bluuebunny/crossref_metadata_2025 huggingface dataset:
Elemental analysis of human erythrocytes
Authors: Livesey S. A. , del Campo A. A. , Griffey E. S. , Ohlmer D. , Schifani T. , Chiovetti R.
Published: June 2020

The aim of this study is to compare methods of sample preparation for elemental analysis. The model system which is used is the human erythrocyte. Energy dispersive spectroscopic analysis has been previously reported for cryofixed and cryosectioned erythrocytes. Such work represents the reference point for this study. The use of plastic embedded samples for elemental analysis has also been documented. The work which is presented here is based on human erythrocytes which have been either chemically fixed and embedded or cryofixed and subsequently processed by a variety of techniques which culminated in plastic embedded samples.

Heparinized and washed erythrocytes were prepared by the following methods for this study :

(1). Chemical fixation in 4% paraformaldehyde/0.25% glutaraldehyde/0.2 M sucrose in 0.1 M Na cacodylate, pH 7.3 for 30 min, followed by ethanol dehydration, infiltration and embedding in Lowicryl K4M at -20° C.
Microstructure of supported platinum-gold bimetallic catalysts
Authors: Sachdev Amit
Published: June 2020

Bimetallic supported catalysts comprised of a Group VIII metal, such as platinum, and a Group IB element, like gold, have been found to possess superior selectivities towards the formation of desired products as well as a decreased rate of deactivation. The correlation between the microstructure of these materials with their catalytic behavior is essential in understanding the reaction kinetics. Previous electron microscopic studies on bimetallic catalysts have primarily concentrated upon systems whose metallic components are immiscible in the bulk. In this project, the partially miscible Pt-Au and the completely miscible Pt-Sn systems were investigated. In Pt-Au catalysts the catalytically inactive Au component is known to dilute the ensembles of the Pt active sites, thereby favoring the production of compounds whose intermediates require fewer adsorption sites. The typical metal particle size distribution in Pt-Au catalysts ranges from 0.5 nm to 40 nm. The microanalysis of particles larger than 10 nm can be easily done by means of small probe microdiffraction and EDX. The structure and composition of the smaller particles, where most of the interesting catalysis takes place, was determined from the structure images of high resolution electron microscopy.
Structural analysis of faceted grain boundaries in Bi-doped Cu
Authors: Luzzi D. E. , Blum B. , Inui H.
Published: June 2020

Conventional(CTEM)and high-resoIution(HREM) transmission electron microscopy have been used to investigate the structure of faceted grain boundaries in Cu doped with Bi. The solubility of Bi in Cu exhibits retrograde behavior with a maximum of 160 at. ppm. at 850 ° C and decreasing above and below this temperature (eg. to < 3 at. ppm. at 600 ° C). When aged at temperatures below this retrograde region, Blis known to segregate tothe grain boundaries. In addition to this segregation, these materials exhibit a reversible faceting-de-faceting transition at 710 ° C which has been postulated asarising from a two-dimensional phase transformation at the grain boundaries. Until the present time, little experimental work has been doneto characterize the structures of these faceted boundaries.

In the present experiments, Kikuchi pattern analysis and edge-on imaging have been used to characterize the five macroscopic degrees of freedom of individual facets. Bulk Cu specimens with 50 at.ppm.
Effect of electrolyte on thin-foil precipitate artifacts in copper-bearing steels
Authors: Thompson S.W. , Krauss G.
Published: June 2020

Copper additions to steel produce significant precipitation strengthening. Transmission electron microscopy (TEM) of aged copper-bearing steels reveals the presence of fine (usually 10 nm or larger), fcc, ε-copper particles. Additionally, very fine (less than 5 nm), Cu-rich bcc clusters or precipitates have been detected. The former particles are easily imaged via TEM, whereas the latter are difficult to detect by conventional TEM. Considerable variability in TEM observations causes concern about artifacts which may be produced during jet polishing. This note describes experiments which demonstrate that the true documentation of Cu-precipitate distributions is sensitive to the electrolyte used to prepare thin foils for TEM examination.

Hot-rolled and quenched 32mm-thick steel plates (provided by Lukens Steel) contained (in wt pct) 0.05C, 1.12Cu, 0.88Ni, 0.50Mn, 0.20Mo, 0.71Cr, 0.28Si, 0.04Nb 0.02Al, 0.0lP, and 0.002S. All specimens were aged at 675°C for one hour. Foils were produced by conventional thinning methods and jet polished with three electrolytes:
High-resolution Electron Microscopy of defects in Ni3Al
Authors: Mills M. J.
Published: June 2020

The improved resolution of the latest generation of intermediate voltage electron microscopes makes possible the direct study of the atomic structure of defects in close-packed metals and alloys. Of particular technological interest are several classes of intermetallic compounds which exhibit desirable mechanical properties at higher temperatures. This paper demonstrates the current application of high resolution transmission electron microscopy (HRTEM) to the study of dislocation cores and interfaces in nickel-based alloys, and the implications of the observations in terms of models of deformation and fracture.

Several intermetallic alloys with the L12 (Cu3Au) structure exhibit an anomalous increase in the flow stress as a function of temperature. The theoretical models that have been proposed to explain this behavior are based upon consideration of a thermally activated cross slip of screw dislocations from {111} to {010}. These models assume that the dissociation of the a superlattice (SL) dislocation occurs by the formation of an anti-phase boundary (ABP) which is bounded by two a/2 superpartial (SP) dislocations with parallel Burgers vectors.
Dislocation structures in deformed Ni3Al
Authors: Subramanian Raja , Robertson I.M. , Birnbaum H.K.
Published: June 2020

The improvement of the ductility of Ni3Al by the addition of boron has revived interest in intermetallic alloys. Addition of up to about 500 wt. ppm of boron increases the ductility of Ni3Al by as much as 50%. This improvement is dependent on the deviation from stoichiometry with optimum effect being obtained for the Ni-rich composition. The ductility enhancement has been attributed to the boron increasing the cohesive energy of the grain boundary and to a disordered boundary layer easing the slip process through the grain boundary.

The dislocation structures produced in deformed Ni3Al with and without boron has been examined in the transmission electron microscope . Samples were deformed to a 3 % strain in bulk form while others were deformed in situ in the transmission electron microscope. (Details of the in situ TEM straining technique can be found in ref.)
Deformation modes in Laves phase intermetallics
Authors: Hall Ernest L. , Livingston James D.
Published: June 2020

There is at present a large amount of interest in the mechanical behavior of intermetallic alloys, and one of the largest classes of these alloys are the Laves phases. There are three basic types of Laves phases: cubic (C15), hexagonal (C14), and dihexagonal (C36), with stacking sequences on the close-packed planes of ABCABC..., ABAB..., and ABAC..., respectively, where each capital letter represents an interpenetrating four-atomic-layer unit. This structural complexity gives rise to a special mode of deformation for Laves phases, called synchroshear, which requires the cooperative movement of adjacent layers in different directions. Very little work has been done to date on the deformation modes in Laves phases because of the inherent brittleness of these materials at room temperature. However, through alloying it is possible to obtain mixtures of the various Laves phase types, and to affect such properties as stacking fault energy, and thus opportunities may exist for increasing ductility. In this study, the deformation microstructures of different Laves phase types were explored.
A Transmission Electron Microscope study of APB in TiAl
Authors: Feng C. R. , Michel D. J. , Crowe C. R.
Published: June 2020

Antiphase domains are usually observed in materials with an ordered superlattice structure and the domain boundaries are termed antiphase boundaries (APB). For the Ll0 structure of TiAl, no micrographs have been presented to confirm the existence of an APB. The primary reason for this is the high APB energy which is associated with the separation of the superdislocations. However, APB also could be formed thermally. The purpose of this paper is to report the observation of a thermally formed APB in TiAl and to describe the character of this APB.

The TEM foils were prepared from a 7.5v% TiB2 particle reinforced Ti-45at% Al alloy, initially produced by Martin Marietta Laboratories through XD™ processing followed by casting. Thin sections were sliced from the block alloy and 3mm discs were cut from the thin sections.
Approaches for TEM imaging of cavitation in toughened nylon
Authors: Wood Barbara A.
Published: June 2020

A controversial topic in the study of structure-property relationships of toughened polymer systems is the internal cavitation of toughener particles resulting from damage on impact or tensile deformation.Detailed observations of the influence of morphological characteristics such as particle size distribution on deformation mechanisms such as shear yield and cavitation could provide valuable guidance for selection of processing conditions, but TEM observation of damaged zones presents some experimental difficulties.

Previously published TEM images of impact fractured toughened nylon show holes but contrast between matrix and toughener is lacking; other systems investigated have clearly shown cavitated impact modifier particles. In rubber toughened nylon, the physical characteristics of cavitated material differ from undamaged material to the extent that sectioning of heavily damaged regions by cryoultramicrotomy with a diamond knife results in sections of greater than optimum thickness (Figure 1). The detailed morphology is obscured despite selective staining of the rubber phase using the ruthenium trichloride route to ruthenium tetroxide.
Morphology study of polyvinyl acetate latex by etching with PTA
Authors: Shaffer O.L. , Dimonie V. , El-Aasser M.S. , Vanderhoff J.W.
Published: June 2020

Transmission electron microscopy has been used extensively for studying the morphology of latex particles. Special techniques have been developed such as preferential staining with osmium tetroxide (OsO4), ruthenium tetroxide (RuO4), freeze fracturing, microtoming and negative staining with phosphotungstic acid (PTA). The purpose of this study is to develop a new technique using PTA as an etching agent for poly(vinyl acetate)(PVAc) latex.

Several latexes were prepared by both batch and semicontinuous emulsion polymerization with poly(vinyl alcohol)(PVA) as a stabilizer. Three types of PVA were used, high molecular weight Elvanol 52-40(DuPont) and Vinol 540(Air Products), and low molecular weight Vinol 205(Air Products). All the alcohols were partially hydrolyzed. A PVAc soap free(no PVA) latex was also prepared. To etch the particles one drop of latex was diluted in approximately one ml of 2% aqueous PTA. The volume of latex used depended upon the solids content of the latex and the size of the particles. The PTA latex dispersions were sampled at several intervals.
Two-stage self-seeding method for preparation of single crystals of poly(phenylene sulfide)
Authors: Chung Sengshiu , Cebe Peggy
Published: June 2020

We are studying the crystallization and annealing behavior of high performance polymers, like poly(p-pheny1ene sulfide) PPS, and poly-(etheretherketone), PEEK. Our purpose is to determine whether PPS, which is similar in many ways to PEEK, undergoes reorganization during annealing. In an effort to address the issue of reorganization, we are studying solution grown single crystals of PPS as model materials.

Observation of solution grown PPS crystals has been reported. Even from dilute solution, embrionic spherulites and aggregates were formed. We observe that these morphologies result when solutions containing uncrystallized polymer are cooled. To obtain samples of uniform single crystals, we have used two-stage self seeding and solution replacement techniques.
Computer-aided parallel EELS techniques: acquisition, processing, & imaging
Authors: Hunt John A.
Published: June 2020

The recent commercial introduction of the parallel detection electron energy-loss spectrometer has undoubtedly made electron energy-loss spectroscopy (EELS) more viable as a technique for routine microanalysis. Additionally, the increased recording efficiency of parallel EELS (PEELS) warrants the use of more involved acquisition and processing techniques than was necessary, or even possible with serial EELS. This increased complexity places greater demands on the computer systems controlling data acquisition. Multichannel analyzers systems with small resources and limited programming facilities are not capable of exploiting the full capabilities of the PEELS spectrometer.

Preliminary efforts of the author with the Gatan PEELS spectrometer were concentrated on development of a flexible acquisition system at National Institutes of Health. Hardware control is performed through machine-language drivers called from high-level languages (HLL) such as FORTRAN and C. The software drivers and hardware were designed to minimize processor involvement in the data collection process, resulting in the capability to collect data while processing continues within the parent HLL. This design simplifies the HLL program structure and minimizes data collection dead time.
A comparison of sensitivities between parallel-EELS and EDXS in biological microanalysis
Authors: Leapman R.D.
Published: June 2020

With recent improvements in electron energy loss spectroscopy (EELS) and energy-dispersive x-ray spectroscopy (EDXS) it is useful to compare detection limits for the two techniques, a question originally addressed by Isaacson and Johnson. We have derived theoretical estimates of relative sensitivities for some elements encountered in biological microanalysis. These results are then compared with experimental data obtained using a Hitachi H700H analytical electron microscope equipped with a Gatan (model 666) parallel EELS and with a Tracor Northern Microtrace EDXS detector. These spectra were collected simultaneously using a Tracor TN5500 computer system to control acquisition and to process the EDXS data. Most of the EELS data were collected in the second difference mode to remove channel-to-channel gain variations in the photodiode array and were further processed on another computer using standard reference spectra and a multiple least squares fitting procedure.
Performance of the Gatan PEELS™ on the VG HB501 STEM
Authors: Krivanek Ondrej L. , Paterson James H. , Poppa Helmut R.
Published: June 2020

Parallel-detection electron energy-loss spectrometers offer several hundred times the detection efficiency of serial-detection spectrometers, as well as improved energy resolution. These advantages should be especially important when using a scanning transmission electron microscope (STEM) with a cold field emission gun (FEG), in which the available beam current is typically 10 to 100 times less than in a conventional TEM, while the beam energy spread is typically only 0.3 eV. We have therefore investigated the performance of the Gatan parallel-detection spectrometer (Gatan model 666 PEELS™) when mounted on the VG HB501 FEG STEM.
Electron spectroscopic imaging of thick crystalline specimens
Authors: Reimer L. , Rennekamp R. , Bakenfelder A.
Published: June 2020

Electron spectroscopic imaging (ESI) by an energy-filtering electron microscope (EFEM, Zeiss EM902) shows the following advantages when compared with the unfiltered bright-field mode:

1.

The zero-loss image does not contain the contribution of inelastically scattered electrons. Though plasmon scattering shows a conversation of Bragg contrast - edge and bent contours and lattice defect images -, the angular distribution of inelastically scattered electrons results in a broader spectrum of excitation errors and a blurring of Bragg contrast.

2.

The zero-loss image avoids the chromatic aberration of inelastically scattered electrons for medium specimen thicknesses and can be applied so long as the intensity of the zero-loss peak in the electron energy-loss spectrum (EELS) is high enough for an exposure in a reasonable time (<100 s).

3.

Thick specimens with negligible zero-loss intensity can be imaged with an energy window at the highest multiple plasmon loss of the Poisson distribution or at the most probable energy of a Landau distribution. The angular distribution of electrons with these energy losses is so broad that the Bragg contrast is blurred, and the contrast is only caused by anomalous absorption effects similar to multi-beam images in the STEM mode when using a large probe aperture.
Epitaxially induced secondary grain growth in Ti:LiNbO3 optical waveguides
Authors: McCoy M. A.
Published: June 2020

Lithium niobate (LiNbO3) is one of the most promising materials for use in hybrid optical waveguide devices because of its high electro-optic coefficient and its availability as large single crystals. Optical waveguides in LiNbO3 are most commonly made by Ti indiffusion in which strips of Ti metal (between 10 and 100 nm thick) are deposited on a single crystal LiNbO3 substrate. The device is then heated to temperatures around 1000°C typically for 6 hours. During this time, the Ti diffuses into the LiNbO3 to form a Ti-rich LiNbO3 solid solution. This solid solution has a higher refractive index than the substrate and forms the waveguide region. Factors controlling the indiffusion process, however, are not very well understood and very little is known about the microstructural changes which occur during Ti indiffusion. In this study, the microstructure of Ti:LiNbO3 optical waveguides was examined as a function of time and temperature using transmission electron microscopy (TEM).
Transmission Electron Microscopy study of lead sulfide whiskers
Authors: Mansour S.A. , Scholz R.
Published: June 2020

This paper describes a transmission electron microscopy (TEM) study of the structure and growth mechanism of lead sulfide (PbS) whiskers. PbS whiskers were grown inside the stainless steel nozzle of a kerosene burner. The nozzle had a 0.5 mm aperture, and was fitted with an Al-spiral coil to filter kerosene impurities. The burner was operated continuously for four weeks at a kerosene pressure of 2-3 bars and a flame temperature of about 350°C before the nozzle clogged. A thick black deposit of fine PbS whiskers was found inside the nozzle.

TEM specimens were prepared by ultrasonically suspending the fine black powder in alcohol. The suspended particles were deposited on a perforated carbon film supported on a copper grid, and examined with a JEM-1200EX transmission electron microscope operated at 120kV accelerating voltage. A JEM-4000EX transmission electron microscope was used for high resolution electron microscopy.

Fig. 1. shows an EM micrograph of typical PbS whiskers. Each appears to have a high-contrast core encapsulated in a lower contrast shell. The electron diffraction pattern of a single whisker protruding over a hole in the carbon film is shown in Fig. 2.
Reconstruction of the NiSi2/Si(100) interface
Authors: Batstone J.L. , Gibson J.M. , Tung R.T. , Loretto D.
Published: June 2020

Cubic NiSi2 grows epitaxially on Si (100) and is of interest as a Schottky contact. Metal layers on n-type Si (100) have a Schottky barrier height, øB of 0.47 eV. Reproducibility of øB appears dependent on the defect structure of epitaxial thin films and attention has centered on the interfacial bonding configurations. Room temperature deposition of Ni “templates” followed by reaction at ∼450°C result in flat, abrupt NiSi2/Si (100) interfaces. High Resolution Electron Microscopy (HREM) has revealed six-fold coordinated Ni atoms in the interfacial plane by the methods of image simulation and rigid shift displacements. The preferred bonding configuration viewed in the [011] direction is illustrated in Figure 1(a) where the arrow indicates the NiSi2 termination leaving two dangling bonds per Ni atom. Alternatively an extra layer of Si could be inserted at the interface shown in Figure lb resulting in 8-fold coordinated Ni and 2-fold coordinated Si. If relaxation of atom positions in the interface plane occurs, in a manner analogous to reconstruction of clean surfaces or dislocation cores, additional interfacial bonding models can be proposed, Figures 1c, 1d.
Atomic-level structure and composition at interfaces
Authors: Smith David J.
Published: June 2020

The latest generation of high-resolution electron microscopes (HREMs) have structural resolution limits on the order of atomic dimensions, thereby opening up the possibilities for direct observation of atomic (re)arrangements at crystal defects and discontinuities such as interfaces. With recent advances in growth methods, novel types of optical, X-ray and electronic devices which are based upon nanometer-scale multilayers (MLS) have been developed. This short review considers the prospects and limitations of the HREM technique for elucidating the structure and composition of interfaces in these layered materials, including such details as the interface roughness, the extent of interpenetration (i.e. compositional gradients) and the coherent/incoherent nature of the interface. The complementary nature of information available from other TEM methods is also briefly discussed.

The common (and essential) requirement for HREM characterization of layered structures is that they must be aligned with their interfaces(s) edge-on with respect to the incident beam direction. It is therefore useful if the multilayers are deposited onto a well-defined surface of a crystalline substrate,typically Si or GaAs, which can then provide a basis for orientation purposes. The development of routine methods for preparing cross-sectional MLS specimens, either by ion-milling or cleavage , has also done much to stimulate recent HREM observations.
High-resolution z-contrast imaging of semiconductor interfaces
Authors: Pennycook S. J.
Published: June 2020

Using a high-angle annular detector on a high-resolution STEM it is possible to form incoherent images of a crystal lattice characterized by strong atomic number or Z contrast. Figure 1 shows an epitaxial Ge film on Si(100) grown by oxidation of Ge-implanted Si. The image was obtained using a VG Microscopes' HB501 STEM equipped with an ultrahigh resolution polepiece (Cs ∽1.2 mm, demonstrated probe FWHM intensity ∽0.22 nm). In both crystals the lattice is resolved but that of Ge shows much brighter allowing the interface to be located exactly and interface steps to be resolved (arrowed). The interface was indistinguishable in the phase-contrast STEM image from the same region, and even at higher resolution the location of the interface is complex. Figure 2 shows a thin region of an MBE-grown ultrathin super-lattice (Si8Ge2)100. The expected compositional modulation would show as one bright row of dots from the 2 Ge monolayers separated by 4 rows of lighter Si columns. The image shows clearly that strain-induced interdiffusion has occurred on the monolayer scale.
Perturbation theory for dynamical diffraction calculations
Authors: Eaglesham D.J.
Published: June 2020

The dynamical diffraction of high-energy electrons may be calculated to a fair degree of accuracy by several methods. The most widespread techniques involve either multislice calculations or Bloch wave diagonalisation, the two giving equivalent results for diffracted beam intensities for a given set of conditions. However, both types of calculation are approximate, in that they involve a truncated expansion (of not only the electron wavefunction but also the crystal potential) in the number of diffracting beams. Bloch wave diagonalisations, for example, involve computation times which increase as the cube of the number of beams included in the calculation, so that truncation of the calculation with the smallest possible number of beams is essential. Unfortunately, dynamical diffraction calculations (using either multislice or diagonalisation) tend to converge extremely slowly with increasing number of beams, so that Bloch wave calculations in particular can be highly time-consuming. In addition, it is generally difficult to estimate the magnitude of the systematic errors that truncation has produced. However, the scattering to the outermost beams is generally weak, suggesting that these higher coefficients of the potential may be treated within perturbation theory. The pupose of this paper is to present the equations for a perturbation treatment of truncation.
Procedures for Point and Space Group Analysis
Authors: Tanaka M.
Published: June 2020

Description of general procedures for point- and space-group determination by convergent-beam electron diffraction(CBED) soon appears in a special issue of J. Electron Microsc. Tech. The essence of them was already given in the flow charts in ref.2. We here demonstrate the procedures using an example of La2 CuO4 - 6, which is the end member of a 40K class superconductor La2-x Mx CuO4 - 6 (M = Ba, Sr and Ca). The CBED method has utilized to date only dynamical extinction(GM lines) appearing in zeroth-order Laue-zone(ZOLZ) reflections for the space-group determination. We emphasize that the use of GM lines appearing in higher-order Laue-zone(HOLZ) reflections makes it easy to determine crystal space-groups.

The substance was already known to belong to the orthorhombic system with the lattice parameters of a=5.3548Å, b=5.4006Å and c=13.1592Å. Fig. 1(a) shows a CBED pattern taken at the [001] incidence, Fig.l(b) being the central part of Fig.l(a). The whole pattern has a symmetry 2mm. This indicates that the crystal has two mirror symmetries perpendicular to each other and that the point group is mmm or mm2.
Development of a high-sensitivity array detector and fast digital data analysis system for coherent nanodiffractlon patterns
Authors: Butler J. H. , Fan G. Y. , Cowley J. M. , Rez P.
Published: June 2020

The spatial limits of conventional narrow beam analytical methods (XRD, SAD and CBED) are still large compared with the microstructural features which govern the properties of many materials. Recent technological advances in computer hardware and sensitive electron array detectors have made it feasible to examine the structure of subnanometer crystal volumes. By placing an extremely small diameter, coherent electron probe over the region of interest and digitally comparing the resultant 'nanodiffraction' pattern to a computer generated pattern which is based on dynamical diffraction in a model structure, it is possible to ascertain the local structure with a minimum of the subjectivity which is inherent in conventional operator interpretations of electron scattering intensities. This is especially important when very small beam diameters are involved, as the diffraction intensities are strongly dependent on crystal tilt and thickness, as well as the position of the beam relative to the unit cell origin.
Studies of magnetic structure of written bits using Lorentz microscopy
Authors: Nguyen T.A. , Alexopoulos P.S. , Lambert S.E. , Sanders I.L. , Hwang C.
Published: June 2020

Understanding the fundamental size limits of magnetic bits for high density information storage requires detailed knowledge of the magnetic structure of the written bits. Bit definition, fringing fields and magnetic structures at and between transition zones are important information for the design of future magnetic media. Using Lorentz microscopy, we have investigated these parameters in Co-alloy thin films as a function of recording density (200, 600 and 1000 fc/mm) on discrete tracks of widths from 0.6 to 10 μm.

The magnetic media consist of a Co-alloy and an underlayer prepared by sputtering onto a sputter-cleaned Si disk. The magnetic parameters for the magnetic layer are: coercive field Hc = 950 Oe, remanent magnetization Mr = 533 emu/cm3 and media thickness d = 400 Å. The discrete tracks were formed on the surface of the disk by sputter-etching through a photoresist mask to remove media between the tracks. This permits the recording characteristics of tracks as narrow as 0.6 μm to be investigated using heads of conventional width.
TEM characterization of dislocation reduction processes in GaAs/Si
Authors: Herring R.A. , Uppal P.N. , Svensson S.P. , Ahearn J.S.
Published: June 2020

A high density of interfacial dislocations are needed at the GaAs/Si interface to alleviate the 4% lattice mismatch between GaAs and Si. Some remnant dislocations thread through the epilayer and follow the growth interface. Current growth methods are not able to obtain acceptable threading dislocation densities (104 – 105) for devices. Many methods can be used to reduce the number of threading dislocations which include misorienting the substrate to enhance the slip of dislocations on specific [110]{111} planes, annealing during and after growth, and adding strained layer superlattices (SLS's) to block dislocations. Conventional TEM (CTEM), performed using a JEM 100c, has been used to characterize threading dislocations in the epilayer of a GaAs/Si material where in situ thermal annealing and SLS's force dislocation reactions and thereby reduce the threading dislocation density. Using TEM we have viewed dislocations under many two-beam diffraction conditions and with the help of a stereogram have determined their Burgers vectors (b), line directions (u) and habit planes (R).
Electron microscopic characterization of diamond thin films and substrates for diamond heteroepitaxial growth
Authors: Posthill J.B. , Burns R.P. , Rudder R.A. , Lee Y.H. , Markunas R.J. , Bachmann K.J.
Published: June 2020

Because of diamond’s wide band gap, high thermal conductivity, high breakdown voltage and high radiation resistance, there is a growing interest in developing diamond-based devices for several new and demanding electronic applications. In developing this technology, there are several new challenges to be overcome. Much of our effort has been directed at developing a diamond deposition process that will permit controlled, epitaxial growth. Also, because of cost and size considerations, it is mandatory that a non-native substrate be developed for heteroepitaxial nucleation and growth of diamond thin films. To this end, we are currently investigating the use of Ni single crystals on which different types of epitaxial metals are grown by molecular beam epitaxy (MBE) for lattice matching to diamond as well as surface chemistry modification. This contribution reports briefly on our microscopic observations that are integral to these endeavors.
In situ experimentation: Seeing is believing
Authors: Butler E. Paul
Published: June 2020

The advent of the high voltage electron microscope (HVEM) in the early 1970's initiated a period of intense interest and growth in dynamic in situ experimentation. The two factors responsible for this change were:

– increased volume in the pole-piece gap

– increased penetration of thicker samples

Increased volume freed up space for the stage designer to construct complex yet robust and reliable stages capable of heating/cooling, deformation and environmental control. His task was made easier in side entry stage configurations, which simplified the job of supplying services to and from the specimen holder and provided one ready made axis of tilt along the rod itself. Increased penetration made it possible to observe the true course of many reactions for the first time, overcoming the effects of high surface/volume ratio which so often resulted in a distortion of reaction events in very thin specimens.
Application of the imaging plate to quantitative analysis of electron-diffraction and high-resolution electron microscopy
Authors: Hiraga K. , Shindo D. , Hirabayashi M. , Oikawa T. , Mori N. , Kersker M.
Published: June 2020

The “Imaging Plate” (IP) has three superior characteristics, i.e., high sensitivity to the electron beam, and a wide dynamic range and good linearity for electron dose compared with conventional EM films. The use of the IP is expected to lead to quantitative analysis of electron microscopy. The purpose of the present work is to examine the possibility of application of the IP to the quantitative analysis of electron diffraction and high-resolution electron microscopy.

By using the TEM-IP System developed by Oikawa et al., which is published in this conference, electron diffraction patterns and high-resolution electron micrographs taken on the IP with an effective size of 102 х 77 mm2 were convertedinto digital data of 2048 х 1536 pixels with 4096 gray levels. Observations of electron diffraction patterns and high-resolution electron micrographs were made with a 200 kV (JEM-2000FX) and a 400 kV (JEM-4000EX) electron microscope, respectively.
A new technique utilizing Scanning Electron Microscopy at low temperature and voltage to analyze native-state reservoir rocks
Authors: Stuart C. J. , Liang L.-C. , Toney J. B.
Published: June 2020

A new analytical technique has been developed to allow direct imaging of native-state petroleum reservoir rocks by the use of the scanning electron microscope (SEM) in a low voltage mode combined with a solid-state cryo-system device. The SEM investigation of native-state reservoir rock samples is important since it enables direct visualization of: (1) the spatial distributions of the fluids in the pore system; (2) clay minerals in their natural hydrated states; (3) the native mineralogy; (4) combined effects on the reservoir's wettability and permeability. The technique uses low voltage SEM to image the uncoated surface of the wet sample at a high vacuum and applies the cryostage to control the vapor pressure of the fluid phase while imaging. A differentially pumped environmental chamber is not required with this approach.

This technique utilizes a solid-state thermoelectric cooler device (TED) to achieve the required sample cooling. The TED operates on the Peltier principle permitting the surface of the TED to reach a temperature as low as 110 degrees centigrade below its reference temperature. A sample stage is refitted with a TED substage which is water-cooled. The water-cooling of the substage coupled with the TED allows a precise control of the sample temperature. The sample is fixed to the substage so that it is in direct thermal contact with the TED. The TED is then biased (by the use of DC currents) to provide the effective cooling necessary to minimize vaporization of the interstitial fluids in the sample. The sample and stage temperatures are constantly monitored by means of two microtype-K thermocouple devices. With this approach, no liquid nitrogen is needed for this technique.
Direct lattice imaging of domain boundaries in N-paraffin binary eutectics formed from the vapor phase
Authors: Zhang W.P. , Dorset D.L.
Published: June 2020

In the past few years, we have been studying the crystal structures of binary paraffin solids in the continuum of states from the stable solid solution through the eutectoid to the fully fractionated eutectic. While electron diffraction data have been very useful to detect microstructures, direct lattice images are needed to depict domain separation.

As an example of an eutectic, C30H62/C40H82 thin films were prepared epitaxially on the (100) cleavage face of KCl substrates kept at room temperature under a vacuum of 10−5 torr using the method described by Ueda and Ashida and in our study of palmitone. The specimens were annealed at 40°C for 2 hours. To enhance the phase contrast of lattice images, no carbon films were evaporated onto the organic crystals. After solvating the KCl substrate in pure water, the thin films were collected on holey-carbon coated copper grids for high-resolution study. The thin crystals were examined with a JEOL JEM-100CX electron microscope at 100 kV, and lattice images were taken on Kodak DEF-5 X-ray films at a direct magnification of 19,000X. A minimum dose system was used to reduce the radiation damage during observation.
The method of replication affects metal film granularity and resolution
Authors: Ruben George C.
Published: June 2020

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.
Film thickness measurement by a cross-sectional SEM
Authors: Nagatani T. , Suzuki T. , Yamada M. , Nakagawa M.
Published: June 2020

It is well known that metal films evaporated or sputtered in vacuum are not continuous at a thickness of less than several ten nanometers, but show fine particle distributions or have island granularities as thickness increases. Morphorogy of deposited thin films have been one of the major investigation areas in nucleation, crystal growth, crystal surface studies and so on. There is a room for discussions concerning physical properties such as non-ohmic conductivities of the thin metal films in relation to morphorogy.

However, almost all micrographs obtained by electron microscopes, both TEMs and SEMs, showing such thin metal films are two dimensional, that is, there is not much information how deposited films are growing on the substrate. Owing to the recent development of a high resolution SEM having a probe size of smaller than 1nm by a combination of highly excited condenser-objective lens and a field emission electron source, three dimensional information for the thin film can be provided as shown in Fig. 1. These specimens are Pt sputter-coated on Si wafers at room temperature with a so-called “magnetron” sputter coater, and then fractured for crosssection study by the HRSEM.
Fast imaging method for native liposomes: cryo Electron Microscopy for use in research and quality monitoring
Authors: Roeding J. F.
Published: June 2020

Because of their high affinity to biological membranes liposomes are used in cosmetics and pharmaceuticals. Encapsulated active agents can be transported through biological barriers into cells. Apart from chemical properties, the physical characteristics of liposomes determine their ability of penetration and resorption: Vesicle size, lamellarity (number of membranes) and homogeneity are criterias for the quality of liposome-formulations and usually can be measured with laser-light-scattering combined with e.g. NMR-spectroscopy. Classification of liposomes in type (lamellarity) and size or differentiation of liposomes from other particles e.g. oil-droplets or crystals however requires imaging of the liposomes in their native state. Cryofixation and subsequent cryo-electron-microscopy enable to recognize the form and the structure of liposomes. In view of the low mass of the liposome shell, contrast in a conventional transmission electron micoscope is too weak for rapid, reliable recording of these structures. Imaging in an energy filtered transmission electron microscope (EFEM), however, provides optimum contrast and hence a basis for the correct assessment of the liposome structure including measurement and classification.

Using a special pair of tweezers, take a hydrophilic perforated film (Triafol) and mount it in the injector. Using a pipette, apply 5μl of liposome suspension on this film so that a clear drop is visible. The excess liquid is removed by placing a piece of paper on the film for about 2 seconds. After this, the injector is immediately shot into the cryogen (ethane liquid). Removed from the cryogen and loaded in the specimen holder the specimen can be tranferred to the cryo EM and observed at minimum electron dose on the TV monitor using the image intensifier camera.
A Cryo-transfer facility for the VG HB501 STEM
Authors: Nicholls A.W. , Bovey P.E.
Published: June 2020

A recently developed cryotransfer facility has been successfully used to transfer both hydrated and dehydrated sections from a cryo-microtome to the column of the HB501 STEM with no significant warming or ice formation during transfer. This new accessory enables X-ray and energy loss analytical work to be carried out on frozen biological sections at much higher spatial resolution than is possible with conventional TEM systems.

The construction and operation of the cryotransfer stage are summarized schematically in Figs. 1 and 2. Fig. 1 shows the central region of the HB501 optical column containing the objective lens (1), the post-specimen dc ana ac scan coil assembly (2), the annular dark field detector (3), the diffraction screen (4) and the airlock (5) through which room temperature specimens are normally loaded into the top-entry stage. A special stage base (6) is used which incorporates a liquid nitrogen-cooled block into which specimens are loaded by means of a side-entry manipulator (10). This manipulator is mounted on a support bracket (7) and enters the column through an isolation valve (8). Movement is achieved by a mechanism (not shown) mounted on the outer end of the bracket (7) and vacuum sealed by a bellows (11). The manipulator is liquid nitrogen-cooled by cooling pipes passing axially through the bellows. Loading and unloading of specimens is via an entry lock (9) which can be vented to dry nitrogen. A liquid nitrogen cooled, shrouded transfer rod (not shown) is used to transport specimens from the cryo-microtome to the entry lock.
Lattice resolution in natural polymers
Authors: Revol J.-F.
Published: June 2020

Recent developments in low-dose electron microscopy have led to reports of crystal lattice fringes in natural polymers extremely sensitive to damage by electron irradiation. In one of these studies, lattice images of (β-chitin from the diatom Thalassiosira-fluviatilis were obtained and subsequent computer processing produced the molecular projection of this biopolymer crystal along its b-axis at 0.35 nm resolution. Similar direct structural studies have not been done yet on the α-chitin which is far the most abundant polymorphic form found in nature. The present work reports the direct imaging of crystallite lattice fringes of α-chitin microfibrils from lobster tendon, with a preliminary analysis of the results in terms of crystallite size and perfection.

A typical preparation of α-chitin microfibrils is shown in Figure 1. The image, recorded by diffraction contrast, shows bundles of long microfibrils as well as smaller elements less aggregated and of different length. These smaller elements, composed of shorter crystallites, are the result of the combined action of the acid hydrolysis and of the ultrasound treatment which broke down the originally long microfibrils. When aggregated into larger ribbons, the width of the microfibrils cannot be detrmined due to overlapping, but when viewed individually, the microfibrils exhibit a lateral size of about 10 to 14 nm (see arrows).
Dynamics of microtubules in higher plant mitosis: Functional kinetochore fiber in Haemanthus endosperm
Authors: Bajer A. S. , Molé-Bajer J.
Published: June 2020

The majority of conceptual interpretations of the molecular mechanism of chromosome transport is based on the centriolar spindle. The prevailing interpretations have been modified and altered frequently and, in spite of considerable progress recently, the molecular mechanism remains elusive. The reasons for this slow progress are multiple. We believe that, underestimated and trivial as it seems, one of the major problems is the emphasis on the centriolar spindle where the presence of the aster obstructs the organization of the spindle pole and clouds the essential problem of the anchorage of the kinetochore fiber. Therefore, we have concentrated deliberately on higher plant endosperm of Haemanthus, which has the largest and clearest acentriolar mitotic spindles known. A large number of dividing cells on each preparation (averaging about 500 with a maximum of about 1800), combined with natural variation and experimental lowering of the available tubulin, have allowed us to characterize division in cells, which we believe have the threshold number of microtubules required for a functional spindle. Our conclusions on how mitosis works are very different from any current interpretation.

Endosperm cells of Haemanthus katherinae Bak. were used as material. Microtubule distribution was analyzed in immunogold stained cells fixed about 45 minutes after preparation. Therefore all cells damaged during and shortly after preparation were excluded because they do not immuno-stain. Over 95% of the remaining cells complete mitosis. Cells with average microtubule numbers (see Figs in ) were compared with cells containing very low numbers of microtubules, occasionally found in controls (Figs. 1-4) and after experimental depletion. Microtubule depletion occurs in about 30% of the cells after routine growing of plants 10°C - 12°C for 10-14 days and is retained for 2-3 days at room temperatures (21°C - 24°C). Observations are based on several hundreds of cells, comprising multiple examples of transitions between various degrees of microtubule depletion.
Does cellulose II occur in nature?
Authors: Roberts E.M. , Saxena I.M. , Brown R.M.
Published: June 2020

Cellulose, a carbohydrate polymer of :ß-D-glucose, occurs in several different crystalline forms called allomorphs. “Cellulose II” is by far the most abundant allomorph found in nature, but a few organisms have been suggested to synthesize another crystalline form called “cellulose II” (summarized in). Some of these reports are now considered uncertain due to the presence of clay contaminants or because extractions requiring high concentrations of alkali can convert cellulose I to cellulose II. Because identification of organisms that synthesize native cellulose II could help further understanding of how cellulose crystallization occurs, we have reexamined several of the organisms suggested to produce this allomorph. Care was taken to minimize the atrifacts mentioned above. Included in this study were the algae HalicystisandEnteromorpha, and the slime mold Dictyostelium.In the course of our studies, we have also found that certain mutants of the bacterium Acetobacter xylinum synthesize cellulose II instead of the cellulose I allomorph produced by the wild type.

Bacterial cellulose was purified from mutants of Acetobacter xylinum as previously described. After extraction in organic solvents, cellulose was purified from Halicystis (UTEX strain 1260) by brief treatment with 15-20% HCl at 100°C and extraction with 1N NaOH and 0.25M NaBH4 (2 x 30 minutes, 100°C). The ultrastructure of these samples were examined by negative staining with uranyl acetate. Cellulose from Enteromorpha (UTEX strain 739) was purified as described above or extracted by soaking overnight in 24% KOH at room temperature. X-ray diffraction powder patterns were recorded with a Debye-Scherrer camera and Cu k-alpha radiation. The crystalline form of cellulose from stalks of Dictyostelium discoidium was studied by electron diffraction. Individual stalks were harvested and cleaned in dilute HCl. Electron diffraction patterns produced at 120 kV were recorded on Kodak 35 mm Tri-X film.