bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural changes of Pt/Ti electrodes in an oxygen ambient
Authors: Park K. H. , Kim C. Y. , Lee J. S. , Kim K. Y. , Jeong Y. W. , Kwon H. J. , Kim S. T.
Published: June 2020

The stability of bottom electrodes during annealing in oxidation environments is crucial for the fabrication of ferroelectric capacitors. The Pt/Ti bilayer has received attention as a promising electrode for Si-based devices. The Ti buffer layer is necessary not only to improve the adhesion of Pt to dielectrics but also to prevent the formation of Pt silicides at high temperatures. When the Pt/Ti electrodes are exposed to O2 atmosphere during heat treatment, the oxidation induced diffusion of Ti into Pt and the oxidation of Ti are observed. In spite of previous researches, the microstructural features of the Pt/Ti bilayers in oxygen ambients have not been cleared up yet. In this study, combined techniques of transmission electron microcopy(TEM), scanning electron nucroscopy(SEM), and Auger electron spectroscopy(AES) have been applied to clarify the correlation between the interdiffusion of Pt/Ti/O and the microstructural evolution.

The chosen system was Pt/Ti/SiO2/Si. The electrode of 80 nm thick Pt was dc-sputter deposited on the 70 nm thick Ti adhesion layer. The Si substrate wafers were covered with 750 nm thick thermally grown oxides. Heat treatments at various temperatures were performed in an oxygen ambient for 30 min.
Facet crystallography of fractured V(2.7 wt% Si) solid solution
Authors: Sutliff J. A. , Bewlay B. P. , Henshall G. A. , Strum M. J.
Published: June 2020

V-Si binary alloys have been investigated as model high temperature alloys. Alloys with compositions between ~4 and 11 wt% Si can be fabricated as in-situ composites composed of the intermetallic V3Si phase and the V(Si) solid solution phase with a eutectic temperature of ~1870°C. The V(Si) phase is thought to be a ductile phase which provides toughness to the composite. We have previously reported on the fracture toughness of V-Si alloys.

In this paper we present results on the fracture surface fractography and fracture facet crystallography of an arc-melted V(2.7 wt% Si) solid solution alloy fractured in bending. Figure 1 is a low magnification SEM micrograph of the surface of one half of a fractured bend bar. Many macroscopically flat facets can be seen and those for which crystallographic analysis was done have been labeled. Actually, the macro-facet surface as seen at higher magnification exhibits significant morphological structure, as can be observed in Figure 2 which shows detail of the facet labeled k.
Observation of solid-state reaction between a thin yttria film and a (0001) α-alumina substrate
Authors: Heffelfinger J. R. , Carter C. B.
Published: June 2020

Transmission-electron microscopy (TEM), scanning-electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to investigate the solid-state reaction between a thin yttria film and a (0001) α-alumina substrate. Systems containing Y2O3 (yttria) and Al2O3 (alumina) are seen in many technologically relevant applications. For example, yttria is being explored as a coating material for alumina fibers for metal-ceramic composites. The coating serves as a diffusion barrier and protects the alumina fiber from reacting with the metal matrix. With sufficient time and temperature, yttria in contact with alumina will react to form one or a combination of phases shown by the phase diagram in Figure l. Of the reaction phases, yttrium aluminum garnet (YAG) is used as a material for lasers and other optical applications. In a different application, YAG is formed as a secondary phase in the sintering of AIN. Yttria is added to AIN as a sintering aid and acts as an oxygen getter by reacting with the alumina in AIN to form YAG.
Characterization of macro-defect-free processing in a Banburry-type mixer
Authors: Gulgun M. A. , Kriven W.M.
Published: June 2020

Macro-defect-free cement (MDF) is a composite material consisting of a tightly bound network of inorganic calcium aluminate (CA) cement grains embedded in an polyvinyl alcohol (PVA) organic matrix. The standard composition starts with a mixed batch made of 83.8 wt% CA, 5.9 wt% partially hydrolyzed PVA, 9.6 wt% water and 0.6 wt% glycerine. The damp powder is further shear-mixed in a Banburry type mixer. During this step, the mix converts into a dough-like, viscoplastic paste which further can be processed by extrusion or molding to a desired shape. Viscoplastic paste formation is a crucial stage in processing and results from mechano-chemical (i.e. mechanically assisted) reactions between the polymer and the hydrating cement phases. The viscoplastic flow is only observed within a certain processing time interval, i.e. window of processability (Regions II and III in Fig. 1). Prolonged shear mixing reverts the system back into a friable, powdery mass. The rheology of the composite paste is monitored in terms of the torque required to flow the mix at a constant rpm.
Beam damage induced “Si flower” in SiO2
Authors: Lee Tan-Chen , Silcox John
Published: June 2020

100 keV electron beams can damage and even cut holes in specimens. It is of great concern for analytical electron microscopy because the damage may result in a change in chemical composition of the irradiated area. During irradiation, low-Z elements tend to be removed faster than the high-Z ones thus leaving a “heavier” substrate. Sometimes, beam damage can not be “seen” via contrast change either in BF (bright field) or ADF (annular dark field). However, it can be observed in the Si first plasmon energy selected image reported in this paper. This image also provides evidence that the oxygen diffuses from the undamaged area to the damaged area.

The experiment was carried out in a VG HB501A STEM which is equipped with EELS and a windowless X-ray detector. A sample with a 5200 Å-thick SiO2 film grown on a Si substrate was used in this study. It is found from X-ray analysis that there are only Si, O and a very small amount of S.
The formation of ω-Zr during the oxidation of Zircaloy-4
Authors: Foord D. T. , Newcomb S. B.
Published: June 2020

The stability of the oxide scales formed on zirconium alloys has added to the attractiveness of their use as fuel cladding and pressure tubes in nuclear reactors. Under some conditions, however, the oxides have been found to undergo changes in either their passive rate of growth or their ability to act as hydrogen diffusion barriers. The mechanisms of the oxidation processes thus need to be determined if these types of behaviour changes are to be avoided and the in-reactor use of the alloy optimised. We have therefore been examining the microstructural development of the scales formed under a variety of conditions and here describe our cross-sectional TEM observations of some of the changes which occur during the oxidation of Zircaloy-4 in pure oxygen at 500°C. A knowledge of the metal-oxide interface microstructure has been found to be particularly useful for following the historical development of the oxide scale and determining how changes in the oxidation process can be initiated but it requires an accurate determination of the lattice parameters of the different phases which can be formed.
Characterization of the oxidation and oxidation-sulfidation of chromium niobium alloys
Authors: Duncan J. C. , Touryan L. , Hobbs L. W.
Published: June 2020

Materials in mixed corrosion environments, such as those in coal gasification processes or other energy conversion systems, may be exposed to both oxygen and sulfur. Alloys that exhibit simultaneous oxidation and sulfidation resistance are sought for these applications. Alloys containing sufficient Al or Cr readily form a protective oxide scale but generally have high sulfidation rates. Refractory metals, such as Nb or Mo, form protective sulfides but oxidize at catastrophic rates. Materials containing additives of one of these groups have been studied for their complex corrosion resistance. A binary alloy containing components from each group (Cr and Nb) has been investigated in mixed oxidants .

Isothermal thermogravimetric measurements give overall scale growth kinetics but do not give details for complex scales or substrates. Multiple layers, different growth regimes and preferential corrosion can complicate interpretation. The environmental SEM with a hot stage attachment allows the observation of scale development at temperature.
Dislocation dissociation in Ll2 ordered alloy Ni3Ge
Authors: Fang J. , Schulson E. M. , Baker I.
Published: June 2020

It is well established that the yield stress of Ni3Ge anomalously increases with increasing temperature from 77 K to 673 K. Above room temperature, the anomaly is generally attributed to the Kear-Wilsdorf (K-W) mechanism. Since no parallel systematic TEM investigation has been performed to characterize the dislocation structures in Ni3Ge, it is not clear whether the yield stress anomaly below room temperature is governed mainly by the K-W mechanism or by other mechanism(s). Thus, detailed TEM characterization of dislocation dissociation has been carried out in polycrystalline Ni3Ge deformed at room temperature. In this report, we briefly describe the main results obtained. The complete analysis can be found elsewhere.

The deformation structure mainly consists of apparently undissociated dislocations with Burgers’ vector parallel to a<110> and of SISF (super intrinsic stacking fault)-coupled partials. Fig. 1 shows an example of SISF dissociation. First, consider dissociation of a perfect dislocation into partials 1 and 2.
A TEM study of the effect of oxygen on nanocavity formation and precipitation in rapid - solidified Fe-16Ni-9Cr stainless steels
Authors: Wisutmethangoon S. , Kelly T. F. , Flinn J.E.
Published: June 2020

Vacancies are introduced into the crystal phase during quenching of rapid solidified materials. Cavity formation occurs because of the coalescence of the vacancies into a cluster. However, because of the high mobility of vacancies at high temperature, most of them will diffuse back into the liquid phase, and some will be lost to defects such as dislocations. Oxygen is known to stabilize cavities by decreasing the surface energy through a chemisorption process. These stabilized cavities, furthermore, act as effective nucleation sites for precipitates to form during aging. Four different types of powders with different oxygen contents were prepared by gas atomization processing. The atomized powders were then consolidated by hot extrusion at 900 °C with an extrusion ratio 10,5:1. After consolidation, specimens were heat treated at 1000 °C for 1 hr followed by water quenching. Finally, the specimens were aged at 600 °C for about 800 hrs. TEM samples were prepared from the gripends of tensile specimens of both unaged and aged alloys.
Microstructural characterization of a Cr2Nb-Nb(Cr) microlaminate composite
Authors: Larsen M. , Rowe R. G. , Skelly D. W.
Published: June 2020

The thrust to weight ratio of an aircraft engine is limited by the density and elevated temperature performance of high temperature structural materials. Many material systems are currently under investigation as potential next generation engine materials. Microlaminate composites consisting of alternating layers of a ductile refractory metal for toughening and a high temperature intermetallic compound for elevated temperature strength have applicability in aircraft engine turbines. The lamellar thickness of such a composite must be small because the intrinsic defect size, a crack across the intermetallic layer, will be controlled by the intermetallic layer thickness. The microstructural characterization of a Cr2Nb-Nb(Cr) microlaminate composite produced by Magnetron® sputtering was carried out by cross-sectional TEM. Both the as-deposited composite and one heat treated at 1200°C for two hours were examined.

Figure 1 shows a micrograph of the as-deposited composite. The metal and intermetallic layers are 2um thick. The metal layer has a composition in atomic percent of 95% Nb and 5% Cr.
Structure of Σ7 grain boundary in Al2O3
Authors: Chu C. C. , Chen F.-R. , Wang C.-Y. , Chang L.
Published: June 2020

In the past, extensive high resolution electron microscopy has been applied to the atomic structure of grain boundaries of cubic symmetry. In order to have a better understanding of generalization of the grain boundary theory, it could be fruiful to study grain boundary structure of non-cubic and low symmetry crystals in which case the exact CSL’s may not exist. Al2O3 has a hexagonal crystal structure ( non-cubic). In the case of hexagonal crystals, three dimensional coincidence site lattices (CSL’s) are only possible for rational values of (c/a), except for rotations about the [0001] axis. The (c/a) of α-Al2O3 is very close to a rational number (15/2) such that constrained coincidence-site lattice (CCSL) misorientations can be found. In this research, we study the atomic structure of Σ7 grain boundary. The misonentation of Σ7 is [011]/180°. The bicrystals of Σ7 were made by diffusion bonding in high temperature and high vacuum.

Figs. 1 (a) and (b). show typical HRTEM images of Σ7 Al2O3 boundary recorded at the underfocus values -48 nm and -96 nm, respectively. The beam direction is parallel to a common axis [20].
Atomic faceting NiSi2/Si interfaces
Authors: Chen F.-R. , Chen W. J.
Published: June 2020

Sutton et al and Brokman et al suggested that long period asymmetrical boundary may facet on an atomic scale into short period symmetrical boundaries. This principle was first confirmed in the case of Σ=3 NiSi2(11)1/(15)2 and NiSi2(001)1/(21)2 asymmetrical boundaries in NiSi2 thin film by Chen et al using high resolution TEM. The asymmetrical boundaries contain a mixture of structural units of the (1)1/(11)2 and the (12)1/(12)2 symmetrical boundaries. The structural units of the (1)1/(11)2 is a 6-atom ring, while (12)1/(12)2 boundary has composite 5 and 7-atom rings. This result is consistent with the chain unit model (CUM) proposed by Wang and Vitek which describes the variation of the boundary structure with the inclination of the boundary plane.

The principle of CUM was shown to be valid in the Σ=3 NiSi2(11)/(15)Si and NiSi2(21)/(001)Si asymmetrical interfaces. There are four possible atomic faceting structures for an asymmetrical interface. Fig. 1(a) shows the coexistence of two atomic faceting interfacial domains in a NiSi2(11)/(15)Si interface.
Measuring projected potential, thickness, and composition from lattice images
Authors: Ourmazd A. , Schwander P. , Kisielowski C. , Baumann F. H. , Kim Y.
Published: June 2020

Lattice images obtained by Transmission Electron Microscopy (TEM) are routinely used to infer the subsurface microstructure of crystalline materials. In principle, a lattice image is a map of the sample (Coulomb) potential, projected along a zone axis (see, e.g., [1]). In practice, it is difficult to extract quantitative information from lattice images. This stems from two primary reasons. First, electrons are multiply scattered during their passage through crystalline samples of realistic thickness (>10Å). This results in a complex, highly nonlinear relationship between the sample potential and the characteristics of the lattice image. This relationship changes rapidly with the sample thickness, and thus from point to point over the sample. Second, electromagnetic lenses have severe aberrations. The image details thus depend sensitively on the (contrast) transfer function of the microscope, and hence the lens defocus. It is not possible to establish a general relationship between the sample potential and the image features.
HREM imaging of PtSn4/PtSn2 interfaces in Pt-Sn thin films
Authors: Dufner D. C.
Published: June 2020

High resolution electron microscopy (HREM) is a very useful technique for studying intermetallic alloy formation resulting from the interdiffusion of metals in thin films. In this work, reactions between Pt and Sn thin films are studied to elucidate mechanisms for structural and compositional changes during the interdiffusion process.

Thin film specimens are prepared by the two-film method introduced by Shiojiri et al. Approximately 50 nm of Pt are vacuum-deposited onto holey carbon films mounted on 3mm diameter TEM grids. Sn films with an average thickness of 20 nm are created by evaporating Sn at rates of 1.5-3.0 nm/sec onto air-cleaved KBr substrates. The Sn films are then wet-stripped and collected on the Pt-coated holey carbon grids. A thin carbonaceous contamination layer exists between the metal films to prevent the onset of interdiffusion until the specimens are heated in situ in the TEM.

TEM observations are carried out on the JEOL 2010 200kV TEM at Texas A&M University and the JEOL 4000EX 400kV TEM at Arizona State University.
Mapping of the potential at the end of buckytubes by electron holography
Authors: Lin X. , Dravid V. P.
Published: June 2020

Measuring the surface and mean inner potential at the end of buckytubes will offer a lot of information about their physical and chemical properties. Such properties are closely related to fundamental mechanisms of the growth of the buckytubes that grow on the cathode with their axes aligned along the direction of the electric field (1), implicating the presence of the field in the formation mechanism.

Direct observations of surface and inner potential distribution at nanometer level by electron holography were reported in several cases (2). Holography is the only imaging technique that can retrieve the phase of the electron wave, which directly related to the surface and inner potential. In this contribution, electron holography was employed to obtain the mapping of the phase of the electron wave traveled through the end of nanotubes.

The holograms were recorded on negatives using a Hitachi HF-2000 with a cold emission gun, operated at 200kv.
Electron and scanning probe microscopies in the study of YBa2Cu3O7 thin-film growth
Authors: Norton M. Grant , Biggers Rand R. , Maartense Iman , Moser E. K. , Brown Jeff L.
Published: June 2020

Electron and scanning probe microscopies are used to examine the microstructure and surface topography of YBa2Cu3O7 (YBCO) thin films formed by pulsed-laser deposition (PLD). A major emphasis of this work has been the correlation of the observed microstructural features and the deposition parameters.

The formation of microscopic features on the surface of thin films deposited by PLD seems to be an undesirable and almost unavoidable feature of this process. One such feature is often associated with microstructural changes produced in the target during laser irradiation. These are apparently spherical particles with diameters ranging from 0.1 to 10μm. These particles are produced by melting of the target and the subsequent solidification of the molten ejecta. Particles may also be produced as a result of changes in the surface morphology of the target during laser irradiation. However, notall surface features observed on the films deposited by PLD are due to ejecta from the target. Figure 1 shows an atomic force microscope (AFM) image of a YBCO film grown on a (100)-oriented LaAlO3 substrate. Usually films grown with our typical deposition conditions on (100)-oriented LaAlO3 substrates arepredominantly c-axis oriented. The film is approximately 150 nm thick. Different types of outgrowth are visible on the film surface.
Extraction replicas for the analysis of second phases in nonferrous alloys using Analytical Electron Microscopy
Authors: Carpenter G. J. C. , Ng-Yelim J.
Published: June 2020

The technique for extracting second-phase particles from steels onto a carbon support film for analysis in the transmission electron microscope (TEM) has been in continuous use since its development by Bradley, nearly 30 years ago. However, the availability of EDX and EELS accessories, capable of giving chemical information, has provided an incentive for the technique to be used with other alloys.The purpose of this presentation is to review some applications of extraction replication to non-ferrous alloys.

Briefly, extraction involves chemically etching only the matrix phase of an alloysothat second-phase particles stand proud and can be extracted onto a carbon film. The most straightforward procedure is to make a single-stage direct-carbon replica, where carbon is evapourated onto the etchedsurface of a mctallographic specimen and subsequently stripped by further etching.An alternative approach is the two-stage technique, where the particles are first stripped from an etched specimen using a plastic film, e.g. cellulose acetate, such as "Bioden". The plastic surface containing theparticles is then coated with a layer of carbon, typically 10˜20nm thick, and the plastic is dissolved, leaving the particles attached to the carbon film. Although the two-stage technique involves anextra operation, it has some advantages. In particular, it is possible to strip films after differentdegrees of etching, without the necessity to re-polish the specimen. Also, with the single-stage technique, an etchant suitable for removing the replica may react so strongly that the thin carbon film breaks up during stripping.
EM of mechanical plated Zn coating on steel
Authors: Chiou W. A. , Lin C. S. , Liu P. C. , Meshii M.
Published: June 2020

Zn and Fe-Zn alloy coatings on steel have been widely used for various applications due to their excellent corrosion resistance. The coatings are usually applied by electroplating or hot-dipping in molten Zn, but the mechanical plating process has also been used commercially and has been found advantageous over the conventional coating technologies in some applications with special requirements. The recent progress in investigating mechanically alloyed metals revealed interesting structural features including the formation of nanocrystalline and amorphous structures. Since the microstructures of electroplated and hot-dipped Zn coatings have been studied, and are known to be different from those of mechanically milled, the different properties of mechanically plated coating must be due to different microstructure. As no microstructural information is available in literature, this research project has been undertaken, along with a study of mechanical properties.

Samples of commercially produced (Johnson Matthey Co.) fine-grained (325 mesh, or 44 (a.m) Zn (99.9%)flakes (1.1 μ m thick) were used as the coating materials.
Simulation and reconstruction of light-microscope images
Authors: Sheppard C. J. R. , Gu M. , Sheridan J. T. , Connolly T. J.
Published: June 2020

Simulation of light microscope image assists in interpretation and allows comparison of different imaging techniques and their associated parameters. Further, reconstruction of specimen properties from images can in some cases be feasible.

Imaging methods can be broadly divided into fluorescent and non-fluorescent techniques, the latterconsisting of brightfield transmission or reflection modes, darkfield or various phase contrast modes. The distinctive feature of these non-fluorescent modes is that they image the material properties of the specimen, including refractive index, absorption coefficient or birefringence. Sometimes the specimen is labelled with a stain, the concentration of which mirrors the concentration of a particularconstituent. In fluorescence microscopy, usually a fluorochrome is used to label particular components or constituents.

In non-fluorescent microscopy, images can be simulated using rigorous diffraction methods, such asmodal analysis or coupled wave theory. Such theories take into account multiple scattering, shadowingeffects and also depletion and aberration of the light as it penetrates the object.
Interactive multiple area spectrum integration (MASI)
Authors: Hunt John A. , Leapman Richard D. , Williams David B.
Published: June 2020

Interactive MASI involves controlling the raster of a STEM or SEM probe to areas predefined byan integration mask which is formed by image processing, drawing or selecting regions manually. EELS, x-ray, or other spectra are then acquired while the probe is scanning over the areas defined by the integration mask. The technique has several advantages: (1) Low-dose spectra can be acquired by averaging the dose over a great many similar features. (2) MASI can eliminate the risks of spatial under- or over-sampling of multiple, complicated, and irregularly shaped objects. (3) MASI is an extremely rapid and convenient way to record spectra for routine analysis. The technique is performed as follows:

Acquire reference image

Optionally blank beam for beam-sensitive specimens

Use image processor to select integration mask from reference image

Calculate scanning path for probe

Unblank probe (if blanked)

Correct for specimen drift since reference image acquisition
Effect of thermal annealing on grain boundary chemistry of polycrystalline TiBa2Ca2Cu3Oy films
Authors: Wang Z. L. , Briant C. L. , DeLuca J. , Goyal A. , Kroeger D. M. , Sutliff J. A. , Specht E. D. , Tkaczyk J. E.
Published: June 2020

Recent studies have shown that spray-pyrolyzed films of the Tl-1223 compound (TlxBa2Ca2Cu3Oy, with 0.7 < × < 0.95) on polycrystalline yttrium stabilized zirconia substrates can be prepared which have critical current density Jc near 105 A/cm2 at 77 K, in zero field. The films are polycrystalline, have excellent c-axis alignment, and show little evidence of weak-link behavior. Transmission electron microscopy (TEM) studies have shown that most grain boundaries have small misorientation angles. It has been found that the films have a nigh degree of local texture indicative of colonies of similarly oriented grains. It is believed that inter-colony conduction is enhanced by a percolative network of small angle boundaries at colony interfaces. It has also been found that Jc is increased by a factor of 4 - 5 after the films were annealed at 600 °C in oxygen. This study is thus carried out to determine the effect on grain boundary chemistry of the heat treatment.
Measurement of Debye-Waller factors of silicon as a function of temperature using energy-filtered CBED rocking-curve technique
Authors: Swaminathan S. , Altynov S. , Jones I. P. , Zaluzec N. J. , Maher D. M. , Fraser H. L.
Published: June 2020

The advantages of quantitative Convergent Beam Electron Diffraction (CBED) method for x-ray structure factor determination have been reviewed by Spence. The CBED method requires accurate values of Debye-Waller (D-W) factors for the estimation of the coefficients of crystal potential of the higher order beams, Vg, the calculation of the absorption potential, V′gusing the Einstein model for phonons, and finally the conversion of the fitted values of the coefficients of crystal potential, V″, to x-ray structure factors. Debye-Waller factors are conventionally determined by neutron or x-ray diffraction methods. Because of the difficulties in conducting high temperature neutron and x-ray diffraction experiments, D-W factors are rarely measured at temperatures above room temperature. Debye-Waller factors at high temperatures can be determined by Convergent Beam Electron diffraction (CBED) method using Transmission Electron Microscopy (TEM) employed with a hot stage attachment. Recently Holmestad et al. have attempted to measure the D-W factors by matching the energy-filtered Higher Order Laue Zone (HOLZ) line intensities near liquid nitrogen temperature.
High-resolution SEM of biological macromolecular complexes
Authors: Wepf R. , Aebi U. , Bremer A. , Haider M. , Tittmann P. , Zach J. , Gross H.
Published: June 2020

For HRSEM imaging of insulating specimens, thin “homogeneous” metal films with a thickness smaller than the SE-escape depth (1-2 nm for metals) and with a neglectable or very low BSE-coefficient (low Z e.g. Cr or Ge), continuous enveloping the surface fine structures, are supposed to reveal a high resolution topographic SE-1 signal (Joy 1984). Hermann and Müller (1991) have reported a resolution of about 3-4 nm on freeze-dried thin biological specimens, coated with Cr at low temperature (−80°C). High resolution SE-images were also shown on ft or W sputter coated, frozen-hydrated yeast cells (Walther et al., 1992 and Hermann and Müller, 1993) and on coated, freeze-dried macromolecular structures (Walther et al. 1992; Ya Chen et al. 1993).

To study the obtainable resolution and the extractable surface information in SEM from a variety of coating techniques and metals, thin specimens (<20nm) were used as test specimens in order to reduce the signal contribution of the background (SEII).
An ultra-high resolution SEM study of the morphology of electrically switchable volume gratings formed from polymer-dispersed liquid crystals
Authors: Vezie D. L. , Bunning T. J.
Published: June 2020

Low-voltage, ultra-high resolution SEM (UHR SEM) is becoming a valuable complementary technique to TEM, X-ray diffraction, and the scanning probe microscopies for determining polymer morphology and polymer structure-property relationships. Imaging organic materials at low voltage without significant loss in resolution allows for the visualization of structurally interesting features on the order of 50 - 1000 Å with reduced charging and improved topographic contrast. The easily interpretable nature of the data obtained from this technique and the ease of sample preparation offer advantages over more commonly used polymer morphology characterization techniques.

Electrically switchable polymer dispersed liquid crystal (PDLC) volume gratings are of considerable interest for applications in diffractive optics. The system presently under investigation is a PDLC diffraction grating formed by a single-step laser induced polymerization of a penta-acrylate monomer, blended with a photoinitiator, crosslinker, and E7 liquid crystal (LC). Upon polymerization, the liquid crystal phase-separates into liquid crystal-rich planes with a periodicity of 0.56 μm.
High-resolution observation of sintered alumina (Al2O3) using the specimen-heated and electron-beam-induced conductivity method in a UHR-SEM
Authors: Ogura K. , Suzuki T. , Nielsen C.
Published: June 2020

In spite of the complicated specimen preparation, Transmission Electron Microscopes (TEM) have traditionally been used for the investigation of the fine grain structures of sintered ceramics. Scanning Electron Microscopes (SEM) have not been used much for the same purpose as TEM because of poor results caused by the specimen charging effect, and also the lack of sufficient resolution. Here, we are presenting a successful result of high resolution imaging of sintered alumina (pure Al2O3) using the Specimen Heated and Electron Beam Induced Conductivity (SHEBIC) method, which we recently reported, in an ultrahigh resolution SEM (UHR-SEM). The JSM-6000F, equipped with a Field Emission Gun (FEG) and an in-lens specimen position, was used for this application.

After sintered Al2O3 was sliced into a piece approximately 0.5 mm in thickness, one side was mechanically polished to get a shiny plane for the observation. When the observation was started at 20 kV, an enormous charging effect occured, and it was impossible to obtain a clear Secondary Electron (SE) image (Fig.1).
Effects of deposition parameters on morphology of Langmuir-blodgett films of poly(γ-Benzyl-L-Glutamate) by scanning-probe-microscopy
Authors: Smith D. L. , Musselman I. H. , Enriquez E. P. , Guarisco V. F. , Samulski E. T.
Published: June 2020

Synthetic homopolypeptides, such as poly(γ-benzyl-L-glutamate)(PBLG) bear oc-helical secondary structure and exhibit liquid-crystalline behavior. These properties are useful for a range of materials applications, among them nonlinear optics (NLO). The α-helical structural motif of PBLG can be exploited by regular substitution of chemical functionalities in the sidechains along the main axis. Macromolecular order can then be established in polypeptide thin films using Langmuir-Blodgett (LB) deposition. Monolayer films of PBLG have been investigated by surface spectroscopic techniques, without having an understanding of the local morphology.

Atomic force microscopy (AFM) has the potential for elucidating the microstructure of LB films, providing a mechanism for relating differing morphologies to deposition parameters. Excessive contact forces exerted by an AFM tip at small size scales, however, make the technique less viable for delicate organic monolayers. By intermittently striking a sample surface with a sharp probe, the tapping mode AFM provides a means for nondestructively imaging such soft samples.
AFM of polymers using force spectroscopy modes
Authors: Eby R. K. , McEvoy R. L. , Marchese-Ragona S.
Published: June 2020

Several novel imaging modes in scanning-probe microscopy are capable of imaging the surface compliance properties of polymers. The atomic-force microscope is used with a silicon nitride cantilever, in contact mode. While scanning, the tip can be modulated with a low amplitude (25 Å) and low frequency (5 kHz), and the amplitude of tip deflection is compared with the input modulation signal. This mode, called modulated force, maps out the surface compliance of a sample, and gives pixel-to-pixel matching with a topography mode image. Alternatively, while scanning a topography mode image, a force-distance curve can be performed at each x-y pixel location. Several data points in the z-direction of the dF-dS curve can therefore be collected at each x-y data position. In result, one obtains a 3D dataset of force-distance curves with corresponding topography data. The dF-dS images that result are slices through the force-distance regime, each with pixel-to-pixel correspondence to the topography image. In this study, various polymer systems are examined with AFM force imaging modes.
Microstructure of thin YBa2Cu3O7−δ films
Authors: Grant Norton M. , Barry Carter C.
Published: June 2020

The microstructure of superconducting thin-films often strongly influences their electrical properties. The actual microstructure of the film will be dependent on the nucleation and early stages of film growth, although the substrate will also be expected to exert an influence during the early stages of growth by the establishment of epitaxy. The highest critical currents have been obtained with films grown on SrTiO3, however MgO is of fundamental interest because patterned films on MgO have been shown to possess Josephson weak-link structure. The presence of the Josephson weak-links has been correlated with the occurrence of misaligned grains in films grown on MgO. Ultra-thin films of high-Tc superconductors are of interest for understanding the properties of these materials and may also be of use in technical applications.

The microstructure of ultra-thin YBa2Cu3O7−δ films prepared by pulsed-laser ablation onto (001)- oriented MgO has been studied using transmission electron microscopy (TEM) and selected-area diffraction (SAD).
Interfaces and defect structures in epitaxial heterostructures of YBa2Cu3O7 and PrBa2Cu3O7
Authors: Jia C. L. , Kabius B. , Soltner H. , Poppe U. , Urban K. , Schubert J. , Buchal Ch.
Published: June 2020

For the realization of electronic devices using high-Tc superconductors it is necessary to produce multilayers of superconducting and nonsuperconducting or insulating films. It was suggested by Poppe et al. to prepare epitaxial heterostructures on the basis of superconducting YBa2Cu3O7 and semiconducting PrBa2Cu3O7. Heterostructures with similar composition have also been investigated by other authors. The two materials are isomorphic and have the advantage of a small lattice mismatch.

The microstructure of YBa2Cu3O7/PrBa2Cu3O7/YBa2Cu3O7 heterostructures, which have been sputtered epitaxially on SrTiO3 substrates, was examined by high-resolution transmission electron microscopy (HREM), Rutherford backscattering (RBS), and energy-dispersive X-ray analysis (EDX). Measurement of the resistivity vs. temperature of the superconducting layer gave a value of about 90 K for the onset of the superconducting transition. Zero resistance was obtained at temperatures between 80 K and 88 K depending on the specific sample.
Effects of local oxygen ordering on superconducting properties of YBa2Cu3O7−x
Authors: Thiel Bradley L. , Sarikaya Mehmet , Javadpour Jafar , Aksay Ilhan A.
Published: June 2020

The amount of oxygen in high temperature superconducting ceramics is generally recognized as a critical factor affecting the superconducting properties. In this work, nanometer-scale variations in the oxygen ordering of powdered YBa2Cu3O7−x samples, having nominally identical oxygen contents, have been quantified using a novel deconvolution technique on electron diffraction patterns. These variations were correlated with the superconducting properties as studied by magnetic flux exclusion.

Microdensitometer traces of the twin-split (110) type spots in the orientation were deconvoluted to extract the orthorhombicity distribution within the diffracting region. The deconvolution process is shown schematically in Fig. 1. The orthorhombicity is defined as:

where a and b are lattice parameters of the orthorhombic unit cell on the Cu-O basal plane. In the samples studied, materials showing the highest Δa/a (about 2.05%) were also those that displayed the highest Tc values. Furthermore, the width of the superconducting onset, ΔTC, reflected the width of the Δa/a distribution.
HREM study of high Tc oxide superconductor wires made by laser heated pedestal growth technique
Authors: Qiao G. W.
Published: June 2020

Laser Heated Pedestal Growth (LHPG) technique has many advantages, such as crucible-free, no contamination, steep temperature gradients, high density and low defects, etc. for preparing the high Tc oxide superconductor fibers with high transport critical current density due to the floating zone melting and textured structure. For incongruently melt compounds, the technique is probably the best available for growing homogeneous crystals of these materials and was successfully used for making Y and Bi system fibers in Stanford University, IMR and MIT.

The HREM investigation was carried out on the grainboundaries situation which plays an important role in reducing the weak links and enhancing the current transporting ability. The as-grown crystals are 0.5-1.5mm in diameters. X-ray diffraction patterns on plane films showed the textured structures with a-b plane parallel to the growth axis both in Y and Bi system compounds. Fig.1 shows the aligned structures in asgrown crystal of BSCCO.
Microstructure and crystal symmetry of Pb2Sr2(Y/Ca)Cu3O9−δ
Authors: Lin Y. P. , Xue J. S. , Greedan J. E.
Published: June 2020

A new family of high temperature superconductors based on Pb2Sr2YCu3O9−δ has recently been reported. One method of improving Tc has been to replace Y partially with Ca. Although the basic structure of this type of superconductors is known, the detailed structure is still unclear, and various space groups has been proposed. In our work, crystals of Pb2Sr2YCu3O9−δ with dimensions up to 1 × 1 × 0.25.mm and with Tc of 84 K have been grown and their superconducting properties described. The defects and crystal symmetry have been investigated using electron microscopy performed on crushed crystals supported on a holey carbon film.

Electron diffraction confirmed x-ray diffraction results which showed that the crystals are primitive orthorhombic with a=0.5383, b=0.5423 and c=1.5765 nm. Convergent Beam Electron Diffraction (CBED) patterns for the and axes are shown in Figs. 1 and 2 respectively.
Epitaxy and texture analysis of Bi-Sr-Ca-Cu-O thin films on (100) MgO using Transmission Electron Microscopy
Authors: Sizemore J. T. , Schlom D. G. , Chen Z. J. , Eckstein J. N. , Bozovic I. , von Dessonneck K. E. , Bravman J. C. , Harris J. S.
Published: June 2020

Investigators observe large critical currents for superconducting thin films deposited epitaxially on single crystal substrates. The orientation of these films is often characterized by specifying the unit cell axis that is perpendicular to the substrate. This omits specifying the orientation of the other unit cell axes and grain boundary angles between grains of the thin film. Misorientation between grains of YBa2Cu3O7−δ decreases the critical current, even in those films that are c axis oriented. We presume that these results are similar for bismuth based superconductors and report the epitaxial orientations and textures observed in such films.

Thin films of nominally Bi2Sr2CaCu2Ox were deposited on MgO using molecular beam epitaxy (MBE). These films were in situ grown (during growth oxygen was incorporated and the films were not oxygen post-annealed) and shuttering was used to encourage c axis growth. Other papers report the details of the synthesis procedure. The films were characterized using x-ray diffraction (XRD) and transmission electron microscopy (TEM).
Modulated structures of Bi-based high-Tc superconducting oxides studied by High Resolution Electron Microscopy and electron diffraction
Authors: Nagakura Sigemaro , Hirotsu Yoshihiko , Yamamoto Naoki , Miyagawa Katsumi , Ikeda Yuji , Nakamura Yoshio
Published: June 2020

In the superconducting Bi-Sr-Ca-Cu-O system, ideal compositions of the low Tc(Tc∼90 K) and the high Tc(Tc∼110K) phases are Bi2Sr2CaCu2Oy(y∼8:2212 phase) and Bi2Sr2Ca2 Cu3Oy (y∼10:2223 phase), respectively. The fundamental structures of these phases are tetragonal with parameters: at=bt=0.54 and ct=3.08 nm for the 2212 phase, and at=bt=0.54 and ct=3.71 nm for the 2223 phase. These phases have incommensurate structures with modulation along their b-axes. In this study, the modulated structures of Pb-doped 2212 and 2223 phases have been investigated by means of high resolution electron microscopy and electron diffraction. Samples Bi2-xPbxSr2CaCu2Oy(x=0-0.4, melt-quenched and annealed) and Bi2−xPbxSr2Ca2Cu3Oy(x=0-0.6, sintered) were observed in high resolution electron microscopes operating at 200 kV and 1 MV.

Analysis of the incommensurate modulated structures of the 2212 and 2223 phases was made by using samples Bi2Sr2CaCu2Oy and Bi1.6Pb0.4Sr2Ca2Cu3Oy. The lattice parameters of the incommensurate superstructures are a=at and c=ct for both of these phases, but b∼5bt and b∼bt for the 2212 and 2223 phases, respectively.
Modulated structures of superconducting oxides Bi-Sr-Ca-Y-Cu-O
Authors: Inoue Y. , Hasegawa M. , Munakata F. , Yamanaka M. , Koyama Y.
Published: June 2020

Bi2Sr2CaCu2Oy and Bi4Sr3Ca3Cu4Ow have been found to be superconductors with Tc of about 80 K. Their crystal structures are layered structures with tetragonal symmetry, which is characterized by the existence of Cu-O layers. The difference between their structures is that in Bi4Sr3Ca3Cu4Ow Ca occupies not only the Ca site in Bi2Sr2CaCu2Oy but also a part of the Sr site. In addition, the one-dimensional modulated structure along the b axis has been observed in Bi2Sr2CaCu2Oy, although no modulated structure has been reported in Bi4Sr3Ca3Cu4Ow. According to the previous works on electrical properties, when Ca is replaced by Y, Tc decreases and reaches zero around x = 0.6, corresponding to the decrease in hole concentration. The semiconductorlike behavior has been found in 0.6 < x ≤ 1.0 and 1.1 < v ≤ 2.0. Moreover, the antiferromagnetic ordering appears near x=1.0. Recently, we have found a characteristic domain structure in the modulated structure in 0.8 < x ≤ 1.0,
Electron Microscopic study of modulated structure in a Bi-Pb-Sr-Ca-Cu-O system
Authors: Kumao Akihiro , Uyeda Shin’ichiro , Endoh Hisamitsu
Published: June 2020

The preparation of high-Tc superconductor Bi-Sr-Ca-Cu-O is difficult because the strict heat treatment is requested. Takano et al. reported that the partial substitution of Pb for Bi in the system increases the volume of the high-Tc phase, namely it relieves the preparation condition of a superconductor both in the composition of starting materials and heating process. In this paper long-period structure and modulated structure in the Bi-Pb-Sr-Ca-Cu-O system is described.

Powders of Bi2O3, PbO, SrCO3, CaCO3 and CuO, which were weighed such that the ratio of Bi:Pb:Sr: Ca:Cu = 0.96:0.15:1:1.1:1.6 (Sample 1), were dissolved in nitric acid. The compound produced by heating and evaporating solvent was ground in an agate mortar and heated in air at 800°C for 12h. After the reaction the mixture was ground again and made as a pellet, which was heated at 850°C for 48h. Other compositions, Bi:Pb:Sr:Ca:Cu = 0.96:0.24:1:1.1:1.6(Sample 2) and =0.7:0.3:1:1:1.8 (Sample 3), were also prepared with the same manner.
Evidence for a new quasicrystalline transition state in Al65Cu20Fe15 alloy
Authors: Zhang Z. , Li N.C. , Urban K.
Published: June 2020

In Al65Cu20Fe15 alloy icosahedral quasicrystals are formed of extraordinary perfection. On the other hand, there are indications that the quasicrystalline phase is only stable at temperatures above about 800°C. Here we report on a transmission electron microscopy study of a new phase which represents a transition stage between the icosahedral quasicrystalline (IQ) phase and a crystalline phase. It can be described by a modulation of the IQ phase along one of the five-fold axes (A5) of the original IQ phase.

The icosahedral phase in Al65Cu20Fe15 was obtained by arc melting the high purity elements and subsequent slow cooling. The material was then heat treated at 700°C for 24 hours and again slowly cooled to room temperature. During this treatment the regular IQ phase transformed into a phase characterized by the occurence of translation periodicity along one of the five-fold axes of the original IQ phase.
This is demonstrated by a commensurate arrangement of electron diffraction spots only along one of the original A5 (Fig. 1). High-resolution electron microscopy (HREM) corroborates this observation (Fig. 2).
Analysis of metastable structures in quenched Cr-Ti alloys
Authors: Sinkler Wharton , Luzzi David E.
Published: June 2020

Metastable water-quenched bcc Cr40Ti60 is reported to undergo solid state amorphization during sub-eutectoid temperature anneals. Electron diffraction of the metastable bcc phase reveals complex patterns of diffuse scattering indicating the presence of deviation, topological, chemical or both, from the ideally random solid solution. The hypothesis that the microstructure causing the diffuse scattering plays a role in the amorphization process is supported by studies in which an electron- irradiated bcc-based Cu-Ti alloy shows similar diffuse scattering just prior to irradiation-induced amorphization.

Diffuse scattering is observed in all major zone axes of the as-quenched alloy except for (111). Analysis of the spatial frequencies of diffuse scattering maxima indicates that in spite of a clear directional relationship between the bcc matrix scattering and the diffuse scattering, at least some diffuse intensity maxima have spatial frequencies which are incommensurate with the bcc matrix. For instance, the streaked diffuse form along <11> in the (110) zone axis pattern (Fig. 1, arrow), which has been determined to be due to kinematical scattering, does not correspond to any possible bcc superlattice spacing along the [11] direction. This suggests that the microstructure of the as-quenched phase includes regions in which static displacements from the bcc equilibrium sites are encountered.