bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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).
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).
Light-cured dental composites characterization by Electron Microscopy
Authors: Culbertson B. M. , Devinev M. L. , Kao E. C. 
Published: June 2020

The service performance of current dental composite materials, such as anterior and posterior restoratives and/or veneer cements, needs to be improved. As part of a comprehensive effort to find ways to improve such materials, we have launched a broad spectrum study of the physicochemical and mechanical properties of photopolymerizable or visible light cured (VLC) dental composites. The commercially available VLC materials being studied are shown in Table 1. A generic or neat resin VLC system is also being characterized by SEM and TEM, to more fully understand formulation variables and their effects on properties.At a recent dental research meeting, we reported on the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) characterization of the materials in Table 1. It was shown by DSC and DMA that the materials are substantially undercured by commonly used VLC techniques. Post curing in an oral cavity or a dry environment at 37 to 50°C for 7 or more hours substantially enhances the cure of the materials.
Contrast symmetry and defect identification
Authors: Skalicky P. 
Published: June 2020

Although the symmetry of the diffraction contrast of defects has received the attention of several authors already some time ago, symmetry rules are mainly based on geometrical arguments without solid proof for their validity in the general case. The symmetry of the diffraction contrast depends on the symmetry of the displacements and on the symmetry of the diffraction conditions (which of course follows from Neumann’s principle). General proofs for thee symmetry of dislocation contrast are given in this paper.The diffraction contrast of a dislocation (or any number of parallel straight dislocations) which are inclined with respect to the surface of the foil and therefore show the so called “oscillating contrast” can only exhibit one of a limited number of symmetries.(SAL): symmetry along the (projected) line of the dislocation(SAM): symmetry about midfoil(SAC): symmetry about center
Calculations and experimental observations of shadow images from multilayers
Authors: Wang Shiyao , Gajdardziska-Josifovska M. , Cowley J.M. 
Published: June 2020

The properties of multilayer thin film materials are strongly influenced by the structure of their interfaces. The numerous applications for these materials motivate electron microscopy studies of cross sectional samples in which the interfaces are observed edge on. High resolution imaging is the most established technique, but other techniques, such as Fresnel fringe method and refraction at interfaces, have also been employed to characterize the structure and abruptness of amorphous/polycrystalline multilayers. The aim of this work is to explore the applicability of shadow images from coherent sources to the studies of multilayers.Coherent interference effects are readily observable in the diffraction plane of a VG HB-5 STEM which is equipped with a cold field emission gun. The shadow image of the studied Si/Mo multilayer is obtained on the detection plane when the specimen is illuminated by a stationary convergent beam. This beam is formed with a very large or no objective aperture. Low magnification images are produced at large values of defocus (Fig. 1a), while for lower defocus the magnification increases and the shadow images become more and more distorted because of the objective lens aberration (Fig. 1b and 1c). In addition to the high sensitivity to the defocus. spherical aberration and probe position, the shadow images also appear to be dependent on the interface abruptness.
Fresnel fringe effects at interfaces of thin multilayer structures
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B. 
Published: June 2020

Recent developments in the TEM Fresnel-fringe technique have provided an alternative method to the determination of structures and morphology of interfaces in multilayer thin film structures. This method has been employed in the investigation of structures and defects in grain boundaries, dislocations, precipitate platelets, twin boundaries, metal interfaces, and multilayer structures. It has been demonstrated that the fringe spacing primarily relates to the layer thickness, while the fringe contrast as a function of defocus relates to the magnitude of the localized change in the scattering potential and thus to the interfacial composition. The profile of the fringes is more closely related to the abruptness of the composition change at the interface. Other factors affecting the Fresnel fringe intensity are the specimen thickness, aperture size, beam convergence, and degree of tilt of the interface from the incident electron beam.Fresnel fringes result from the electrons experiencing an abrupt change in the inner scattering potential parallel to the electron beam path. Most previous calculations of the Fresnel contrast with defocus have simulated models based on one square or symmetrical trapezoid-shaped potential well, which are applicable only to a single interface or grain boundary, or to a few layer pairs of the multilayer.
A SISF formation mechanism in Ni3Al
Authors: Lin Dongliang , Hen Mao 
Published: June 2020

In the ordered Ll2 structure, the superlattice intrinsic stacking fault (SISF) has often been observed to be formed through two steps, the formation of antiphase boundary (APB) by dissociation of superlattice dislocation at first and then the conversion of the APB to the SISF(1,2). The present paper studied the SISF in NijAl by TEM and found that the SISF can also be formed by superlattice dislocation dipoles.The tensile deformation of the directionally solidified Ni3Al (of composition in wt% of 82.88Ni, 8.5A1, 0.8Zr, 7.8Cr, and 0.02B) specimens was performed at room temperature. Thin foils were made normal to the specimen axis (parallel to [001]) and studied at 200 kv in H-800.As shown in Fig.l, a SISF is formed at the end of a superlattice dislocation dipole, according to the SISF-type dissociation [10] =1/3 [11]+1/3[2l] on (111) plane. In Fig.2, a superlattic dislocation dipole is moving away from a SISF.