bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of grain boundary parameters using high-resolution Electron Microscopy
Authors: Buckett M. I. , Merkle K. L.
Published: June 2020

With the advances in instrumentation and the capability of point-to-point resolution better than 0.2 nm, high resolution electron microscopy (HREM) is becoming more widely used for the quantitative study of both surfaces and internal interfaces. The elegance of the technique lies in its ability to deduce atomic-scale information on a localized scale. Without the proper analysis, however, HREM images can easily be misinterpreted. We investigate the considerations necessary for quantification of HREM images, using the measurement of the grain boundary volume expansion via the lattice fringe displacement technique as an example. The volume expansion, a parameter directly related to the grain boundary energy, is measured (in length units on the order of tenths of Å) as a rigid body translation normal to the boundary. It can be determined experimentally using statistical techniques which locate and fit the peak and valley positions in an experimental HREM image such that a direct measurement of the lattice fringe displacements is made.
Visualization and quantitation of cellular and tissue anatomy by 3D light microscopy
Authors: Turner J. N. , Roysam B. , Holmes T. J. , Szarowski D. H. , Lin W. , Bhattacharyya S. , Ancin H. , Mackin R. , Becker D.
Published: June 2020

Many areas of biomedical research require the visualization and quantitation of 3D micro- and tissue level anatomy. Both are possible by utilizing confocal or wide-field light microscopy in combination with computational methods, including deblurring and 3D image analysis. The three-dimensionality of the specimen, required image resolution, and parameters to be quantitated dictate the methods of choice. Applications under study by our group range from automatically quantitating a few cell layers in cervical/vaginal smears, or hundreds of cell nuclei or immunologically labeled cells in thick brainslices, to tracing individual neurons for long distances in 3D space. Examples of our wide-field deconvolution methods and automated detection and counting of nuclei in thick tissue are shown.

Image restoration by blind deconvolution of portions of the axonal fields of two rat hippocampal pyramidal cells injected with biocytin and contrasted with horseradish peroxidase and diaminobenzidine6 is shown in Figure 1. The original data is projected along and perpendicular to the optic axis in Fig. 1a while 1b is a similar set of restored image projections.
An algorithm for estimation of chromosome motion in Four-Dimensional microscopic images
Authors: Marshall Wallace , Agard David , Sedat John
Published: June 2020

Analysis of the three-dimensional organization of chromosomes within the nucleus has revealed a number of characteristic structural features. Yet imaging of living nuclei indicate that chromosomes undergo considerable random motion. Maintenance of nuclear organization in the face of such motion is thought to involve the attachment of chromosomes to the nuclear envelope or matrix. Yet while such attachments have been proposed to play a variety of functional roles as well as maintain nuclear organization, direct evidence for the existence of these mechanical interactions in vivo has been lacking. One way to demonstrate such attachment directly would be to estimate the motion of chromosomes and attempt thereby to demonstrate the presence of fixed points, which would indicate attachment of chromatin to some fixed superstructure.

We have previously presented a motion estimation algorithm that is designed for tracking the motion of nonrigid and featureless objects such as chromosomes. This algorithm starts with a structural representation for the set of chromosomes at each time point, and then finds a correspondence between elements of the representations at successive time points.
Diffraction contrast and Huang scattering in dark-field imaging of diffusely scattered electrons
Authors: Wang Z. L.
Published: June 2020

It has been demonstrated that dark-field, atomic number sensitive images can be obtained either inscanning transmission electron microscopy (STEM) using a high-angle annular dark field detector (HAADF) or in transmission electron microscopy (TEM) using an on-axis objective aperture under the hollow cone beam illumination. The images are formed using the high-angle diffusely scattered electrons presuming that the high angle Bragg reflections are weak. Diffuse scattering can be generated by both thermal diffuse scattering (TDS) and Huang scattering, The local lattice distortion due to the presence of defects, dislocations, lattice relaxation, surfaces, or interfaces, is a source for generating diffuse scattering (or Huang scattering). In these cases, the final image contrast may not be sensitive to the local composition, thus eliminating the Zcontrast effect. The diffraction effect in the imagesformed by diffusely scattered electrons is easily seen in the TEM case. In the diffraction pattern of gold shown in Fig. 1, <110> streaks produced by TDS are clearly seen. The bright field image shows some bending and strain contrast. Most of the features observed in the bright field imageappear in the dark field image of the diffusely scattered electrons.
Applications of high-spatial-resolution microanalysis in materials science
Authors: Gu H. , Mayer J. , Müllejans H. , Rühle M.
Published: June 2020

The development of advanced materials frequently requires control over the presence and propertiesof interfaces. In order to establish the relationship between the microstructure and the macroscopic behaviour of the material both, the structure and the composition of the interfaces have to be revealed at a resolution at or close to the atomic level. In this paper new techniques in analytical electron microscopy with high spatial resolution will be discussed. The analysis is based on electron energy-loss spectroscopy (EELS). Spatial resolution can either be obtained by applying an energy filteringTEM (EFTEM) or a small probe in a field emission dedicated STEM. Both techniques have been applied toa number of model systems and the achievable detection and resolution limits will be compared. The experimental studies were performed at (i) a Zeiss EM 912 Omega instrument equipped with a 1024 × 1024 slow scan CCD camera and (ii) a VG HB 501 equipped with parallel EELS.
Analysis of co-deposited Ti-Hf thin film on (0001)6H-SiC by HREM, energy-selected and hollow-cone images
Authors: Bow J. S.
Published: June 2020

Solid solution binary alloys are attractive for defect-free thin film semiconductor contacts because lattice matching can be obtained by composition adjustment, but chemical homogeneity is required. Highly composition sensitive energy-selected and hollow cone (HC) dark field imaging were evaluated for heterogeneity detection in Ti-Hf films using an Ω filter/Zeiss 912 TEM. Conventional HREM, which relatively insensitive to spatial composition variations in this case, was used to observe structural defects in the films near the interfaces.

Thin films of pure Ti deposited via UHV electron beam evaporation at room temperature on n-type, vicinal (0001) 6H-SiC showed good epitaxy. This contact displayed rectifying characteristics. The interface was both structurally and chemically sharp. However, misfit dislocations at “stand off” positions were found, due to 4 % mismatch between the basal parameters of Ti and SiC. same column with Ti in the periodic table and has hexagonal crystal structure, but larger lattice parameter (aHf = 3.196 Å, and aTi = 2.950 Å). The Ti-Hf solid solution system obeys Vergard's law well, that is, the lattice parameters of this alloy change linearly with composition.
Microstructure and chemistry of MgO- and CoO-doped nickel-titanate spinels
Authors: Anderson I. M. , Carter C. B. , Bentley J.
Published: June 2020

When NiO-rich powder mixtures of NiO and TiO2 are equilibrated in air above ∼1425°C and subsequently quenched, X-ray diffraction patterns of the resulting specimens can be indexed with a single set of reflections in the Fd3m space group. Originally this result was cited as evidence of a highly nonstoichiometric single phase. However, subsequent TEM investigations showed that these specimens are composed of periclase- and spinelstructured phases with small domains and coherent phase boundaries. Periclase-structured domains are distributed throughout the spinel with two distinct morphologies: cuboidal particles, faceted on {100}, of uniform size that increases from 30 to 150 run with increasing NiO-mole-fraction; and an isotropic interconnected twophase microstructure, also of uniform size, varying from 2 to 5 ran seemingly independent of composition. The finer-scale features strongly resemble those arising from spinodal decomposition in an isotropic medium and can be ascribed to decomposition of a nonstoichiometric spinel phase during quenching. It has recently been suggested that the faceted particles coexist with the nonstoichiometric spinel at the equilibration temperature.
Studies of poorly conducting samples by the low-loss electron method in the SEM
Authors: Wells O. C. , Rishton S. A.
Published: June 2020

The low-loss electron (LLE) image in the scanning electron microscope (SEM) shows stronger topographic contrast, less sensitivity to specimen charging and a shallower information depth in comparison with the more familiar secondary electron (SE) imaging method. When working with a poorly conducting or insulating sample the beam energy must be reduced to typically ~1.5 keV to minimise the net charging current at the surface of the specimen. Even if this is done correctly the topographic contrasts in the LLE image can still be considerably stronger than in the SE image.

Fig. 1(a) shows the original LLE detector in which the sample is inclined at 45° to the electron beam. Fig. 1(b) shows a new detector which operates with a specimen tilt of 20°. Both have been used in a Cambridge Instrument Co. S250 Mk.III SEM.

The possibility of obtaining a LLE image with a 20° specimen tilt is demonstrated with uncoated photoresist in Fig. 2 (tungsten filament) and with a “Crystal“ image store to capture and replay the image.
Comparison of image analysis results on α-β microstructures in NbTi superconductors using BSE imaging in FESEM and STEM
Authors: Yang N. Y. C. , Headley T. J. , Seuntjens J. M.
Published: June 2020

The critical current density (Jc) of NbTi multifilamentary superconductors having α-β microstructures is affected by the volume fraction, size, and spacing of small oc-Ti precipitates dispersed in the β-matrix. These morphological parameters are controlled in processing by interspersed cold drawing and heat treatment. They can be readily quantified by image analysis techniques, provided that representative binary images can be obtained which include the entire population of small α-Ti precipitates (0.03-0.4 μm). We have obtained BSE images of these α-β microstructures that are suitable for conversion to binaries and subsequent image analysis using either a FESEM or a high voltage STEM. Here we report on BSE imaging at low voltage in a FESEM and compare results with those previously reported for BSE imaging in a 300 kV STEM.
High-resolution SEM imaging of model catalytic materials
Authors: Datye A. K. , Völkl E. , Allard L. F. , Nolan T. A.
Published: June 2020

Studies of metal/support interactions in catalytic materials have been facilitated by use of model catalysts consisting of metals deposited on substrates of simple geometry suitable for direct imaging in the transmission electron microscope. An example of such a catalyst/substrate system is a model combustion catalyst comprised of nanometer-sized particles of Pd deposited on amorphous silica microspheres. These materials have recently been characterized both by high resolution TEM imaging and electron holography techniques, as well as by ultra-high resolution SEM imaging. TEM and holography results indicated that the particles, which range from 5 to 15 nm in diameter, were single crystals. In addition, depending upon preparation conditions, these nanocrystals typically contained a single void that was shown by holography to be empty. Figure 1 shows a TEM image of a typical particle on the SiO2 sphere, where the void is clearly evident. The high resolution SEM imaging results from these specimens of known geometry are presented in this paper.
AFM of phospholipid membranes: From ripples to domains to interdigitation
Authors: Shao Zhifeng , Yang Jie , Mou Jianxun , Czajkowsky Czajkowsky
Published: June 2020

In the past few years, a great deal of effort was made in many laboratories in the development of suitable specimens and better instrumentation for biological applications of atomic force microscopy (AFM) for its promise of high spatial resolution imaging of biological samples under physiological conditions. This effort has resulted in the publication of a number of excellent and reproducible images of various bio-macromolecules. Most notables include plasmid DNA and DNA fragments at, gap junction plaques, and cholera toxin, among others. However, the majority of these work were aimed at the methodology and the characterization of the AFM. Very little information was actually revealed about the biological systems being studied. This has been one of the major criticisms from many biologists and electron microscopists, that nothing new was learned by biological AFM.

This situation has started to change recently. Rees et al. showed by AFM in air that the DNA template at the site of DNA-RNA polymerase complex bent differently in the presence of open or elongation promoter.
Effects of deformation of electron-beam-grown microtips on measurements taken with the Atomic-Force Microscope
Authors: Mooney C. B. , Thornton J. T. , Russell P. E.
Published: June 2020

When imaging with an Atomic-Force Microscope (AFM), the image resolution is a complex function of the relative tip and sample geometries. When imaging or measuring high aspect ratio features, sharp and slender tips offer the possibility of probing down into extremely small topographical features. The most commonly used contact mode AFM tips are thin film cantilevers of Si3N4 with an integrated pyramidal structure used as the tip. It has been shown that microtips, which are fabricated by electron beam induced growth of carbonaceous material on the apex of the pyramid, can reduce the artifacts associated with integrated pyramidal AFM tips. A SEM micrograph of a microtip grown on the apex of an integrated pyramid is shown in Figure 1. Use of grown microtips in metrology demands an understanding of the dynamics of microtip deformation while scanning.
Transport critical currents and microstructure of yttrium barium cuprate
Authors: Smith D. A. , Clarke D. R. , Chisholm M. F. , Batson P. E. , Olsson E.
Published: June 2020

The transport critical current density, Jc , has been measured as a function of grain misorientation in thin film bicrystals of YBa2Cu3O7−x 1-2-3. The bicrystals were grown epitaxially on oriented bicrystal substrates of strontium titanate. Jc decreases as the misorientation increases up to about 20 degrees and subsequently remains constant. For misorientations of 20 or more degrees Jc is reduced by a factor of about 50 relative to its single crystal value. Although this is a large reduction it is still significantly smaller than the approximately three orders of magnitude reduction in Jc at 77K which is found when single crystals and polycrystalline samples are compared. It is concluded that the Jc of polycrystalline material is not, at present, intrinsically limited by the mismatch at grain boundaries but rather by one or more extrinsic features. Some possible origins for this observed weak link behavior are: intergranular phases, segregation, and lattice strain (affecting the superconducting pair potential).
Indications of flux pinning by chemical defects in 123
Authors: Li D.J. , Zhang J.P. , Qin L.C. , Marks L. D.
Published: June 2020

A problems with bulk high temperature superconductors for some time has been obtaining specimens which show high critical currents; typical critical currents in bulk materials lie in the range of 103 Amps/cm2 whereas thin film specimens now routinely reach the 106 Amps/cm2 range. There has recently been indications of higher critical currents in some materials, with suggestions that there is flux pinning by 1/3(301) type defects. We have previously studied in some detail bulk materials with excess copper that contain large number of such defects. In the light of the recent results, we have returned to these materials to study the critical current in addition to the structure.

Details of the specimen preparation will be reported elsewhere. The key point is that with the correct preparation conditions, the bulk materials show a fairly sharp transition at 9IK and magnetization measurements indicate (reproducibly) a Jc of more than 106 at 4.5K, using the total size of the specimen and not a smaller grain size.
Dislocations in YBa2Cu3O7−δ (δ = 0.77)
Authors: Zhu Yimei , Zhang Hong , Moodenbaugh A.R. , Suenaga M.
Published: June 2020

Abundant dislocations and dislocations associated with stacking faults were observed and characterized in YBa2Cu3O7−δ (δ= 0.77). The crystallographic orientation of the dislocation and the fault were analyzed using Kikuchi patterns matched with computer generated Kikuchi maps. The Burgers vector of the dislocation and the displacement vector of the fault were determined by using the g·b = 0 and g · R=0 criteria.

Bulk samples of YBa2Cu3O7 were produced by standard pressing and sintering up to 970 °C. Samples were heated in air, then quenched into liquid nitrogen to reduce oxygen content. Subsequent anneal at 200 ° C took place with samples sealed in silica with 1/2 atm. of argon. TEM specimens were thinned by ion mill and examined in a JEOL 2000FX electron microscope operating at 200kv.

X-ray powder diffraction and convergent beam electron diffraction with 200 Å spot size show that YBa2Cu3O6.23 has a tetragonal structure.
Direct observation of the defect structure and structural interfaces in laser-deposited Y-Ba-Cu-O thin films
Authors: Ramesh R. , Ravi T.S. , Hwang D.M. , Chang C.C. , Xi X.X. , Inam A. , Li Q. , Wu X.D. , Venkatesan T.
Published: June 2020

One of the earliest applications of the newly discovered high temperature oxide superconductors is in the area of microelectronics, involving the fabrication of epitaxial thin films and heterostructures on suitable substrates. After examining several thin films deposition techniques, the pulsed excimer laser deposition technique has been found to yield films with excellent superconducting properties including a Tc of 90-91K, a superconducting transition width of less than 0.5°, transport critical currents of 5×106A/cm2 or higher and good microwave properties. The higher critical currents in the thin films, compared to bulk materials, have been attributed to the presence of a wide variety of structural defects that act as flux pinning centers. Hence, we have undertaken a systematic study of the atomic nature of the structural defects. In addition to high resolution electron microscopy(HREM), microdiffraction and analytical electron microscopy are being used to study the microstructure. Specifically, HREM is being carried out using the 1.6A point-to-point resolution and ±45° goniometric tilt capability of the Berkeley Atomic Resolution Microscope(ARM).
Intergrowth of modulated structures in high Tc Bi-Sr-Ca-Cu-O superconductors
Authors: He A.Q. , Qiao G.W. , Zhu J. , Ye H.Q.
Published: June 2020

Since the first discovery of high Tc Bi-Sr-Ca-Cu-O superconductor by Maeda et al, many EM works have been done on it. The results show that the superconducting phases have a type of ordered layer structures similar to that in Y-Ba-Cu-O system formulated in Bi2Sr2Can−1CunO2n+4 (n=1,2,3) (simply called 22(n-1) phase) with lattice constants of a=0.358, b=0.382nm but the length of c being different according to the different value of n in the formulate. Unlike the twin structure observed in the Y-Ba-Cu-O system, there is an incommensurate modulated structure in the superconducting phases of Bi system superconductors. Modulated wavelengths of both 1.3 and 2.7 nm have been observed in the 2212 phase. This communication mainly presents the intergrowth of these two kinds of one-dimensional modulated structures in 2212 phase.
Nucleation and Heteroepitaxy of YBa2Cu3O7-δ thin films
Authors: Grant Norton M. , Barry Carter C.
Published: June 2020

The nucleation and heteroepitactic growth of YBa2Cu3O7−δ thin-films has been studied by transmission electron microscopy (TEM). The films were formed by pulsed-laser ablation and then observed in the TEM without further sample preparation. Direct observation of the early stages of film growth is possible due to the utilization of a new specimen-preparation technique. The films were deposited directly onto specially prepared electron-transparent substrates. The substrate material used in this study was single-crystal, (001)-oriented MgO. The thin-foil substrates were prepared from bulk single-crystal substrates in the following manner. Discs of 3mm diameter were cored, polished and dimpled to produce a final sample thickness of 10 - 20μm. The samples were ion milled to perforation using 5 kV Ar+ ions, then chemically cleaned. The cleaned foils were annealed in air at 1350°C for 10min. The annealing temperature is such that sufficient atomic mobility enables the formation of a series of steps on the surface.
Structural and superconducting study of the system (Pb,Bi)-Sr-Ca-Cu-O
Authors: Aurisicchio C. , Calestani G.L. , De Blasi C. , Fiorani D. , Manno D. , Palmisano M.
Published: June 2020

The results of a study of the structural and superconducting properties performed on a (Pb, Bi) - Sr - Ca - Cu - O systei by x rays, transmitted electron aicroscopy (CBED) and magnetic susceptibility measurements are reported.

The sample was prepared by solid state reaction of a mixture of Bi2O3, PbO, SrCO3, CaCO3 and CuO, according to the starting composition Bi2PbO.4Sr2Ca3Cu4Ox. A slight excess of Ca and Cu, with respect to the stoichiometric formula (Bi, Pb)2Sr2Ca2Cu3Ox was utilized in agreement with in order to minimize the reaction time required for the obtainment of the c= 3.7 nm phase and to avoid the presence of the c-shorter phase (−3.1 nm) in the final product. The mixture was ground, heated at 780 oC for 8h and then cooled to room temperature in air and annealed again at 840 oC for 60h. Finally a textured sample was obtained by pressing the powder into a pellet which was annealed at 840 oC for 8h.
Effect of Microstructures on Properties of YBa2Cu3O7-x
Authors: Xiang-yun Song , Shulin Wen , Mei-yu Zhao , Zhen-en Li
Published: June 2020

The purpose of this investigation is to reveal the correlation between microstructures and curitical current density (Jc) in YBCO ceramic superconductors by TEH. Further analyses have shown that these microstructural features are denpendent on Cu-O planes behaviour of two dimensions and key to explain the mechanism of the relation between microstructure and Jc. Three YBCO samples which have the same composion but different processing were measured and compared. The Tc values of three samples were approximately the same (90K) but the Jc values were quite different:30A/cm2 for sample S1 300A/cm2 for sample S2 and 2000A/cm2 for sample S3. Hundreds pictures for three samples were randomly taken in low magnification by TEM. Using the statistical method, the microstructural information were measured from TEM pictures.

A number of observations by TEM have found that three kinds of microstructural features, including the grain of c/a≥3 (grain length c, width a),the grain boundary between parallel-straight grains and the grain with twin domains play a major role in YBCO ceramics superconductors as shown in Fig. 1. The results of investigation have been shown that their content increases as Jc value are increased and as a function of Jc as shown in Fig. 2.
Short-range order in amorphous FeTb
Authors: Tewes M. , Zweck J. , Hoffmann H.
Published: June 2020

The importance of amorphous rare-earth/transition-metal (Re-TM) alloys for use as magneto-optic (MO) storage media has been shown first in 1973. First atomic structural data of amorphous Fe2Tb were given in 1974 and compared with those of a crystalline counterpart, which is the well-known Laves phase. Significant differences of short range order (sro) in amorphous and crystalline Fe2Tb have been found. Similiar results were given in 1986 for a composition Fe79Tb21, to be used for MO-recording.

In this work we present pair distribution functions (PDF’s) determined from electron diffraction data for amorphous FeTb alloys. It has been shown that Fourier transformation of the experimental observed diffraction intensities gives the original infinite lattice of an investigated (crystalline) specimen multiplied by its selfcorrelation-function. Therefore the PDF approaches zero for r-values greater than the distance ro representing the mean dimension of a crystal.
Modulated structure of Laves phase in a cast Mg-Zn-RE alloy
Authors: Wei L. Y. , Dunlop G. L.
Published: June 2020

Comparison of the two SAED patterns (Fig.l) obtained from Laves phase in Mg-9Zn and Mg- 8Zn-1.5RE (RE: rare earth additions made by adding misch metal), shows that the small amount of rare earth additions has a considerble influence on the crystal structure of this phase. The diffraction features suggest that the crystal structure of the Laves phase in the Mg-Zn-RE alloy is modulated by planar translation interfaces which are equivalent to a uniform sequence of antiphase boundaries (APBs) in a long period superstructure. From the splitting distance of the superlattice spots as illustrated in the schematic diagram in Fig. 1(c), the mean half period, which is measured in units of (100) interplanar spacings, is M ≈ 4.86. As shown by Van Dyck et al. the superstructure reflections (or the satellites of the basic spots) of a periodic APB structure are peaked at positions given by: g' = g - (1/d)(m - g.R),
Microstructure of materials
Authors: Nordén Hans
Published: June 2020

The systematic development of materials with controlled properties has always proceeded in hand with the study of their microstructure and composition. The development of modem analytical and microscopic techniques with improved spatial resolution has permitted more and more detailed information to be obtained. In order to fully characterize a microstructure it is often necessary to extract information on both a nanometer and a μm scale so it is advantageous to apply a combination of microscopic and microanalytical techniques.

The range of topics covered by the tide of this talk is obviously too wide to be included in a short overview and the main emphasis will therefore be on a few example where a combination of analytical methods have been used to reach a better understanding of complex problems in materials science.
CBED analysis of impurity distributions in AlN
Authors: Callahan Daniel , Thomas G.
Published: June 2020

Oxygen impurities may significantly influence the properties of nitride ceramics with a strong dependence on the microstructural distribution of the impurity. For example, amorphous oxygen-rich grain boundary phases are well-known to cause high-temperature mechanical strength degradation in silicon nitride whereas solutionized oxygen is known to decrease the thermal conductivity of aluminum nitride. Microanalytical characterization of these impurities by spectral methods in the AEM is complicated by reactions which form oxygen-rich surface phases not representative of the bulk material. Furthermore, the impurity concentrations found in higher quality ceramics may be too low to measure by EDS or PEELS. Consequently an alternate method for the characterization of impurities in these ceramics has been investigated.

Convergent beam electron diffraction (CBED) is a promising technique for the study of impurity distributions in aluminum nitride ceramics. Oxygen is known to enter into stoichiometric solutions with AIN with a consequent decrease in lattice parameter.
Factors affecting microstructural scale in liquid crystalline polymers
Authors: Dannels Christine M. , Viney Christopher
Published: June 2020

Processing polymers from the liquid crystalline state offers several advantages compared to processing from conventional fluids. These include: better axial strength and stiffness in fibers, better planar orientation in films, lower viscosity during processing, low solidification shrinkage of injection moldings (thermotropic processing), and low thermal expansion coefficients. However, the compressive strength of the solid is disappointing. Previous efforts to improve this property have focussed on synthesizing stiffer molecules. The effect of microstructural scale has been overlooked, even though its relevance to the mechanical and physical properties of more traditional materials is well established. By analogy with the behavior of metals and ceramics, one would expect a fine microstructure (i..e. a high density of orientational defects) to be desirable.

Also, because much microstructural detail in liquid crystalline polymers occurs on a scale close to the wavelength of light, light is scattered on passing through these materials.
Microstructure and composition of lead-magnesium-niobate ceramics by Transmission Electron Microscope
Authors: Yegnasubramanian S. , Ling H. C.
Published: June 2020

Ceramic dielectrics in the PbO-MgO-Nb2O5 based system, have been extensively investigated for their use in the capacitor industry. Effects of dopants on the dielectric properties of this class of materials have been also studied in detail in the literature. A TEM investigation of a ceramic piezoelectric material, lead zirconate titanate (PZT) sintered with 3 weight% excess of PbO, revealed an amorphous boundary layer showing a higher lead content than the bulk material. A detailed SEM and TEM study of Ca and Nb doped barium titanate ceramics has been reported which unambiguously identifies the different ferroelectric domain boundaries in this class of ceramics. Compositional determination of the pyrochlore phase in a lead magnesium niobate (PMN) ceramic led to a chemical formula of Pb2Nb1.75 Mg0.25O6.62.
Locating Al in the DABCO catalyst before and after Al extraction
Authors: Reuter Kathleen B.
Published: June 2020

The reaction rate and efficiency of piperazine to 1,4-diazabicyclo-octane (DABCO) depends on the Si/Al ratio of the MFI topology catalysts. The Al was shown to be the active site, however, in the Si/Al range of 30-200 the reaction rate increases as the Si/Al ratio increases. The objective of this work was to determine the location and concentration of Al to explain this inverse relationship of Al content with reaction rate.

Two silicalite catalysts in the form of 1/16 inch SiO2/Al2O3 bonded extrudates were examined: catalyst A with a Si/Al of 83; and catalyst B, the acid/phosphate Al extracted form of catalyst A, with a Si/Al of 175. Five extrudates from each catalyst were fractured in the transverse direction and particles were obtained from the fracture surfaces near the center of the extrudate diameter. Particles were also obtained from the outside surfaces of five extrudates.
Effect of finite volume on core loss fine structure in small particles
Authors: Batson P.E. , Bruley J. , Dori L.
Published: June 2020

During the past several years, experimental and theoretical results have established that collective excitations in the low energy loss region are affected strongly by the relative size and geometry of the probe and the probed volumes. Non-dipole transitions have also been found to play an important part. In contrast, core loss scattering has been shown to be dominated by dipole excitations to localized final states showing little sensitivity to nearby surfaces. Thus, quantitative elemental concentrations may be obtained from simple intensity sums.

We now have electron spectrometers which are capable of obtaining the near edge fine structure in the STEM. In large volumes the results are still explained by the standard theory. In small volumes, however, the near edge results are quite different.
Temperature dependence of cellular growth front faceting in Cu—4%Ti
Authors: Fonda R.W. , Shiflet G.J.
Published: June 2020

The growth front of the cellular (discontinuous) precipitation reaction has long been considered to be a disordered, incoherent interface. In our investigation into the extent of the role of crystallography in this transformation we have observed structures at the growth front that are not in full agreement with this opinion. This paper will discuss these structures as well as their variation with changes in temperature.

The alloy used in this investigation, Cu—4 wt% Ti, is fcc (α’) at high temperatures and decomposes discontinuously below ∼745° C to a less saturated fcc phase (α) and an ordered orthorhombic phase (β) of formula Cu4Ti. It was prepared by induction melting high purity materials, homogenizing, then rolling to 50%, followed by a solutionization at 900° C and isothermal heat treatment at 740° C for 1 h or at 690° C for 30 min.

Examination of a typical cellular reaction front formed at 740° C (Figure 1) shows strongly faceted interfaces between the Cu4Ti precipitates and the supersaturated matrix. Each facet along the growth front is in a parallel direction, which implies that there is a crystallographic habit plane between these two phases.
Quasiperiodic interfaces: HREM observations of grain and phase boundaries
Authors: Merkle K. L.
Published: June 2020

The atomic structures of internal interfaces have recently received considerable attention, not only because of their importance in determining many materials properties, but also because the atomic structure of many interfaces has become accessible to direct atomic-scale observation by modem HREM instruments. In this communication, several interface structures are examined by HREM in terms of their structural periodicities along the interface.

It is well known that heterophase boundaries are generally formed by two low-index planes. Often, as is the case in many fcc metal/metal and metal/metal-oxide systems, low energy boundaries form in the cube-on-cube orientation on (111). Since the lattice parameter ratio between the two materials generally is not a rational number, such boundaries are incommensurate. Therefore, even though periodic arrays of misfit dislocations have been observed by TEM techniques for numerous heterophase systems, such interfaces are quasiperiodic on an atomic scale. Interfaces with misfit dislocations are semicoherent, where atomically well-matched regions alternate with regions of misfit. When the misfit is large, misfit localization is often difficult to detect, and direct determination of the atomic structure of the interface from HREM alone, may not be possible.
Effect of crystal and beam tilt on simulated high-resolution TEM images of interfaces
Authors: Howe J.M. , Rozeveld S.J.
Published: June 2020

It is well known that only a few milliradians of crystal or beam tilt can produce image artifacts in HRTEM images of perfect crystals. One important application of HRTEM is for determining the atomic structures of interfaces. While it is intuitive that alignment of an interface parallel to the electron beam should be critical for obtaining reliable HRTEM images of interfaces, a systematic study of the effects of crystal and beam tilt on HRTEM images of interfaces has not been performed.

In this investigation, the effects of crystal and beam tilt on HRTEM images of planar, coherent interfaces were determined by multislice image simulations. Interfaces in metallic systems ranging from simple twin boundaries in f.c.c. Al and b.c.c. Ti to relatively complex interphase boundaries between ordered h.c.p. and b.c.c. phases in the Ti-Al system were examined and compared. Although this study was limited to coherent interfaces, similar effects are expected to occur in comparable nonmetallic systems such as semiconductors and ceramics and for less coherent interfaces as well.
Grain boundary structure of A ZnO-Bi2O3-CoO varistor
Authors: Suyama Yoko , Tomokiyo Yoshitsugu , Terasaka Kunihiro
Published: June 2020

The nonhomic property of ZnO-based varistors has been considered to depend on grain boundary structures. The microstructures of ulticomponent varistors are very complicated and quite sensitive to concentration and thermal history. It is not clear which microstructures play an important role for the electrical properties such as nonlinear coefficient and varistor voltage, and for the degradiation. In the present paper the microstructure of ZnO varistor was investigated by means of analytical electron microscopy to elucidate the relation between the microstructures and the electrical properties. In order to obtain local information on the microstructures of grain boundary and multiple junction, we combined the various TEM techniques such as high-resolution imaging (HREM), microprobe diffraction (μ ED), convergent-beam electron diffraction (CBED) and energy dispersive x-ray spectroscopy (EDX).

ZnO varistor samples with addition of 0.5molZ% Bi2O3 + 0∼0.5molZ% CoO were prepared by conventional mixed-oxide ceramic technology. The thin foils prepared from the samples sintered at 800, 900 and 1000 °C were examined either by an analytical TEM, JEM-2000FX at 200 kV or a high resolution TEM, JEM-4000EX at 400 kV. The diameters of electron probe were less than 10 nm for μ ED and about 20 nm for EDX and 10∼20 nm for CBED.
The behavior of an α-alumina twist grain-boundary in the presence of silica
Authors: Maggard Jeffrey G. , David Theodore N. , Barry Carter C.
Published: June 2020

Grain boundaries and polyphase boundaries can control the electrical, optical, and mechanical properties of many ceramic materials. The study of such boundaries is therefore essential for understanding these materials. Some studies of grain boundaries in alumina have reported a thin layer of amorphous intergranular material coating nearly all boundaries while others question this interpretation. The quality and structure (crystalline or amorphous) of an intentionally-added siliceous intergranular phase has been found to affect the mechanical properties of polycrystalline α-alumina and tetragonal zirconia. It is therefore of interest to examine the behavior of various α-alumina grain boundaries in the presence of controlled amounts of amorphous silica. A recent study characterized the behavior of low-angle [0001] twist boundaries in the presence of silica which had been intentionally incorporated during the course of grain boundary fabrication. The present study is aimed at characterizing the behavior of low-angle rhombohedral (102) twist boundaries under similar conditions.

Single crystal wafers of α-alumina were mechanically polished parallel to the (102) plane. Silica was deposited to a thickness of 260Å on one of the wafers using plasma deposition. The silica-coated wafers were then placed face-to-face with clean, uncoated wafers and pressure-sintered at 1980°C for 3 hours. The temperature was chosen to lie above the melting point of silica and below that of alumina. A low pressure (∼50 psi) was used to hold the wafers together. The pressure and furnace heating and cooling cycles had to be carefully controlled to prevent fracture of the crystals.
High-resolution Z-contrast imaging in the STEM
Authors: Pennycook S. J. , Jesson D. E. , Chisholm M. F.
Published: June 2020

With a high-angle annular detector in a STEM, incoherent imaging can be realized at atomic resolution. This provides improved image resolution, from 0.66 CS¼λ¾ to 0.43 CS¼λ¾, based on the Scherzer definition of point-to-point resolution, although in both cases finer scale detail can be transmitted to the image at higher defocus values. Equally important, the incoherent mode provides a simply interpretable image; no contrast reversals occur with defocus or sample thickness, no Fresnel fringe effects are seen at interfaces and no speckle pattern is seen within an amorphous phase. In addition, the high-angle (Rutherford) scattering imparts a strong compositional sensitivity to the image through the practically Z2 dependence of the cross section.

How these effects occur have been discussed in detail elsewhere. The three components of high-angle scattering for a zone axis orientation are the HOLZ reflections, the zero layer reflections, and the thermal diffuse (Rutherford scattering) component. The contribution of the HOLZ is simple to estimate experimentally in selected area diffraction, either from bright field line traces or from the high-angle channeling pattern, which is obtained from the annular detector (Fig. 1). A HOLZ reflection would be visible in the center of the channeling pattern only if its intensity was greater than the total diffuse scattering reaching the annular detector.
Is there a non-channeling orientation?
Authors: Eades J. A. , Christenson K. K. , Andreessen M. L.
Published: June 2020

In the standard form of ALCHEMI, the aim is to calculate the fraction of an impurity that is substitutional on each different sublattice of the host crystal. The result is calculated from the ratios of the of the intensities of the x rays emitted by the elements present. The ratios vary as a function of the angle of the incident electron beam because of electron channeling in the crystal structure. The channeling has the effect of making the electron density different in different parts of the unit cell. If the x-ray yield of one element goes up, the electron yield of any other element on the same sites (i.e. the same sublattice) in the crystal structure will go up in the same proportion. This variation can be used to calculate the fraction on each site.

The calculation requires the measurement of the x-ray ratios at at least one angle with a strong channeling effect but also requires the measurement of the ratios at a condition of the incident beam that is “nonchanneling”, that is when the electron flux is uniform across the unit cell.
Understanding crystal bonding: The contribution of electron diffraction
Authors: Fox Alan G. , Tabbenor Mark A. , Fisher and Robert M.
Published: June 2020

Some of the most incisive information about bonding mechanisms in materials can be obtained from accurate X-ray crystal structure factors and Debye-Waller factors. This has long been known by diffraction workers in all fields, and in the last twenty years intensive efforts have been made to accurately measure structure factors by a variety of means. At the same time theoreticians have made progressively more sophisticated band structure calculations of structure factors (usually of cubic elements). Three experimental methods have emerged as being able to determine structure factors with the required accuracy for crystal bonding studies:- these are (i) X-ray Pendellosung methods (see e.g. 1 and 2) (ii) Gamma-ray diffraction (see e.g. 3) and various electron diffraction techniques (see e.g. 4 to 6). The best accuracy possible with all three methods is around 0.1%.

The potential of electron diffraction for the accurate measurement of low-angle structure factors was first recognised in the late sixties by Goodman and Lehmfuhl (convergent beam-rocking curve method), Gjonnes and Hoier (intersecting Kikuchi line, IKL, method) and Nagata and Fukuhara (critical voltage, Vc, technique).
The use of charging effects in Al/Al2O3 metal matrix composite materials as contrast mechanism in the SEM
Authors: Borchert Andreas M.
Published: June 2020

In Al/Al2O3 MMC's the metal/ceramic interfacial structure is of great concern because aluminum does not wet (i.e. bond) well to alumina. One proposed method to overcome this problem is to form a magnesium-rich spinel (MgAl2O4) as an additional phase between the aluminum matrix and the alumina particle. The spinel forms by diffusion of Mg from the matrix and improves the bonding. Typically the SEM would be the most suitable instrument to study the spinel, but this particular material combination (alumina/spinel) does not have sufficient secondary or backscattered electron contrast to allow for normal imaging. The purpose of this work was to develop a technique for examining the growth and morphology of this spinel at the Al/Al2O3 interface. Samples of an Al/Al2O3 MMC with a spinel at the particle interface were prepared according to standard metallographic procedures. Certain samples were sputter coated with a gold film of approximately 12 nm thickness; other samples were examined uncoated. Nonconductive, uncoated specimens charge under the incident electron beam if the accelerating voltage is below E1 or above E2 in Figure 1. In both of cases (below E1 and above E2) the number of electrons entering the sample is higher than the number of electrons leaving the sample. The resolving power of the SEM is usually degraded by this effect and therefore nonconductive specimens are coated with a layer of conductive material prior to observation. Figure 2 shows how this effect can create contrast between two materials due to its effect on the secondary electron detector bias voltage. Figure 3 shows that this contrast mechanism exists for the material combination alumina/spinel. The secondary electron image of a coated sample (3a) shows almost no contrast between alumina and spinel whereas the uncoated sample (3b) shows good contrast due to the different charging characteristics of the materials. The alumina charges stronger than the spinel and appears brighter in the image. The assumption that the effect is due to secondary electrons is supported by Figure 4. The micrograph in Figure 4a was obtained by backscattered electrons only and shows poor contrast whereas the micrograph in Figure 4b was obtained by secondary and backscattered electrons and shows good contrast. Figure 5 shows micrographs obtained at different operating voltages. The reduction in contrast at lower operating voltages is due to reduced charging.
Characterization of submicrometer fluid Inclusions in minerals by Analytical/Transmission Electron Microscopy and electron diffraction
Authors: Guthrie George , Veblen David
Published: June 2020

The nature of a geologic fluid can often be inferred from fluid-filled cavities (generally <100 μm in size) that are trapped during the growth of a mineral. A variety of techniques enables the fluids and daughter crystals (any solid precipitated from the trapped fluid) to be identified from cavities greater than a few micrometers. Many minerals, however, contain fluid inclusions smaller than a micrometer. Though inclusions this small are difficult or impossible to study by conventional techniques, they are ideally suited for study by analytical/ transmission electron microscopy (A/TEM) and electron diffraction. We have used this technique to study fluid inclusions and daughter crystals in diamond and feldspar.

Inclusion-rich samples of diamond and feldspar were ion-thinned to electron transparency and examined with a Philips 420T electron microscope (120 keV) equipped with an EDAX beryllium-windowed energy dispersive spectrometer. Thin edges of the sample were perforated in areas that appeared in light microscopy to be populated densely with inclusions. In a few cases, the perforations were bound polygonal sides to which crystals (structurally and compositionally different from the host mineral) were attached (Figure 1).