Use Of High-resolution Electron Microscopy Research Articles

Raziskave oborin v aluminijevih zlitinah z visokoresolucijsko elektronsko mikroskopijo in računalniško simulacijo

Raziskave oborin v aluminijevih zlitinah z visokoresolucijsko elektronsko mikroskopijo in računalniško simulacijo

MEMS platform for on-chip nanomechanical experiments with strong and highly ductile nanofibers

A new nanoscale tension testing platform with on-chip actuation and the unique capability for nanoscale mechanical characterization of highly deformable and strong nanostructures is presented. The specimen force and extension measurements are based on optical imaging, supported by digital image correlation, which allows the resolution of 20 nm specimen extensions and force measurements better than 30 nN, without the use of high-resolution electron microscopy. The breakthrough of this nanomechanical testing platform is the ability to study the mechanical behavior of nanostructures subjected to a wide range of forces (30 nN–300 µN) and displacements (20 nm–100 µm), which are significantly beyond the limits of typical surface micromachined MEMS with on-chip actuators, such as comb-drives and thermal actuators. The utility of this device in experimental nanomechanics is demonstrated by investigating the mechanical behavior of electrospun polyacrylonitrile nanofibers with diameters of 200–700 nm subjected to strains as high as 200%. The mechanical property measurements were compared to and agreed well with off-chip measurements by an independent testing method, which validates the capability of this on-chip testing platform to characterize strong and highly ductile nanomaterials.

Preparation and Microstructural and Textural Characterization of Single-Phase Aluminum Oxides

Conditions for the preparation of single-phase η-, θ-, and χ-aluminas were determined. The structures of η- and χ-aluminas were characterized. With the use of high-resolution electron microscopy, it was found that η-Al2O3 particles exhibited the most developed {111} face and consisted of coherently joined domains with a pronounced platelet shape. Planar defects in the (111) plane occurred in the η-Al2O3 particles. Microstructural differences between single-phase η-Al2O3 and γ-Al2O3 with a defect spinel structure were revealed. It was found that the η-Al2O3, χ-Al2O3, and θ-Al2O3 oxides are characterized by uniformly porous structures with average pore diameters of 47, 55, and 110 A, respectively.

Ultrastructure of basement membranes in monkey and shark teeth at an early stage of development

The basement membrane, which separates the inner enamel epithelium from the dental papilla in the early stages of tooth development, is known to play a significant role in odontogenesis. In this review article, this basement membrane was described in detail based on our recent findings with the use of high-resolution electron microscopy. Tooth germs of a monkey (Macaca fuscata) and a shark (Cephaloscyllium umbratile) were processed for thin-section observations. During the early stage of development, the basement membrane of the inner enamel (dental) epithelium was composed of a lamina lucida, lamina densa, and much wider lamina fibroreticularis. At higher magnification, the lamina densa in both species was made up of a fine network of cords, which are generally the main constituents of the basement membranes. In the monkey tooth, the lamina fibroreticularis was rich in fibrils, which were now characterized as basotubules, 10-nm-wide microfibril-like structures. The space between the basotubules was filled with a cord network that extended from the lamina densa. Dental papilla cell processes were inserted into the lamina fibroreticularis, and their surface was closely associated with numerous parallel basotubules via 1.5- to 3-nm-wide filaments. In the shark tooth during its early stage of development, the basotubules were absent in the lamina fibroreticularis and only narrow extensions, 60-90 nm wide and 1-2 microm long, of the cord network of the lamina densa were present. The dental papilla cells were immobilized by means of the binding of their processes to the extensions. These results indicate that basement membranes in both monkey and shark teeth at early stage of development are specialized for functions as anchoring and firm binding, which are essential for the successful differentiation of the odontoblasts.

High-resolution imaging of n-alkane crystals by atomic force microscopy

X-ray and electron crystallography of polymethylene chain compounds are known to be hindered by the very strong scattering from a dominant sublattice, and the use of high-resolution electron microscopy is severely limited by radiation damage. This study shows that these problems may be overcome by using highresolution atomic force microscopy (AFM) imaging. The work was performed on four types of linear alkane crystal, namely n-C26H54, n-C30H62, n-C36H74 and n-C44H90, of different molecular lengths. They were prepared by vapour deposition and from solution and deposited on mica and on highly oriented pyrolytic graphite. The results show that firstly AFM may complement, at a molecular and a submolecular level, the data provided by X-ray and electron crystallography, secondly alkane crystals may be prepared with different orientations and the type of substrate has no influence, and thirdly AFM may be used to induce orientational and conformational changes.

HREM Image Analysis up to Structure Determination of SbCrSe 3: A New 1D Ferromagnet

The combined use of high-resolution electron microscopy (HREM), image analysis, and X-ray refinement techniques enabled us to determine the structure of SbCrSe 3as orthorhombic (space group Pnma, a=9.1689(30), b=3.7957(12), 13.4637(44) Å). The structure model of SbCrSe 3has been derived directly from the HREM image along the [010] direction. It consists of edge sharing CrSe 6octahedra forming double rutile chains along the b-axis and separated by Sb atom columns located approximately in pentagonal tunnels of Se atoms. The structural model was refined by the full profile XRD powder Rietveld method. The compound SbCrS 3( a=8.68, b=3.62, c=12.88 Å) is isostructural to SbCrSe 3. Below the Curie temperature both compounds exhibit features which suggest 1D ferromagnetism.

The Structure of Amyloid Fibrils by Electron Microscopy and X-Ray Diffraction

Publisher Summary The chapter discusses the structural analysis of amyloid fibrils by electron microscopy and X-ray diffraction. A method to isolate amyloid fibrils from tissue was developed, and such preparations of purified fibrils exhibited the classic staining and birefringent characteristics of crude amyloid samples. The further use of high-resolution electron microscopy, examining ultrathin sections of tissue and isolated material, confirmed the fibrillar form as the characteristic appearance of amyloid in the electron microscope. With the ability to prepare samples of isolated amyloid fibrils it began to be possible to probe the molecular structure of the fibrils using X-ray diffraction. The initial use of this technique produced diffraction patterns that showed that the fibrils were composed of polypeptide chains, extended in the so-called cross-β-conformation. Subsequent analyses by X-ray diffraction on a variety of amyloids and also by NMR analysis have confirmed that the protein chains in all amyloid fibrils are predominantly in the cross-β-conformation. The structures of the soluble, globular forms of several amyloidogenic proteins have been determined by the single crystal X-ray crystallography. The origins of the different amyloidoses appear quite diverse, with some arising from a genetic mutation and others apparently from polypeptide misprocessing or from an unusual accumulation of full-length wild-type protein.

High-resolution ultrastructural study of the rat glomerular basement membrane in aminonucleoside nephrosis.

In the initial stages of aminonucleoside nephrosis, functional alterations in the glomerular basement membrane occur, as evidenced by the development of proteinuria. However, it has not been possible to observe important ultrastructural modifications at the level of the basement membrane, probably because the changes are taking place at the molecular level. In this study, by the use of high-resolution electron microscopy, an attempt was made to evaluate such changes in rat glomerular basement membrane during acute aminonucleoside nephrosis. As previously reported, in control animals the glomerular basement membrane is composed of a network of 4-nm-wide irregular anastomosing strands, referred to as "cords," which are known to contain a core filament of type IV collagen surrounded by a "sheath" of other components, such as laminin and heparan sulfate proteoglycan (HSPG). The most conspicuous ultrastructural alteration of the nephrotic glomerular basement membrane, recognizable only at high magnification, is that the cords were denuded leaving only the core filament through the loss of the sheath material. Thus, the cord network was transformed, with the progress of pathological conditions, into a network of fine filaments. On the other hand, abundance and distribution of HSPG molecules known to be present in the form of 4.5- to 5-nm-wide ribbon-like "double tracks," were found to be similar in control and nephrotic tissues. Since HSPG is one of the charge proteins of the basement membrane, the little changes observed for HSPG are difficult to interpret in view of reported decreases in basement membrane anionic sites in nephrosis. In conclusion, the glomerular basement membrane in aminonucleoside nephrosis loses its cord network components and replaces them with a more perforated network, which could be a cause for the increased permeability of this basement membrane.

Electron Microscopy Study of NiW/Al2O3-F(x) Sulfided Catalysts Prepared Using Oxisalt and Thiosalt Precursors

Two different series of sulfided NiW catalysts supported on alumina modified with different amounts of fluoride, in the range 0.0–2.5 wt%, have been prepared by using two different tungsten precursor salts: ammonium metatungstate and ammonium tetrathiotungstate. Samples of both catalyst series have been examined by the use of high-resolution electron microscopy. For the oxisalt-prepared catalysts the results indicate that fluoride incorporation increases the size of WS2crystallites but has little effect on the number of layers. On the other hand, the change of precursor salt significantly influences the stacking of WS2crystallites without greatly affecting their size. The thiosalt method of preparation also leads to an excess of sulfur in the catalysts, which is distributed in a nonhomogeneous way.

Pseudomorphic transformations of euhedral crystals of γ-AlOOH into aluminas

The thermal transformation of synthetic well-shaped hexagonal laths of boehmite-AlOOH was studied between 200°C and 1500°C by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD), to characterize the transition aluminas that appear before the formation of α-Al 2O 3. It was observed in the single crystals that dehydroxylation produces, between 400°C and 500°C, pores regularly organized and parallel to the larger diameter cf the hexagons which have the same direction (100) as the original boehmite crystal; this gives a striated appearance to the pseudomorphs, which is maintained until after heating at 900°C, when the transformation from the γ phase coexist; the pores have lost their orderly disposition and larger pores or openings are now irregularly distributed in the mixed single crystals, whose crystalline structure can be observed in the lattice image by the use of high-resolution electron microscopy. The α-alumina pseudomorphs exists as platy elongated single crystals at 1100°C and coalesce at 1200°C; from 1300°C to 1500°C the pseudomorphs coalesce into round polygonal particles of α-alumina, whose crystalline structure could be demonstrated by SAED, XRD or lattice images.

Structural studies on Superconducting materials and fullerites by electron microscopy

High‐resolution electron microscopy (HREM) has proved invaluable in the study of local structure—i.e. defects—which in many cases govern the physical, chemical, and electrical properties of materials. The use of HREM in investigations of cuprate high‐temperature superconductors is reviewed, especially for compounds in which substituents replace some of the copper. HREM can also be very successfully combined with other techniques, such as electron diffraction, as is demonstrated by results of research on the structure and phase transitions of C60 and C70.

The use of HREM in studying clay minerals

A wider scope of clay research has been opened by investigators in various branches of science and technology due to their increasing interest in such materials. Electron microscope is one of the important methods for studying clay and clay minerals. Although a previous contribution of electron microscopy was to clarify the morphology and later electron diffraction (ED) of fine clay particles.However with the continous improvement of instrument and high resolution electron microscopy (HREM) techniques has provided more detailed information of clay minerals. This paper presents the use of HREM in stúdying clay minerals among our research.1. Analysis of the structure of clay minerals Recent advances in crystal structure analysis have indicated that disordered features are commonly revealed to various extents in clay mineral structure, such as polytypes,stacking disorders,mixed-layers.......etc. When the fraction of disordered feature is rather low, which cannot be distinguished by other method such as x-ray diffraction,however by using HREM lattice imaging, ED, and computer simulating (CS), which can be distinguished distinctly and sensitively. Fig.1a shows the structure of kaolinite with enantio morphic types i.e. left-handed and right-handed kaolinite. The computer simulated image (CSI) and electron diffraction pattern (EDP) are included for interpretation. It was also found that dickite is exhibited as intergrowth or stacking faults in the koalinite.

Atomic imaging of Au/Ni multilayers

The role of interfaces in materials often plays a decisive part in determining physical properties. The order/disorder state of the interfacial structure, induced during the composition modulated synthesis, becomes increasingly property significant as the multilayer period decreases, i.e. the proportional number of interfaces increases. The presence or lack of interlayer coherency is dependent on the atomic misfit between host lattices compounded with short-long-range interactions, as well as the deposition-dependent growth morphology. The use of high-resolution electron microscopy (HREM) to atomically image the structure of Au/Ni multilayers will provide unique insight into the interfacial role in the “supermodulus” effect-a severalfold increase in the biaxial modulus above homogenous solution values which takes place over a narrow layer thickness range. This critical range of multilayer periods, between 1 and 3 nm, corresponds to a high interface volume fraction. A strain-wave description of atomic displacements coincident with the multilayer period appears appropriate to explain the highly distorted, “single phase” structure observed on an atomic scale.

Defects in β-rhombohedral boron formed during the synthesis of LaB 6

Beta-rhombohedral boron ( a = 10.139 Å, α = 65.20°, Z = 104.9, space group R 3m ), formed during the synthesis of LaB 6 has been investigated with the use of high-resolution electron microscopy. In a sample of gross composition La 0.81B 6, β-rhombohedral boron crystals were found. Microanalysis showed that some of these contained minor amounts of La, Si, and O. They were rich in defects of various kinds, such as point defects, line defects, stacking faults, and twinning. Structure models are suggested for some of the defects.

Intergrowth structures: the chemistry of solid-solid interfaces

Most chemists are familiar with two kinds of intergrowths: epitaxy, which involves the oriented overgrowth of one crystalline solid upon another, and polytypism, which arises when individual sheets in a layered material are stacked in different sequences. Epitaxy is currently of technological interest since it dictates the laying down of thin, single-crystal films of semiconductors on to a substratum suitable for the production of integrated microelectronic circuits. It also occupies a central role in the phenomena of biomineralization and urinary calculi where an inorganic crystal such as CaCO3 or Si02 grows in registry with crystalline slivers of polysaccharide, protein, or purine.l Polytypism is less important technologically. Nonetheless, two extreme polytypic forms of ZnSe-one with hexagonal (ABAB), the other with cubic (ABCABC) packing-have2 significantly different electronic band gaps (2.863 and 2.810 eV) and hence different luminscent and other photophysical properties. When polytypic regions are separated spatially on a nanometer scale in semiconducting materials such as GaAs and CdTe, so-called quantum wells may form. There are many other types of solid-solid interfaces of interest to the chemist. Although few of these are of immediate commercial relevance , they are all of considerable fundamental significance . Our discussions of such seemingly unrelated phenomena as chiral turnover in molecular crystals, of infinitely adaptive inorganic structures, of coincidence boundaries in zeolites, the origins of gross nonstoichiometry, and the occurrence of modulated structures all entail an understanding of crystalline intergrowths. Almost all of the facts we discuss in relation to the phenomenology of intergrowths-in particular their structural characteristics-has been obtained by use of high-resolution electron microscopy (HREM). This

On crystal symmetry and crystal structure determination from high-resolution electron micrographs

Despite the widespread use of high-resolution electron microscopy for characterizing crystalline defects down to the atomic level, the determination of crystal structures ab initio from electron micrographs remains far from straightforward. This is partly because, as well as being focus‐ and thickness‐dependent, images are generally sensitive to both beam and crystal tilt, with 1mrad. of the former typically being sufficient to cause considerable spurious image detail even in very thin (<25Å) crystalline regions. Whilst careful attention to alignment can normally correct for loss of symmetry, the absence of dynamically‐allowed reflections in certain projections due to systematic cancellation results in extreme image sensitivity; these reflections quickly increase in amplitude with any slight relative misalignment. Under these conditions, tilt correction becomes virtually impossible and erroneous conclusions about crystal symmetry are well‐nigh inevitable. Crystal symmetry operators associated with tilt sensitivity are (a) a glide plane normal, and/or (b) a screw axis, perpendicular to the electron beam. All except a few of the lowest symmetry space groups have at least one zone satisfying one, or both of these criteria.

High-resolution microscopy of nonstoichiometric Nb22O54crystals: point defects and structural defects

With the use of high-resolution electron microscopy, defects have been observed in crystals of Nb22O54: two types of point defects and extended Wadsley-type defects having a structure corresponding to Nb12O29. For one type of point defect a model is proposed which contains two displaced metal atoms and two interstitial oxygen atoms within a 'block'. For the other, one metal atom and three oxygen atoms are considered to be missing from a tetrahedral site. Contributions made by the three types of defects to the non-stoichiometry of the crystals are discussed.