bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic structures of faceted low-energy Pd/Al2O3 interfaces
Authors: Cosandey F. , Lu P. , Brun N. , Hagege S.
Published: June 2020

Recently, it has been demonstrated that alpha alumina fibers having the stable trigonal structure can be grown in Pd by internal oxidation. The alumina fibers are oriented with respect to Pd and exhibit strong faceting. In this paper, we present HREM results on the atomic structures of the faceted interfaces.

Oxidation experiments were done in air at 1000 °C for 48 hrs on a Pd-10.8 at.% Al alloy. Selected samples were subsequently annealed at 1000 °C for 0.5 hrs in an Al vapor. All HREM observations were done using a Topcon-002B high resolution microscope. For image analysis, the interfaces were modeled using EPITAX and multislice image simulations were performed using EMS programs.

The alumina fibers grown by internal oxidation, grow along the <110>Pd oxidation front direction. The orientation relationship between Al2O3 fibers and Pd is not unique, however, most fibers are faceted with primary low energy interfaces between Pd and Al2O3 corresponding to (110)//(0001), (111)//(0001) and (111)//(11-20).
“Dynamic” charging of polymers in the LVSEM
Authors: Butler J. H. , Joy D. C. , Bradley G. F.
Published: June 2020

Recently we have been using a field emission LVSEM with an immersion-type objective lens extensively for the examination of polymers at low (<2 keV) incident beam energies. During the course of these studies it became apparent that, even though operating in the vicinity of E2 (the accelerating voltage at which no electrostatic charge builds up on the sample surface), sample charging effects of a most curious nature do, in fact, abound.

In general the LVSEM has been successful in producing a wealth of exciting information. However, when nonconducting polymers are the subject of observation at E2, an unexpected and unusual charge build-up behavior is almost always encountered on the sample surface under irradiation (c.f. Figure 1). Thus for strongly insulating materials, it is not as easy to work in the realm of E2 as earlier predicted. For example, in some polymeric materials, it appears that charging is a function of magnification: at very high magnifications the sample will charge "positively", at lower magnifications (with all other parameters the same) the same sample will charge negatively, and at even lower magnifications the same sample will revert back to a positive charging situation.
Solvent-assisted osmium staining of butyl acrylate and ethylene-propylene-diene in a styrene acrylonitrile matrix
Authors: Hutchins Gudrun A.
Published: June 2020

In order to optimize the toughening effect of elastomers in engineering polymers, it is necessary to characterize the size, morphology and dispersion of the specific elastomer within the polymer matrix. For unsaturated elastomers such as butadiene or isoprene, staining with osmium tetroxide is a well established procedure. The residual carbon-carbon double bond in these materials is the reactive site and forms a 1,2-dilato complex with the OsO4. Incorporation of osmium tetroxide into the elastomer not only produces sufficient contrast for TEM, but also crosslinks the elastomer sufficiently so that ultramicrotomy can be accomplished at room temperature with minimal distortion.

Blends containing saturated elastomers such as butyl acrylate (BA) and ethylene propylene diene monomer (EPDM) cannot be stained directly with OsO4 because effective reaction sites such as C=C or -NH2 are not available in sufficient number. If additional reaction sites can be introduced selectively into the elastomer by a chemical reaction or the absorption of a solvent, a modified, two-step osmium staining procedure is possible.
Ceramics in the environmental Scanning Electron Microscope
Authors: McKeman Stuart
Published: June 2020

Several recent advances have had a major potential impact on the microscopy of ceramic materials. The ability of modern scanning electron microscopes to image uncoated materials, at low voltage for example, whilst still maintaining high resolution should make possible a wide variety of experiments that were hitherto impossible to contemplate. This ability to look at the unmodified surface of a ceramic enables iterative or dynamic experiments to be done with a lot more confidence in the results than has been possible before. A second advance has been the introduction of microscopes capable of operating at higher pressures than was previously possible. This makes possible the ability to image specimens in a variety of different environments. The environmental scanning electron microscope (ESEM) exploits of both of these novel areas. The aim of this review is to highlight areas where the unique capabilities of the ESEM may be applied to advance our understanding of ceramics.
Stacking faults in deformed α-silicon nitride single crystals
Authors: Suematsu H. , Petrovic J. J. , Mitchell T. E.
Published: June 2020

Silicon nitride(Si3N4) is well known for its high toughness and strength. This is the reason why it is selected for ceramic turbo charger rotors in automobile engines. However, the high strength of most sintered Si3N4 products drops above 1200°C because sintering aids like Y2O3 and MgO are required which form glassy phases with low melting points on the grain boundaries. This secondary phase degrades the high temperature characteristics of Si3N4. In order to overcome this deficiency, much work has been reported which aims at crystallizing or removing the glassy phase. If this aim could be successful, resulting in an increase in high temperature strength, other processes would determine the high temperature performance of Si3N4, such as diffusional creep and dislocation slip. Line and planar defects in Si3N4 play an important role in such the processes particularly in slip, however, available knowledge about them is limited. In the present work, stacking faults in deformed Si3N4 single crystals are investigated using high resolution electron microscopy(HREM).
Low-temperature Mo-catalyzed growth of crystalline Si3N4 by CVD
Authors: More K.L. , Lowden R.A. , Besmann T.M.
Published: June 2020

Silicon nitride possesses an attractive combination of thermo-mechanical properties which makes it a strong candidate material for many structural ceramic applications. Unfortunately, many of the conventional processing techniques used to produce Si3N4, such as hot-pressing, sintering, and hot-isostatic pressing, utilize significant amounts of densification aids (Y2O3, Al2O3, MgO, etc.) which ultimately lowers the utilization temperature to well below that of pure Si3N4 and also decreases the oxidation resistance. Chemical vapor deposition (CVD) is an alternative processing method for producing pure Si3N4. However, deposits made at temperatures less than ~1200°C are usually amorphous and at slightly higher temperatures, the deposition of crystalline material requires extremely low deposition rates (~5 μm/h). Niihara and Hirai deposited crystalline α-Si3N4 at 1400°C at a deposition rate of ~730 μm/h. Hirai and Hayashi successfully lowered the CVD temperature for the growth of crystalline Si3N4 by adding TiCl4 vapor to the SiCl4, NH3, and H2 reactants. This resulted in the growth of α-Si3N4 with small amounts of TiN at temperatures as low as 1250°C.
Using convergence and spread-of-focus parameters to model spatial and temporal coherence in HRTEM image simulations
Authors: Malm Jan-Olle , O’Keefe Michael A.
Published: June 2020

In all HRTEM images, the incident electron beam suffers from the effects of limited spatial and temporal coherence. These effects produce a smearing of the image, and provide the ultimate limits as to how high a spatial frequency can be transferred to the image (i.e. resolution). The effect of partial temporal coherence is manifested as a spread of focus, and that of partial spatial coherence as incident beam convergence. The effects of partial coherence can be included in HRTEM image simulations by summing images in real space, or by applying an appropriate transmission cross-coefficient (TCC) when computing the image intensity spectrum in reciprocal space. Figure 1 shows a method of including the effects of incident beam convergence by real-space summation. The degree of convergence is estimated by measuring the spot size in the experimental diffraction pattern (a). Each spot in the diffraction pattern is sub-sampled (b), and a series of images is computed at incident beam angles appropriately sampling the convergence cone.
Incoherence in atomic-resolution Z-contrast imaging
Authors: Jesson D. E. , Pennycook S. J.
Published: June 2020

Incoherent imaging of atomic clusters, monolayer rafts, or low index crystal projections at atomic resolution in a scanning transmission electron microscope (STEM) offers a number of distinct advantages over coherent imaging methods. These include an improved “interpretable” resolution and no experimental contrast reversals with specimen thickness or objective lens defocus. However, considerable controversy and confusion has arisen concerning the conditions under which the image of a given object can be interpreted using incoherent imaging theory. Here, we attempt to clarify the situation.

Firstly, we consider the case of very thin specimens, such as heavy atoms, clusters of atoms, or extremely thin crystals. Experimentally, these specimens demand a relatively low annular detector inner radius to achieve an acceptable signal-to-noise ratio in the image. It is usual, therefore, to match the detector inner radius to the radius of the directly transmitted disc. In this conventional geometry, the annular dark-field signal will be dominated by coherent scattering, and the use of incoherent imaging theory may give rise to appreciable error close to the resolution of the STEM instrument.
Structure of the Σ=5 (310) interface in NiAl
Authors: Fonda Richard W. , Luzzi David E.
Published: June 2020

The atomic structure of the Σ=5 [001] (310) grain boundary in NiAl was examined by high resolution electron microscopy and multislice image simulation. As in most other intermetallic compounds, the grain boundaries in NiAl are intrinsically brittle at low temperatures. Although there have been few studies on this alloy, the energies of NiAl grain boundaries have been calculated using embedded atom potentials for both stoichiometric and non-stoichiometric structures. These studies are consistent with the results of Bradley and Taylor, which indicate that nickel-rich compositions result from nickel antisite defects on the aluminum sublattice, while aluminum-rich compositions produce constitutional vacancies on the nickel sublattice, and with recent field ion microscopy results on nickel-rich alloys.

The Σ=5 grain boundary was prepared by diffusion bonding at 1000 °C. A JEOL 4000EX was used for HREM imaging and the NUMIS multislice simulation program was used to simulated images. Analysis of these images considered the effects of grain boundary expansion, rigid body displacements along the boundary, grain boundary stoichiometry, and point defects at the boundary.
Structure and chemical composition of nanophase particles in Mg-based alloys
Authors: Radmilovic V. , Thomas G.
Published: June 2020

Conventional and high resolution transmission electron microscopy, as well as microchemical analyses, are playing an important role in identifying precipitates in Mg based alloys for aerospace applications, especially for nanometer sizes. During aging of Mg-Al-Nd-Zn based alloys, Al-Nd-Zn based particles precipitate which affect the mechanical properties. These alloys, which serve as the metal matrix for MMC materials containing SiC particulates as reinforcement, are processed by rapid solidification/powder metallurgy techniques, and they are designed for relatively high temperature (250-300° C) applications.

Figure 1 shows the typical structure of second-phase particles in the Mg-based matrix. The spread in the particle size range is quite large, e.g., roughly between 70 and 100 nm. Close examination of these particles shows (Fig. 2) that there is no coherency with the Mg-based matrix, and no specific crystallographic relationship has been established. In some cases the growing direction of large particles was found to be within 5° of the C-axis of the Mg matrix.
Characterization of the dislocation core structure of partial dislocations in SiC(011) using HRTEM: a theoretical study
Authors: Geipel T. , Pirouz P.
Published: June 2020

The mobility of a dislocation in compound semiconductors of zincblende or wurtzite structure depends on its core structure i.e. its chemical composition. Present analytical techniques are not able to resolve the nature of the atomic species at the dislocation core and although HRTEM is capable of resolving the atomic arrangement in the core, its chemical characterization is difficult. In single crystalline regions the chemical composition can be determined using chemical mapping but this method cannot be applied to dislocations, viewed end-on, because these are non-periodic features. In a HRTEM image of a compound material, different scattering factors of the constituent elements may lead to spots of different brightness, but these contrast differences are very small. The only distinct characteristic of a HRTEM image is the spacings between bright or dark spots which can be measured easily. In this paper a practical concept for chemical distinction between Si and C in the cores of partial dislocations in SiC(011) is presented.
Multislice calculations of RHEED patterns from vicinal Si (001)
Authors: Lordi Scott
Published: June 2020

Vicinal Si (001) surfaces are interesting because they are good substrates for the growth of III-V semiconductors. Spots in RHEED patterns from vicinal surfaces are split due to scattering from ordered step arrays and this splitting can be used to determine the misorientation angle, using kinematic arguments. Kinematic theory is generally regarded to be inadequate for the calculation of RHEED intensities; however, only a few dynamical RHEED simulations have been attempted for vicinal surfaces. The multislice formulation of Cowley and Moodie with a recently developed edge patching method was used to calculate RHEED patterns from vicinal Si (001) surfaces. The calculated patterns are qualitatively similar to published experimental results and the positions of the split spots quantitatively agree with kinematic calculations.

RHEED patterns were calculated for unreconstructed (bulk terminated) Si (001) surfaces misoriented towards [110] ,with an energy of 15 keV, at an incident angle of 36.63 mrad ([004] bragg condition), and a beam azimuth of [110] (perpendicular to the step edges) and the incident beam pointed down the step staircase.
UHV-TED study of clean Si(100) surface structures
Authors: Jayaram Ganesh
Published: June 2020

Detailed information about the structure of silicon surfaces is very important prior to deposition of metal contacts. Though transmission electron diffraction is sensitive to the atomic structures of both the surface and the bulk, under appropriate conditions, information on the structure of the surface can be obtained from a careful analysis of the diffraction spot intensities.

Since Si(100) surface is highly reactive (sticking coefficient for water = 1), preparation and observation of clean surfaces necessitates ultra-high vacuum (UHV) conditions. A thin sample of Si(100) (B doped to 1 ohm-cm) was prepared for observation inside a Hitachi UHV-H9000 300keV electron microscope (stable operation pressure ∼9xl0-11 Torr). It was mechanically polished, dimpled and ion-milled before being transferred into a UHV surface science chamber attached to the microscope. In situ sample preparation carried out inside this chamber involved a combination of sputtering using 2-4 keV argon ions (to clean the surface) and electron-gun annealing cycles (to order the surface).
Convergent beam electron diffraction interferometry using an electron biprism (CBED+EBI)
Authors: Herring R.A. , Pozzi G. , Tanji T. , Tonomura A.
Published: June 2020

Recently, a new method of interferometry has been realized which is capable of providing important information of crystals, crystal defects and electron-optical information of the microscope such as its spherical aberration surface. The method produces interferograms by using an electron biprism to interfere diffracted beams produced from a small convergent beam probe of ∼10 nm. The electron biprism uses an applied voltage of ∼15 to 100 V to deflect and compensate for the diffracted beam(s) of 2θB (typically ∼5 mrad) (Fig. 1). The biprism ∼0.3 μm dia) is inserted in between and perpendicular to the diffracted beam(s). Two biprism positions were successfully used. An “upper” biprism is placed in the selected area aperture position which is between the objective lens and 1st intermediate lens. A “lower” biprism is further down the optic axis and is placed between the 1st and 2nd intermediate lenses. In Fig. 1, the virtual image of a biprism is shown with respect to the specimen plane.
Development of a 300 kV field emission TEM
Authors: Ishida Y. , Bando Y. , Kitami Y. , Tomita T. , Kersker M.
Published: June 2020

The 300 kV analytical electron microscope, as compared with the 100 to 200 kV instruments, have excellent features such as the high resolution of TEM images, high P/B ratio of EDS and PEELS, and high spacial resolution in analysis.

We hereby report the principal specifications of an ultrahigh sensitivity and ultrahigh resolution field emission type electron microscope, which, capable of giving full play to the above-mentioned features of the 300 kV analytical instrument, allows elemental analysis at the single atomic layer level (nm regions).

Its electron gun, simply operated by CPU control, allows emission current to be obtained at the touch of a single button. As the emitter, a W (100)-TF emitter, which can be used simply, stably, and for a long period of time, is employed. After build-up, this emitter can obtain about 10 times the angular current density of the W (310) emitter. Around the emitter are provided three electrodes to make emission current variation and electrostatic lens function independent of each other.
Observation of crystal structures by image restoration in electron holography
Authors: Tanji Takayoshi , Ishizuka Kazuo
Published: June 2020

Off-axis electron holography has been applied to crystal structure images using digital image processing.

Three important factors pertaining to the correction of aberrations in electron holography are:

(1)

interference fringes narrower than one third of the required resolution,

(2)

a Signal to Noise (S-N) ratio in the hologram which is high enough for high resolution reconstruction, and

(3)

the estimation of the amount of aberrations.

We have obtained interference fringes with a spacing of below 0.03 nm , which is sufficient for a resolution of 0.1 nm in the reconstructed image. The S-N ratio depends on the instrument used to record the hologram and whether the specimen causes strong scattering or weak scattering.

Some ways of estimating the amount of aberration have been proposed. Here we adopted an algorithm which involves minimizing the contrast of the reconsturcted image by optimizing the processing parameters (Cs and df), because it is applicable not only to weak phase objects but also to general phase objects and, in principle, only one hologram is needed to determiner the parameters.
Electron holography of electrostatic fields
Authors: Joy D. C. , Zhang X. , Mohan A. , Cunningham B.
Published: June 2020

Electron Holography allows both the amplitude and phase of a transmitted wavefront to be stored and subsequently recovered by a reconstruction of the hologram. Since both magnetic and electric fields change the phase of an electron wave that passes through them electron holography can therefore be used to directly, and quantitatively, image such fields. Significant experimental applications have already been made of this technique to the study of magnetic fields and materials, and electric fields have been studied in ferroelectric materials. Such a technique has particular value when applied to the study of semiconductor devices since these rely for their operation on the electric fields produced internally at P-N junctions or Shottky barriers. Holographic imaging of these fields will make it possible to accurately find the active regions of junctions as well as making it possible to measure the electrostatic fields that are present. Consider a cross-sectioned P-N junction of thickness t placed normal to the beam (figure 1).
Implant-induced strain-relaxation in SiGe/Si layers
Authors: David Theodore N. , Tam Gordon
Published: June 2020

SiGe is being extensively investigated for use in heterojunction bipolar-transistors (HBT) and high-speed integrated circuits. SiGe is typically used as an epitaxial base material in HBTs. To obtain extremely high-performance bipolar-transistors it is necessary to reduce the extrinsic base-resistance. This can be done by increasing the base-doping or by widening the base link-region by ion implantation. A problem that arises however with the use of implantation is that blanket implants have been found to enhance strain-relaxation of SiGe/Si. Strain relaxation will cause the bandgap-difference between Si and SiGe to decrease; this difference is maximum for a strained SiGe layer. The electrical benefits of using SiGe/Si arise largely from the presence of a significant bandgap-difference across the SiGe/Si interface. Strain relaxation reduces this benefit. Furthermore, once misfit or threading dislocations result (during strain-relaxation), the defects can give rise to recombination-generation in depletion regions of the device; high electrical leakage currents result.
A novel UHV-REM as applied to observation of reconstruction of Pt(100) surface
Authors: Takeguchi Masaki , Akita Tomoki , Takai Yoshizo , Shibata Kichiro , Shimizu Ryuichi
Published: June 2020

Direct observation of surface reconstruction under reflection electron micros-copy(REM) provides an intimate insight into basic processes on the surface, leading to more comprehensive understanding of surface physics in atomic scale. For this purpose we have developed a special UHV-specimen chamber, which allows various types of attachments, e.g., evaporator, ion gun, cooling facility, gas inlet and STM if necessary, to be mounted. This chamber was mounted in a 200kV transmission electron micro scope(TEM), Hitachi H-700H, to construct a novel UHV-REM for surface study.

Fig.l shows a schematic diagram of the UHV-TEM constructed in the present work. The specimen chamber is evacuated with turbomolecular pump and Ti sublimation pump to the vacuum pressure of ~10-9 Torr. Some additional ports for, evaporator, gas-inlet, etc. are also attached around the specimen stage. Feedthrough metal bellows for driving system allows specimen holder to be translated in X- and Y-directions and to be tilted against electron beam without deterioration of vacuum pressure.
TEM observations of surface-step and hole-edge faceting in acid-etched and annealed MgO thin foils
Authors: King Simon , Barry Carter C.
Published: June 2020

Surface-steps formed during the cleavage of MgO on {100} planes, the smaller steps of which may be of atomic height, have been observed in Reflection-Electron Microscopy investigations to be accurately aligned along <001> directions. Steps of atomic height also have been identified on MgO smoke-particle platelets; these steps may be curved or straight, with the straight steps showing evidence for faceting along <001>. Reference also is made to faceting along <011> and <012> directions. Straight steps ∼2 unit cells high, with edges along <100> also have been imaged by High-Resolution Profile-Imaging at the peripheries of MgO smoke microcubes. After etching in aqua-regia and annealing in air, however, high densities of “large” steps several unit cells high, as well as numerous holes, are formed. It is faceting in these foils that is reported here.

As can be seen in fig 1, obvious faceting of the surface-step traces is extremely rare in these foils, in marked contrast to substrates such as LaAlO3 and SrTiO3, on which surface-step traces facet readily after a similar preparation treatment.
Imaging microstructural contact damage in silicon
Authors: Morris Jonathan C.
Published: June 2020

The indentation of single crystal silicon has been shown to produce a metal to semiconducting structural phase transformation. This phase transformation dominates the effect of contact damage from both indentation and scratching at low loads and hence affects the results of related mechanical tests. We are examining the microstructure of contact damage in silicon in order to understand better the mechanisms which control its low-load mechanical and tribological behavior. Extensive transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) have been used to characterize both morphological and structural changes brought about by contact damage.

The plan-view bright field image in Figure 1 exhibits strong crystallographic contrast outside of the indented area. The indented area as well as the extrusions emanating from it are amorphous as evidenced by their lack of crystallographic contrast regardless of tilt as well as their diffuse illumination in dark field. Small bits of fragmented polycrystalline silicon are visible at the indentation borders as well as at the tip of one extrusion.
Characterization of the oxidation-sulfidation of a preoxidized ODS FeCrAl alloy
Authors: Pint B. A. , Banks B. M. , Duncan J. C. , Garratt-Reed A. J. , Hobbs L. W.
Published: June 2020

Preoxidation is a common technique used to protect alloys from environmental degradation. A dense, adherent oxide is grown on an alloy before placing it into a more aggressive environment. Thus, under conditions such as the mixed O-S atmosphere found in coal gasification, the rapid formation of sulfide can be avoided.

While several studies have looked at the formation of protective alumina scales in mixed H2-H2O-H2S environments, none of these studies have considered the formation of less-protective, metastable aluminas on the oxidation behavior at temperatures less than 1000°C where θ-Al2O3 is commonly formed. This is especially important because in order to form an adherent alumina scale, an oxygen-active element such as Y, Ce, Hf or Zr is routinely added and these types of elements have been found to stabilize the lower-temperature alumina phases and inhibit the transformation to α-Al2O3. Furthermore, the transformation from θ- to α-Al2O3 involves a 13% volume reduction and cracking through the scale which could compromise the protectiveness of the scale.
A high-resolution EM study of grain boundaries in Pr and Co-doped ZnO ceramics
Authors: Solórzano I.G. , Vander Sande J.B. , Baek K.K. , Tuller H.L.
Published: June 2020

Metal oxide varistors are multijunction materials whose nonlinear current-voltage characteristics derive from the electrical activity of their grain boundary regions. The high degree of nonlinear-ity in polycrystalline ZnO has been attributed to the synergistic action of two types of cations added in sufficient concentrations: transition metals, such as Co and Mn which have ionic radii similar to that of the ZnO matrix, and dopants with large ionic radii, such as Bi and Pr which segregate at grain boundaries and usually form intergranular phases. The present investigation was undertaken with the objective to clarify the role of dopants in an electrically active Pr and Co doped ZnO ceramic by studying the structure and chemistry of individual grain boundaries through high-resolution electron microscopy (HREM) and analytical electron microscopy (AEM).

Bulk specimens containing 1 mol% Pr and 1 mol% Co were prepared by conventional sintering at 1400° C. Some samples followed an oxidative anneal at 650° C for 3 h to further enhance their electrical activity.
Characterization of copper oxide deposited on α-Al2O3 by pulsed-laser ablation
Authors: Bench M.W. , Sartain K.B. , Mallamaci M.P. , Carter C.B.
Published: June 2020

The Cu-Al-O system is of considerable interest for electronic packaging, where thin copper wires are bonded to alumina substrates. In order to optimize the adhesion properties of Cu to alumina, it has been suggested that a ternary bonding environment is necessary at the interface. In comparison to a model oxide system such as NiO/alumina, where NiO is the only stable oxide of Ni and only one phase forms during the reaction, the situation is more complex in the Cu-Al-O system. First, two oxides of copper can form with CuO stable at room temperature and Cu2O stable above 1020°C in air. In addition, two copper aluminate reaction products (CuAl2O4 and CuAlO2) can form in the Cu-Al-O system. In a previous study it was found that both form during reactions in air at 1100°C, with the relative positions of each dependent on the crystallographic orientation of the alumina substrate.
Coherency-induced morphological instability in NiAl-type precipitate
Authors: Ghosh G. , Olson G. B. , Fine M. E.
Published: June 2020

In many commercial alloys, phase transformation involves nucleation and growth of coherent precipitates. The elastic strain fields around individual coherent precipitates and the overlap of such strain fields constitute an “elastically constrained system” in which the precipitates exhibit shape transition and anomalous coarsening behavior. Results of classical γ-γ’ system shows that an individual precipitate may split into two parallel plates (or doublet) or eight smaller cuboids (or octate) with their faces parallel to the {100} directions. Theoretical modeling of such shape transitions imply that the process is governed by the competition between interfacial and elastic energies. Here, we report the shape transitions observed in an elastically constrained system involving bcc structures.

Polycrystalline specimens of Fe-6.42Al-14.8Ni (alloy#l) and Fe-8.08Al-12.2Cr-18.2Ni (alloy#2) were studied. Alloy#l was solution treated at 1100°C followed by continuous cooling at 0.01°C/s to 950°C and subsequently helium quenched. Similarly, alloy#2 was solution treated at 1200°C and continuously cooled at 0.01875°C/s to 1065°C and helium quenched to room temperature.
Study of factors affecting corrosion of aluminum automotive wheels
Authors: Plummer H. K. , Simmons R. N. , Ocobock R. W. , Honey T. A. , Paputa Peck M. C.
Published: June 2020

Aluminum automotive wheels, which have been used since the mid 1970’s, have proven to be very rugged, but early wheels discolored with time. Since 1976 the machined “bright” exterior surfaces, have been coated with a chromium based “conversion” pretreatment, and painted with a “clearcoat” of polyester or acrylic to preserve appearance. These coated wheels can exhibit “filiform” corrosion between the Al surface and the clearcoat (Fig. 1). The corrosion is filamentous and closely follows aluminum grain boundaries. Corrosion results from oxidation of the aluminum (anode) in the presence of water and oxygen at a break (cathode) which intrudes through the clearcoat and conversion coat into the aluminum (Fig. 2). Current specifications require ≤ 1.6 mm filiform corrosion from a scratch after 400 h of accelerated corrosion testing. This paper correlates accelerated corrosion with the composition of the clearcoat paint, the UV absorbance of the paint and the microstructure of the Al / Cr conversion coat / clearcoat interface to learn the necessary parameters to produce Al wheels with enhanced protection. Production Al wheels, from a variety of sources, wheels prepared to our specifications and a design of experiments (DOE) wheel series prepared in our laboratories were examined.

The accelerated corrosion test exposes the test piece to UV weathering (400 h) with four water spray cycles every 23 h. After UV exposure the surface is scratched through the surface layers into the Al metal with a carbide scribe, followed by exposure to HCl vapor (1 h).
Microstructure of superconducting Y1Ba2Cu3O7-x/Nd1.85Ce0.15CuO4-y bilayer films
Authors: Prasad Beesabathina D. , Salamanca-Riba L. , Mao S. N. , Xi X. X. , Venkatesan T.
Published: June 2020

Superconducting bilayers of Y1Ba2Cu3O7-x(YBCO) and Nd1.85Ce0.15CuO4-y (NCCO) are of particular interest for the study of the interaction between p-type superconductors(YBCO) and n-type superconductors for possible device applications. The microstructural study is crucial since the crystallinity and interface quality of the bilayers effect the characteristics of heterojunctions. In this report, we present details of the microstructure of superconducting NCCO/YBCO bilayers.

NCCO/YBCO bilayers were deposited on three different single crystal substrates of (001) LaAlO3, (001) SrTiO3, and (001) Y-ZrO2(YSZ) using pulsed laser depositon. The details of the deposition and superconducting properties are reported elsewhere. The samples reported in this report have typical YBCO thickness of 2000 A and NCCO thickness of 4000 A.

Figure 1(a) shows a bright field image of a NCCO/YBCO bilayer grown on YSZ and exhibits a Moire’ fringe pattern in some regions of the NCCO film. The Moire’ fringes have a spacing of ∼ 31.01 Å.
Cryomicroscopy of low-Tg latex particles via freeze drying
Authors: Reffner J. R.
Published: June 2020

Transmission Electron Microscopy (TEM) is a powerful tool for investigating the structure of latex particles. However, examining low Tg (glass transision, Tg < room temperature) latex particles requires special techniques due to the significant deformation which occurs if the particles are dispersed onto a substrate at room temperature. Here a freeze drying (FD) technique is presented which permits individual emulsion particles, including stained particles, to be examined in a manner that minimizes deformation by maintaining the particles at temperatures below Tg.

Typically, particle morphology is determined from images of individual latex particles dispersed onto a supporting ultra-thin substrate or from images of ultra-microtomed sections of films cast from the latex. Examining particles dispersed onto a substrate is often advantageous, allowing direct determination of particle shape and characterization of the morphology prior to the film formation process. Although low Tg materials can be examined using this technique, information about the size, shape and morphology of phase separated domains can be obscured by the deformation which occurs when the particles are examined at room temperature.
Morphological behavior of compatibilized ternary blends prepared by mechanical mixing
Authors: Smith S.D. , Spontak R.J. , Melik D.H. , Buehler S.M. , Kerr K.M. , Roe R.-J.
Published: June 2020

When blended together, homopolymers A and B will normally macrophase-separate into relatively large (≫1 μm) A-rich and B-rich phases, between which exists poor interfacial adhesion, due to a low entropy of mixing. The size scale of phase separation in such a blend can be reduced, and the extent of interfacial A-B contact and entanglement enhanced, via addition of an emulsifying agent such as an AB diblock copolymer. Diblock copolymers consist of a long sequence of A monomers covalently bonded to a long sequence of B monomers. These materials are surface-active and decrease interfacial tension between immiscible phases much in the same way as do small-molecule surfactants. Previous studies have clearly demonstrated the utility of block copolymers in compatibilizing homopolymer blends and enhancing blend properties such as fracture toughness. It is now recognized that optimization of emulsified ternary blends relies upon design considerations such as sufficient block penetration into a macrophase (to avoid block slip) and prevention of a copolymer multilayer at the A-B interface (to avoid intralayer failure).
Dirac-fock calculations of scattering factors and mean inner potentials for neutral and ionised atoms
Authors: Rez David , Rez Peter
Published: June 2020

Tables of X-ray and electron scattering factors are essential for programs that calculate diffraction intensities or simulate images. These tables are calculated from atomic charge densities derived from Hartree Fock programs for atoms. The most frequently used results are those due to Doyle and Turner who used Coulthard's relativistic Hartree Fock program. They did not calculate scattering factors for all elements and other results using different programs were used to complete the tables given in the International Tables for Crystallography. As microscopy and diffraction become more quantitative it has become important to reexamine the calculation of atomic scattering factors using more recent Hartree Fock codes to quantify more precisely differences due to solid state effects. We also feel it is desirable to calculate all naturally occuring elements, and their common ionised states, using the same program.

The charge densities were calculated using the Multi-Configuration Dirac-Fock code of Grant et al.
Simulating electron microscope diffraction mode with a Macintosh-based program
Authors: Zuo J. M. , Zhu H. R. , Spence Andrew
Published: June 2020

With the recent trend towards to the quantification of electron diffraction patterns, there is an increasing need for simulating the geometry of convergent beam electron diffraction patterns, and especially the high order Laue zone (HOLZ) lines in such patterns. The simulation program is useful in the way that the simulated and the experimental pattern can be compared, and then the important diffraction parameters such as reflection indices, beam directions and lattice constant could be found and used. Here we describe a Macintosh based program, which simulates electron diffraction pattern in the same way as the operation of electron microscope diffraction mode. The program has a control panel with the ‘scroll bar’ control devices for x and y tilt of specimen stage, x and y deflection of diffraction pattern and camera length (see figure 1). The user can change the simulated diffraction pattern by changing the ‘control devices’ with a pointing device such as a mouse.
Electron microscopy and diffraction of crystalline dendrimers and macrocycles
Authors: Buchko C. J. , Wilson P. M. , Xu Z. , Zhang J. , Lee S. , Moore J. S. , Martin D. C.
Published: June 2020

The synthesis of well-defined organic molecules with unique geometries opens new opportunities for understanding and controlling the organization of condensed matter. Here, we study dendrimers and macrocycles which are synthesized from rigid phenyl-acetylene spacer units, Both units are solubilized by the presence of tertiary butyl groups located at the periphery of the molecule. These hydrocarbon materials form crystalline and liquid crystalline phases which have been studied by differential scanning calorimetry, hot stage optical microscopy, and wide-angle x-ray scattering (WAXS).

The precisely defined architecture of these molecules makes it possible to investigate systematic variations in chemical architecture on the nature of microstructural organization. Here we report on the transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high resolution electron microscopy (HREM) studies of crystalline thin films formed by deposition of these materials onto carbon substrates from dilute solution. Electron microscopy is very attractive for gaining structural information on new molecules due to the scarcity of material to grow single crystals suitable for conventional crystallography.
Improvement of amplitude-divided electron holography
Authors: Ru Q. , Endo J. , Tonomura A.
Published: June 2020

Compared with the wavefront-divided electron holography obtained by an electron biprism, the amplitude-divided one proposed by Matteucci et al. has some essential advantages: less necessary coherency, wide interference area and available to most of transmission electron microscopes. In order to confirm and achieve these advantages in practical use, we introduce some improvements in both hologram formation and reconstruction steps. Two electron-optical setups and experimental results are presented for small objects (<1 μm) and much large objects (>1 μm), respectively.

The electron-optics for taking the holograms of small objects is illustrated in Figure 1. A single crystal thin film (gold film of 0.2nm lattice spacing is used in our experiment) is placed on the objects (latex particles of 120 nm on a thin carbon film are used here) with a certain gap. In fact, the gap is spontaneously made by the microgrids of the specimen film and the crystal film.
Secondary ion imaging microanalysis
Authors: Levi-Setti R. , Chabala J. M. , Girod-Hallegot C , Hallegot P. , Wang Y. L.
Published: June 2020

The goals of high spatial resolution and high elemental sensitivity in the imaging microanalysis of biological tissues and materials have, to a large extent, been attained by using the method of secondary ion mass spectrometry (SIMS) following bombardment of a sample surface by a focused beam of heavy ions. The instrument that we will discuss and which has achieved these goals is a scanning ion microprobe originally developed in collaboration with Hughes Research Laboratories (UC-HRL SIM). It utilizes a 40-60 keV Ga+ probe, extracted from a point-like liquid metal ion source, that can be focused to a spot as small as 20 nm in diameter. During the past five years, much effort has been devoted to a reappraisal of well known SIMS methodologies in regard to their applicability to a range of lateral resolution (20-1000 nm) previously unexplored. Furthermore, of particular concern has been the identification of research areas whose demands could most profitably be matched by the performance of this new class of microprobes. The results of this effort are contained in over 21 topical publications and 14 review articles covering both instrumental aspects of our development and applications to a variety of interdisciplinary problems.
Roughness measurements of nonlinear optical polymer films by scanning tunneling microscopy
Authors: Musselman I. H. , Chen R.-T. , Russell P. E.
Published: June 2020

Scanning tunneling microscopy (STM) has been used to characterize the surface roughness of nonlinear optical (NLO) polymers. A review of STM of polymer surfaces is included in this volume. The NLO polymers are instrumental in the development of electrooptical waveguide devices, the most fundamental of which is the modulator. The most common modulator design is the Mach Zehnder interferometer, in which the input light is split into two legs and then recombined into a common output within the two dimensional waveguide. A π phase retardation, resulting in total light extinction at the output of the interferometer, can be achieved by changing the refractive index of one leg with respect to the other using the electrooptic effect. For best device performance, it is essential that the NLO polymer exhibit minimal surface roughness in order to reduce light scattering. Scanning tunneling microscopy, with its high lateral and vertical resolution, is capable of quantifying the NLO polymer surface roughness induced by processing. Results are presented below in which STM was used to measure the surface roughness of films produced by spin-coating NLO-active polymers onto silicon substrates.
Direct imaging of nucleic acid conformation in water by scanning tunneling microscopy
Authors: Lindsay S.M. , Nagahara L. , Thundat T.
Published: June 2020

We have developed methods for imaging biopolymers under water by scanning tunneling microscopy (STM). The STM gives fairly high resolution images of small biopolymers. Larger polymers may be imaged with the atomic force microscope. Both techniques allow biological processes to be studied as they occur. Both suffer limits on resolution which are a consequence of the distortion of soft biological molecules by the contact force of the probe. The chemical sensitivity of the STM can be exploited to overcome this limitation, and we will discuss methods for nucleic acid sequencing.

A number of images of nucleic acids in various configurations are displayed on the following page. All are perspective projections looking into the substrate at an angle of about 45° with respect to the axes. (A) shows a random-sequence fragment of double helical DNA. The 36Å helix repeat is clearly visible. (B) shows a single strand of poly (rU). (C) Shows (left side) three complete 146 base-pair fragments of DNA from the nucleosome. (D) shows a kinked nucleosome fragment.
Current and future directions of on-line Transmission Electron Microscope image processing and analysis
Authors: O’Keefe Michael A. , Kilaas Roar
Published: June 2020

Image processing and analysis are increasingly employed in order to extract the maximum amount of useful information from transmission electron micrographs. Whereas most processing is carried out a posteriori, i.e. from images that have been recorded on film then digitized for computer processing, it is obviously useful to be able to improve the on-line image in near-real time for the benefit of the microscope operator. In addition, interfacing an external computer to the internal controls of modern TEMs allows on-line image analysis to provide the first step in algorithms designed to assist the operator in adjustment of microscope parameters such as alignment, astigmatism and defocus.

The hardware required for on-line image processing can be as simple as a detector coupled to a TV camera, the signal from which is digitized, stored and averaged by a set of cards controlled by a host computer, with a monitor displaying the image stored in the memory card.
Multislice calculation of Kikuchi patterns
Authors: Fant G. Y.
Published: June 2020

The diffraction of the inelastically and pseudo-elastically scattered electrons in a crystal gives rise to the diffuse background in a diffraction pattern, including Kikuchi patterns as they are known, which are very sensitive to the direction of electron incidence relative to the crystal orientation. In the exact zone orientation, i.e., when the electrons are travelling along a major zone axis, a Kikuchi-band pattern is formed which reflects the crystal symmetry about that axis; otherwise, the pattern is known as Kikuchi-line pattern (thereafter collectively referred to as K-patterns).

For localized inelastic events, such as interactions of incident electrons with shell electrons and various crystal point defects, in which intra-process coherence is negligible, the K-patterns can be simulated using the method described below.

An inelastic event creates a spherical wave which, however, is strongly peaked in the forward direction of electron traveling, as given by the typical form f(θ)e-kr/r, where symbols have their usual meanings.
Condenser/objective lens SE-I Imaging of chromium-coated biological specimens using a Schottky field emission source
Authors: Apkarian R.P.
Published: June 2020

We have had experience with high resolution SE-I enriched imaging of chromium(Cr) coated soft and hard biological tissue. SEMs equipped with condenser/objective (c/o) lens stages and LaB6(ISI DS-130) or cold cathode field emission (CFE)(Hitachi S-900) sources operated at high voltage(15-30 KeV) were assessed by the comparison of emission properties and image contrasts generated from ferritin test specimens. Practical source performance during the imaging of metal coated bulk biological tissues is subject to the metal film quality which is responsible for generating accurate topographic contrasts at high magnifications of biologically significant structures in the 1-10 nm range. Recently a thermionically assisted Schottky field emission source(SFE) has been designed for the c/o lens optics of the ISI DS-130 SEM. A practical consideration for the imaging of biological microdomains at high magnification must be: how does the SFE source compare with the LaB6 emitter on the same optical column and can the SFE compare with the CFE for producing quality ultrahigh magnification (500,000x) topographic contrasts in the nanometer range.