High-resolution Scanning Electron Microscopy Observations Research Articles

Effects of manual washing with three alkaline sterilizing agent solutions on egg quality during storage

This study aimed to investigate the abundance of microorganisms and quality of eggs washed with different washings (tap water, 0.03% calcium hypochlorite solution, 0.25% hydrogen peroxide solution, or 1% sodium percarbonate solution) and unwashed for 28-day storage. The results showed that the washing significantly decreased the abundance of microorganisms in all cases. Washing with one of the three alkaline sterilizing agent solutions significantly inhibited the deterioration of egg quality (evidenced by lower weight loss, air cell depth, albumen pH, yolk pH, and total volatile base nitrogen, but higher Haugh unit and yolk index) during storage, while washing with tap water showed opposite effects. The texture profile analysis and high-resolution scanning electron microscopy observation showed that all washings had slight negative effects on eggshell quality (eggshell breaking strength and microstructure), and washing with the alkaline sterilizing agent solution had no additional effects. The results might be attractive to egg preservation industry.

In-situ high-resolution scanning electron microscopy observation of electrodeposition and stripping of lead in an electrochemical cell

A compact electrochemical cell capped with a silicon nitride (SiN) film of 50 nm thick as an electron window was developed for a side-entry holder of a high-resolution scanning electron microscope (SEM). Electrodeposition and stripping of lead (Pb) were examined on a gold electrode formed on the SiN film, which was faced inside the cell filled with an aqueous solution of lead nitrite. The SEM images of growth and dissociation of Pb were recorded simultaneously with cyclic voltammograms, controlled with a two-terminal potentiostat. Particulate growth of Pb at the edge of a gold (Au) electrode was observed at the underpotential deposition of Pb, followed by dendrite growth of Pb at higher deposition potentials. The growth mode changed depending on the edge morphology of the Au electrode. This indicated that in-situ microscopic observation was invaluable for understanding the phenomena of electrodeposition in electrochemistry.

Morphological and functional heterogeneity in olfactory perception between antennae and maxillary palps in the pumpkin fruit fly, Bactrocera depressa.

The morphology and ultrastructure of the olfactory sensilla on the antennae and maxillary palps were investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their responses to five volatile compounds were measured using electroantenogram (EAG) and electropalpogram (EPG) techniques in the pumpkin fruit fly, Bactrocera depressa (Shiraki; Diptera: Tephritidae). Male and female B. depressa displayed distinct morphological types of olfactory sensilla in the antennae and maxillary palps, with predominant populations of trichoid, basiconic, and coeloconic sensilla. Basiconic sensilla, the most abundant type of olfactory sensilla in the antennae, could be further classified into two different types. In contrast, the maxillary palps exhibited predominant populations of a single type of curved basiconic sensilla. High-resolution SEM observation revealed the presence of multiple nanoscale wall-pores on the cuticular surface of trichoid and basiconic sensilla, indicating that their primary function is olfactory. In contrast, coeloconic sensilla displayed several longitudinal grooves around the sensillum peg. The TEM observation of individual antennal olfactory sensilla indicates that the basiconic sensilla are thin-walled, while the trichoid sensilla are thick-walled. The profile of EAG responses of male B. depressa was different from their EPG response profile, indicating that the olfactory function of maxillary palps is different from that of antennae in this species. The structural and functional variation in the olfactory sensilla between antennae and maxillary palps suggests that each plays an independent role in the perception of olfactory signals in B. depressa.

An experimental study of organic matter, minerals and porosity evolution in shales within high-temperature and high-pressure constraints

Abstract The development and evolution of porosity in organic-rich shales (ORSs) is critical to the commercial exploitation of shale oil and gas resources. In this paper, we present the results of high-temperature and high-pressure experiments on typical marine and lacustrine shales to investigate porosity changes. The samples were taken from the Proterozoic Xiamaling Formation in the North China Platform, the Permian Lucaogou Formation in the Junggar Basin, the Triassic Chang 7 member in the Ordos Basin, and the Silurian Longmaxi Formation in the Sichuan Basin, all in China. We found that the key factors influencing porosity evolution include the extent of compaction, abundance of organic matter, degree of thermal evolution, and organic matter–inorganic mineral framework. The effects of thermal evolution on the pore structure of high-mature shales are more obvious than those on low-mature shales. Although the porosity evolution is positively correlated with maturity, we found evidence for different porosity evolution in ORSs in the oil window. High-resolution scanning electron microscopy observations of experimental and actual core samples indicate that liquid hydrocarbon is adsorbed and dissolved in organic matter in the oil window, leading to swelling of the organic material. This explains why there are few organic matter pores in lacustrine shales in China. The pore structure evolution is similar for marine and lacustrine shales, suggesting that kerogen has a stronger influence on the porosity evolution of shale than does the depositional environment. The lower limit of vitrinite reflectance values (Ro) at which abundant organic pores develop is 1.5%–2.5%, and the degree of pore development in ORSs is highest when Ro values are 2.5%–3.0%. These results have important implications for shale oil and gas exploration.

Microwave-assisted synthesis of copper tungstate nanopowder for supercapacitor applications

Microwave assisted synthesis of copper tungstate (CuWO4) nanopowder has been developed. Synthesized CuWO4 nanopowder was systematically characterized by X-ray diffraction spectroscopy (XRD) and high resolution scanning electron microscopy (HR-SEM). The XRD pattern revealed the formation of orthorhombic and anorthic phase for the as-prepared and calcined powders, respectively. The average particle sizes of ca. 19.3 and 44.0nm were estimated using the Scherrer equation for Cu-WO3 and microwave irradiated powder samples, respectively. The HR-SEM observation showed the morphological homogeneity with an aggregate of very small spherical and rod shaped particles. Nanocomposite films onto glassy carbon electrode have been fabricated using CuWO4 nanopowder. The electrochemical behavior of the nanocomposite film electrodes has been investigated using electrochemical impedance spectroscopy and cyclic voltammetry techniques. The maximum specific capacitance of 77Fg−1 was achieved for the CuWO4 nanopowder.

Ultrastructure of submandibular salivary glands of mouse: TEM and HRSEM observations

The fine structure of submandibular glands of mouse were analyzed using light microscopy (LM), high resolution scanning electron microscopy (HRSEM), and transmission electron microscopy (TEM) methods. For LM, the specimens were embedded in Spurr resin, stained by toluidin blue solutions. For TEM, the tissues of submandibular salivary glands were fixed with modified Karnovsky solution and postfixed with osmium tetroxide. For HRSEM, the tissues were fixed with 2% osmium tetroxide solution in 1/15M sodium phosphate buffer (pH 7.4). The samples were immersed successively in dymethylsulphoxide and freeze cracked. The maceration was made in diluted osmium tetroxide for 24-48 h. The samples were examined by high resolution scanning electron microscopy. The intracellular components of acinar and ductal cells revealed clearly the Golgi apparatus, rough endoplasmic reticulum, secretory granules, and mitochondria. The end bulbs of Golgi lamellae and flattened cisterns of rough endoplasmic reticulum showed the luminal surface. A few mitochondria were identified intermingling between the rough endoplasmic reticulum and the mitochondriales cristae in three-dimensional HRSEM images. Secretory granules were numerous and presented different sizes. Small granules of ribosomes were attached on cistern surface, measuring 20-25 nm in diameter. Numerous arranged microvilli were found on the luminal surface of secretory canaliculus. The contact surfaces of acinar cells revealed complicated interdigitations by cytoplasmic processes. The mitochondria of duct cells were disposed vertically and surrounded by basal infoldings of plasma membranes. Basement membrane showed a spongy-like structure having an irregular surface with various strands and meshes of fine collagen fibrils.

Mitochondrial metabolism and morphology in a rat model of NAFLD

NAFLD (non-alcoholic fatty liver disease) is a condition, characterized by fatty liver, that, if untreated, can progress to NASH (non-alcoholic steatohepatitis) and, finally, to cirrhosis. Mitochondrial dysfunction is a crucial element for the progression of NAFLD to NASH. Our objective was studying both morphological and physiological mitochondrial alterations in a rat model of NAFLD and NASH. Sprague Dawley rats were fed either by a standard diet (35% of energy from fat) or by a high fat diet (HFD) (71% of energy from fat). Diets were given ad libitum for a maximum of four weeks and then rats were killed by decapitation after 1, 2, 3, and 4 weeks. A portion of liver samples was processed for light and transmission electron microscopy (TEM) for steatosis assessment, a part for high resolution scanning electron microscopy (HRSEM) to evaluate 3D mitochondria morphology, the remaining part for oxidative phosphorylation experiments (OXPHOS). Measurements of OXPHOS were performed on freshly isolated mitochondria in a Clark-type oxygen electrode. Several substrates were added to mitochondria to test the efficiency of electron transport chain complexes (ETC) and to test the efficiency of several enzymes involved in fatty acid oxidation (FAO). At three and four weeks of HFD, signs of hepatic steatosis were evident (as an increased amount of intracellular lipid droplets) on histological sections and TEM images. OXPHOS measurements indicated that, compared to controls, in the first week, HFD rats had an increased oxygen consumption with each substrate, in the second, third and fourth week OXPHOS efficiency had a tendency to decline with substrates inherent to glycolitic metabolism, but it was higher with substrates stimulating FAO. There were not notable differences in Respiratory Control Ratio and ADP/O ratio between HFD and controls, proving that the integrity of mitochondria was preserved and coupled to phosphorylation. HRSEM observations indicated that variations on inner mitochondrial morphology in HFD rats, appeared in the third and fourth week, when mitochondrial cristae were less, and cristal shape was often lamellar rather than tubular. Concluding, following HFD mitochondria exhibited first an increase in oxidative metabolism (with normal ultrastructural morphology) and later an alteration in the oxidative phosphorylation apparatus associated to mitochondrial cristae injury. These preliminary results suggest that in order to develop a consistent mitochondrial impairment associated to NASH is necessary to extend HFD treatment for longer. This study was supported by a grant by RAS (Regione Autonoma della Sardegna).

Characterization of Highly Porous Polymeric Materials with Pore Diameters Larger than 100 nm by Mercury Porosimetry and X-ray Scattering Methods

Highly porous polymeric materials with pore sizes ranging from 100 nm to 1 microm are a very challenging class of materials not only to prepare synthetically (due to the high capillary pressures generated upon solvent removal) but also to characterize structurally. Through the examples of three different types of porous compounds synthesized in our laboratory (i) high-density melamine-based "MF-hd" with monomodal pore diameters around 500-900 nm, (ii) low-density melamine-based "MF-ld" with bimodal pore size distribution and average diameters around 2.3 microm and 350 nm, (iii) highly porous polyurethane "PU" with monomodal pore sizes around 150 nm, we confirm the limitations of mercury porosimetry as a means to investigate the architecture of materials with very high porosity (>80 vol %) and low compressive strength. Instead, a combination of high-resolution scanning electron microscopy and small-angle and ultrasmall-angle X-ray scattering (SAXS and USAXS, respectively) studies of these three types of materials helps in determining both the network and the pore structures. This work elucidates the need and applicability of the SAXS/USAXS techniques in characterizing such porous materials. For instance, the polyurethane specimens can only be quantitatively characterized by scattering techniques, the results of which are corroborated by high-resolution scanning electron microscopy observations.

Structural study of highly ordered mesoporous silica thin films and replicated Pt nanowires by high-resolution scanning electron microscopy (HRSEM)

We have investigated the structures of mesostructured (before calcination) and mesoporous (after calcination) silica thin films and replicated Pt nanowires by high-resolution scanning electron microscopy (HRSEM). Highly ordered lamellar, two-dimensional (2D) hexagonal, and three-dimensional (3D) hexagonal mesostructured/mesoporous silica thin films were synthesized by adjusting the concentration of triblock copolymer (EO20PO70EO20; P123) used as a structure-directing agent. Direct HRSEM observation of these mesostructured/mesoporous silica thin films demonstrated that they have inherent external structures on the top surfaces: (1) the lamellar mesostructured silica film exhibits a smooth plane; (2) the 2D hexagonal mesoporous silica film exhibits curved stripes; (3) the 3D hexagonal mesoporous silica film exhibits 2D porous arrangements (e.g. 6-fold symmetry and pseudo 4-fold symmetry). The removal of P123 by calcination had no effect on the surface structure but caused an anisotropic contraction, as found from cross-sectional images. Methods for the formation of the 2D hexagonal mesoporous film affected the orientation of mesochannels. Pt replicates, electrodeposited in the mesochannels of the 2D hexagonal mesoporous silica films, exhibited new structures, i.e., S-shaped, Y-shaped, and swirling-shaped nanowires with ellipsoidal cross section. Direct HRSEM observation of the mesostructured/mesoporous silica thin films on the top surface and cross section provides detailed information on the external and internal structures, which is significant and useful for various applications of these thin films.

Observation of heavy-ion tracks in polyimide by means of high-resolution scanning electron microscopy

The etching diameter of seven-year old latent tracks created in polyimide by 7.5 MeV/A 238U ions has been derived through high-resolution scanning electron microscopy observations and analysis according to an etching model presented herein. The diameter extracted, 6.9±1.4 nm, matches the mean width of few-weeks old latent tracks as determined recently by transmission electron microscopy. Three conclusions emerge. First, the track region that manifests itself in a highly-elevated chemical reactivity coincides with the primary structurally-altered region of the track. Second, chemical reactivity is enhanced not only by reactive alteration products but also by free volume resulted from ion-initiated processes. Third, there is no evidence of any significant healing of ion-damaged sites.

Vapour-etching-based porous silicon: a new approach

We present a new approach of porous silicon (PS) formation using a vapour-etching (VE)-based technique. We detail the principle of the method and explain how PS layers (PSLs) form, taking into account all influencing preparation parameters. The structural properties of the obtained PSLs were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained results show clear evidence of the formation of a porous layer when Si substrates are submitted to VE. High-resolution SEM observations show that both p and p + type PSLs are composed of small interconnected clusters with sizes ranging from 20 to 50 nm. TEM observations reveal that these clusters are essentially composed of dot-like crystalline Si particles embedded in an amorphous phase with sizes not exceeding 5 nm. The photoluminescence (PL) of the PSLs was found to be related to the crystalline Si dots. It was found that PL emission occurs at high energies as compared to conventional techniques. The dependence of the PL spectra with some preparation parameters is also discussed.

High-resolution scanning electron microscopy study of sputtered nanolaminated Ti/TiN multilayers

This work presents the morphologic and structural study of nanolaminated Ti/TiN multilayers using high-resolution scanning electron microscopy (HR-SEM), coupled to x-ray reflectometry (XRR). The multilayers have been deposited by reactive rf-sputtering on silicon substrates. For large period thickness (lambda=40 nm, 10 periods), in XRR, the low number of interfaces makes the interference less structured. An experimental pattern with broad and weakly intense Braggs peaks is obtained, but is difficult to simulate. On the other hand, HR-SEM observation of cross sections gives excellent pictures of the multilayer, so that precise measurements of the thickness can be achieved: a 42 nm thick period is observed, formed with 17 nm of Ti and with 25 nm of TiN. For small (Ti+TiN) period thickness (lambda=2.5 nm, 120 periods), the XRR pattern exhibits intense and narrow Bragg peaks: the number of interfaces is sufficient to structure the interference and an intense signal is obtained. The best fit of simulation is obtained for a 2.6 nm thin period, made of 0.9 nm of Ti and 1.7 nm of TiN. No laminated structure has been observed by cross-section HR-SEM observation because its resolution (around 2 nm at 10 kV) is larger than the layer thickness in a period. High-resolution SEM and XRR are thus two complementary techniques for the routine characterization of multilayers.

The Plasticity Response Of 6H-Sic and Related Isostructural Materials to Nanoindentation: Slip vs Densification

As part of a programme investigating whether slip (by dislocation motion at some critical resolved shear stress) or densification (by structural collapse at some critical hydrostatic pressure) dominates the plastic deformation response of open-crystal-structured ceramics having the diamond, zinc blende or simply-related structures, transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HRSEM) are being used to characterise the deformation structures in, and around, nanoindentations made over a range of loads in single crystal samples of Si, Ge, SiC and various III-V and II-VI compound semiconductors. Since SiC is believed to lie close to the boundary between those materials which slip and those which densify as primary plasticity responses to contact with Vickers and Berkovich indenters, this part of the study has focused on establishing the deformation mechanisms of 6H-SiC during nanoindentation. TEM of nanoindentations in (0001) 6H-SiC samples has established that dislocation slip is indeed the sole mechanism of plastic deformation from the nucleation of a few dislocation loops - at or near the theoretical strength - to extensive dislocation plasticity. Also, HRSEM observations have revealed slip steps of limited extent in 6H-SiC samples with more extensive slip steps arrays found in all the other compounds. By contrast, both Si and Ge show evidence of heavily deformed - and sometimes extruded - material believed to be a characteristic of structural collapse accommodating at least some part of the indentation strain before any dislocation slip occurs.

Calcification of Porcine Bioprosthesis Implanted into Human Heart: High Resolution Scanning Electron Microscopic and Scanning Tunneling Microscopic Investigation

High-resolution scanning electron microscopy (HR-SEM) combined with scanning tunneling microscopy (STM) was used to investigate the calcification mechanism occurring in the porcine bioprostheses implanted into the human heart. Eleven explanted porcine heart valves obtained during open heat surgery were prepared for HR-SEM and STM observations. HR-SEM examinations of all explanted valves with secondary and backscattered electron imaging revealed abnormal accumulation of calcium in various shapes and sizes on the defective valve surface and in the underlying basement membrane. Calcific deposits were consistently observed within the pinhole defects on the valve surface and in the subsurface structures of the valve tissues along the surface defects. In addition, calcium-containing crystals were often present just underneath the disrupted valve surface. STM examinations also showed that calcific deposits were frequently accumulated in or around the pinhole defects on the valve surface. Thus, STM findings were compatible with HR-SEM observations. In view of the occurrence of calcific deposits in the vicinity of the surface defects on the valve tissue and frequent observation of calcific spots and crystals in the subsurface structures just beneath the defective valve surface, our results prove the hypothesis that alteration of the valve surface is an important factor for calcification occurring in the implanted bioprosthetic heart valves.

Molecular beam epitaxial growth of GaAs, AlAs and Al 0.45Ga 0.55As on (111) A-(001) V-grooved substrates

Molecular beam epitaxial (MBE) growth of GaAs, AlAs, and AlGaAs on V-grooved GaAs substrates are studied. Observing the morphology of the heterostructures grown on the various part of V-grooves with scanning electron microscopy (SEM), it is shown that GaAs, AlAs and AlGaAs have different elemental growth parameters such as surface diffusion and atom incorporation, leading to the difference in growth behavior. Under appropriate growth conditions, in particular, the growth of AlAs results in very smooth surface on the (111)A sidewalls and drastic sharpening at the bottom of the V-grooves, whereas the growth of AlGaAs and GaAs do not show such phenomena. MBE growth mechanisms, both on the V-grooved substrates and on the (111)A flat surface, are discussed based on the phenomena observed in our experiments. Furthermore, we investigate the growth temperature dependence of the morphology and the surface diffusion of atoms during the growth of GaAs/AlAs heterostructures on the V-grooves, and demonstrate the successful fabrication of GaAs multiple quantum-wire structures at the bottom of the V-grooves by high-resolution SEM observations and cathodoluminescence measurements at 16K.

Poor intergrain connectivity of PbMo6S8 in sintered Mo-sheathed wires and the beneficial effect of hot-isostatic-pressing treatments on the transport critical current density

The microstructure of Mo-sheathed Chevrel-phase superconducting wires was investigated by high-resolution scanning electron microscopy (SEM). Excess Pb forms small nodules (10–30 nm) on the Chevrel-phase grains or wetting layers between the Chevrel grains. The critical current density Jc is strongly reduced when wetting layers are present. However, second-phase Mo exists as islands as large as 2–10 μm and has little harmful effect on Jc. Although some Mo-sheathed wires sintered at 700 °C show relatively high Jc ( ≥ 2 × 108 A/m2 at 8 T), the Chevrel phase in these wires has a very porous microstructure, and the Jc values measured with a magnetic field parallel to the current, Jc(∥), were only about 10% higher than the Jc values measured with a field perpendicular to the current, Jc(⊥). This clearly suggests that the transport current flows percolatively in these wires. Much denser microstructures were obtained by hot-isostatic-pressing (HIP) treatments at 1200 °C, and very high Jc values, ≳ 5 × 108 A/m2 at 8 T and 9.3 × 107 A/m2 at 23 T, which are of the order of the highest Jc values so far reported, were observed. High-resolution SEM observations of HIP’ed wires demonstrate that the interconnectivity between the Chevrel grains was much improved.