Electron microscopic study of novel threadlike structures on the surfaces of mammalian organs

The ultrastructures of novel threadlike structures (NTSs) and corpuscles on the surfaces of internal organs of rats were investigated using electron microscopy. The samples were studied in situ by using a stereomicroscope and were taken for further morphological analysis. Scanning electron microscope (SEM) images revealed a bundle structure of threadlike tissue, which was composed of several 10-micro m-thick subducts. The surfaces of the corpuscles were rather coarse and fenestrated. The corpuscles had cucumber-like shapes with an average length of about 2 mm and a thickness of about 400 micro m. Transmission electron microscope (TEM) images disclosed disordered collagen fibers, which formed the extracellular matrix of the threadlike tissue, and immune-function cells, like macrophages, mast cells, and eosinophils. Sinuses of various diameters, which were thought to be cross-sections of the lumens of the subducts, were observed in the TEM, cryo-SEM and focused-ion-beam SEM images. These SEM images were obtained for the first time to reveal the detailed structure of the NTSs that were only recently discovered.     

Simple modifications for accurate high-temperature gas exposures using scanning electron microscopy

Relatively low-cost modifications to standard commercial scanning electron microscopes (SEM) that allow accurate exposure of sample(s) to noncorrosive gases at ambient and high temperatures are outlined. Energy-dispersive spectroscopic analysis of sample(s) exposed to noncorrosive gases at high temperatures is demonstrated. Gas exposure is limited to pressures of less than 10^?4 torr (1.33 × 10^?2 Pa) as a result of limitations on SEM system operation and SEM safety interlocks. Gases are limited to noncorrosive types as a result of potential damage to system detection devices and internal mechanical parts.     

Electron energy loss spectra and reflection images from surfaces

There is renewed interest in the interaction of high energy electron beams with surfaces at glancing angles of incidence, due partially to recent improvements in, and consequential resurgence of, reflection electron microscopy. In this paper electron energy loss of beams running parallel to a surface or at glancing incidence to it are studied and compared with predictions arising from the classical theory of dielectric excitation by a moving charge. There is good agreement for both the Cu and MgO surfaces studied here. It is pointed out that small angle energy loss from high energy electrons is insensitive to surface reconstructions or surface steps. Reflection energy filtered micrographs of the Cu surface are shown and the similarity between the zero and various energy loss images shows the preservation of contrast mechanisms for elastic and inelastic electrons.     

The use of helium gas to reduce beam scattering in high vapour pressure scanning electron microscopy applications

Both image quality and the accuracy of x-ray analysis invariable pressure scanning electron microscopes (VPSEMs) are often limited by the spread of the primary electronbeam due to scattering by the introduced gas. The degree of electron scattering depends partly on the atomic number Z of the gas, and the use of a low Z gas such as helium should reduce beam scattering and enhance image quality. Using anuncoated test sample of copper iron sulphide inclusions in calcium fluorite, we show that the reduction in beam scatter produced by helium is more than sufficient to compensate for its reduced efficiency of charge neutralisation. The relative insensitivity to pressure of x-ray measurements in a helium atmosphere compared with air, and the consequent ability to work over a wider range of working distances, pressures, and voltages, make helium potentially the gas of choice for many routine VPSEM applications.     

Electron microscopy study of different stages of oxidation of Ti-47Al-2Nb-2Cr-0.15B and Ti-45Al-15Nb at 900°C

The initial stage of oxidation of Ti-47Al-2Nb-2Cr-0.15B and Ti-45Al-15Nb alloys was studied. Studies reveal that the X and NbCr₂ phases will form in advance in the transition layer of the 2Nb2Cr alloy compared with the 15Nb alloy. The adherence between the nitride layer and underling layer is good. However, an obvious boundary exists between the mixed layer and the inner layer. The recrystallizing of the base alloy leads to an increase of the volume fraction of grain boundaries that can increase the oxidation rate at the initial oxidation stage. An Nb-based compound forms in the transition layer, which can prevent the formation of X phase.     

Thermal effects of the electron beam and implications of surface damage in the analysis of bone tissue

Electron beam interactions with specimens in the scanning electron microscope (SEM) can lead to increased surface temperatures and damage. These changes may have significant consequences in the analysis of bone tissue. An investigation was performed to measure the surface temperature changes associated with the electron beam on a thermocouple with systematic variations in operating conditions. Probe currents, magnifications, and accelerating voltages were incrementally adjusted to measure the temperature changes and to make assessments for determining optimal operating conditions for the SEM in future analyses of bone tissue. Results from this study suggest that thermal effects were minimal at lower accelerating voltages (< 20 kV), lower probe currents (< 10 nA), and lower magnifications, but surface damage may still occur during the analysis of bone tissue.     

Defining the radiation chemistry during liquid cell electron microscopy to enable visualization of nanomaterial growth and degradation dynamics

We present a critical review of methods for defining the chemical environment during liquid cell electron microscopy investigation of electron beam induced nanomaterial growth and degradation. We draw from the radiation chemistry and liquid cell electron microscopy literature to present solution chemistry and electron beam–based methods for selecting the radiolysis products formed and their relative amount during electron irradiation of liquid media in a transmission electron microscope. We outline various methods for establishing net oxidizing or net reducing reaction environments and propose solvents with minimal overall production of radicals under the electron beam. Exemplary liquid cell electron microscopy experiments in the fields of nanoparticle nucleation, growth, and degradation along with recommendations for best practices and experimental parameters are reported. We expect this review will provide researchers with a useful toolkit for designing general chemistry and materials science liquid cell electron microscopy experiments by ‘directing’ the effect of the electron beam to understand fundamental mechanisms of dynamic nanoscale processes as well as minimizing radiation damage to samples.     

S—250MK3型扫描电子显微镜故障及维修

介绍了剑桥Ｓ－２５０Ｍ型扫描电子显微镜在实际操作中出现的典型故障及维修方法。     

扫描电子显微镜放大倍数校准方法研究

随着科技的发展进步,扫描电子显微镜现有检定规程提出的部分校准方法已不适用.本文对扫描电子显微镜放大倍数示值误差的校准提出了新的方法和计算过程,利用像素坐标表征标记线长度,以减少图像输出及测长仪使用过程中引入的误差.     

A method for personal expertise-independent evaluation of image resolution in scanning electron microscopy

The two conventional methods currently employed for the evaluation of image resolution in scanning electron microscopy are the gap method and a fast Fourier transform (FFT) method. These can be highly dependent on personal expertise on the distinction between signal information and noise contained in a micrograph. Hence, the present paper proposes an alternative method (referred to as a contrast-to-gradient (CG) method) that can determine the image resolution of a micrograph without requiring personal expertise on the judgment of noise. The image resolution in the CG method is defined as a weighted harmonic mean of the local resolution, which is proportional to the quotient of the threshold contrast divided by the local gradient. The local gradient is calculated from the quadratic function that best fits the local pixel intensities over 5 x 5 pixels. It has been shown that the CG method, compared with the FFT method, has a broader range of applications for various types of images, such as low-contrast, noise-containing, filter-processed, highly directional, and quasi-periodic feature images.     

Characterization of lead zirconate titanate--lanthanum ruthenate thin film structures prepared by chemical solution deposition

In this work, the results of compositional and microstructural analysis of lead zirconate titanate--lanthanum ruthenate thin film structures prepared by chemical solution deposition are discussed. The cross-section transmission electron microscope (TEM) micrographs of the La-Ru-O film deposited on a SiO2/Si substrate and annealed at 700 degrees C revealed RuO2 crystals embedded in a glassy silicate matrix. When the La-Ru-O film was deposited on a Pt/TiO2/SiO2/Si substrate, RuO2 and La4Ru6O19 crystallized after annealing at 700 degrees C. After firing at 550 degrees C randomly oriented lead zirconate titanate (PZT) thin films crystallized on the La-Ru-O/SiO2/Si substrate, while on La-Ru-O/Pt/TiO2/SiO2/Si substrates PZT thin films with (111) preferred orientation were obtained. No diffusion of the Ru atoms in the PZT film was found. Ferroelectric response of PZT thin films on these substrates is shown in comparison with the PZT film deposited directly on the Pt/TiO2/SiO2/Si substrate without a La-Ru-O layer.     

Electron scattering in ice and organic materials

Scattering cross-sections for the interpretation of the scattering-absorption contrast of microscopical images of amorphous biological specimens are calculated. The constituent atoms are treated as independent particles and their atomic potential is approximated by a modified Lenz-Wentzel potential. Both elastic and inelastic scattering processes are considered. Formulas of the effective elastic and inelastic atom scattering cross-sections are derived for both a CTEM with hollow-cone illumination and a STEM using an annular detector. The scattering-absorption contrast is plotted as a function of the atomic number for a CTEM applying parallel illumination and a STEM using a dark-field detector with maximum collection efficiency. The presented results are valid for acceleration voltages U in the range 20 kV<U<150 kV. Employing these data the ‘angular mass thicknesses’ of representative constituents of biological materials are determined. The application of the listed data is demonstrated by means of a special example.     

Azadirachta indica exhibits chemopreventive action against hepatic cancer: Studies on associated histopathological and ultrastructural changes

The present study was designed to evaluate the anticarcinogenic potential of Azadirachta indica against N-nitrosodiethylamine (NDEA)-induced hepatocarcinogenesis. Further, the associated histopathological and ultrastructural changes were also analyzed. Hepatic cancer model was developed by the intraperitoneal administration of NDEA to mice at weekly intervals, in successive increasing doses, for a period of 8 weeks. Aqueous A. indica leaf extract (AAILE) was administered orally at a dosage of 100 μg/g body weight thrice a week till termination of the study. A relationship between histopathological grading and chemopreventive effect of A. indica had been established at various stages of carcinogenesis. Anticancer activity of A. indica was evaluated in terms of tumor incidence, tumor multiplicity, and survival rate. A significant reduction in tumor incidence (33%), tumor multiplicity (42%), and increase in survival (34%) was observed upon administration of AAILE to NDEA-abused mice. Transmission and scanning electron microscopic investigations showed severe alterations in organelle organization, cellular arrangement, degree of differentiation, cellular metabolism, and morphology of the hepatocytes. These changes appeared to be distinctly delayed upon AAILE supplementation. The results suggest A. indica may have anticancer potential against NDEA-induced hepatic cancer.     

Electron microscopy of unstained,freeze-dried macromolecular assemblies

A rapid cooling/cryotransfer system was designed to achieve a high reproducibility in vitrifying thin water films containing biological specimens. In order to improve the contrast these unstained specimens were deliberately freeze-dried in situ in the electron microscope. The preservation of the structure obtained by freeze-drying at 180 K and subsequent microscopy at 90 K is very encouraging as has been shown with two types of test specimen. Tubular photosynthetic membranes were used to examine the effects of a variety of freeze-drying conditions on structural preservation, as judged by flattening of the tubes. A two-dimensional protein crystal was used to evaluate problems of low-dose microscopy of unstained, freeze-dried proteins, e.g. optical density of films, motif detection by cross-correlation and transferring the accurate molecular positions from medium-dose to corresponding low-dose micrographs. The radiation sensitivity of the unstained, freeze-dried protein crystal was investigated by a dose series covering a wide range.     

Reflection electron imaging and spectroscopy studies of aluminium metal reduction at α-aluminium oxide (0,1,2) surfaces

Cleaved α-aluminium oxide (0,1,2) surfaces are studied using combined techniques of scanning reflection electron microscopy and reflection electron energy-loss spectroscopy. An α-aluminium oxide (0,1,2) surface can terminate with a layer of either oxygen or Al atoms depending on where the bonds break. Aluminium metal can be reduced only from the domains initially terminated with oxygen by an intensive electron beam. The interpretation of this damage effect is based on the desorption process of oxygen atoms after Auger decay. The resistance to beam damage of the domains initially terminated with Al is found to be due to the protection of the surface adsorbed amorphous oxygen layer.     

Investigation of Si–Au vicinal surfaces using scanning tunnelling microscopy and reflection high-energy electron diffraction

Silicon vicinal surfaces can be successfully used as substrates for the preparation of one‐dimensional nanostructures. The quality of the structures prepared may be controlled using scanning tunnelling microscopy, as shown in this work. Additionally, it is possible to obtain valuable information using reflection high‐energy electron diffraction. A typical way of employing reflection high‐energy electron diffraction is to observe patterns of scattered electrons on a screen. However, it is possible to obtain more detailed information on the arrangement of atoms at the surface if azimuthal plots are collected. Azimuthal plots are measured by recording the intensity of specularly reflected electrons during the rotation of the sample around an axis perpendicular to its surface. So far, only flat surfaces have been examined in such a way. In this work, it is shown that such data, containing interesting features, can also be collected for vicinal surfaces.     

The reduction of the beam gas interactions in the variable pressure scanning electron microscope with the use of helium gas

This paper presents experimental observations on electron scattering by gases (helium and air) in the specimen chamber of a variable pressure scanning electron microscope. It shows an important reduction of the beam scattering with the use of helium gas, and the consequences for the x-ray microanalysis are discussed.     

Histology and ultrastructure of the testis and vas deferens in Pseudochorthippus parallelus parallelus (Orthoptera,Acrididae)

Pseudochorthippus parallelus parallelus (Zetterstedt, 1821) (Orthoptera, Acrididae) is a widespread species in Europe, and also it is localized in some regions in Turkey such as Bursa, Eski?ehir, Ankara, Bolu, Düzce, and Çank?r?. The features of the reproductive organs such as the numbers and shapes of testes and follicles can be used as taxonomical characters. For this purpose, the ultrastructural and histological features of testis and vas deferens in P. parallelus parallelus were examined with using light microscope, scanning electron microscope, and transmission electron microscope. The mature P. parallelus parallelus has two conjugated testes produce spermatozoa. Each testis is composed of numerous testis follicles in which different stages of spermatogenesis and spermiogenesis develop. First, spermatocytes are formed by the mitosis division of the germ cells at the distal end of the follicles. Then, spermatocytes form spermatids by meiosis division in the middle region of the follicles. Finally, spermatids are differentiated to spermatozoa at the proximal region of the follicles. After maturation of the spermatozoa, sperm tails come together as the sperm bundles called as spermatodesm. Each follicle is connected to vas deferens via vas efferens to discharging spermatozoa. In spite of some differences, the testes and the vas deferens in P. parallelus parallelus are highly similar to the those of other species, especially Orthopteran species.     

A procedure to prepare cultured cells in suspension for electron probe X-ray microanalysis: application to scanning and transmission electron microscopy

We describe a simple procedure to prepare cultured cells in suspension to analyse elemental content at the cellular level by electron probe X-ray microanalysis. Cells cultured in suspension were deposited onto polycarbonate tissue, culture plate well inserts, centrifuged at low g , washed to remove the extracellular medium, cryofixed and freeze-dried, and analysed in the scanning mode of a scanning electron microscope. We tested the effect of different washing solutions (150 m m ammonium acetate, 300 m m sucrose, and distilled water) on the elemental content of cultured cells in suspension. The results demonstrated that distilled water was the best washing solution to prepare cultured cells. In addition, the low Na content, high K content and high K/Na ratio of the cells indicated that this procedure, based on the centrifugation at low g followed by cryopreparation, constitutes a satisfactory method to prepare cultured cells in suspension. We also investigated the effects of different accelerating voltages on X-ray signal collection. The results showed that moderate accelerating voltages, i.e. 10–11 kV, should be used to analyse whole cells in the scanning mode of the scanning electron microscope. We show that this method of preparation makes it possible to prepare cryosections of the cultured cells, thus permitting analysis of the elemental content at the subcellular level, i.e. nucleus, cytoplasm and mitochondria, using a scanning transmission electron microscope.