be seen using only LM. The geologically older Afropollis operculatus and A. zonatus are characterised by operculate and ring-like apertures, therefore the ulcus in A. jardinus must be a derived type and is probably a result of convergent evolution.

Correlation of Acoustic Emission with Fractography in Bending of Glass\u2013Epoxy Composites

Damage processes in glass fiber reinforced plastic composites have been examined extensively by many analytical and experimental methods, including acoustic emission. While damage phenomena in mezo- and macro-scale are well described, the subtle mechanisms in micro-scale are still under discussion. The goal of this work was to apply the acoustic emission to examine damage initiation in fiber reinforced epoxy resin composites with different continuous glass-fiber architectures. Basic lay-ups were used: unidirectional, cross-ply and angle-ply, each with varying fiber volume content in epoxy matrix. Detection of fine micro-cracks was possible owing to merging the mechanical monotonic and step-load tests in 4-point bending with acoustic emission monitoring and detailed scanning electron microscopy observations. Clear images of macroscopically undamaged samples after interruption of step-loading cycles revealed the initiation of micro-cracks by debonding of fiber-matrix interfaces, in agreement with acoustic emission signal analyses, featuring use of historic index and rise time/amplitude ratio.

Effects of resin pre-coating on interfacial bond strength and toughness of laminar CFRP with and without short aramid fibre toughening

The brittle adhesive layer in carbon fiber-reinforced polymer (CFRP) laminates was strengthened by using short aramid fibers in this study. To ensure the feasibility and effectiveness of short aramid fiber interfacial toughening at the interface between the carbon-fiber face sheets, the self-prepared short aramid fibre tissue and the wettability treatment technology with resin pre-coating were applied to enable short aramid fibres to be well embedded in the uneven regions in the CFRP fabrics with fibres oriented at 0° and 90° to form a strong pulling resistance. The ultimate load and the mode I interlaminar fracture toughness have been improved by 75% and 103.9% from the double cantilever beam mode I crack propagation tests, respectively. The reinforcing mechanisms within the “composite adhesive layer” as a result of short aramid fibres are discussed together with detailed scanning electron microscopy observations and comparison test results.

Adlafia moseri and A. tjibaoui two new diatom species (Bacillariophyta) from New Caledonia with further observations on Adlafia muscora and Kobayasiella saxicola

During a recent survey of epilithic diatoms in running waters of New Caledonia, two unknown Adlafia Moser, Lange-Bertalot & Metzeltin species were found. Both species are described as new based on light and scanning electron microscopy (LM and SEM). Adlafia moseri sp. nov., is characterised by its margins morphology, its large size and its low stria density, clearly visible in LM. Adlafia tjibaoui sp. nov. shows a very long internal intermissio with curved proximal raphe endings and a very high stria density. Since the generitype Adlafia muscora (Kociolek & de Reviers) Moser, Lange-Bertalot & Metzeltin was poorly described, its diagnosis is emended based on more detailed scanning electron microscopy observations. Kobayasiella saxicola (Manguin) Lange-Bertalot, only described in light microscopy, occurs frequently in some running waters in New Caledonia. An emended description of this taxon is likewise proposed based on additional SEM data.

Failure Investigation of an AlSi9Cu3 Alloy Die-Cast Cavity Insert

The examination of a fractured cavity insert, cooperated die to finish geometry intricate aluminum alloy die-casting product, is described. The dominating failure mechanism in the investigated insert is the combination of thermal fatigue cracking and stress concentration. A visual fractographic examination was performed at the cavity insert and crack initiated at the periphery adjacent to a sharp corner. Detailed scanning electron microscopy observations and energy-dispersive X-ray suggest that the crack growth was facilitated by a number of elements: oxidation of the cracks’ surfaces, filling of cast alloy, and high stress concentration of the sharp corner. The thermal cracks were also produced product around the inside wall of the cooling channel. Similarly, these cracks were also subjected to oxidation and filling with scale deposit and oxide. Finally, the schematic of the cavity insert fracture evolution during die-casting is discussed.

Fatigue and hardness effects of a thin buffer layer on the heat affected zone of a weld repaired Bisplate80

Abstract Heat-affected zones (HAZs) in extensively weld-repaired Bisplate80, or the parent metal (PM), have been studied and examined using hardness measurements in conjunction with fatigue crack growth measurements and detailed scanning electron microscopy (SEM) observations. Three different groups of specimens have been prepared, i.e. as-received PM, weld-repaired PM with a thin 4 mm BL between PM and weld metal (WM), and weld-repaired PM without BL. The extended compact tension (E-CT) specimens for fatigue measurements are prepared according to the ASTM specifications, which are also used for hardness measurements. Hardness and fatigue crack growth variations across the boundaries between WM, BL and PM have been measured together with detailed SEM observations. It has been found that the welding process without BL reduced both hardness and fatigue resistance, especially around the weld interface and within the HAZ. Incorporation of a thin soft BL between WM and PM has increased both hardness and fatigue resistance around the weld interface and within the HAZ.

Description of Eggs ofAnastrephaspp. (Diptera: Tephritidae) in theSpatulataGroup using Scanning Electron Microscopy

AbstractWe provide detailed scanning electron microscopy observations of eggs of three Anastrepha species in the spatulata group: Anastrepha manihoti Lima, Anastrepha montei Lima, and Anastrepha pickeli Lima, for the first time. Eggs were dissected from females captured in McPhail traps and examined using both scanning electron and optical microscopes. The eggs are tapered at both ends, have a papilla at the anterior pole, and the micropyle is located on the dorsal side near the anterior pole. Diagnostic characters for differentiating among these three species include the location of aeropyles, presence of a respiratory horn in A. manihoti and A. pickeli, and a pronounced rim of the chorion with a smooth surface surrounding the micropyle. Eggs of A. montei have a narrow patch of seemingly porous surface on the ventral side of the anterior pole. Such a character has not been reported previously for eggs of Tephritidae.

Failure mechanisms of H13 die on relation to the forging process – A case study of brass gas valves

In the hot forging industry, die life is an important process factor because of the cost involved in lost production, replacement of die blocks and operative handling of the dies. There is still no consensus, however, on the type of wear affecting dies or the dominant mechanisms for die failure, which varies from one situation to another. This metallographic study of a failed industrial hot forging die used to forge gas cylinder valves has indicated various failure modes. Although plastic deformation and thermal fatigue are usually quoted as the main causes of damage, oxidative and abrasive wear, fatigue cracking and chipping appeared to bet he most important in this study. Feedback coupling of fatigue and wear effects are detected. Detailed scanning electron microscopy observations and energy-dispersive X-ray and optical profilometry analysis suggest that these failures might very depending on their localisation on the die surfaces and show a complex mechanisms related to the variation of process parameters.

Effect of molybdenum and chromium contents in sliding wear of high-chromium white cast iron: The relationship between microstructure and wear

High-chromium white cast irons are commonly used in applications requiring excellent abrasion resistance, as in the mining and mineral ore processing industry. Their excellent abrasion resistance is mainly due to their solidification microstructures. During their solidification, high levels of chromium (16–32%) lead to the formation of a high-volume fraction of eutectic M 7C 3-carbides, which may or may not be associated with primary carbides in a heterogeneous austenitic/martensitic dendritic structure. Generally, in common white high-chromium cast iron, the molybdenum content is less than 3 wt.% (by weight) so as to avoid a perlitic transformation. It is reported that by addition of molybdenum in quantities of more than 3 wt.%, new carbides (M 2C, M 6C) are formed which greatly increase the high-temperature wear resistance. In this paper, 15 high-chromium white cast alloys containing different chromium contents (16 wt.%Cr to 32 wt.%Cr) and molybdenum (Mo free to 9 wt.%Mo) are examined. For each alloy, the chemical composition and volume fraction of carbides and matrix have previously been determined. The matrix microstructure and the type of carbides depend on the relative contents of molybdenum and chromium. The wear experiments are carried out on a pin-on-disc tribometer at room temperature. The pin is made of cast iron. The wear mechanisms are observed by scanning electron microscopy (SEM). It is observed that the pin height loss, the evolution of friction versus time curves and the mean friction coefficient are largely dictated by the matrix microstructure. The carbides volume fraction and the macroscopic hardness both play only a minor role. The pin height loss is significant for a single-phased matrix and the mean friction coefficient is high. When the matrix is multiphased, the pin height loss tends towards zero and the coefficient of friction is lower. Detailed SEM observations and analysis of the evolution of the friction versus time curves indicate the substantial contribution of the large carbides in friction contact.

Zygnematalean zygospores: Morphological features and use in species identification

Suitable morphological characteristics for identification of zygnematalean algae were determined using a combination of classical light microscopy (LM) techniques, fluorescence microscopy (with blue and green excitation), scanning electron microscopy (SEM) and specialized culture methods. Characteristics of spore germination, growth and reproduction under culture conditions identified Zygnema chalybeo-spermum in a mixture of zygnematalean spores collected from a small fishpond in Czechia. Reproduction in general, particularly aplanospore formation and lateral conjugation was more frequent and occurred earlier in a nutrient poor medium than in a nutrient rich medium, where vegetative growth was more vigorous. Variability in spore size was wide and influenced by the origin (sexual and/or asexual) of the spores. Asexual spores, particularly partenospores were rounded and significantly smaller than sexual ones. Thus spore morphology alone (size and shape) is not a particularly helpful characteristic for species identification. The mesospore of mature spores contained lipids and a sporopolenin-like material (algaenan), which showed green autofluorescence with blue excitation. The mesospore ornamentation, the only characteristic found that is suitable for identification purposes, can be observed easily in LM and SEM after exospore removal by KOH treatment. Detailed LM and SEM observations of the zygospores of all Zygnema species thus could provide basic data necessary for the preparation of an atlas and key for species identification which, after completion with molecular methods, brings clarification into the genetic relationships between morphospecies.

Fabrication of Single‐Crystalline Silicon Nanowires by Scratching a Silicon Surface with Catalytic Metal Particles

AbstractA novel strategy for preparing large‐area, oriented silicon nanowire (SiNW) arrays on silicon substrates at near room temperature by localized chemical etching is presented. The strategy is based on metal‐induced (either by Ag or Au) excessive local oxidation and dissolution of a silicon substrate in an aqueous fluoride solution. The density and size of the as‐prepared SiNWs depend on the distribution of the patterned metal particles on the silicon surface. High‐density metal particles facilitate the formation of silicon nanowires. Well‐separated, straight nanoholes are dug along the Si block when metal particles are well dispersed with a large space between them. The etching technique is weakly dependent on the orientation and doping type of the silicon wafer. Therefore, SiNWs with desired axial crystallographic orientations and doping characteristics are readily obtained. Detailed scanning electron microscopy observations reveal the formation process of the silicon nanowires, and a reasonable mechanism is proposed on the basis of the electrochemistry of silicon and the experimental results.

Microstructural characterization of silica aerogels using scanning electron microscopy

In this paper the experimental results of microstructural characterization of silica aerogels using scanning electron microscopy (SEM) are reported. In order to understand the reasons for shrinkage, opacity and cracking of the aerogels, detailed SEM observations have been made on the aerogels prepared using various molar ratios of precursors, catalysts and solvents; gel ageing periods and supercritical drying conditions. It has been observed that strong acidic catalysed gels resulted in smaller pore and particle sizes, and hence more transparent but readily cracked aerogels; whereas weak-basic catalysed gels gave larger pore and particle sizes, and hence slightly less transparent and monolithic aerogels. Microstructures of very low density (0.05 gm cm−3) gels indicate that the gels form a highly crosslinked polymer network and, then, the spherical particles form on the network at higher aerogel densities. Gel ageing resulted in neck growth between SiO2 particles. Precise control of pore and particle sizes using sol-gel parameters have been found to be necessary in order to obtain highly transparent and monolithic silica aerogels. In addition, autoclave heating and solvent evacuation rates of around 25°Ch−1 and 4 cm3 min−1, respectively, resulted in the best quality silica aerogels in terms of monolithicity and transparency.