Потенциальные изображения сегнетоэлектрических доменных структур в кристаллах ниобата лития после формирования электронным лучом

Ferroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector P _ s of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.

Evaluating the Use of Synthetic Replicas for SEM Identification of Bloodstains (with Emphasis on Archaeological and Ethnographic Artifacts)

Some archaeological or ethnographic specimens are unavailable for direct examination using a scanning electron microscope (SEM) due to methodological obstacles or legal issues. In order to assess the feasibility of using SEM synthetic replicas for the identification of bloodstains (BSs) via morphology of red blood cells (RBCs), three fragments of different natural raw material (inorganic, stone; plant, wood; animal, shell) were smeared with peripheral human blood. Afterwards, molds and casts of the bloodstained areas were made using vinyl polysiloxane (VPS) silicone impression and polyurethane (PU) resin casting material, respectively. Then, the original samples and the resulting casts were coated with gold and examined in secondary-electron mode using a high-vacuum SEM. Results suggest that PU resin casts obtained from VPS silicone molds can preserve RBC morphology in BSs, and consequently that synthetic replicas are feasible for SEM identification of BSs on cultural heritage specimens made of natural raw materials. Although the focus of this study was on BSs, the method reported in this paper may be applicable to organic residues other than blood, as well as to the surface of other specimens when, for any reason, the original is unavailable for an SEM.

Human Bloodstains on Biological Materials: High-Vacuum Scanning Electron Microscope Examination Using Specimens without Previous Preparation

Studies of human bloodstains on nonbiological materials have been previously carried out using a high-vacuum scanning electron microscope (HV-SEM) in secondary-electron mode without any sample treatment. To assess whether biological substrates can affect the morphology of human erythrocytes in bloodstains, three fragments of different biological material (bone, shell, and wood) were smeared with peripheral human blood. Afterward, the bloodstains were directly examined in secondary-electron mode by an HV-SEM following a procedure initially standardized to be used in uncoated human bloodstains on stone. The obtained results suggest that HV-SEM is suitable for examining untreated bloodstains on biological substrate and that the morphology of erythrocytes in human bloodstains is not affected by the biological nature of the substrate. A cautionary issue regarding bloodstains on nondehydrated biological substrates is that the waiting time required for initiating the HV-SEM examination is by far higher than when using inorganic bloodstain substrates.

The application of high-resolution SEM and EPMA to the study of coatings and interfaces of materials

Microchemical and micro-structural analysis are often required when characterizing coatings and interfaces in materials. For coatings the interface between substrate and coating and between coating and the surface are of particular interest. The scanning electron microscope (SEM) and electron probe microanalyzer (EPMA) are often employed in characterizing interfaces in materials particularly because solid samples can be studied and sample preparation is usually restricted to developing a suitable flat polished surface for analysis. Both these instruments are essentially the same although the EPMA is equipped with wavelength dispersive detectors (WDS) and is dedicated to quantitative microchemical analysis.The spatial resolution for high resolution SEM where microstructural analysis of the surface is desired is now in many ways comparable to the transmission electron microscope (TEM). Magnifications of over 100,000 X are available in SEMs equipped with a field emission gun using the secondary electron mode. Figure 1 shows the interface region of a retained austenite region in the Tazewell iron meteorite shown in both TEM and SEM mode and Figure 2 shows the morphology of crystals, 0.3 μm wide by 1.5 μm long containing ledges 30-50 nm wide in an electrodeposited Zn coating on a steel in both TEM and SEM mode.

Detection of Small (5-15 nm) Gold-Labelled Surface Antigens by Back- Scattered Electrons

In contrast to thin section transmission electron microscopy, scanning electron microscopy (SEM) permits “three dimensional” analysis of events occurring at the cell surface. Since it is now generally recognized that many important cellular functions are initiated and regulated via interactions taking place at the cell surface, SEM studies of surface antigens have become an area with increasing applications. Surface antigens have been visualized using antibody coupled phages, latex spheres, colloidal gold, i.e. markers that are recognized in the SEM either by their specific shape or because of their uniform size. An ideal marker, however, should be as small as possible to reduce the problems of sterical hinderance. All known markers smaller than approx. 15 nm (colloidal gold, ferritin) are round particles which in the secondary electron mode (SE) are hardly discerned from surface structures or contaminants of similar size. Therefore the markers must be amenable to verification using additional information such as backscattered electrons (BSE).

A Micromanipulator for Use in the Column of a Scanning Electron Microscope

Used in the secondary electron mode, the Scanning Electron Microscope (SEM) produces an image of the outside surface of a microscopic sample which looks very similar to what one might expect to see if the sample was a diffusely illuminated macroscopic object viewed with the unaided eye. Part of the familiarity of such an image is associated with the fact that one seems to look at the sample rather than through it, as in the case with the conventional electron microscope or the high resolution light microscope. A resulting limitation is the fact that an object of interest cannot be observed if it is below the outer surface. It has been shown (Gane and Bowden 1968) that useful surface hardness information can be obtained on a micro scale by observing the deformation produced when a small stylus, attached to a D'Arsonval meter movement, is brought to bear on the surface of a sample while it is in the SEM.