Analytical scanning electron microscopy for solid surface

A scanning electron microscope of ultra-high-vacuum (UHV-SEM) with a field emission gun (FEG) is operated at the primary electron energies of from 100 eV to 3 keV. The instrument can form the images that contain information on surface chemical composition, chemical bonding state (electronic structure), and surface crystal structure in a microscopic resolution of several hundred angstroms (Å) using the techniques of scanning Auger electron microscope, scanning electron energy loss microscope, and scanning low-energy electron diffraction (LEED) microscope. A scanning tunneling microscope (STM) also has been combined with the SEM in order to obtain the atomic resolution for the solid surface. The instrumentation and examples of their applications are presented both for scanning LEED microscopy and STM.     

Laser scanning microscopy of surface spread polytene chromosomes

A new type of a Laser Scan Microscope (Zeiss) was used for the analysis of the band-interband pattern of polytene chromosomes in Chironomus. In contrast to the previously used techniques of transmission light and electron microscopy, we used differential interference contrast (DIC) in incident light to depict the pattern. Instead of using common squash preparations, we carried out this investigation with surface spread polytene (SSP) chromosome preparations of salivary glands. The combination of techniques used enabled a more detailed light microscopic presentation of polytene structures in individual preparations than conventional techniques used so far for chromosome mapping.     

High-resolution surface scanning electron microscopy of mineralized tissues

By using an ion-pumped SEM with high brightness gun, resolution of the order of 5 nm has been demonstrated on the mineral matrix of animal bone and tooth enamel. Measurements of collagen fibril diameter have also been obtained.     

Analysis of simulated scanning of atomic-scale silicon surface by atomic force microscopy

This study constructs a contact-mode atomic force microscopy (AFM) simulation measurement model with constant force mode to simulate and analyze the outline scanning measurement by AFM. The simulation method is that when the probe passes the surface of sample, the action force of the atom of sample received by the atom of the probe can be calculated by using Morse potential. Through calculation, the equivalent force on the cantilever of probe can be acquired. By using the deflection angle equation for the cantilever of probe developed and inferred by this study, the deflection angle of receiving action force can be calculated. On the measurement point, as the deflection angle reaches a fixed deflection angle, the scan height of this simulation model can be acquired. By scanning in the right order, the scan curve of the simulation model can be obtained. By using this simulation measurement model, this study simulates and analyzes the scanning of atomic-scale surface outline. Meanwhile, focusing on the tip radii of different probes, the concept of sensitivity analysis is employed to investigate the effects of the tip radius of probe on the atomic-scale surface outline. As a result, it is found from the simulation on the atomic-scale surface that within the simulation scope of this study, when the tip radius of probe is greater than 12 nm, the effects of single atom on the scan curve of AFM can be better decreased or eliminated.     

Imaging of thermal and elastic surface properties by scanning electron acoustic microscopy

Scanning electron acoustic microscopy is a new technique for imaging the thermal and elastic properties of surfaces and detecting subsurface flaws. It can be carried out in a modified scanning electron microscope. The effects of electron beam energy and phase angle on scanning electron acoustic images of the thermal and elastic properties of surfaces were studied with an alumina fiber/aluminum matrix composite for fiber directions both transverse and coaxial to the surface. Images produced with 10- and 30-keV electrons at beam modulation frequencies of 80–1200 kHz appeared to be identical, with the exception of a lower signal-to-noise ratio for the lower electron energy. This observation suggests that the energy input from the beam can be considered to occur at the surface for electron energies below 30 keV and frequencies below 1200 kHz. Images recorded at 0° phase angle mapped regions of different thermal and elastic properties. Images recorded at 90° phase angle highlighted the boundaries between such regions. Scanning electron acoustic microscopy can image features of different thermal and elastic properties at greater depth than traditional imaging with backscattered electrons. The practical application of the technique to the study of surfaces is illustrated by the imaging of grain structure and subsurface particles for an extruder barrel.     

Surface investigations on HgBr2 single crystals by using confocal scanning laser microscopy

A confocal scanning laser microscope operating at 514 and 488 nm has been used to obtain two-dimensional (2-D) images of the mercuric bromide (HgBr2) crystal surface by photoluminescence, reflection, and transmission phenomena. Our measurements indicate that regions showing a strong photoluminescence may appear on the surface. By processing the 2-D images. we obtained the three-dimensional images, which offer a better possibility for the investigation. The analysis of spectral lines may be correlated with the presence of the Hg impurities.     

Quantifying surface modification events from scanning force microscopy images

Scanning force microscopy (SFM) is widely used to monitor surfaces and surface modification processes. Some surface modification processes involve the addition (or removal) of discrete entities to (or from) a surface in circumstances where the absolute number of entities is related to some aspect of the process. A two-dimensional surface characterisation parameter – the surface area ratio (SAR) – was previously developed as a means of quantifying such modification and can be readily obtained from SFM images. Simulations have shown that the SAR parameter is superior for quantification purposes to conventional surface roughness parameters such as roughness average S_a, the area equivalent of R_a. Key features of SAR are as follows: its linear dependence with coverage; dependence of linearity slope on coverage mechanism; and its independence from the form, waviness or roughness of the underlying surface. A further advantage of this method is its simplicity given that the SAR parameter is readily obtained from SFM images. Simulations of adsorption onto flat surfaces have been validated using SFM images of polystyrene spheres adsorbed onto mica.     

An investigation of surface failure of surface-hardened gears by scanning electron microscopy observations

The tooth surface of surface-hardened gears often becomes grey stained under a heavy load before pitting or spalling occur. The grey-stained area increases with running time and this failure causes degradation of the tooth profile.The nature of grey staining and the influence of surface conditions on the phenomena are investigated by scanning electron microscopy observations of the surfaces of gear teeth and rollers. It is established that the grey staining consists of many microcracks and micropits. Their formation and wearing off occur successively. It is reconfirmed that surface roughness has a significant influence on grey staining.     

A study of hydrogenated carbon fibers by scanning electron microscopy and confocal laser scanning microscopy

The hydrogen absorption process is studied in carbonaceous fibers produced from a mixture of methane and hydrogen. The absorption of the hydrogen was examined in two types of fibers, in “as-grown” state and after a process of desorption during an annealing to 1.473 K under vacuum. Later to its production process, the fibers withstand an oxidation in air to 973 K. The fibers were examined by means of scanning electron microscopy (SEM) and confocal microscopy by reflection. Differences in the behavior during the oxidation were observed between the fibers in as-grown state and those subjected to a further annealing. It could be verified that the fibers were really constituted by two different phases. In one of the phases, the storage of the hydrogen absorbed took place, whereas in the other phase there was no alteration. The process of annealing prior to the absorption of the hydrogen has an appreciable effect on the desorption rate of the hydrogen. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc.     

Imaging of individual atoms on an Al(111) surface by scanning tunnelling microscopy

Due to the delocalized character of metal valence electrons the atomic corrugation of metal surfaces observed in Scanning Tunnelling Microscopy (STM) is found to be much smaller than in the case of semiconductor surfaces. In fact, there is only a single study in the literature which reports the resolution of the individual atoms on a metal surface (Hallmark et al., 1987). The present paper demonstrates the resolution of individual atoms on a close packed surface of a nearly free electron metal, Al(111), and presents systematic experiments on the physical origin of this phenomenon. A more detailed discussion will be given elsewhere (Wintterlin et al., 1988).     

Application of environmental scanning electron microscopy to determine biological surface structure

The use of environmental scanning electron microscopy in biology is growing as more becomes understood about the advantages and limitations of the technique. These are discussed and we include new evidence about the effect of environmental scanning electron microscopy imaging on the viability of mammalian cells. We show that although specimen preparation for high-vacuum scanning electron microscopy introduces some artefacts, there are also challenges in the use of environmental scanning electron microscopy, particularly at higher resolutions. This suggests the two technologies are best used in combination. We have used human monocyte-derived macrophages as a test sample, imaging their complicated and delicate membrane ruffles and protrusions. We have also explored the possibility of using environmental scanning electron microscopy for dynamic experiments, finding that mammalian cells cannot be imaged and kept alive in the environmental scanning electron microscopy. The dehydration step in which the cell surface is exposed causes irreversible damage, probably via loss of membrane integrity during liquid removal in the specimen chamber. Therefore, mammalian cells should be imaged after fixation where possible to protect against damage as a result of chamber conditions.     

High-resolution scanning electron microscopy of the surface of red blood cells

Examination of normal human red blood cells with a high (2.5 nm) resolution scanning electron microscope revealed a definite surface pattern. The pattern was slightly more pronounced in specimens dried in air after fixation than in those dried by the critical-point method. There was a radial arrangement of filament like elevations at the periphery of the red cell and a more reticular pattern to wards the centre of the cell. The appearances probably represented a network of elenin fibres lying just under the surface of the red cell.     

Free-standing graphene by scanning transmission electron microscopy

Free-standing graphene sheets have been imaged by scanning transmission electron microscopy (STEM). We show that the discrete numbers of graphene layers enable an accurate calibration of STEM intensity to be performed over an extended thickness and with single atomic layer sensitivity. We have applied this calibration to carbon nanoparticles with complex structures. This leads to the direct and accurate measurement of the electron mean free path. Here, we demonstrate potentials using graphene sheets as a novel mass standard in STEM-based mass spectrometry.     

Imaging an optical disc by the combined use of scanning tunnelling microscopy and scanning electron microscopy

We present the data obtained by scanning tunnelling microscopy combined with scanning electron microscopy of the digitally encoded structure on a stamper used to fabricate optical discs. The combination allows us to focus the STM tip on a preselected spot with a precision of ?0·3 μm. The data show the superiority of STM for a more detailed characterization of shape, width, length, height and fine structure appearing on the sample. We also show the influence of tip shape on STM resolution. Simultaneous use of both microscopes is possible but high electron doses produce an insulating layer of contaminants thick enough to make STM operation impossible.     

Feed-forward compensation of surface potential in atomic force microscopy

We introduce a feed-forward technique for lift-mode Kelvin probe force microscopy to minimize electrostatically induced errors in topography scans. Such errors typically occur when a grounded tip is scanned over a heterogeneous sample with differences in local work function or areas of local surface charging. To minimize electrostatic forces during the topography scan we bias the tip with the surface potential recorded in the previous Kelvin probe scan line. With this method we achieve an error free topography on samples with large variations in local surface potential. Compared to conventional tapping mode, we further observe a significant reduction of tip-induced surface charge modifications on charge patterns written in electret films.     

Characterization of an oil-degrading Microcoleus consortium by means of confocal scanning microscopy, scanning electron microscopy and transmission electron microscopy

A consortium of microorganisms with the capacity to degrade crude oil has been characterized by means of confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The analysis using CLSM shows that Microcoleus chthonoplastes is the dominant organism in the consortium. This cyanobacterium forms long filaments that group together in bundles inside a mucopolysaccharide sheath. Scanning electron microscopy and transmission electron microscopy have allowed us to demonstrate that this cyanobacterium forms a consortium primarily with three morphotypes of the heterotrophic microorganisms found in the Microcoleus chthonoplastes sheath. The optimal growth of Microcoleus consortium was obtained in presence of light and crude oil, and under anaerobic conditions. When grown in agar plate, only one type of colony (green and filamentous) was observed.     

Surface topography and intracellular organization of human cells in suspension as revealed by scanning electron microscopy

This report presents a new procedure to study the ultrastructure of human cells in suspension by means of scanning electron microscopy. Living cells were maintained in suspension within cell culture flasks located on a rotating tilting table within an incubator. These cells were injected into warm glutaraldehyde/formaldehyde fixative. After washing in buffer, fixed cells were attached to propylamine-derived glass carriers. However, saturating free aldehyde groups of fixed cells and blocking amine groups of the derived glass carriers prevented cells from attachment to these carriers. Thus, we postulated that bonds between the fixed cell-free aldehyde groups and the carrier amine groups were responsible for cell-to-carrier attachment. Fixed cells attached to the carriers were subsequently dehydrated, dried, and coated for surface topography studies. For studies of internal cell organization, these attached cells were immersed in agar or gelatin as extracellular embedments and infused with sucrose or polyvinyl-pyrrolidone as cryoprotectants. Cells then were frozen and fractured. Fractured cells were either thawed, dehydrated, critical point dried, and ion beam sputter-coated, or freeze-substituted, dried, and planar magnetron sputter-coated. Finally, cell preparations were observed in the scanning electron microscope. Due to high cell attachment yield, both approaches samples observed in the electron microscope were representative of the entire cell population.