bluuebunny/crossref_metadata_2025 huggingface dataset:
Flux-pinning-related defect structures in melt-processed YBa2Cu3O7-x
Authors: Wang Z. L. , Kontra R. , Goyal A. , Kroeger D. M. , Allard L.F.
Published: June 2020

Previous studies of Y2BaCuO5/YBa2Cu3O7-δ(Y211/Y123) interfaces in melt-processed and quench-melt-growth processed YBa2Cu3O7-δ using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) have revealed a high local density of stacking faults in Y123, near the Y211/Y123 interfaces. Calculations made using simple energy considerations suggested that these stacking faults may act as effective flux-pinners and may explain the observations of increased Jc with increasing volume fraction of Y211. The present paper is intended to determine the atomic structures of the observed defects. HRTEM imaging was performed using a Philips CM30 (300 kV) TEM with a point-to-point image resolution of 2.3 Å. Nano-probe EDS analysis was performed using a Philips EM400 TEM/STEM (100 kV) equipped with a field emission gun (FEG), which generated an electron probe of less than 20 Å in diameter.

Stacking faults produced by excess single Cu-O layers: Figure 1 shows a HRTEM image of a Y123 film viewed along [100] (or [010]).
The interfacial structure of orthogonally oriented twins in YBa2Cu3O7
Authors: Zhu Yimei , Suenaga M. , Tafto J.
Published: June 2020

Interfaces such as the twin boundary and grain boundary in YBa2Cu3O7-δ are thought to be important in reconciling the large discrepancy between the low critical-current density observed in bulk polycrystalline. Recently, we studied another type of frequently encountered interface, i.e., the interface between the orthogonally orientated (110) and (-110) twins. In the vicinity of the interface, the crystal has a characteristic geometry because of additional constrains due to the impediment and the local orientational difference. The impinging twins usually have a wedge shape (Fig. la), and when the wedge slope is large, the tip of the twin splits (Fig. lb). A HREM image of a tapered twin is shown in Fig.2. Four twin variants give rise to five boundaries. Boundaries between IV-III, III-IV, IV-II, and II-IV are twin boundaries, while II-III, which has no apparent structure, is the interface of the orthogonal twins. If there is no constrain, the orientation of II and III should be equivalent (Fig.3a and 3b); however, we observed that the lattice in II does not align with that in III.
Low-Tc phase formation at the grain boundaries and electromagnetic granularity in (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed tapes
Authors: Feng Yi , Umezawa A. , Edelman H. S. , Larbalestier D. C.
Published: June 2020

High resolution transmission electron microscopy (HRTEM) was performed on progressively heat treated Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes and was correlated with their transport critical current densities, DC magnetization and AC susceptibility. HRTEM reveals the presence of a small number of half layers of the low Tc Bi2Sr2CaCu2Ox (2212) phase clustered at the numerous (001) twist grain boundaries. This residual 2212 phase produces electromagnetic granularity in a temperature range around 77K and thus directly controls the critical current.

The Bi(Pb)-Sr-Ca-Cu-0 (BSCCO) Ag-clad tapes with the stoichiometric 2:2:2:3 starting composition were prepared by a standard powder-in-tube method. Sample A was heat treated at 817°C for 5 hours only. Sample B was first heat treated at 817°C for 24 hours, and then heat treated for 100 hours at the same temperature after two intermediate pressings. Sample C was heat treated at 830°C for 72 hours, and then heat treated for additional 196 hours after one intermediate pressing.
The effect of time and temperature on the segregation of foreign ions to grain boundaries in growing α-Al2O3 scales
Authors: Pint B. A. , Garratt-Reed A. J. , Hobbs L. W.
Published: June 2020

The addition of small quantities of certain oxygen-active or “reactive” elements (REs) such as Y, Zr, Hf and Ce produces a tremendous improvement in the oxidation behavior of both chromia and alumina-forming alloys. However, few of the hypotheses that have been put forth to explain this phenomenon have been confirmed by careful characterization of the oxidation process.

The segregation theory emphasizes the role of RE segregation to oxide grain boundaries and has been successful in correlating the presence of Y and Zr segregants to changes in the oxidation mechanism (thus reducing the oxidation rate) of chromia and alumina scales. Improvements in oxide adhesion have been attributed to the segregation of REs to the metal-alumina interface on doped β-NiAl and FeCrAl alloys. All of these studies employed FEG-STEM equipped with XEDS in order to detect the interfacial segregation.

The RE is also found in the scale as RE-rich particles which have been observed after high temperature oxidation using XEDS on SEM and FEG-STEM and detected using glancing-angle (0.5° incident angle) x ray diffraction.
New titanium oxide precipitates in Ti-doped sapphire
Authors: Xiao S. Q. , Phillips D. A. , Heuer A. H.
Published: June 2020

When Ti-doped α-Al2O3 single crystals are annealed at 1400°C, needle-like rutile TiO2 precipitates form on the basal plane of α-Al2O3 and cause the asterism in star sapphire. Tetragonal rutile has a = 0.459 nm and c = 0.296 nm, and has the following orientation relationship with the α-Al2O3 matrix: (100)r // (0001)s and <011>r // <100>s, where the subscripts r and s refer to the rutile and sapphire, respectively. Moon and Phillips studied the precipitation in natural blue sapphire containing both Fe and Ti. They found that rutile precipitates formed after annealing at 1350°C but an orthorhombic α-TiO2 precipitate formed after annealing at 1150°C. In this study, Ti-doped α-Al2O3 single crystals were annealed at 1300°C. TEM specimens were prepared with their plane normals parallel to <110>s, <100>s and <0001>s, respectively, and ion beam thinned to electron transparency.

Three different types of precipitates are present in the α-Al2O3 matrix. The first is the needlelike rutile precipitate lying on (0001)s, with the needle axes parallel to <100>s.
Contrasts of planar defects in reflection electron microscopy
Authors: Tsai Feng , Cowley J. M.
Published: June 2020

Reflection electron microscopy (REM) has been used to study surface defects such as surface steps, dislocations emerging on crystal surfaces, and surface reconstructions. However, only a few REM studies have been reported about the planar defects emerging on surfaces. The interaction of planar defects with surfaces may be of considerable practical importance but so far there seems to be only one relatively simple theoretical treatment of the REM contrast and very little experimental evidence to support its predications. Recently, intersections of both 90° and 180° ferroelectric domain boundaries with BaTiO3 crystal surfaces have been investigated by Tsai and Cowley with REM.

The REM observations of several planar defects, such as stacking faults and domain boundaries have been continued by the present authors. All REM observations are performed on a JEM-2000FX transmission electron microscope. The sample preparations may be seen somewhere else. In REM, the incident electron beam strikes the surface of a crystal with a small glancing angle.
Reflection electron microscopy of as-grown diamond surfaces
Authors: Wang Z.L. , Bentley J. , Clausing R.E. , Heatherly L. , Horton L.L.
Published: June 2020

It has been found that the abrasion of diamond-on-diamond depends on the crystal orientation. For a {100} face, the friction coefficient for sliding along <011> is much higher than that along <001>. For a {111} face, the abrasion along <11> is different from that in the reverse direction <>. To interpret these effects, a microcleavage mechanism was proposed in which the {100} and {111} surfaces were assumed to be composed of square-based pyramids and trigonal protrusions, respectively. Reflection electron microscopy (REM) has been applied to image the microstructures of these diamond surfaces.

{111} surfaces of synthetic diamond:

The synthetic diamonds used in this study were obtained from the De Beers Company. They are in the as-grown condition with grain sizes of 0.5-1 mm without chemical treatment or mechanical polishing. By selecting a strong reflected beam in the reflection high-energy electron diffraction (RHEED) pattern, the dark-field REM image of the surface is formed (Fig. 1).
Microstructure and magnetic Structure of Co-based thin-film recording medium
Authors: Futamoto M. , Honda Y. , Inaba N. , Matsuda Y. , Suzuki M.
Published: June 2020

Knowledge of the relationship between microstructure and microscopic magnetization configuration is strongly required to improve Co-based thin film media. The purpose of this paper is to report some of these properties measured for a thin film longitudinal recording medium and to discuss their inter-relationship.

Figure 1 shows an SEM micrograph of fractured cross-section of CoCrPt/CoCrPtSi dual-layered medium which was used to demonstrate the feasibility of 2 Gb/in2 magnetic recording. The Cr underlayer is used to control the orientation, size, and distribution of magnetic crystals. Magnetic crystal grains, whose size ranges between 20-30nm, form chain-like clusters consisting of several crystals as shown in the plan-view TEM micrograph(Fig.2). Neighboring clusters are separated physically with an average distance of 3nm. Magnetic separation among magnetic crystals and/or clusters is important to reduce the medium noise which is related to magnetic coupling between crystals. The crystalline easy axes of the grains are randomly oriented in the film plane.
Magnetic domain wall movement in iron silicon
Authors: Wittig J.E.
Published: June 2020

Lorentz microscopy in the transmission electron microscope directly images magnetic domains. By changing the magnetic field of the electromagnetic lenses relative to the specimen plane, the movement of the magnetic domain walls and their interaction with microstructural features can be observed in situ. This type of experiment has successfully analyzed the microstructure-domain wall interactions in spinel ferrites and iron-rare-earth-boron magnetic materials. The domain wall motion reveals the qualitative pinning potential of grain boundaries, precipitates, inclusions, stacking faults, and cracks. In addition, these in situ experiments display the dynamics of magnetic domain nucleation. The current study investigates the magnetic domain wall movement in iron silicon alloys. Since magnetic properties such as intrinsic coercivity and permeability are structure sensitive, the influence of microstructure on domain wall movement dictates the soft magnetic behavior.

Thin foils of iron-6.5 wt% silicon were prepared by electropolishing ribbons produced by melt spinning techniques. The magnetic domain walls were imaged in the defocused (Fresnel) mode with a Philips CM20T operated at 200 kV.
Real-time observation of vortex lattices in a superconductor
Authors: Harada K. , Matsuda T. , Bonevich J.E. , Igarashi M. , Kondo S. , Kasai H. , Yoshida T. , Pozzi G. , Kawabe U. , Tonomura A.
Published: June 2020

Previous observations of magnetic flux-lines (vortex lattices) in superconductors, such as the field distribution of a flux-line, and flux-line dynamics activated by heat and current, have employed the high spatial resolution and magnetic sensitivity of electron holography. And recently, the 2-D static distribution of vortices was also observed by this technique. However, real-time observations of the vortex lattice, in spite of scientific and technological interest, have not been possible due to experimental difficulties. Here, we report the real-time observation of vortex lattices in a thin superconductor, by means of Lorentz microscopy using a 300 kV field emission electron microscope. This technique allows us to observe the dynamic motion of individual vortices and record the events on a VTR system.

The experimental arrangement is shown in Fig. 1. A Nb thin film for transmission observation was prepared by chemical etching. The grain size of the film was increased by annealing, and single crystals were observed with a thickness of 50∼90 nm.
Exploratory work on coherent diffraction and electron holography using a hitachi Hf 2000
Authors: Steeds J W , Vincent R , Spellward P , Deng X F
Published: June 2020

Now that coherent electron diffraction can be performed routinely on appropriately chosen specimens in a standard commercial instrument there are a number of applications of the technique which are in progress.

One of these is in crystal structure determination. For sufficiently thin crystals, the fringes in the overlap between adjoining reflections n and n+1 give the relative phases (ϕn + 1 - ϕn+δ) of their complex structure factors, apart from an unknown phase factor, δ, which depends on the probe position. In a systematic row of reflections, the next overlap between reflections n + 1 and n + 2 gives (ϕn + 2 - ϕn + 1+δ) and so the difference between these two phasings becomes (2ϕn + 1 - ϕn - ϕn + 2), eliminating the unknown factor δ. Now that coherent diffraction has been achieved in the zero order Laue zone of a zone axis pattern it is possible to phase the whole two dimensional mesh relative to the central beam (Figure 1).
On-line reconstruction of electron holograms
Authors: Ran W.D.
Published: June 2020

Electron-off-axis holography has proven to be a most promising tool for the collection of the complete information about amplitude and phase modulation of the complex electron image wave in one single micrograph. Then amplitude and phase can be reconstructed numerically, offering almost any wave-optical possibility for the evaluation of the electron object wave at the exit surface, including the elimination of the influence of coherent aberrations of the objective lens in the image wave. Bottle-neck of the whole two step - registration and reconstruction - procedure has long been the need for highly accurate conversion of the holograms to numerical data as well as the available computational power, since the necessary Fast Fourier Transforms are time consuming numerical operations. Modern CCD slow-scan detectors and the permanently increasing computing power speed up this process and. combined with state of the art FEG microscopy, supply the reconstructed amplitude and phase of the image wave to the microscopist on-line.
High-resolution coherent imaging in STEM
Authors: Cowley J.M. , Gribelyuk M.A.
Published: June 2020

The ultimate aim of high resolution electron microscopy is the accurate determination of the positions and types of the atoms in a specimen. The coherent imaging theory for STEM is reviewed with the emphasis on its potential for achieving this aim by holographic methods. The STEM modes of holography are in many respects equivalent to the corresponding TEM modes, but have the advantage that, because with a FEG electron source the focussed probes have sub-nanometer diameter, a strong signal is obtained from the illuminated region and the problem of shot-noise is much less important.

The original proposal for holography by Gabor envisaged the use of a reconstruction process on the recorded hologram to correct for the lens aberrations and hence improve the image resolution. The more general and more challenging problem is to reconstruct the aberration-free wave function at the exit face of the specimen (with its real and imaginary, or amplitude and phase, components) and then to invert the dynamical diffraction process and derive the projected potential distribution of the object.
Electron holography of interfaces in electroceramics
Authors: Dravid Vinayak P. , Ravikumar V. , Plass Richard
Published: June 2020

With the advent of coherent electron sources with cold field emission guns (cFEGs), it has become possible to utilize the coherent interference phenomenon and perform “practical” electron holography. Historically, holography was envisioned to extent the resolution limit by compensating coherent aberrations. Indeed such work has been done with reasonable success in a few laboratories around the world. However, it is the ability of electron holography to map electrical and magnetic fields which has caught considerable attention of materials science community.

There has been considerable theoretical work on formation of space charge on surfaces and internal interfaces. In particular, formation and nature of space charge have important implications for the performance of numerous electroceramics which derive their useful properties from electrically active grain boundaries. Bonnell and coworkers, in their elegant STM experiments provided the direct evidence for GB space charge and its sign, while Chiang et al. used the indirect but powerful technique of x-ray microchemical profiling across GBs to infer the nature of space charge.
HRTEM study of heavy ion irradiation damage in Ca2La8(SiO4)6O2
Authors: Wang L.M. , Weber W.J.
Published: June 2020

Radiation effects in complex ceramic materials, including the crystalline phases with the apatite structure are of interest to the materials science, geoscience and biomedical communities. It has been shown by in situ TEM experiments that these materials can easily be rendered amorphous under heavy ion irradiations. Detailed study at atomic level using HRTEM on this crystalline to aperiodic transition is necessary for the fundamental understanding of the process. The results reported below are from a systematic HRTEM study on 1.5 MeV Kr ion irradiated synthetic Ca2La8(SiO4)6O2.

The TEM samples were prepared from (0001) thin foils by Ar ion-milling which was finished at 3.5 kV and 13°. As shown in fig. 1, the width of the amorphous rim at the sample edge after ion milling is less than 2 nanometers. The pre-thinned TEM samples were irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory.
Radiation damage in ion-irradiated pyrolytic graphite
Authors: Kenik E.A. , Pedraza D.F. , Withrow S.P.
Published: June 2020

Several grades of graphite are used in nuclear applications; as moderators in fission reactors, primary fuel containment in high temperature gas-cooled reactors, and plasma facing materials in fusion reactors. Whereas high temperature (<800°C) radiation damage response is reasonably well understood, the low temperature response is less well understood, including amorphization under irradiation. This study examined this response for ion-irradiated, highly-oriented pyrolytic graphite (HOPG). Electron transparent flakes of HOPG were prepared by repeated cleavage. Folding grids were used to hold the flakes during ion irradiation and electron microscopy. Specimens were irradiated with either 35 or 165 keV carbon or 300 keV xenon ions to fluences up to 1 × 1016 and 3×1015 ions/cm2, respectively, at nominal temperatures from room temperature to 600°C. The low energy carbon and xenon ions were selected to give similar ion ranges (∼84 nm). The range of the 165 keV carbon ions was 330 nm.
Elemental analysis of single atmospheric particles influencing visibility at the grand canyon
Authors: Turpin Barbara J. , Huang Po-Fu , Roos Amy , McMurry Peter H.
Published: June 2020

Collection and preservation strategies and a routine analysis procedure were developed for elemental analysis of individual atmospheric particles using a scanning-transmission electron microscope (STEM) equipped with a super ultra-thin window energy dispersive x-ray detector. These techniques were applied to airborne particles collected at Meadview, AZ, a remote site just downriver of the Grand Canyon. Collection, preservation and beam damage issues of concern in electron microscopic analysis of atmospheric particles will be discussed. Aerosol compositions are usually determined from bulk particle measurements, and it is assumed that compounds are either internally mixed (all present in each particle) or externally mixed (particles each contain a single compound). Insight into the microscopic mixing characteristics of atmospheric aerosols will ultimately further the understanding of atmospheric particle transformation, visibility degradation, and the fate of airborne pollutants.

Particles were collected in the summer of 1992 in three size fractions (1.0-0.5 μm, 0.5-0.26 μm, 0.26-0.12 μm in diameter) using a Hering Low Pressure Impactor and a 250 Å thick silver film substrate supported by a silver TEM grid.
Microstructure of fly ash containing concrete, with emphasis on the aggregate-paste boundary
Authors: Gillott Marcelle A. , Naik Tarun R. , Singh Shiw S.
Published: June 2020

Concrete is a highly heterogeneous structural material that is subjected to complex stresses. It has been well established that concrete is weakest in the interfacial region between coarse aggregates and the hydrated cement paste. Although there have been several studies on the microstructure of fly ash containing cement pastes, relatively less is known about the effect of fly ash on the aggregate-paste boundary in concrete.

Air entrained plain portland cement concrete mixtures were prepared to produce a design strength of 6000 psi at the 28-day age. The air and H2O-cementitious ratios were held approximately constant for both the control and fly ash containing preparations. ASTM Class C fly ash replaced 15% to 70% of the cement in various samples. Measurement of mechanical properties indicated compressive strength increased for concrete with up to 30% fly ash; only slight differences in tensile strength were observed among the control, 15% and 30% fly ash replacements.
δ’ (Al3Li) dissolution as a thermal probe in shear-banding studies
Authors: Wen Chen Roa , Vecchio Kenneth S.
Published: June 2020

The Al-Li alloy system can provide a unique opportunity to study the thermal history of shear-band formation by following the thermal dissolution of the precipitate phase δ’ (Al3Li) as a function of Li concentration and δ’ solvus temperature. The Al-Li system was chosen primarily for the rather rapid precipitation and dissolution kinetics resulting from the high diffusivity of Li in the Al lattice. δ’ is a spherical, coherent and metastable precipitate which is the main strengthening phase in dilute Al-Li alloys. Although δ’ is metastable, the location of the δ’ solvus in the Al-Li phase diagram has been well documented for dilute Li additions (<5 wt.% Li).e.g.1 The metastable δ’ solvus increases in temperature with increasing Li concentration. As such, the dissolution of δ’ within the shear bands, as a function of Li alloy concentration, can provide an internal temperature probe to study the thermal history of the shear band.
Electron microprobe and electron diffraction study of a new ferric iron sanidine from the leucite hills, wyoming
Authors: Kuehner S.M. , Joswiak D.J.
Published: June 2020

The group of minerals classified as feldspars are among the most common rock-forming minerals in the earth’s crust. The majority of feldspar compositions fall within the ternary system NaAlSi3O8-KAlSi3O8-CaAl2Si2O8, though substitution of other elements, usually in minor amounts, is common. Described here is a naturally occurring ferric iron sanidine feldspar composition in which up to ∼70 mole% of the KAlSi3O8 molecule is replaced by KFe3+ Si3O8. It thus constitutes a new end-member feldspar composition and the data have been submitted to the Commission on New Mineral Names for evaluation.

The ferric iron sanidine is found in the 1.1ma volcanic rocks of the Leucite Hills, Wyo. The composition of these lavas and plugs is unusually rich in K and Fe3+, and depleted in Al compared to typical basaltic rocks. Sanidine grains are among the last phase to crystallize in the groundmass of the rocks classified as orendites, and rarely exceed 150um in length.
A TEM and EDS Study on the effect of back melting on directionally solidified HgZnTe
Authors: Zuo H.J. , Griffin R.D. , Andrews R.A. , Janowski G.M.
Published: June 2020

Bulk growth of II-VI semiconductors such as HgZnTe (MZT) is difficult because of the gravity-induced convection that occurs during solidification. This convection can lead to crystal defects (primarily dislocations and subgrain boundaries) and composition inhomogeneities which may limit device performance. Crystals grown in the low-gravity environment of space should have fewer of these defects. However, the limited duration of space shuttle experiments and the need for uniform composition make it imperative that the initial composition transient that occurs in directionally solidified alloys be eliminated. One proposed solution to this problem is back-melting. In the first stage of this process, a section of the specimen is directionally solidified and the remainder is quenched. The quenched portion is then remelted and directionally solidified. In the flight experiment, the remelting and second directional solidification step will be carried out in space.
Comments on the use of the relativistic schrödinger equation in high-electron diffraction
Authors: Op de Beeck Marc
Published: June 2020

1.Introduction

In high energy electron diffraction the electrons are accelerated to a velocity which becomes comparable to the velocity of light. It is therefore obvious that in principle the Relativistic Dirac Equation (RDE) should be used to describe the diffraction process. However, in 1961, Fujiwara published his famous paper in which he derived that the transition probabilities calculated with the RDE agreed, up to a very good approximation, with these of the Schrödinger equation, provided the relativistic corrections to the values for the electron mass and wavelength are taken into account. As this Relativistic Schrödinger Equation (RSE) is much easier to handle, it became the fundament of all theoretical developments in electron microscopy and of all commercially available simulation packages. It is our believe however that the results of Fujiwara have been misinterpreted. The correct interpretation will lead to a correction of more than 15% on the kinetic energy of the electron.
Scanning tunneling microscope images of doped polypyrrole on ITO glass
Authors: Bilger R. , Cantow H.-J. , Heinze J. , Magonov S.
Published: June 2020

Scanning tunneling microscopy (STM) becomes an excellent tool for surface structure studies in the case of conductive and semiconductive materials. The STM has advantage of extending the range of SEM and TEM studies to topography measurements in the angstrom scale. This method also does not require special sample preparations and can be used in air. The polymers with electronic conductivity are among compounds to be studied by STM. Recently the STM images of doped polypyrrole were obtained for polymer molecules deposited on graphite. The authors claimed the observation of single polypyrrole chains with helical structure and diameter approximately 1.2 nm. We had tried the electrochemical deposition of conductive polymers on ITO for preparing structured polypyrrole layers on a smooth conductive glass surface. These samples were studied by STM.

The STM images of the surface of polypyrrole samples were obtained in air with the Nanoscope II).
A study on α-RuCl3 crystal structure by scanning tunneling microscopy
Authors: Cantow H.-J. , Hillebrecht H. , Magonov S. , Rotter H. W. , Thiele G.
Published: June 2020

From X-ray analysis, the conclusions are drawn from averaged molecular informations. Thus, limitations are caused when analyzing systems whose symmetry is reduced due to interatomic interactions. In contrast, scanning tunneling microscopy (STM) directly images atomic scale surface electron density distribution, with a resolution up to fractions of Angstrom units. The crucial point is the correlation between the electron density distribution and the localization of individual atoms, which is reasonable in many cases. Thus, the use of STM images for crystal structure determination may be permitted. We tried to apply RuCl3 - a layered material with semiconductive properties - for such STM studies. From the X-ray analysis it has been assumed that α-form of this compound crystallizes in the monoclinic space group C2/m (AICI3 type). The chlorine atoms form an almost undistorted cubic closed package while Ru occupies 2/3 of the octahedral holes in every second layer building up a plane hexagon net (graphite net). Idealizing the arrangement of the chlorines a hexagonal symmetry would be expected. X-ray structure determination of isotypic compounds e.g. IrBr3 leads only to averaged positions of the metal atoms as there exist extended stacking faults of the metal layers.
Imaging polymers, proteins and dna in aqueous solutions with the atomic force microscope
Authors: Gould S.A.C. , Drake B. , Prater C.B. , Weisenhorn A.L. , Lindsay S.M. , Hansma P.K.
Published: June 2020

The atomic force microscope (AFM) is an instrument that can be used to image many samples of interest in biology and medicine. Images of polymerized amino acids, polyalanine and polyphenylalanine demonstrate the potential of the AFM for revealing the structure of molecules. Images of the protein fibrinogen which agree with TEM images demonstrate that the AFM can provide topographical data on larger molecules. Finally, images of DNA suggest the AFM may soon provide an easier and faster technique for DNA sequencing.

The AFM consists of a microfabricated SiO2 triangular shaped cantilever with a diamond tip affixed at the elbow to act as a probe. The sample is mounted on a electronically driven piezoelectric crystal. It is then placed in contact with the tip and scanned. The topography of the surface causes minute deflections in the 100 μm long cantilever which are detected using an optical lever.
Scanning tunneling microscopy of the enzymes of muscle glycogenolysis
Authors: Edstrom R. D. , Meinke Marilyn H. , Yang R. , Yang X. , Evans D. F.
Published: June 2020

In skeletal muscle, glycogen metabolism occurs in particulate complexes consisting of glycogen and the enzymes responsible for its synthesis and degradation and the enzymes and other factors which regulate those processes. Glycogenolysis is the result of phosphorylase a acting on glycogen to form glucose 1-phosphate which is then metabolized for energy production. The activity of phosphorylase is regulated by a network of kinases and phosphatases which respond to hormonal and neuronal stimuli. The enzymes phosphorylase and phosphorylase kinase have been examined by scanning tunneling microscopy.

Phosphorylase b and phosphorylase kinase were prepared from rabbit muscle and dialyzed vs. pH 7.0, 10 mM imidazole buffer containing 100 μM CaC12and 100 μM MgCl2. The final concentration of each protein solution was adjusted to 1 mg/ml and two 0.5 μl portions were applied to the atomically flat graphite surface and the solutions dried under a stream of filtered nitrogen for a few moments.
A five-axis computer-controlled stage for the Transmission Electron Microscope
Authors: Mackenzie J. M. , Bergensten R. W.
Published: June 2020

A new five axis computer controlled stage system for the transmission electron microscope has been developed. The current design uses the existing stage of a Philips 400T without internal modification. The motors are all synchronous and employ feedback control from shaft encoders rather than “steps”.

The X and Y translation controls have an increment of 15 nm and are engaged by electronic clutches. The alpha tilt control can be incremented in 0.0625 degree units which allows 16 “steps” per degree. The beta tilt has an increment of 0.0017 degrees (approximately 500 counts per degree). The Z axis control has a 3 nm increment and can be controlled by a set of manual override switches. The position of the stage is monitored by shaft encoders in such a way that manual positioning does not effect motorized repositioning.

All five axes are calibrated for speed to determine the log/linear range of movement (Figs. 1-4). From the graphs, three speeds are chosen.
Internal and external computer control: The ins and outs of the CM Microscope
Authors: Otten Max T.
Published: June 2020

The rapid advances in computer technology in the past decades have led to an increasing demand for computer control of Transmission Electron Microscopes, partly to release the microscopist from tedious routine but time-consuming aspects of microscopy. Another factor in the demand for computer control is the fact that the TEM had become a powerful all-round research instrument with so many different techniques that very few microscopists could use any system to its full capability. More techniques and, hence, additional information would become available to the microscopist if a large part of the required operational know-how could be built into a computer control system. Previously such control systems consisted of an external computer connected to an existing microscope. A schematic diagram of this type of external control is shown in Fig. la. The disadvantage of such a system is the substantial amount of additional hardware required for controlling the microscope, making the control hardware even more complicated than it already is, with an increased risk of undesired interference between different functions.
Magnetron sputter coating for ultra high resolution Scanning Electron Microscopy (Simultaneous coating of platinum and tungsten using a magnetron sputter coater)
Authors: Ogura K. , Adachi S. , Satoh T. , Watabe T. , Kersker M. M.
Published: June 2020

The resolution of the SEM has been remarkably improved by means of the in-lens SEM with a field emission gun. Consequently, the thin metal coating on the specimen surface for ultra high resolution imaging has become very important. In the age of imaging with 2-3nm resolution at 100,000x magnification, a very thin platinum (Pt) coating on the specimen surface using the magnetron sputter coater has yielded successful results. However, in an ultra high resolution scanning electron microscope with better than 1nm resolution at higher than 200,000: magnification, the fine granularity of magnetron sputter coating of Inra thick Pt will be observed on the specimen surface. Therefore, a thinner metal coating with smaller grain size than that of Pt is strongly required. Recently, we tried tungsten (W) coating on many variety of specimens in argon (Ar) gas atmosphere by using a magnetron sputter coater. Using a W coated carbon film, the granularity of W was examined by both an UHR-SEM and a TEM at a minimum magnification of 250,000x.
Information capacity and bandwidth limitations in the SEM
Authors: Joy D. C. , Bunn R. D.
Published: June 2020

The information available from an SEM image is limited both by the inherent signal to noise ratio that characterizes the image and as a result of the transformations that it may undergo as it is passed through the amplifying circuits of the instrument. In applications such as Critical Dimension Metrology it is necessary to be able to quantify these limitations in order to be able to assess the likely precision of any measurement made with the microscope.

The information capacity of an SEM signal, defined as the minimum number of bits needed to encode the output signal, depends on the signal to noise ratio of the image - which in turn depends on the probe size and source brightness and acquisition time per pixel - and on the efficiency of the specimen in producing the signal that is being observed. A detailed analysis of the secondary electron case shows that the information capacity C (bits/pixel) of the SEM signal channel could be written as :
The JSM-890 ultra high resolution Scanning Electron Microscope
Authors: Kersker M. , Nielsen C. , Otsuji H. , Miyokawa T. , Nakagawa S.
Published: June 2020

Historically, ultra high spatial resolution electron microscopy has belonged to the transmission electron microscope. Today, however, ultra high resolution scanning electron microscopes are beginning to challenge the transmission microscope for the highest resolution.

To accomplish high resolution surface imaging, not only is high resolution required. It is also necessary that the integrity of the specimen be preserved, i.e., that morphological changes to the specimen during observation are prevented. The two major artifacts introduced during observation are contamination and beam damage, both created by the small, high current-density probes necessary for high signal generation in the scanning instrument. The JSM-890 Ultra High Resolution Scanning Microscope provides the highest resolution probe attainable in a dedicated scanning electron microscope and its design also accounts for the problematical artifacts described above.

Extensive experience with scanning transmission electron microscopes lead to the design considerations of the ultra high resolution JSM- 890.
The CM20/STEM: A new 200-kV Scanning Transmission Electron Microscope
Authors: Otten Max T. , de Jong Marc J.C
Published: June 2020

With the rapid advances in new materials and production techniques in fields such as ceramics, semiconductors, metals, polymers and composites, the demands on analytical techniques for studying these materials are ever increasing. The TEM is ideally suited because of its spatial resolution and large number of different signals (bright-field and dark-field imaging, high-resolution imaging, convergent beam diffraction. X-ray and energy-loss analysis, scanning with bright-field, dark-field, backscattered and secondary electrons, etc). Many TEM’s suffer, however, from an unnecessary restrictiveness in the techniques provided, e.g. top-entry TEM’s without X-ray microanalysis or TEM systems without scanning. In order to provide the materials scientist with a powerful solution for current and future demands in materials research, the new Philips CM20 (Fig. 1) has been designed specifically to incorporate as many techniques as possible with the highest possible performance.

In addition to its high electron-optical performance, the CM20’s MICROCONTROLLER, a microprocessor control system with ergonomic control-panel lay-out, ensures ease of use, greatly speeding up operation and enhancing the microscopist’s productivity.
Fourier transform “darkfield” techniques
Authors: Fraundorf P. , Fraundorf G. K.
Published: June 2020

The standard approach to localizing single crystal regions in a transmission electron microscope (TEM) is to form tilted-illumination darkfield images with a diffracted beam down the microscope axis, and other electrons cut off by a centered objective aperture.This capability for localizing periodicities is powerful and shared by few other diffraction techniques.High resolution TEM’s with point resolution and information limit below the spacing between atoms (e.g. 0.2 nm) are capable of putting information on all of the large crystal periodicities directly into phase contrast images.The refinement of techniques for finding and characterizing the crystals associated with spots, corresponding to the diffracted beams, in power spectra from such images has thus become a regular subject in the microscopy literature [e.g. 1-3]. Here, we illustrate that such techniques are useful for more than localizing crystallite boundaries.We also suggest one strategy for improving on the useful, but ad hoc, strategies now in hand.
Hollow-cone illumination in simulated ADF STEM
Authors: Loane R. F. , Silcox J.
Published: June 2020

The overlap regions between CBED disks are a source of lattice fringe contrast in ADF STEM images of crystals. For sufficiently small lattice spacings, the Scherzer focus convergence angle is too small for the CBED disks to overlap, and the lattice is not visible. By increasing the convergence angle beyond the Scherzer angle to create an overlap region, and by using stationary phase defocus, smaller lattices can be imaged However, with larger convergence angles, lens aberrations spread the incident beam and small aperiodic structures, such as adatoms, become difficult to image. If the specimen Bragg angle is known, an annular objective aperture can be designed to pass the overlap regions of the incident beam, while blocking the central, non-overlap region which produces a large constant background. The annular probe size is minimized by choosing an annulus width and defocus which balance the spherical aberration across the annulus (close to stationary phase defocus). Simulations indicate hollow cone illumination may allow both adatoms and smaller lattices to be imaged simultaneously. This approach presumes knowledge of the specimen, and must be used in conjunction with standard methods for correct image interpretation. An incorrectly applied annulus will produce image artifacts.
HREM images of interfaces containing misfit dislocations lying parallel to the surface of the sample
Authors: Rasmussen D. René , McKernan Stuart , Carter C. Barry
Published: June 2020

A detailed interpretation of HREM micrographs often has to rely on comparisons with simulated images. When analyzing micrographs of defects, a simplified structure is usually assumed, i.e., secondary “complications” are disregarded. Such complications may be introduced during the specimen preparation, e.g., an interface may be associated with surface grooves because of preferential mechanical damage at the interface, or with a surface step on one side of the interface. The influence of these artifacts on the matching of simulated and experimental micrographs has been discussed previously. Other complications which are usually ignored when considering high-resolution images of interfaces include the dislocations which may be an intrinsic part of the interface structure but which lie parallel to the plane of the foil. This paper presents initial results of a computer simulation study of the possible effects on the HREM images of misfit dislocations (MD) present in such interfaces.
Analysis of embryonic cell division patterns using laser scanning confocal microscopy
Authors: Summers Robert G. , Cheng Ping-chin
Published: June 2020

As embryogenesis in the sea urchin proceeds, cell number increases and overall synchrony of cell division decreases. Beyond 16 cells, it becomes increasingly more difficult to observe individual cells or populations of cells in whole-mounted embryos because of their thickness (up to 150 μm) and superimposition of nuclei. As a consequence, the patterns of cell division (eg. its timing and synchrony within subpopulations of cells, orientation of the mitotic apparatus relative to axes of embryonic symmetry etc.) in sea urchins and other developing systems remain unclear. Confocal microscopy affords the opportunity to analyze intact embryos and to gain an understanding of the role which cell division plays in morphogenesis of the embryo.

Sea urchins (Strongylocentrotus purpuratus) were obtained from Northern California and maintained in artificial sea water. Gametes were obtained and cultures of embryos were prepared in the usual fashion and synchronous cultures of embryos were reared at 15°C. Fixation and Feulgen staining were performed per Nislow and Morill.
Confocal laser scanned microscopy: Optimized reflection mode
Authors: Turner JN , Szarowski DH , Barnard DP , Deitch JS , Swann JW , Smith K
Published: June 2020

Most biological applications of confocal laser scanned microscopy (CLSM) involve the use of selective stains. Some of these stains provide image contrast by reflecting more light than the background. Unfortunately, reflected light from internal optical surfaces can also reach the detector, and the resultant spurious signal be superimposed on the image. When the specimen signal approaches or is less than that of the internal reflections, image degradation results. Due to the low reflectivity of biological stains, this situation is common. The image signal is also reduced as a function of depth in the specimen due to attenuation by surrounding tissue (stained or unstained), making the problem more severe because the internal reflections remain constant. This attenuation can limit the maximum depth at which optical sections are recorded. The spurious signals from these internal reflections can saturate parts of the field suppressing image information, and/or adversely influencing digital processing by establishing unrealistic intensity baselines and scales. Polarization optics have been proposed to reduce the effect of internal reflections. We report the installation of such components, and their use in imaging three important selective stains.
Three-dimensional images of DAB-labeled neurons by confocal scanning laser microscopy
Authors: Deitch JS , Smith KL , Lee C , Swann JW , Turner JN
Published: June 2020

The ability to correlate neuronal morphology and physiology has been greatly advanced by intracellular labeling through the recording pipette. However, visualizing the filled neuron required physically sectioning and reconstructing areas of interest, often resulting in figures that are two-dimensional. We have visualized the three-dimensional morphology of filled neurons reacted with nickel-intensified diaminobenzidine (DAB/Ni) using the confocal scanning laser microscope (CSLM).

Neurons in slices of rat hippocampus were filled with biocytin, fixed in 4% paraformaldehyde, incubated in avidin-HRP (1:200) in 0.5% Triton X-100, and reacted with DAB in 0.04% nickel ammonium sulfate. Optical sections and three-dimensional images were recorded by using a Bio Rad MRC-500 CSLM with an argon ion laser.

Biocytin filled all aspects of the neuron, including fine axons and spines. Fig. 1 is a conventional micrograph of a single neuron labeled with DAB/Ni. Figs. 2a and b are stereo pairs of the apical and basal dendrites of the neuron in Fig. 1.
Fading of the diaminobenzidine reaction product in the confocal scanning laser microscope
Authors: Deitch JS , Smith KL , Swann JW , Turner JN
Published: June 2020

Neurons labeled with horseradish peroxidase and reacted with diaminobenzidine (DAB) can be imaged using a confocal scanning laser microscope (CSLM) in the reflection mode. In contrast to fluorescent markers, the DAB reaction product is thought to be stable and can be observed by both light and electron microscopy. We have investigated the sensitivity of the DAB reaction product to laser irradiation, and present the spectrophotometric properties of DAB before and after exposure in the CSLM.

Pyramidal neurons in slices of rat hippocampus were injected with biocytin (a biotin-lysine complex), fixed overnight in 4% paraformaldehyde, and vibratome sectioned at 75 μm. Biocytin was detected with avidin-HRP (1:200) in 0.5% Triton X-100, incubated in DAB (0.5 mg/ml) with or without 0.04% nickel ammonium sulfate (Ni), dehydrated, and imaged in a Bio Rad MRC-500 CSLM with an argon ion laser (488 and 514 nm). Spectrophotometric measurements of the soma were made on a Zeiss microspectrophotometer, as a function of laser exposure (100-1000 scans) and staining protocol.
Oxidation, reduction, and stability of the BaLa4Cu5O13±δ system
Authors: Davies P. K. , Katzan C. M.
Published: June 2020

The electronic and structural properties of most of the high temperature superconducting copper oxides are highly dependent upon the oxidation conditions used to prepare the cuprate compounds. Until recently superconductivity had only been observed in highly oxidized compounds, however recent work has shown that under certain circumstances superconducting transitions can also occur in n-doped, reduced cuprates. In an effort to understand some of the chemical factors that lead to the stabilization of both oxidized and reduced cuprates, we have investigated the stability of several cuprates. In this paper we report our results on the metallic, non-superconducting BaLa4Cu5O13±δ (“145”) system.

At high temperature most of the highly oxidized cuprates are reduced as oxygen is reversibly removed from the perovskite lattice and the Cu valence is lowered to ≤ 2. However, for compounds with the 145 stoichiometry there is no significant oxygen loss in “non-reactive” gases such as air, O2 or He, and even at 1000°C Cu is apparently stable in a valence state greater than 2.3+.