bluuebunny/crossref_metadata_2025 huggingface dataset:
HRTEM of Initial Oxidation of Carbon Nanotube Tips
Authors: Lordi V , Yao N
Published: July 2020

High resolution transmission electron microscopy (HRTEM) and diffraction technique, with their high sensitivity to small variations in periodic structure or lattice imperfections within individual crystals, have made it possible to relate nanostructure to physical properties of individual fullerenes(C60, C70, etc.) and carbon nanotubes. Using HRTEM imaging, in tandem with dynamic image simulation, we have examined the etching patterns of carbon nanotubes in terms of tip geometry and bond strains. Our studies indicate that the progression of oxidation is not random, and is fully determined by the tip structure, of which only a finite number of classes exist. Oxidation of carbon nanotubes prefers to start at the positions which are most strained, which is associated with the arrangement of pentagons.

Carbon nanotubes were synthesized using the carbon arc method similar to that used for the synthesis of fullerences. The carbon nanotubes are often capped by carbon shells that fit continuously on the ends of the long cylinder
TEM Study of Nanocrystalline AgxNi1-x Solid Solutions
Authors: Chiou W A , Tong C Y , Lin H M
Published: July 2020

Research on nanocrystalline materials, a new class of materials with a grain size of less than 20-30 nm in diameter, has flourished in the last decade because of their unique properties and Characteristics. While enormous amounts of nanocrystalline intermetallic alloys have been made by high energy mechanical alloying, little of this research has been carried out to study the formation of alloys of very low solid solubility elements such as Ag and Ni (0.1 at % at 750 °C).Upon quenching atoms in a state of high mobility, they can be “frozen” into unconventional random positions and thermodynamically metastable or unstable phases can be formed. This research was thus undertaken to synthesize nanocrystalline AgxNi1-x solid solution because fiber composites of this system have been widely used in low-voltage electrical circuits. This paper presents a TEM/AEM investigation of the traditionally immiscible nanocrystalline AgxNi1-xsolids formed by gas evaporation - vapor quenching method.
Surface Structures of Shape-Controlled Platinum Nanoparticles
Authors: Wang ZL , Ahmadi TS , Petroski JM , El-Sayed MA
Published: July 2020

The selectivity and activities of platinum (Pt) particles strongly depend on their sizes and shapes. A technique has been recently reported for controlling the shapes and sizes of Pt particles [1]. Pt particles were prepared by bubbling Ar gas through the solution of K2PtCl4, and the Pt ions were reduced by flowing H2 gas through the solution. The shape control was performed by changing the ratio of the concentration of the capping polymer material to that of the platinum cations used in the reductive synthesis of colloidal particles in solution at room temperature [2]. High percentage of cubic, tetrahedral and octahedral particles have been prepared at room temperature, making it possible for studying the chemical activities of particles with different shapes and facets. This paper aims to study the surface structures of Pt particles prepared by the shape-controlling synthesis technique using high-resolution transmission electron microscopy (HRTEM).
Graphitic Cones
Authors: Krishnan A , Dujardin E , Bisher M E , Treacy M M J , Hugdahl J , Lynuir S , Ebbesen TW
Published: July 2020

New structural forms of carbon have been discovered in recent years, the most notable being the fullerenes and nanotubes. The notion that curvature is readily accommodated by graphite sheets has led to speculation about other possible topologies that incorporate pentagons or heptagons in hexagonal graphite nets. by consideration of Euler’s theorem and the symmetry of a graphite sheet, five conical structures can be predicted. If pentagonal defects only are present, cone angles are completely determined by the total number of pentagons, n, where 0≤n≤6 for open structures. In the absence of heptagons, growth of any graphitic structure containing more than 6 pentagons leads inevitably to the closed n =12 form. Consequently, five cone angles are possible, with disk (n=0) and tubular (n=6) forms representing the end-members of the topological series. Ge and Sattler1 have observed the smallest-angle member of this series with a cone angle of 19.2° (n=5).
Identification of Metal-Impurity Gettering Sites in Silicon Formed by Supersaturation Boron Implantation and Annealing Using HRTEM and STEM Micro Analysis
Authors: Headley T J , Michael J R , Myers S M , Petersen G A , Aselage T L , Bruley J
Published: July 2020

Future Si microelectronic devices will require increasingly stringent limits on transition-metal impurities. There is thus a need to develop new methods for impurity gettering that rely on gettering sites that are active for arbitrarily small impurity concentrations, below the characteristic solid solubility at which metal suicides precipitate. These sites must also be highly preferred relative to solution sites in the Si matrix even at elevated temperatures. One such method has been developed that is also expected to be compatible with front (device) side gettering enabling smaller diffusion lengths for lower processing temperatures. This method involves boron implantion in the front side to levels above the boron-saturation limit and annealing to generate the gettering sites. The gettering layer is introduced at a depth beneath the device zone through appropriate choice of implantation energy. SIMS compositional profiling shows transition metals are strongly gettered within the boron-supersaturated layer. The purpose of this study was to identify the structure and composition of the gettering sites within the boron-supersaturated layer.
The Microstructure of GaAs Grown on Glass Substrates by Molecular Beam Deposition
Authors: Jones Kim M , Friedman Dan J , Al-Jassim MM
Published: July 2020

In the mid to late 80's there was considerable effort directed at the hetroepitaxial growth of III-V's (GaAs, GaP and InP) on Si substrates for solar cell applications. The primary incentive for this work was the cost reduction of expensive substrate materials. This is particularly important when considering large scale production of terrestrial photovoltaic modules. In the U.S. these efforts produced cell efficiencies up to 21% and continued development of this solar cell structure is currently being pursued in Japan. Similar cost effective structures are being investigated at NREL such as the growth of polycrystalline GaAs films on inexpensive glass substrates for solar cell applications. Polycrystalline films, however, tend to contain a high density of grain boundaries which are regions for carrier recombination and enhanced dopant diffusion which can limit cell performance. In order to reduce the detrimental effects of grain boundaries, the growth of large grain (hence low boundary area) GaAs is being investigated
TEM Observation of Delamination Behavior of c-BN Thin Film
Authors: Kim Ig-Hyeon , Sung Changmo , Lee Sang-Ro
Published: July 2020

Cubic boron nitride films were prepared by helicon wave plasma CVD process on (100) Si. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. The delamination behavior of c-BN film was investigated with transmission electron microscopy. It is found that moisture in the air, surface roughness of the film and substrate, as well as severe compressive stresses in the film are the primary contributors to film delamination. An aqueous oxidation was verified by EDXS analysis, which generate local stress by volume expansion at the crack region in the c-BN layer.

The cross-sectional TEM micrograph of c-BN film in Fig. 1 shows that a very thin layer of h-BN is deposited before the c-BN layer starts to grow at an early stage of film growth. A columnar structured thin h-BN layer about 20 nm thickness at the interface is clearly separated from the c-BN layer in an aspect of microstructure.
Characterization of Crystal Polarity Across Twin Boundaries in GaP
Authors: Cohen Dov , McKernan Stuart , Barry Carter C
Published: July 2020

The measurement of the absolute crystal polarity is crucial to understanding the structural properties of planar defects in the sphalerite structure. Due to the directionality of the chemical bond between cations and anions in this lattice, grain boundaries in sphalerite can be described by two distinct structural models. Each model is distinguished by the relative orientation of the polar axis in the grains adjoining the interface. In order to evaluate the polarity of twinned grains in GaP, a dynamical diffraction technique is used to determine the Ga to P bond direction across a coherent twin boundary.

The characterization of the polarity in GaP was performed using a convergent-beam electron diffraction technique developed by Tafto and Spence.CBED can be used to identify the direction of the crystal polarity by observing asymmetries in dynamical diffraction contrast in reflections from crystal planes of opposite polarity. Such contrast arises when the Ewald sphere intercepts a weak {002} reflection plus two or more higher order, odd indexed reflections.
Visualizing Sub-Micron Burried Metal Line in VLSI Devices using a SEM
Authors: Drouin D , Hovington P , Gauvin R , Beauvais J
Published: July 2020

In recent years, the critical dimension in “Very Large Scale Integrated” devices has dramatically decreased. The microelectronics industry road map predicts that by the year 2000 the critical dimension will be below 250 nm. This reduction in scale will imply the development of new techniques to control the fabrication of such devices. This paper presents a novel approach to characterize VLSI devices based on Monte Carlo calculations. The principle of this technique is to use information from backscattered electrons (BE). The energies of those electrons are related to their maximum range within the structure. Thus it is possible to distinguish the layer from which they are backscattered. In order to collect this information an energy filtered backscattered electron detector must be used.

Figure 1 shows a cross section of a structure produces using a typical VLSI process. The two metal layers are usually patterned to define small lines and contacts.
On the Influence of Specimen Thickness in TEM Images of Super-Conducting Vortices: II
Authors: Bonevich J , Capacci D , Patti R , Pozzi G , Harada K , Kasai H , Matsuda T , Tonomura A
Published: July 2020

In our previous papers on the same topic we have shown how the finite thickness of the specimen influences the magnetic field distribution associated to a single superconducting vortex. Fortunately, Clem found an approximate, but analytical, solution for this problem predicting that the field lines are bent within the specimen and fan out near the surfaces, giving an external field topography broader than the bulk one. This is shown in Figure 1 (a) which reports the projected phase maps of the magnetic field, i.e., the phase shift experienced by a coherent electron plane wave in an ideal experiment where the beam direction is parallel to the specimen surface and the apparent infinite thickness of the specimen is overlooked. The specimen thickness has been taken equal to 2 λL, the bulk London penetration depth. Figure 1 (b) shows the trends of the z-component of the magnetic field calculated up to a distance from the core of 5 λL at the film surface (lower curve), at the film center (intermediate curve) and, for reference, the bulk Clem model (upper curve).
Theoretical Foucault Images of Superconducting Fluxons
Authors: Beleggia M , Pozzi G , Harada K , Kasai H , Matsuda T , Yoshida T , Tonomura A
Published: July 2020

Individual flux lines in superconducting specimens have been recently observed using a 300kV holography electron microscope equipped with a cold field emission gun in the transmission mode by means of the out-of-focus method. In this way it has been possible to observe the dynamic behaviour of fluxons depending upon the variations of the temperature and/or the applied magnetic field or current. The main disadvantage of this method is that correlation with structural defects is troublesome owing to the large defocus distance (of the order of 1 cm for conventional superconductors) necessary for the detection of flux lines.

This drawback is not present in the Foucault technique, where the contrast is generated in the focused image by masking part of the transmitted beam by means of an aperture. Therefore, some preliminary calculations have been made recently using one-dimensional models, which allow for a quick and easy simulation of the factors affecting the experimental conditions.
Differential Microscopy by Electron Holography With an Electron Trapezoidal Prism
Authors: Tanji T , Manabe S
Published: July 2020

Electron holography has been successfully used in the observation of phase objects such as magnetic fields and electrostatic potentials. Electron holograms are constructed by the interference of a modulated object wave and a well-defined reference wave and in most cases the reference wave is required to be a plane wave. Frequently, however, the magnetic or electric field extends beyond the interference region, resulting in a distorted reference wave. The reconstructed wave from a hologram made with a distorted reference wave does not accurately express the object wave but the difference from the reference wave.

Differential interferometry is a useful technique in the absence of a well-defined reference wave. Some electron holography techniques using two-beam illumination for differential interferometry have been proposed. We have also proposed a new technique for differential microscopy by conventional electron off-axis holography, which utilizes an electron biprism to shear the object wave. Shearing of the object wave is essential for differential interferometry.
Magnetic and Crystallographic Microstructure of SrRuO3 Studied by Lorentz Transmission Electron Microscopy
Authors: Marshall AF , Klein L , Dodge JS , Ahn CH , Reiner JW , Mieville L , Geballe TH , Beasely MR , Kapitulnik A
Published: July 2020

SrRuO3 is a low temperature ferromagnet (Tc ≌ 150K) which has recently been investigated in thin film form due to its structural compatibility with other thin film perovskites materials of practical interest, including high-temperature superconductors. Magnetization studies of thin films of SrRuO3 deposited on cubic SrTiO3 indicate strong uniaxial anisotropy with the easy direction approximately along either the a or b axis, which are difficult to distinguish. The orthorhombic structure of SrRuO3 (a = 5.53, b = 5.57, c = 7.84 Å) has six symmetry-related orientations on the cubic substrate (a = 3.9Å). Using Lorentz transmission electron microscopy both the magnetic and the crystallographic domain microstructure are characterized.

For TEM imaging the films are readily removed from the substrate by chemical etching, using a HF:HNO3:H2O etch of approximately 1:1:1 dilution. Free-floating SrRuO3 films of 300-1000Å in thickness are then supported on standard carbon/formvar films on Cu substrates.
Magnetic Contrast in the cFEG SEM Using the Upper (Above-the-Lens) Detector
Authors: Brewer LN , Dravid VP
Published: July 2020

An unconventional and important use of the SEM is in the study of magnetic phenomena of materials. Many magnetic phenomena occur on the surfaces of materials as is the case for magnetic recording in computer memory and audio tapes. The “above-the-lens” or “upper” detector of the cFEG SEM(Hitachi S4500) is especially suited to probing surface phenomena (Fig. 1). The upper detector is used in combination with a magnetic “snorkel” lens which pulls secondary electrons (SE) up to the detector, resulting in an extremely high and pure SE yield. While magnetic imaging in a standard, side-mounted Everhart-Thornley (lower) detector is well understood, the image contrast mechanism for the upper detector is not presently known. We tested both energy filtering and trajectory contrast as possible magnetic contrast mechanisms using a cassette recording tape (Fe2O3 based) and barium hexaferrite ceramic magnets.

Two sets of experiments were performed to explore the magnetic contrast.
Segregation at Adherend Interphases in Fiber-Reinforced Epoxies
Authors: Arayasantiparb D , Siangchaew K , Libera M , McKnight S
Published: July 2020

The fact that there is a region at the epoxy/adherend interface known as the interphase whose chemistry and structure are different from that of bulk epoxy is well established (1-2). The specific nature of the interphase depends on the resin and curing agent, the adherend surface-chemical properties, and the adherend sizing treatment if any, among other possible variables. The interphase is critically important, since it is responsible for stress transfer between the matrix and reinforcing fibers. While it has been studied by a variety of analytical methods (eg. 3-5), none have had sufficient spatial or spectral resolution to establish the physical extent of the interphase or its compositional deviation from bulk epoxy. This research exploits high-spatial-resolution analysis in a field-emission STEM to study the interphase in epoxy/adherend systems using high-angle electron scattering (HAADF-STEM) and energy-loss spectroscopy (PEELS).

Thin specimens were cut by ultramicrotomy using a diamond knife from single-fiber tensile bars consisting of anodized aluminum wire embedded in an epoxy matrix (Fig 1.)
Interfacial Segregation in Al-Cu-Mg Alloys
Authors: Ford RG , Carpenter RW , Kim MJ , Sieradzki K
Published: July 2020

The corrosion behavior of Al-Cu-Mg alloys, specifically 2024 alloy (nominally, in weight %, 4.4 Cu, 1.5 Mg, 0.6 Mn), is thought to depend on heterogeneous Cu and Mg distribution through the existence of segregation-dependent local electrochemical cells at the corrosion interface. Few nanospectroscopy measurements of segregation have been made for this or similar alloys. These alloys are precipitation hardenable. The primary precipitating phases are S and the well known Θ(CuAl2) and their metastable intermediates. TEM analysis of aged alloys in this subgroup showed that the orthorhombic S phase (a=4.0Å, b=9.25Å, c=7.15Å) occurred as a thin plate type variant, called S´, within matrix grains and as larger monolithic particles on grain boundaries. Intragranular pricipitate particle densities were heterogeneous particularly near grain boundaries, indicating that strong segregation was present that would result in local electrochemical cells where grain boundaries and large precipitates intersected the alloy surface.

HRTEM and nanospectroscopy are used to analyze the structure and chemistry of heterophase interfaces and grain boundaries.
AEM Analysis of Grain Boundary Segregation and Precipitation in Al-Mg Alloys
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Vetrano JS , Bruemmer SM
Published: July 2020

Magnesium is an important and common solid solution strengthening agent for aluminum alloys. It has been known for many years that Mg segregation to grain boundaries (GBs) and other structural inhomogeneities can lead to precipitation of the ² (Al3Mg2) phase during low-temperature aging. This phase is anodic with respect to the matrix so its presence degrades the stress corrosion cracking (SCC) resistance of the alloy. The details of P-phase precipitation have been studied in detail in binary Al-Mg alloys [3-5] but there is some indication that ternary elements can alter the precipitation kinetics and spatial distribution which in turn will affect SCC. Therefore we are studying the segregation and precipitation of Mg in a commercially important Al-Mg alloy which contains Mn and Cr as grain refining particles.

Specimens were prepared from a commercial 5083 heat with the composition 4.47% Mg, 0.61% Mn, 0.08% Cr, 0.09% Si, 0.21% Fe, 0.05% Cu, bal. Al (all compositions in weight percent). Following cold rolling they were given a recrystallization anneal of 10 min. @ 500°C and air cooled.
Electron Backscattered Diffraction (EBSD) with a Cold Held Emission Gun (cFEG) SEM: Resolution, Sensitivity and Applications
Authors: Isabell Thomas C , Dravid Vinayak P
Published: July 2020

A thorough and complete assessment of microstructure of materials requires a wide variety of analytical techniques, which should be sensitive to at all length scales - from mms to atomic scale. While there have been rapid advances in imaging and spectroscopy techniques for microstructural analysis - at all length scales, techniques for crystallographic analysis of microstructure have primarily relied on bulk x-ray/neutron diffraction and TEM. X-ray and neutron diffraction techniques, though very powerful, are primarily bulk techniques and extraction of local crystallography is formidable if not impossible. On the other hand, TEM diffraction techniques provide precise crystallographic information, but at a much smaller length-scale and suffer from poor statistics and tedious specimen preparation procedures. With the advent of commercially available electron backscattered diffraction (EBSD) and orientational imaging (OIM) systems for SEM, and sophisticated pattern recognition procedures, it is now possible to bridge the length-scale gap between bulk and TEM diffraction techniques.
Analysis of Multiphase Materials Using Electron Backscatter Diffraction
Authors: Wright SI , Field DP
Published: July 2020

Image analysis techniques coupled with crystallography computer codes have been used to index electron backscatter diffraction patterns (EBSPs). The ability to automatically obtain the crystallographic orientation from EBSPs coupled with computer control of the electron beam (or stage) in a scanning electron microscope (SEM) provides a much more complete description of the spatial distribution of crystallographic orientation in polycrystalline materials than has been previously attainable using conventional metallography techniques. Orientation data obtained using this technique can be used to form images reflecting the spatial arrangement of crystallographic orientation in a microstructure. Such images enable the topological features of a microstructure to be linked with the orientation characteristics. The formation of these images, as well as the data collection technique, is sometimes termed Orientation Imaging Microscopy (OIM). The utility of this technique for exploring the property/structure relationship in polycrystalline material has been demonstrated by numerous researchers. However, as yet, this technique has almost exclusively been applied to single phase materials.
The Influence of Microtexture on Fatigue Behavior in Titanium Alloys
Authors: Woodfield A P , Sutliff J A
Published: July 2020

Automated electron backscatter diffraction pattern (EBSP) measurements were conducted in an attempt to relate low cycle fatigue (LCF) behavior to underlying microtexture in alpha-beta forged and heat treated Ti-6242 materials. Conventional load control, R=0 LCF tests were conducted with two wave forms, 30 cycles per minute (30 cpm), and 2 minute hold at peak stress, (dwell). The fracture surfaces and adjacent microstructures of the LCF specimens were examined using light microscopy, scanning electron microscopy (SEM), and orientation imaging using automated EBSP.

Fracture surfaces of dwell LCF specimens frequently contained large macroscopically flat, shiny facets, while 30 cpm specimens showed no such evidence of facets. Additionally, the dwell LCF specimens that contained facets had very low lives, typically around 1000 cycles at 126 ksi maximum stress. EBSP measurements directly on the facets, and on cross-sections through the facets revealed that the facet fracture plane was on, or close to (0001) of the primary alpha grains, Fig. 1, and was approximately perpendicular to the stress axis.
Controlled Environment (ECELL) HREM
Authors: Boyes Ed
Published: July 2020

The ability to control the environment inside the electron microscope is a very desirable general capability and one long pursued for higher vacuum or chemical reactions (1,2) Here we are primarily concerned with providing the essential facilities for realistic in-situ dynamic studies of chemical reactions between gases or vapors and solids. The compromises with microscope performance have been reduced substantially compared with previous gas experiments (2,3).

The primary applications for the present instrument are to reaction catalysts and the products of reactions where they are solid state materials of commercial value. Firstly, the catalyst may have to be (re)processed after transfer through the air or other hostile (i.e. non-reactor) environment. Secondly, the high vacuum atmosphere in a typical TEM may not be a compatible environment for the catalyst or other material (e.g. if it is solvated). Thirdly, the sequence of events in changes in the microstructure of a chemically active species will likely depend on the atmosphere in which those changes take place or are promoted (e.g. by heating).
An Ex-SituReactor with Anaerobic Specimen Transfer Capabilities for TEM Studies of Reactive (Catalyst) Specimens
Authors: Allard L F , Ailey K S , Datye A K , Bigelow W C
Published: July 2020

The optimization of currently available catalysts and the development of new ones requires a detailed understanding of the effects of both microstructure and composition on their function. Previous work has demonstrated that information at the atomic-scale on heterogeneous catalysts can be derived using high resolution transmission electron microscopy (TEM). Under favorable conditions, the morphology of heavy metal catalytic particles can be related to catalytic activity. It has been shown that preoxidation can disrupt the surface of small metal particles causing altered activity and selectivity in reactions such as alkane hydrogenolysis. Metals such as Pt, Rh, or Ru are noble and pick up no more than a monolayer of oxygen when exposed to air during sample preparation for microscopy. This oxygen monolayer is not imaged in the microscope, most likely because the oxygen desorbs during exposure to the high energy electron beam. However, when metals such as Fe, Co, Ni, Pd or Cu are exposed to air, there is a corrosive interaction that alters particle structure quite dramatically.
In-Situ Observations of the Effect of Electron Irradiation on the Defect Microstructure of Alumina
Authors: Chen S-J , Dahmen U , Howitt DG
Published: July 2020

The interaction of radiation produced point defects with a dislocation microstructure at high temperature is of considerable interest and careful high voltage microscopy experiments can provide valuable insight into the mechanisms. Veyssière and Westmacott carried out in-situ experiments monitoring the partial dislocation climbs in Ni3Al induced by thermal vacancies as well as by Frenkel pairs produced during irradiation.1 We report here the results of some preliminary experiments we performed on alumina (A12O3) single crystals with high dislocation densities to study the modification of the microstructure by electron irradiation at high temperature.

The dislocation microstructures were produced by shock wave deformation using a high-velocity impact technique. The technique is capable of producing a very high density of defects consisting primarily of basal twins, and slips on the basal, pyramidal and rhombohedral planes in alumina. The dislocations are all of glide type, mostly forming shear bands. A typical microstructure prior to irradiation is shown in figure la.
The Observation of Hierarchical Structures in Biopolymer Phase Separation : Novel ESEM Contrast Mechanisms
Authors: Bache C , Anderson V J , Jones R A L , Donald A M
Published: July 2020

Gelatin and dextran are two water soluble biopolymers of considerable importance in the food industry, both separately and in combination. A solution of gelatin and dextran (∼ 10% total polymer concentration) forms a single phase at high temperatures, and on cooling undergoes phase separation, which may occur simultaneously with the gelation of the gelatin. The exact phase distribution in the final microstructure is dependent on the initial polymer concentrations, and the relative rates of gelation and phase separation. Much work has been done on such systems in the past, using a variety of techniques. Most recently, optical microscopy and small angle light scattering (SALS) have been used to characterise the structure of this particular system, especially for systems at the critical concentration. However due to the constraints imposed by sample preparation, very little Scanning Electron Microscopy (SEM) has been carried out on such systems - freeze drying and the problems of obtaining contrast between the phases without staining make such experiments difficult and sometimes inconclusive.
Effects of Space Charge on ESEM Gas Amplification
Authors: Thiel BL , Hussein-Ismail MR , Donald AM
Published: July 2020

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.

In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.
ESEM and Video Microscopy Studies in Stone Conservation
Authors: Doehne Eric
Published: July 2020

Observation of stone deterioration using in situ,time-lapse microscopy techniques has revealed previously undescribed material behaviors that help to explain the destructive effects of several important processes in wall paintings, historic structures and monuments. It has long been acknowledged that cyclic stresses imparted by humidity changes, wet-dry cycling, and the crystallization and hydration of soluble salts, are important agents in the deterioration of these porous structures. The crystallization of salts is a particularly serious conservation problem (Arnold, 1975). Over time, cyclic salt crystallization results in the physical breakdown of the material (Goudie, 1993). Objects affected by such processes are often difficult to conserve since they are weak to begin with and the presence of salt inhibits the curing of some common conservation materials (Price and Kumar, 1994).

Sodium sulfate is one of the most damaging of salts, apparently because it expands during the transition from the anhydrous phase (Na2SO4; thenardite) to the decahydrate form (Na2SO4•l0H2O; mirabilite).
solid-state reactions in the presence of an electric field
Authors: Johnson Matthew T , Carter CBarry
Published: July 2020

It is well known that diffusion in ionic materials occurs primarily by the movement of charged species. Therefore, an electric field should provide a very powerful driving force for mass transport. In the present study, solid-state reactions, in the presence of an electric field, have been carried out between thin films of In2O3 and bulk monocrystalline MgO ﹛001﹜. In solid-state reactions of this type, reaction rates and interfacial stability are affected by the transport properties of the reacting ions. by applying an electric field across the sample, at elevated temperatures, the reaction rates and interfaces are affected as a result of ionic conductivity. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated, in this spinel forming system, to gain a better understanding of the influence of an electric field on interface morphology and solid-state reactions.

The reaction couples used in this study were produced by means of pulsed-laser deposition (PLD).
Crystallization of Cordierite Glass Ceramics for Joining SiC: Must Phase Separation Via Spinodal Decomposition Precede Nucleation?
Authors: MoberlyChan Warren J , Perham T J , DeJonghe L C
Published: July 2020

The crystallization of glass ceramics provides processing advantages for difficult shapes. Machining and sintering are limited to produce complex parts; similarly (superplastic) forming is limited to special ceramics. In theory, however, a liquid (or glass) may be simply poured into any shape, and then crystallized (or partially crystallized) to provide a strong, tough ceramic. In this work, a thin layer of glass ceramic, cordierite (2MgO.2Al2O3.5SiO2), joins SiC [1]. Tailoring secondary phases and percent crystallization provide flexible control of the coefficient of thermal expansion to minimize strain mismatches between the joint components.

Three processing steps are involved in crystallization of glass ceramics: first a fast quench produces the initial glass; the second step is a lower temperature “nucleation” anneal, where phase separation and/or precursors and/or the final structure is nucleated and ideally as a fine dispersion; the third step is the higher temperature “crystallization” anneal, where renucleation and/or growth develops a homogeneous (ideally fine grained) final crystalline product [2, 3].
Structural Characterization and Modeling of the Aluminum (111) / Aluminum Oxide (0001) Interface
Authors: Medlin DL , Smugeresky JE , McCarty KF , Tepesch PD , Quong AA , Baskes MI
Published: July 2020

We are investigating the structure of the Al (11l)/Al2O3 (0001) interface. Interfaces for this study were produced by epitaxial thin film deposition of aluminum metal onto (0001) oriented single crystal α-Al2O3. The majority of grains within the films are oriented with:

(0001)Al2O3 || (lll)Al [10Î0]Al2O3 || [ī10]Al

This relationship results in a matching of the close-packed planes and directions of the aluminum metal with those of the oxygen ion sub-lattice in the Al2O3and allows for two variants related by 180° rotations about the aluminum [111] axis. A diffraction pattern showing these two variants is given in Figure 1. Figure 2 shows a HRTEM image of the heteroepitaxial aluminum/Al2O3 interface. The Al2O3 substrate and aluminum overlayer are imaged along the [10Ï0]Al2O3 and [ī10]A1 zones. Over the width of the image, the interface is sharp to within a few atomic layers.

The calculated lattice misfit for the Al/Al2O3 system, taken as the difference between the translation vectors of a/3[10ī0]Al2O3 (2.7447 Å) and a/2[ī10]AI (2.8634 Å), is 4.3%. A fundamental issue is the manner in which this misfit is accommodated.
The Structure of Twin Boundaries in Cluster Compounds: Potassium Barium Oxomolybdate
Authors: Ramlau R , McCarley R E , Simon A
Published: July 2020

K0.19Ba3.18Mo22O34is a representative of the quaternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n trans edge-sharing molybdenum octahedra. The general concept of cluster condensation is discussed elsewhere. In the case of n being finite the clusters are designated as ‘oligomeric’. The individual clusters are interconnected via common oxygen atoms and arranged in layers. For the title compound with n = 5, the clusters consist of 5 molybdenum octahedra and are accompanied by 4 counter-cations (potassium and barium).

The real structure of K0.19Ba3.81Mo22O34 has been recently studied with a Philips CM30/ST (Cs = 1.15 mm) by HREM, SAED, and EDXS. Besides chemical intergrowth of oligomeric clusters with n = 2—18 in the matrix consisting of pentameric clusters, polytypism was observed. Three ordered polytypes (modifications) were found, whereas only one of them, lM (Ramsdell notation), was detected and analyzed with x-ray methods.
Microstructure Characterization of Ni-V Splat Quenched Foils
Authors: Sieber H , Allen DR , Perepezko J
Published: July 2020

Although the thickness of splat quenched (SQ) foils is normally less then 100 μm the solidified microstructure is usually not homogenous, but rather is determined by a cooling rate dependent nucleation and growth behavior of the different phases. The cooling rate and thus the microstructure changes significantly with distance from the edge to the middle of the SQ foils. Rapidly quenched nickel-vanadium (Ni-V) foils consist of three phases formed during solidification, a Ni-fcc, a V-bcc and a intermetallic σ phase [1-3]. To interpret the microstructure evolution in detail, a special TEM cross section sample preparation was applied. The SQ foil was ground to 30 μm, glued on a copper grid and ion-milled parallel to the foils (Fig.1a). In Ni-49V SQ foils seven typical microstructure regions (see Fig. 1 b) could be identified and were analyzed in detail by TEM investigations in plan view and cross section geometries. Furthermore, three solidification pathways were identified.
Microstructural Characterization of α2 + γ Titanium Aluminides
Authors: Larson D J , Miller M K
Published: July 2020

Two-phase α2+γ TiAl alloys with microalloying additions, Fig. 1, are of interest due to the high strength-to-weight ratio they can provide in automotive and aircraft applications. In boron-doped α2+γTiAl containing Cr, Nb, and W, the B levels were found to be significantly depleted below the nominal alloy content in both the α2 andγ phases. The boron solubilities in the γ and α2 phases were 0.011 ± 0.005 at. % B and 0.003 ± 0.005 at. % B, respectively in Ti-47% Al-2% Cr-1.8% Nb-0.2% W-0.15 % B that was aged for 2 h at 900°C (base alloy). The majority of the B was in a variety of borides including TiB, TiB2 and a Cr-enriched (Ti,Cr)2B precipitate. With the exception of the smaller (< 50 nm thick) Cr-enriched (Ti,Cr)2B precipitates, Fig. 2, most of the borides were larger than ∼100 nm. A significant proportion of the microalloying additions is in these borides, Table 1.
Study of Precipitates Morphology and Composition Evolution using Scanning Electron Microscopy (SEM) and Energy Dispersive X Ray Spectroscopy (eds) in as Cast, Forged and Heat Treated Complex Aluminium Bronzes
Authors: de Arenas I B , Centeno L , Arenas F
Published: July 2020

The Aluminium Bronzes are successfully used in heat exchanger tubes, particularly in chemical and oil industries, where they are subjected to sligthly acid conditions or higher temperatures and stresses than other copper alloys allow. For a maximun resistance to corrosion an understanding of the effects of composition and metallurgical structure is desirable. This work study the different precipitates appearing in ASTM B148-C95800 complex Al bronze alloy, due to the structural development in as cast,forged and heat treated conditions, the presence of Fe and Ni as additions enhance the presence of many different precipitates all over the structure, changing the corrosion resistance and mechanical properties.

In this type of alloy the non-stoichiometric β phase breaks down progresively during cooling from high temperatures: 750° - 950°C to give a finely divided iron - nickel - aluminium “kappa” (κ) phase in a copper rich (α) matrix. Such α + κ alloys generally can contains small quantity of β and none γ2 (deleterious to all properties), showing excellent corrosion resistance combined with high tensile strength.
Interfacial Reaction Between Tin-Zinc Based Solders and Copper
Authors: Ghosh G , Fine M E
Published: July 2020

Due to the interfacial reaction between the solder and substrate, either during manufacturing or in service, the solder joints may contain one or more intermetallic layers at the interface. While such intermetallic layers may provide strong bonding, they may also be responsible for problems associated with solderability and reliability of joints. Certain physical and mechanical properties of the intermetallic may determine the integrity and reliability of solder assembly. So far detailed analysis, modelling, and testing of simulated and actual joints have been performed with Pb-Sn solders. However, in view of the increasing environmental and legislative concerns, lead-free solders are currently being developed and designed for microelectronics applications. As the solder joints in high-performance electronic circuits are expected to carry increasing mechanical, electrical and thermal burdens, it is essential to address the technological and reliability issues for lead-free solders. Among the lead-free solders, tin-zinc based alloys can be designed to achieve melting and solidification behavior similar to those of lead-tin eutectic or near eutectic alloys.
Synthesis, Properties and Characterization of Red Phosphor Particles of Y2O3:Eu
Authors: Jiang Y D , Wang Z L , Zhang F , Paris H G , Summers C J
Published: July 2020

High resolution and high efficiency planar display, one of the national priorities for advanced technologies and commercial applications, require highly efficient phosphor materials with crystalline monodispersive fine particles [1,2]. Europium oxide activated yttrium oxide (Y2O3:Eu) is a potential red-emission phosphor powders to be used in high efficiency electroluminescence and field emission displays. In this paper, a novel hydrolysis technique is employed to prepare phosphor particles of Y2O3: Eu, and the structure characterization is reported.

In this synthesis technique, urea reacts with water to release OH−, cations of Y3+ and Eu3+ combine with OH− to form (Y1−xEux)(OH)3 precipitates. Y2O3 particles doped with Eu are formed after the precipitates being fired at a given temperature [3]. The particles prepared by this method are nearly spherical, and have an average diameter of ∼200 nm (Fig. 1). The distribution of particle sizes is narrow, and almost no agglomeration among particles is observed. The particle sizes remain approximately the same before (Fig. 1a) and after (Fig. 1b) being fired at 1200°C.
Analytical TEM and EPMA Study of Decomposition Reactions in an Oxygen-Separation Membrane Material
Authors: Christoffersen R , Kim S , Yang YL , Jacobson AJ
Published: July 2020

Mixed-conducting oxides with appropriate values of electronic and ionic conductivity have the potential to be used as ceramic “membranes” for the separation of oxygen from other gases. The separation is based on oxygen transport from an O2-rich, and hence oxidizing, gas reservoir on one side of the membrane to an O2-lean, and hence reducing, take-up reservoir on the membrane's other side. The oxide Sr(Co1-xFex)O3-δ (SCFO), which has a cubic perovskite structure, is one such potential membrane material. Although the permeation flux of oxygen through SCFO membranes has been mea-sured, the microstructural evolution of SCFO membranes during permeation has been little studied in comparison to other potential membrane oxides. Several of these other systems do show segregation and/or decomposition phenomena that potentially may affect membrane properties. Here we report preliminary results of a systematic microanalytical study of SCFO membranes using scanning electron microscopy and microanalysis in an electron probe microanalyzer (EPMA), as well as transmission electron microscopy in an analytical TEM.
HVEM-Tandem and Eels Study of Radiation Damage in Zirconolite
Authors: Smith Katherine L , Zaluzec Nestor J , Lumpkin Gregory R
Published: July 2020

Zirconolite (CaZrTi2O7) is the major host phase for actinides in Synroc, a promising waste form for the immobilisation of high-level radioactive waste. The effect of radiation damage on the structure and durability of zirconolite are important to predictive modelling of zirconolite's behaviour in the repository environment and risk assessment.

In this study, radiation damage effects in zirconolite were investigated by irradiating samples with 1.5 MeV Kr+ ions using the HVEM-Tandem at Argonne National Laboratory (ANL) and energy loss electron spectroscopy (EELS). The HVEM-Tandem consists of a modified AEI high votage transmission electron microscope interfaced to to a 2 MV tandem ion accelerator. EELS spectra were collected using a Philips 420 TEM, operated at 120 kV, fitted with a Gatan Model 607 Serial EELS. EELS data were recorded at resolutions of ˜1.0 eV and at a dispersion of about ˜0.25 eV.

Selected area diffraction patterns (SADs) of individual grains of various zirconolites were monitored as a function of dose to establish the critical dose for aniorphisation (Dc).
Interfacial Segregation in Oxide Scales on Nicrai-Based Alloys
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Prüβner K , Alexander K B , Pint B A , Tortorelli P F , Wright I G
Published: July 2020

Previous studies addressing the segregation of reactive elements in protective oxide scales and their beneficial effect on scale adhesion have primarily concentrated on primary alumina-formers (e.g. β-NiAl + FeCrAl).In our study the oxidation behaviour of three NiCrAl alloys, which form complex scales was studied in air at 1423 K and at 1473 K, both in isothermal (100 h) and in cyclic oxidation (100 x lh). The composition (in at.-%) of these alloys is the following: General Electric alloy René N5 (64.9 Ni, 7.8 Cr, 13.9 Al, 0.1 Fe, 2.1 Ta, 0.05 Hf, 1.6 W, 1.0 Re, 0.15 Si, 7.3 Co, 0.9 Mo, 0.003 Y, 0.003 Zr, 4 ppm S, 0.25 C), Ni-7Cr-6.5Al+Y (80.1 Ni, 7.2 Cr, 12.5 Al, 0.01 Fe, 0.14 Si, 0.012 Y, 18 ppm S, 0.05 C) and Ni-10Cr-10Al+Y (71.2 Ni, 9.9 Cr, 18.8 Al, 0.01 Fe, 0.02 Si, 0.041 Y, 16 ppm S, 0.04 C).
Characterization of Tubercles in Cast Iron Water Distribution Pipes Using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS)
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Sarin P , Kriven WM , Snoeyink VL
Published: July 2020

Corrosion of cast iron (C.I.) pipe often results in the formation of “tubercles” on the inner surface of the pipe. Tubercles are layered deposits formed by the stacking of several layers of corrosion products one on top of the other (Fig.l). Tubercles not only increase the amount of energy required for transport of water but are also considered the main source of turbidity in potable water. Their chemical and physical characteristics are important factors which affect the release of iron into the bulk water.

Tubercles are extremely complex systems. They may be highly crystalline in nature, with iron occurring in chemical structures, such as siderite (FeCO3), goethite (α-FeOOH), magnetite (Fe3O4) and lepidocrocite (γ-FeOOH) or they may be highly amorphous. Tubercles vary in height from a few millimeters to a few centimeters. They exhibit distinct layers which are formed over varying periods of time ranging from a few months to a century.
The Birefringence of thin filaments measured with the Pol-Scope
Authors: Oldenbourg R , Salmon Edward D , Tran Phong T
Published: July 2020

The living cell is criss-crossed by dense networks of filaments providing mechanic stability, site directed molecular transport and support of other vital cell functions. With the polarized light microscope we can observe the birefringence associated with thin filaments or partially oriented filament networks and measure the birefringence directly in the living cell (Fig. 1). Filament birefringence is a consequence of the elongated shape of the molecules and occurs naturally without the need to stain or label them, as is necessary in fluorescence imaging.

We have measured the birefringence of microtubules and axoneme filaments using the new polarized light microscope (Pol-Scope).The design of the Pol-Scope is based on the traditional polarized light microscope in which the crystal compensator is replaced by a universal compensator made from two liquid crystal variable retarders. Electronic image acquisition in the Pol-Scope is synchronized to liquid crystal settings to capture a sequence of four images with circular and elliptical polarization.