Stepped surfaces of sapphire (alpha-Al2O3) with low Miller indices.

Oxygen-annealed surfaces of sapphire with low Miller indices ((0001), [1010], [1120], [1011]) have been studied in both transmission electron microscopy (TEM) and reflection electron microscopy (REM) configurations. The significance of REM diffraction conditions for the determination of the nature of the step heights is discussed. The relationship between the TEM and REM images is explained. The structural features are those that might be expected from considerations of the atom arrangement in the low Miller index planes. The structural features on the surfaces varied with respect to annealing temperature and surface condition. Thermally stable structures that might appear from consideration of the equilibrium-annealing temperature are proposed.     

Scanning reflection electron microscopy of surface topography by diffusely scattered electrons in the scanning electron microscope

In this paper, the technique of scanning reflection electron microscopy (SREM) by diffusely scattered electrons in the scanning electron microscope is described in detail. A qualitative account of the formation of image contrast in SREM is also described. It is assumed that, for grazing geometry, forward-scattered electrons reflect from regions close to the surface, following a few scattering events within the first few atomic layers, and lose very little energy in the process. The penetration depth of the primary electrons is very limited, resulting in strongly peaked envelopes of forward-scattered electrons. It is also assumed that a surface containing topographic features presents a range of tilt angles, resulting in different reflection coefficients. Tilt contrast results because each facet has a different scattering yield, which is dependent upon local surface inclination. Full details of the instrumentation designed for SREM are described, and to illustrate the technique, results recorded from an epitaxial GaAs on GaAs crystal, Pb₂(Zr,Ta)O₆ thin film on silicon, and SiO₂ amorphous film on silicon are presented.     

Recent studies of surface dynamic processes by reflection electron microscopy.

Reflection electron microscope studies of surface dynamic processes are reviewed and illustrated with recent new observations. They include: surface electromigration and current dependent structures of Si surfaces; surface etching by oxidation of Si surface; and growth of two dimensional alloyed adsorbate by co-deposition of metals on Si surface. The observations revealed details of the surface dynamic processes, which are difficult to obtain with other surface analysis techniques.     

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.     

Preparation of cross-section specimens for transmission electron microscopy from alpha-Al2O3/Ni solid state bonded bicrystal interfaces.

The technique which is described combines the advantages of the techniques formerly proposed in the literature in each stage of the preparation of transmission electron microscopy (TEM) specimens including a single metal-ceramic interface. It allows easy handling of the thin foils in spite of their brittleness. Preferential thinning of the softer material in the two-phase foil is prevented, and both sides of the interface are thinned down to comparable thicknesses. The nickel-alumina bicrystal interface observed in TEM is neat and free from any reaction layer. This method is easily adaptable to other metal-ceramic systems.     

Characterization of tribological surfaces by scanning electron acoustic microscopy

Scanning electron acoustic microscopy, a useful new technique for analyzing wear surfaces, can be carried out in a modified scanning electron microscope. With this technique the thermal and elastic properties of surfaces can be imaged and surface and subsurface cracks throughout the specimen can be detected from their effect on the image. The technique is valuable in the study of surface fatigue wear, the identification of cracks likely to lead to spalling and the mapping of alloy phases in the upper 5–10 μm of the wear surface. Some examples illustrate the origin and interpretation of scanning electron acoustic micrographs and the use of the technique in the study of wear.     

Characterization of paired helical filaments by scanning transmission electron microscopy

Paired helical filaments (PHFs) are abnormal twisted filaments composed of hyperphosphorylated tau protein. They are found in Alzheimer's disease and other neurodegenerative disorders designated as tauopathies. They are a major component of intracellular inclusions known as neurofibrillary tangles (NFTs). The objective of this review is to summarize various structural studies of PHFs in which using scanning transmission electron microscopy (STEM) has been particularly informative. STEM provides shape and mass per unit length measurements important for studying ultrastructural aspects of filaments. These include quantitative comparisons between dispersed and aggregated populations of PHFs as well as comparative studies of PHFs in Alzheimer's disease and other neurodegenerative disorders. Other approaches are also discussed if relevant or complementary to studies using STEM, e.g., application of a novel staining reagent, Nanovan. Our understanding of the PHF structure and the development of PHFs into NFTs is presented from a historical perspective. Others goals are to describe the biochemical and ultrastructural complexity of authentic PHFs, to assess similarities between authentic and synthetic PHFs, and to discuss recent advances in PHF modeling.     

Seed morphoanatomy of the genus Passiflora L. (Passifloraceae) by scanning electron microscopy and light microscopy

Morphoanatomical analysis of seeds contributes to knowledge of the development of seedlings and identification of species, as well as supporting conservation studies. The conservation of the species belonging to the Passiflora genus is crucial due to of the threats to the genetic resources of these species. Thus, the objective of this study was to morphoanatomically characterize Passiflora seeds, verify possible injuries to the tissues after cryopreservation and thus contribute to the conservation strategies of the species of this genus. Initially, seeds of Passiflora coccinea, P. edulis, P. gibertii, P. maliformis, P. morifolia, P. setacea, P. suberosa, and P. tenuifila collected from the Passion Fruit Active Germplasm Bank of the Embrapa Cassava and Fruits research unit (Embrapa Mandioca e Fruticultura) were analyzed. Then, their length, width and thickness, shape of the base and tip, and ornamentations present on the body and edge of the seeds were evaluated. The seeds of the species were placed in cryotubes and immersed in liquid nitrogen to assess possible cryoinjuries. The tegument and tissues of the seeds were examined by scanning electron microscopy. The seeds had varied biometric data, with average values of 4.63 mm for length, 3.28 mm for width, and 1.51 mm for thickness. Six ornamentation types were observed: reticulate for the species P. coccinea; finely reticulate for P. edulis; foveolate reticulate for P. gibertii and P. setacea; alveolate reticulate for P. maliformis and P. tenuifila; coarsely reticulate for P. morifolia; and falsifoveolate reticulate for P. suberosa. Some seeds suffered tegument cracks due to the freezing in liquid nitrogen, but without physiological damages to the embryo and endosperm. The cryopreservation of the seeds in the presence of the tegument significantly reduced the cryoinjuries caused to the embryo. Cryopreservation can be promising for long-term conservation of passion fruit seeds.     

Characterization of polymer blends by low voltage scanning electron microscopy

A technique for characterization of polymer blends by low voltage scanning electron microscopy is described. The method allows observation of the distribution of phases in a blend due to good topographical and compositional contrast. This is possible because of lower beam penetration and high secondary emission coefficient (δ ? 1) at low accelerating voltages. Uncoated polymer samples are imaged with no charging or beam damage problems. The technique has a great advantage over conventional transmission electron microscopy techniques because the sample preparation is minimal and larger areas can be prepared for viewing.     

CrB2(0001)表面特性和电子结构的第一性原理研究

基于第一性原理的密度泛函平面波赝势方法,对两种不同终端CrB2(0001)的表面性能:表面弛豫、表面能和电子结构等进行了计算和分析.当CrB2(0001)表面结构原子层数达到9时,表面层间距快速收敛.通过分析差分电荷密度和态密度(PDOS),可以得出硼终结CrB2(0001)表面结构比铬终结CrB2(0001)具有较小的界面能和较强的电子相互作用,表面更稳定.     

Characterization of 4H-SiC (0001) surface processed by plasma-assisted polishing

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO₂. CeO₂ was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced.     

Characterization of the near-surface layers of carbon steels modified by interaction with intense pulsed plasma beams: scanning electron microscopy investigations

Modification of materials is a wide area in materials science, especially surface modification. To investigate the results of the modification process, treated and nontreated samples were compared. Intense plasma pulses of argon or nitrogen were used to irradiate the carbon steels. In all samples, the near‐surface layer was melted. Results of scanning electron microscopy investigations of the surface morphology and cross‐sections, as well as the results of tribological tests, are presented. The obtained results allowed us to draw conclusions about changes in material properties and to propose subsequent studies using other investigation techniques.     

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.     

Characterization of reflection scanning near-field optical microscopy and scanning tunnelling optical microscopy/photon scanning tunnelling microscopy working in preliminary approach constant height scanning mode

The resolution in near-field images is currently determined by the visual inspection of recorded images. One of the major questions in near-field optical microscopy is 'what resolution can be reached, the tip-to-sample distance being known?' This knowledge is critical when choosing the scanning step and the distance between the tip and the sample, in a preliminary scan. This preliminary scan is often the only way to detect the interesting parts of the sample, with limited risk of tip crash and topographical artefacts. The method proposed here needs two scans of the same area, of the same sample, in constant height mode, recorded at two tip-to-sample distances. The pseudotransfer function is the ratio of the Fourier transform of these two data maps. This function enables the evaluation of the limit of resolution. Theoretical considerations are introduced to assess the method.     

Characterization of reflection scanning near-field optical microscopy and scanning tunnelling optical microscopy/photon scanning tunnelling microscopy working in preliminary approach constant height scanning mode

The resolution in near-field images is currently determined by the visual inspection of recorded images. One of the major questions in near-field optical microscopy is 'what resolution can be reached, the tip-to-sample distance being known?' This knowledge is critical when choosing the scanning step and the distance between the tip and the sample, in a preliminary scan. This preliminary scan is often the only way to detect the interesting parts of the sample, with limited risk of tip crash and topographical artefacts. The method proposed here needs two scans of the same area, of the same sample, in constant height mode, recorded at two tip-to-sample distances. The pseudo-transfer function is the ratio of the Fourier transform of these two data maps. This function enables the evaluation of the limit of resolution. Theoretical considerations are introduced to assess the method.