bluuebunny/crossref_metadata_2025 huggingface dataset:
High Resolution Electron Beam Fabrication Using STEM
Authors: Broers A.N. , Cuomo J. , Harper J. , Molzen W. , Laibowitz R. , Pomerants M.
Published: June 2020

Recent work on electron beam lithography has centered on improving
overlay precision, reducing cost per exposure and perfecting electron
resists and processes for the fabrication of silicon integrated circuits.
These efforts have produced experimental integrated circuits with higher
density than had previously been possible, and have led to cost reductions
in manufacturing environments where quick turn-around is essential. High
resolution (linewidths < 0.25 /jm) has not been of direct interest
although its pursuit has given information about electron scattering effects
which influence resist profiles and give rise to proximity effects. Both of
these effects can still be important at larger dimensions particularly when
linewidth control is of primary importance. In the last two years, new
interest in high resolution has arisen because it has become possible to
make useful structures with dimensions of a few tens of nanometers. These
nanostructures can be handled readily and it is possible to make electrical
contact to them. They are of interest in exploring the physical nature of
electrical conductivity especially in superconducting structures exhibiting
Josephson effects. It should also be possible to use similar techniques to
make optical elements for soft x-rays such as zone plates and
pinholes.
Characterisation of Lattice Defects
Authors: Hirsch P.B.
Published: June 2020

Transmission electron microscopy (TEM) is a powerful technique for characterising lattice defects. Image contrast arises from local changes in scattering either due to displacements of atoms or change of type of atom, vacancies, interstitials, etc. The intensities of the diffracted beams are changed in a manner characteristic of the type of defect, and there is a corresponding characteristic image in the TEM.

Basically two types of technique based on diffraction are available:- 1) Those in which defect images are produced without resolving the crystal lattice or structure. 2) Those in which the crystal structure is resolved. The first of these has so far had more general application, and the interpretation of the contrast effects of most variant of this technique is based on the many-beam dynamical theory of electron diffraction foi imperfect crystals developed by Howie and Whelan (1961).
Intrinsic Structure in Grain Boundaries and Boundary Mobility
Authors: Clarebrough L.M. , Forwood C.T.
Published: June 2020

An outstanding experimental contribution to the knowledge of grain
boundary structure in the 1970's is the work of Balluffi and his colleagues
at Cornell University on artificially fabricated boundary interfaces in thin
films of gold (e.g., Balluffi, Komem and Schober, 1972; Balluffi, Goodhew,
Tan and Wagner, 1975). In particular, for high-angle boundaries they have
shown that secondary grain boundary dislocations (g.b.d's.) do exist and
accommodate a deviation from a low-energy misorientation corresponding to an
exact C.S.L. relationship. Further, following the results of Spyridelis,
Delavignette and Amelinckx (1967) they have shown that a network of g.b.d's.
can act as a diffraction grating, causing extra reflections whose spacing is
reciprocally related to the separation of the g.b.d's. (Balluffi, Sass and
Schober, 1972). The description of high-angle grain boundaries in terms of
secondary g.b.d's. accommodating a departure from an exact C.S.L.
orientation is based solely on geometrical considerations, but it has been
pointed out that other low-energy configurations may be preferred when
account is taken of the nature of interatomic forces (Gleiter and Pumphrey,
1976; Hermann, Gleiter and Baro, 1976; Smith, Vitek and Pond,
1977).
Recent Applications of High Resolution Electron Microscopy to Crystalline
Arrays of Virus Particles
Authors: Horne R.W.
Published: June 2020

The technique of surrounding virus particles with a neutralised electron
dense stain was described at the Fourth International Congress on Electron
Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many
years the negative staining technique in one form or another, has been
applied to a wide range of biological materials. However, the full potential
of the method has only recently been explored following the development and
applications of optical diffraction and computer image analytical techniques
to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968;
Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974;
Crowther & Klug, 1975). These image processing procedures have allowed a
more precise and quantitative approach to be made concerning the
interpretation, measurement and reconstruction of repeating features in
certain biological systems.
The Structure of One and Two Dimensional Polymers of Tubulin and their Role in Nucleation of Microtubule Assembly
Authors: Erickson H.P.
Published: June 2020

The microtubule is a long hollow cylinder, 23 nm outside diameter and of indeterminate length, often many micrometers long. The wall of the microtubule, a curved sheet of 5 nm thickness, is seen to best advantage where it is split open and flattened against the carbon film as a non-overlapping, single sheet (fig. 1). Optical diffraction and image reconstruction techniques show that the wall is composed of subunits arranged on a 4 x 5 nm lattice (fig. 2). Each of these 4 x 5 nm subunits corresponds to a 55,000 MW protein subunit characterized biochemically and called tubulin.

It is well established that microtubules are composed of two similar but distinct types of tubulin, called alpha and beta. In most negatively stained specimens, however, the 4 x 5 nm subunits are identical in structure. A small structural difference between alternate 4 x 5 nm subunits is seen under certain conditions (Amos and Klug, 1974; Baker and Amos, 1978), but in the present discussion we will ignore the distinction between alpha and beta subunits and pretend that the microtubule is composed of a single type of subunit.
Split Membrane Lipids and Polypeptides
Authors: Fisher K.A.
Published: June 2020

It is currently accepted that the biological membrane is composed of
amphiphilie lipids arranged in bilayers with functionally important proteins
embedded in, or spanning, the hydrophobic interior of the bilayer (Singer,
1977). Support for this view comes from a variety of chemical and physical
methods. Enzymatic and chemical modification reactions have established the
basic property of membrane asymmetry for lipids (Verkleij et al., 1973) and
proteins (Steck, 1978) and the results of many physical studies are most
easily interpreted in the context of structural and functional asymmetry.
Such studies often rely on the modification of biomembranes by probes;
relatively few methods exist, however, to study the transbilayer
concentration of native molecules directly. Moreover, the accessibility of
reagent or probe molecules to membrane molecules or domains, or their
distribution within or across the plane of the membrane, remain in some
instances uncertain. In such instances it is desirable to have the means to
determine their location directly by an independent method such as electron
microscopy.
Immunoferritin Electron Microscopy and the Structure of Membranes
Authors: Singer S.J.
Published: June 2020

The fluid mosaic model (Singer, 1971; Singer and Nicolson, 1972) is currently widely accepted as a general scheme for the molecular organization of membranes. It was originally based on thermodynamic considerations, which led to the proposal that the integral proteins of membranes are globular molecules with amphipathic structures, much like those exhibited by membrane phospholipids (Lenard and Singer, 1966; Wallach and Zahler, 1966). It was suggested that such molecules possessed a hydrophobic domain adjacent to one or two hydrophilic domains: with the hydrophobic domain embedded in the non-polar lipid interior of the membrane, and the hydrophilic segments protruding into the aqueous phase. This structure generated a mosaic of protein and lipid molecules in the plane of the membrane (Glaser et al., 1970) and led to the prediction that there would be no long-range order in that plane. In fact, if the lipid was a fluid at a particular temperature, the entire structure would be that of a two-dimensional solution, as was so vividly demonstrated by the immunofluorescence studies of Frye and Edidin (1970) and of Taylor et al. (1971).
Transcription in the Interphase Nucleus
Authors: Simard R. , Royal A. , Lacoste-Royal G. , Banville D.
Published: June 2020

Normal Nuclear Fine Structure

The Nucleolus

Excellent reviews on nucleolar fine structure have been published in
past and recent years, and it is not our intention to duplicate them. There
are four distinct nucleolar components in most mammalian cells: (1) 150- to
200-A dense granules randomly dispersed in the nucleolus, (2) a loose
fibrillar reticulum composed of 50- to 80-A fibrils, (3) an amorphous matrix
of low electron opacity, and (4) nucleolus-associated chromatin with
intranucleolar ramifications. The granular and fibrillar components are
partially extracted with ribonuclease and disappear completely if digestion
with the nuclease is followed by pepsin (Marinozzi and Bernhard, 1963). They
can be referred to as granular and fibrillar ribonucleoproteins (RNP). The
granular RNP are similar to the cytoplasmic ribosomes in their staining
properties, but they are smaller, more irregular, and never arranged in
subunits. Thin filaments about 20 A in width have been demonstrated in the
granules; these filaments are RNase-sensitive (Smetana et al.,
1968a).
Supranucleosomal and Non-Nucleosomal Chromatin Configurations
Authors: Franke W.W. , Zentgraf H. , Scheer U.
Published: June 2020

A significant contribution to the understanding of chromatin organization was the discovery of the nucleosome as a globular repeating unit of the package of DNA (Hewish and Burgoyne, 1973; Woodcock, 1973; Kornberg, 1974; Olins and Olins, 1974; for review see Oudet et al., 1978a). In accord with the original definition and in agreement with most workers in this field of research we identify a nucleosome as a spherical or slightly oblate granular particle 10-13 nm in diameter, containing about 200 base pairs of DNA and two of each of the four histones H2a, H2b, H3 and H4. It is this structure in which the bulk of the nuclear chromatin is organized in most eukaryotic cells, with the exception of the dinoflagellates (Rae and Steele, 1977; dinoflagellate DNA, however, can be packed into nucleosomal structures in vitro by addition of the appropriate amounts of histones;the same reference).
Basic Protein Film Methods in the Electron Microscopy of Nucleic
Acids
Authors: Davidson N.
Published: June 2020

I wish to discuss applications of the basic protein film method for
mounting nucleic acids for electron microscopy. In this method, the nucleic
acid and an excess of a positively charged low molecular weight globular
protein (cytochrome-c is commonly used) are dissolved in a suitable
electrolyte solution (ammonium acetate or Tris works well). The electrolyte
concentration should be high enough so that the electrostatic binding of the
positively charged protein to the negatively charged nucleic acid does not
cause precipitation. This solution is layered on to a hypophase which
contains a lower concentration of the electrolyte. Some of the protein
denatures and forms a film on the surface of the hypophase. Because of the
increased strength of the electrostatic interactions at the reduced
electrolyte concentration, some of the nucleic acid molecules bind to the
positively charged protein film.
Electron Microscopy of Cytoplasmic Contractile Proteins
Authors: Pollard T.D. , Maupin P.
Published: June 2020

In this paper we review some of the contributions that electron microscopy has made to the analysis of actin and myosin from nonmuscle cells. We place particular emphasis upon the limitations of the ultrastructural techniques used to study these cytoplasmic contractile proteins, because it is not widely recognized how difficult it is to preserve these elements of the cytoplasmic matrix for electron microscopy.

The structure of actin filaments is well preserved for electron microscope observation by negative staining with uranyl acetate (Figure 1). In fact, to a resolution of about 3nm the three-dimensional structure of actin filaments determined by computer image processing of electron micrographs of negatively stained specimens (Moore et al., 1970) is indistinguishable from the structure revealed by X-ray diffraction of living muscle.
Structural Studies on Mitotic Spindle Fibres
Authors: Mcintosh J.R.
Published: June 2020

The mitotic apparatus is a structure of obvious biological and medical interest, but it has proved to be a difficult cellular machine to understand. The chemical composition of the spindle is only slightly elucidated, largely because of the difficulties in preparing useful isolates of the structure. Chemical studies of the mitotic spindle have been reviewed elsewhere (Mcintosh, 1977), and will not be discussed further here. One would think that structural studies on the mitotic apparatus (MA) in situ would be straightforward, but even with this approach there is some disagreement in the results obtained with various methods and by different investigators. In this paper I will review briefly the approaches which have been used in structural studies of the MA, pointing out the strengths and problems of each approach. I will summarize the principal findings of the different methods, and identify what seem to be fruitful avenues for further work.
The Structure of Tight Junctions
Authors: Bullivant S.
Published: June 2020

The tight junction, or zonula occludens, is generally found as a continuous belt, joining adjacent cells in the apical region of the border between them. It forms a seal across the intercellular space and hence regulates paracellular permeability. Farquhar and Palade (1963), recognised the belt-like sealing character, and showed that in thin sections the junction was seen as either punctate or linear fusions of the two membranes, often with the loss of the outer leaflet of the unit membrane at the fusion. With thin sections it can only be inferred that the junction forms a continuous belt, but with freeze-fracturing it can be seen directly. Moreover, in the junctional region the membrane structure is modified by a series of interconnected fibrils approximately parallel to the line of the belt (Kreutziger, 1968; Staehelin et al, 1969; Goodenough and Revel, 1970), and within the interior of the membrane Tchalcroft and Bullivant, 1970). The fibrils are at the lines of membrane fusion.
Possible indirect transmission of COVID-19 at a squash court, Slovenia, March 2020: case report
Authors: Brlek A. , Vidovič Š. , Vuzem S. , Turk K. , Simonović Z.
Published: June 2020

Since the beginning of the COVID-19 epidemic, there is an ongoing debate and research regarding the possible ways of virus transmission. We conducted an epidemiological investigation which revealed a cluster of five COVID-19 cases, linked to playing squash at a sports venue in Maribor, Slovenia. Acquired data raises possibility that the transmission occurred indirectly through contaminated objects in changing room or squash hall or via aerosolisation in squash hall.
A REVISION OF GAGNEPAINIA AND HEMIORCHIS (GLOBBEAE: ZINGIBERACEAE)
Authors: Tan S. , Hollands R. , Pavlíková M. , Fér T. , Newman M. F.
Published: June 2020

The species of Gagnepainia K.Schum. and Hemiorchis Kurz are revised throughout their ranges. These genera are shown with evidence from morphological and molecular studies to be distinct, although closely related to each other. Two species of Gagnepainia and three of Hemiorchis are recognised. A key to the genera of Globbeae and keys to the species of Gagnepainia and Hemiorchis are given, all names are typified and descriptions are provided. Conservation assessments of all taxa are proposed.
Dark-Field Imaging with the Albany 1.2 MV High-Voltage Electron Microscope
Authors: Mannella C.A. , Ratkowski A.J. , Marko M. , Parsons D.F.
Published: June 2020

High-resolution images of naked biological structures have been produced with conventional electron microscopes operated in dark-field mode. The use of higher accelerating voltages offers several important advantages, including decreased plural scattering and decreased chromatic aberration for thin, low-Z specimens. Despite impressive early results at the Toulouse HVEM facility there has been little application of high-voltage dark-field techniques to the study of biological specimens of low mass-thickness.

The increased contrast inherrent to dark-field imaging is illustrated in Fig. 1 for a conventionally-stained, very thin (20nm) section of rat brain taken at an accelerating voltage of 1.0 MV. Fig. 1A is a bright-field micro-graph taken with a 30-μm diam Pt object apenture. Micrographs B and C are dark-field images of the same field generated, respectively, by tilting the zero-order beam into the edge of the 30-μm aperture (“beam-tilt” dark-field) or by blocking the zero-order beam with a 20-μm-thick Cu bar (“strioscopy”). The much higher collection efficiency of strioscopic relative to beam-tilt dark-field is reflected in the exposure times for micrographs B and C (10vs1 sec). Although all 3 micrographs display features (e.g., myelin intraperiod line widths) at the effective specimen preparation resolution limit (2.5-3.0 nm), dark-field HVEM micrographs taken using strioscopic techniques are generally not as sharp as those obtained with beam-tilt. Because radiation damage associated with the latter dark-field mode may be excessive in proposed studies of unstained biological structures, we have undertaken a study of the factors limiting the resolution and contrast of the more efficient strioscopy. Our findings suggest that dark-field resolution with non-crystalline, low-Z specimens may be a sensitive function of HVEM lens design and of collimation as well as dark-field aperture arrangement.
An Improved Double-Tilt Stage for the AEI EM7 High-Voltage Electron
Microscope
Authors: Turner J. N. , Ratkowski A. J.
Published: June 2020

Specimens approximately a micron thick are routinely examined in the
HVEM as a result of its increased penetrating power. This large specimen
thickness is advantageous for the study of three-dimensional structure, and
it increases the sampling statistics significantly for observing a
particular image detail. However, each image in the HVEM represents a volume
of the specimen and cannot be assumed to be a plane as is common practice
for the CTEM. Therefore, image details in the HVEM often overlap or are not
optimally oriented with respect to the beam. Thus, a specimen stage with
sufficient degrees of freedom to position the specimen in any orientation
relative to beam is required (Turner and Chang, these proceedings). Our
double-tilt stage shown in fig. 1 and built by P. R. Swann (1972) has this
capability.
Theory of Optimal Scanning in the STEM
Authors: Crewe A.V.
Published: June 2020

Many of us have taken it for granted that the STEM produces a faithful
image of the specimen, perhaps because the novelty of the instrument made it
surprising that it produced an image at all. Little attention has been paid
to the imaging process and yet it is a very complicated one. This brief
study of the process indicates that almost no one (including ourselves) has
used the instrument properly and that much is to be gained by
optimisation.
Microprobe and Nanoprobe Analysis in TEM
Authors: Thompson M.N.
Published: June 2020

The application of TEM/S(T)EM systems to problems in the materials
science and life science is an accepted and growing trend. Considerable
information benefits have been derived from the new information which
secondary electron, back-scattered electron and X-ray line scan and mapping
images have provided. This is also true of the STEM mode with respect to the
visualisation of low-contrast specimens, the application of annular D.F.
detectors and signal mixing techniques.

In the general case, however, the STEM mode is used specifically to view
an area for the purpose of locating a small probe for point X-ray analysis
or microdiffraction. As there is no clear evidence to date that the STEM
mode has specific advantages under conditions analogous to normal TEM
observation the greater proportion of normal thin specimen work has remained
the domain of the basic TEM mode. The reasons for this TEM preference for
transmission work are the intrinsically simple operation, the convenience of
real time, wide-field imaging and the high resolution images available for
viewing and recording particularly at relatively low
magnifications.
Some Aspects of Exelfs Analysis in the Electron Microscope
Authors: Johnson D. E. , Csillag S.
Published: June 2020

Recently, the applications area of analytical electron microscopy has
been extended to include the study of Extended Energy Loss Fine Structure
(EXELFS). Modulations past an ionization edge in the energy loss spectrum
(EXELFS), contain atomic fine structure information similar to Extended
X-ray Absorbtion Fine Structure (EXAFS). At low momentum transfer the main
contribution to these modulations comes from interference effects between
the outgoing excited inner shell electron waves and electron waves
backscattered from the surrounding atoms. The ability to obtain atomic fine
structure information (such as interatomic distances) combined with the
spatial resolution of an electron microscope is unique and makes EXELFS an
important microanalytical technique.
Computerized Processing and Subtraction of Energy-Filtered Electron
Images as an Aid to Elemental Analysis
Authors: Douglas M. A. , Hui S. W. , Costa J. L. , Bailey J. J.
Published: June 2020

Recent work has documented the use of energy-filtered electron images
for examination of the elemental composition of organic and inorganic
materials (1,2). In order to obtain an accurate elemental map, images
recorded with electrons at an energy immediately below a characteristic edge
must be compared in a quantitative fashion with images recorded utilizing
electrons within an energy window encompassing the edge of interest. This
presentation describes a scheme for the interactive computerized processing
and comparison of energy-filtered images, a series of manipulations which
should be useful for producing composite elemental maps.
On The Limitations of X-Ray Microanalysis of Heterogeneous Specimens
Using Analytical Electron Microscopy
Authors: Zaluzec N. J. , Kenik E. A. , Maziasz P. J.
Published: June 2020

X-ray microanalysis in an analytical electron microscope is becoming a
routinely used technique in materials science and it is important to
appreciate its limitations in the quantitative analysis of inhomogeneous
elemental distributions. Situations in which this can occur are in the
measurement of precipitate compositions or the determination of
concentration gradients at defects or interfaces. This subject was treated
in part by Zaluzec1 where he indicated the errors
associated with attempting analysis of precipitates embedded in a host
matrix and proposed that the solution to this problem was to isolate the
second phase from the surrounding matrix. This usually amounts to extraction
of the precipitate from the parent phase which is not always simple. The
subject of this note is to outline a procedure in which semiquantitative
analysis may be obtained in situations where precipitate extraction is
difficult or impossible.
Sputter-Deposited Films as Standards for Tem X-Ray Analysis
Authors: Marshall A. F. , Zercher C.
Published: June 2020

Quantitative energy dispersive x-ray analysis in the transmission
electron microscope is generally obtained in the form of relative
concentrations using the equation:

where CA, CB are the
concentrations and IA, IB are the
peak intensities of elements A and B, and kAB is a
constant which is independent of specimen composition and specimen
thickness, assuming the thin film criterion is satisfied.
kAB may be determined experimentally from standards
(Cliff-Lorimer technique1), or may be calculated from
considerations of x-ray generation and detector efficiency for the elements
being analyzed2. Due to differences in detector
parameters, kAB may vary from instrument to
instrument.
An Electron Microscope Study of Native Copper
Authors: Murr L.E.
Published: June 2020

Copper is found in the free metallic state in nature and this native
copper was used by neolithic man as a substitute for stone in the fashioning
of crude hammers, knives, and other utensils. It was melted and cast into
desired shapes over campfires after 6000 B.C., an occurrence which
eventually lead to the reduction of ore for copper recovery and the birth of
metallurgy. Deposits of native copper occur in amygdoloid or conglomerate
rock mainly in Michigan, but can be found throughout the major porphyry
copper deposits of the United States. Native copper occurring in many areas
becomes mixed with other copper minerals especially oxides.
The Substructures Before and After Fatigue in Thermomechanically Treated
Pure Aluminum
Authors: Jahn M.T. , Lin Tsann , Wan C.M.
Published: June 2020

Substructures in Metals can be formed either by thermomechanical
treatment or by fatigue process. It is interesting to study how the
pre-existing substructures introduced by thermomechanical treatment affect
the substructures formed after fatigue and how the substructures are
correlated to the fatigue properties. The effect of pre-existing
substructure on fatigue properties of pure aluminum was seldom studied
before1. The pre-existing substructure studied by Jahn et al.1 was
concentrated only in well-defined subgrains of size approximately 2 pm.
Since there are different size and various kinds of substructure like
dislocation tangles, dislocation cells and subgrains we examine
experimentally in this study how the shape and size of pre-existing
substructure affect the fatigue property of pure aluminum.
High Resolution Low Loss Microscopy of Crystalline Surfaces
Authors: Krakow William , Broers Alec N.
Published: June 2020

Low-loss scanning electron microscopy can be used to investigate the
surface topography of solid specimens and provides enhanced image contrast
over secondary electron images. A high resolution-condenser objective lens
has allowed the low-loss technique to resolve separations of Au nucleii of
50Å and smaller dimensions of 25Å in samples coated with a fine grained
carbon-Au-palladium layer. An estimate of the surface topography of fine
grained vapor deposited materials (20 - 100Å) and the surface topography of
underlying single crystal Si in the 1000 - 2000Å range has also been
investigated. Surface imaging has also been performed on single crystals
using diffracted electrons scattered through 10−2 rad
in a conventional TEM. However, severe tilting of the specimen is required
which degrades the resolution 15 to 100 fold due to image
forshortening.
Long-Period Polytypism in Polycrystalline SiC: High-Resolution
T.E.M.
Authors: Ogbuji Linus U.
Published: June 2020

Long-period polytypism is common in SiC and other, isostructural
ceramics. This phenomenon is essentially a one-dimensional version of the
superlattice structure encountered in the phase transformation of certain
metallic alloys (eg. AuCu). However, while in the case of metals an
explanation can be found in electronic processes at the Brillouin zone, no
such processes can occur in semiconducting and insulating ceramics; and
while the theory of Frank offers an equally neat and attractive explanation
valid for ceramics, it is only applicable to single crystals grown from a
liquid or vapor. T.E.M. evidence is presented here to show that the origin
of long-period polytypism in polycrystalline SiC+ lies
in a structural peculiarity of the phase transformation process in this
material. Because the fundamental events occur at unit-cell levels, their
elucidation required the application of lattice fringe imaging
techniques.
Accurate Microcrystaliography in the S.E.M.
Authors: Venables J.A. , Harland C.J. , Akhter P.
Published: June 2020

Three crystallographic techniques have been developed for use on bulk
samples in the SEM. They are the electron channelling pattern (ECP), the
X-ray Kossel Line (XKL), and the electron back-scattering pattern (EBSP).
This last technique consists of observing the angular distribution of
back-scattered electrons on a screen and interpreting the crystallographic
contrast (Kikuchi bands) present to obtain accurate crystal orientations. A
small solid angle back-scattered electron detector (SAD) can pick up these
Kikuchi bands to create SEM pictures with enhanced crystallographic
contrast. Together these EBSP and SAD techniques show that orientation to∼ ±
0.5°accuracy can be obtained from small (sub-lOOnm) areas of bulk samples.
In this paper these techniques are described and examples given to show how
the techniques can be used.
Experimental Assessment of the Accuracy of Foil Thickness Measurements
from Convergent-Beam Diffraction Patterns
Authors: Allen Samuel M. , Hall Ernest L.
Published: June 2020

Convergent-beam electron diffraction (CBED) patterns can be analyzed to
determine foil thickness by a simple graphical technique based on the
two-beam approximation to dynamical diffraction theory. Errors incurred in
such measurements are due to several causes, including: the effect of the
two-beam approximation itself, measurement errors in analyzing the fringe
positions in the patterns, and geometrical factors relating the thickness in
the beam direction to the true foil thickness. This study was undertaken to
determine typical errors that might be encountered in experimental
applications of the technique.
Microstructure of Pitch-Based Carbon Fibers
Authors: Lyman C E. , Shen T. H.
Published: June 2020

Graphitized carbon fibers for use in composite materials have been made
from pitch for several years.1,2 Two types of pitch
have been used for producing carbon fibers. Aromatic pitch, which is
isotropic, needs a high strain rate and rapid quenching to spin into a
highly oriented fiber. The other type, known as high molecular weight pitch,
forms an anisotropic liquid (mesophase) upon heating and spins at a
relatively low speed to form oriented fiber. Usually commercial pitch
contains both of these types. The pitch is melt-spun so that the mesophase
will form rod-like elongated fibrils embedded in an isotropic matrix. The
fiber is oxidized to thermoset the isotropic pitch and then carbonized and
graphitized at higher temperature to form a completed 1Oμm diameter carbon
fiber.
Scanning Transmission Electron Microscopy of Polyethylene
Crystals
Authors: Khoury F. , Bolz L. H.
Published: June 2020

The lateral growth habits and non-planar conformations of polyethylene
crystals grown from dilute solutions (<0.1% wt./vol.) are known to vary
depending on the crystallization temperature.1-3 With
the notable exception of a study by Keith2, most
previous studies have been limited to crystals grown at <95°C. The trend
in the change of the lateral growth habit of the crystals with increasing
crystallization temperature (other factors remaining equal, i.e. polymer
mol. wt. and concentration, solvent) is illustrated in Fig.l.

The lateral growth faces in the lozenge shaped type of crystal (Fig.la)
which is formed at lower temperatures are {110}. Crystals formed at higher
temperatures exhibit 'truncated' profiles (Figs. lb,c) and are bound
laterally by (110) and (200} growth faces. In addition, the shape of the
latter crystals is all the more truncated (Fig.lc), and hence all the more
elongated parallel to the b-axis, the higher the crystallization
temperature.
Electron Microscopy Studies of Polymer Blends
Authors: Hobbs S.Y. , Watkins V.H. , Kambour R.P. , Bopp R.C.
Published: June 2020

Scanning and transmission electron microscopy have been used to
investigate the phase separation behavior of blends of brominated poly
(2,6-dimethy1 -1 ,4-phenylene oxide) known trivially as poly (xylenyl ether)
(PXE) and polystyrene. DSC scans show that when more than 85% of the PXE
rings are brominated, the blends exhibit two glass temperatures centered at
100°C and 290°C and the polymers are immiscible.1 At
lower bromine concentrations, a single composition dependent
Tg characteristic of a one phase system is
observed. Microscopic studies, however, indicate that separate phases which
can not be detected ca1orimetrica11y may persist to considerably lower
levels of bromination and may thus provide a more sensitive measure of
segregation behavior.
Stem Vs. Ctem of Polymer Crystals: Effects of Accelerating Voltage and
Substrate Thickness on Image Resolution Limited by Beam Damage
Authors: Krause S. J. , Allard L. F. , Bigelow W. C.
Published: June 2020

Several advantages of scanning transmission (STEM) versus conventional
transmission electron microscopy (CTEM) imaging of beam sensitive polymer
crystals have been discussed in previous papers (1,2). However, the effects
on image resolution of variations in carbon substrate thickness and
accelerating voltage have not been quantified. Both variables dramatically
affect the number of electrons inelastically scattered as the beam passes
first through the sample and then through the substrate; causing resolution
as limited by beam damage to be greatly affected. In this paper, the
influence of accelerating voltage and substrate thickness on inelastic
scattering and subsequent degradation of resolution are compared in the STEM
and the CTEM in both bright (BF) and dark field (DF) imaging modes.
Coordinated Scanning Electron Microscopy and Light Microscopy for the
Evaluation of Chemical Element Heterogeneity Among Individual Fly Ash
Particles
Authors: Hayes T. L. , Lai C. E. , Fisher G. L. , Prentice B. A.
Published: June 2020

Fly ash, a major air pollutant associated with coal combustion, has been
shown by bulk analysis technique to contain many elements toxic to the lung
system and the exposure of lung cells to the foreign elements contained in
fly ash can be strongly influenced by the distribution of these elements
among individual fly ash particles. Light microscopy has been utilized by
Fisher et al. (I) to identify 14 classes of particles on the basis of color,
internal structure and opacity. The present study was undertaken in an
attempt to evaluate the segregation of chemical elements among the various
types of fly ash particles identified by light microscopy and to verify
directly the suggested elemental composition of certain of the
classes.
Focusing Corrections in Sector Magnets
Authors: Ottensmeyer F. P.
Published: June 2020

Sector magnets are becoming increasingly important as accessories or
integral components of analytical electron microscopy. Their long use in
steering and focusing charged particle beams in high energy physics would
lead one to suspect that the transfer of knowledge and expertise from that
field to electron microscopy should be easy. However, the requirements of
electron microscopy appear to be much more demanding whether one considers
spatial resolution of the images passed through such a system, energy
resolution of the spectrum of losses characteristic of the specimen,
acceptance angle of a sector magnet used as analyser, desirable detector
geometries for simultaneous recording of spectra or combinations of these.
Thus a thorough understanding of the focusing properties of such magnets, of
the factors that contribute to loss in resolution and of the approximations
made in attempts to correct such losses, is of great value when considering
the introduction of such an element into an existing electron optical
system.
A New Possibility for Correcting Cs
Authors: Crewe A. V.
Published: June 2020

In 1936 Scherzer (1) showed that the spherical aberration constant
(Cs) of round lenses always has the same design. In
addition one can show that no realizable field of distribution can have
Cs=0. In the period between then and now many
authors have sought to design lenses with the minimum possible value of
Cs and it seems fair to state that the field has
been fully explored. We now have the minimum values and no further reduction
can be expected. Since Cs also determines the available
resolving power, no further improvement in that parameter can be
expected.
A Practical High-Resolution Electron Spectrometer
Authors: Egerton R. F.
Published: June 2020

Assuming the use of post-specimen coupling lenses where
necessary1, the performance of a magnetic electron
spectrometer is limited mainly by second order aberrations.
UHV Transmission and Reflection Electron Microscopies for Surface Studies
Authors: Yagi Katsumichi
Published: June 2020

This paper reviews recent results of surface structure studies of mono-layer levels done in our group with use of an UHV electron microscope (EM) of 10-8∿10-10Torr, which was originally designed for in-situ thin film growth studies [1]. Our techniques of UHV EM and of in-situ deposition and clean surface preparation were applied to studies of microtopographies of surfaces, in which previous surface researches mainly done by LEED, AES and RHEED are lacking. Some efforts to get topographic informations were done with use of AES and RHEED in scanning mode [2] but their resolutions were much poorer than that of conventional EM. We observed surfaces in two modes, transmission (TEM) and reflection (REM). TEM had been considered to be insensitive to details in depth direction in contrast to its high resolving power in lateral directions. Recent reports, however, showed that atomic steps stand out both in bright and dark field images with appreciable contrast due to diffraction extinction effects [3]. The REM method is based on the fact that RHEED is sensitive to surface structures [4]. The previous REM works, however, did not succeeded in observing clean surfaces on account of poor vacuum of the microscope and lack of preparation techniques of specimens with clean surfaces [5].
Structure of Ion-Implanted Silicon After Electron Beam Annealing
Authors: Smith P. J. , Leas J. M. , Leighton A. T.
Published: June 2020

High dose ion-implantation into single crystal silicon produces an
amorphous layer which must be removed by high temperature annealing. Laser
and electron beam annealing, which bring only the top surface of the silicon
to a high temperature, can produce more perfect single crystal material than
conventional thermal annealing while avoiding the disadvantages of heating
the entire wafer. We have found that electron beam annealing of oxide-
defined silicon devices can produce dislocation-free single crystal material
from amorphous ion-implanted layers, but the results are strongly dependent
on both the electron beam parameters and the initial device
structure.
Rhenium Effect on Creep Behavior of Ni-Base Superalloys
Authors: Lin L.S. , Giamei A.F. , Doiron R.E.
Published: June 2020

Modified MAR-M-200 single crystals with various amounts of rhenium were
tested in tensile creep in <111>, <011> and <001>
orientations. With the addition of rhenium, a significant improvement in
creep resistance was attained. This is illustrated clearly in Figure 1. In
order to understand the effect of the rhenium addition on the creep strength
of Ni-base superalloy single crystals, transmission electron microscopy was
used to analyze the microstructures and dislocation behavior. Creep samples
with gauge length of 10 mm and diameter of 2.5 mm were tested at 900°C/380
MPa unless otherwise specified. The chemical composition of the alloy
studied is 5Al-2Ti-lNb-9Cr-12(W + Re) with the balance Ni (in weight
percentage). The rhenium contents were 0, 2, 1, or 6 wt. $ at the expense of
tungsten. The samples were fully heat treated (l290°C/4 hrs. + 1080°C/4 hrs.
+ 870° C/32 hrs.) before testing. The oriented crystals (with 0 and 6 wt. $
Re, respectively) were creep tested to a strain of ~ 0.2$. Their detailed
transmission microstructures are shown in Figures 2 and 3. In <111>
crystals, cube slip, {001} <110> was observed while in <011>
crystals, octahedral slip, {111}<101> was observed. Results similar to
the <011> case were found in <001> crystals tested at 980°C/220
MPa.
The Microstructure of Electron-Beam Welds in Inconel 718
Authors: Vincent R. , Steeds J.W.
Published: June 2020

Electron-beam welds in the Ni-base superalloy, Inconel 718 are
freauently found to contain an extensive system of micro-cracks radiating
from the weld boundary into the heat-affected zone (HAZ) of the matrix. To
study precipitation in cross-sections of weld samples*
over a large area adjacent to the weld, extraction replicas were prepared
from the electro-polished and etched surfaces. Some preliminary
identification of the extracted particles has been made by EDX analysis and
convergent-beam diffraction, combined with scanning microscopy and EDX
analysis of the electro-polished or ion-eroded surfaces. The welds are 1 cm
deep, and near the top surface, where most of the long U+2018cracks’ occur
(Fig.1a), the weld is 1.5 mm wide. The FAZ, as defined by a suitable etchant
(10% HC1-methanol), extends for a further 1mm on each side. The grain size
(50-100μm) is unchanged across the matrix-FAZ boundary. EDX spectra from the
large precipitates (2-10μm) in the matrix and HAZ (Fig.la) show a strong Mb
peak coupled with a weak Ti peak; the other alloy elements are entirely
absent. Additional evidence from convergent-beam diffraction patterns
(Fig.3) and measurement of the lattice constant2
(ao = 4.42 + 0.015 Å), proves that the majority of
the particles are carbides, (Nb,Ti)C, with a F-centred cubic structure.
These precipitates are absent from the weld, and the backbone of the
dendritic weld precipitation is formed by thin, branched platelets (Fig.4).
These are also carbides, (Nb,Ti)C, which recrystal 1ize from the melt.
However, the FDX snectra now show weak additional peaks from most of the
alloy elements (Ni, Cr, Fe, Mo).
Satellite Dark Field Microscopy of Charge Density Wave Domains in
Transition-Metal Dichalcogenides
Authors: Fung K. K. , Steeds J. W.
Published: June 2020

Transition-metal dichalcogenides are layer compounds which exhibit
anomalies in their transport properties at low temperatures. Diffraction
studies have shown that the anomalies are associated with the formation of
charge density waves (CDW) coupled to periodic lattice distortions (1). This
is manifested as satellite spots decorating Bragg reflections. The satellite
spots can be used to image the structure associated with the CDW transitions
in dark field. This is accomplished by tilting the specimen so that a
satellite spot is strongly excited. In this way, we have imaged domains in
the incommensurate and commensurate states of transition-metal
dichalcogenides. The existence of CDW domains has been predicted
theoretically (2). Using a commercial single-tilting hot stage and a
liquid-helium-cooled double-tilting stage built in this laboratory in a
Philips EM400 microscope we have studied the nature of domains in several IT
polytype transition-metal dichalcogenides between 40K and 600K.
The Oriented Growth of Precipitates on Dislocations in Al-Zn-Mg
Authors: Allen Robert M. , Vander Sande John B.
Published: June 2020

Precipitate particles which nucleate hetergeneously on dislocation lines
may have their subsequent growth assisted by the presence of these
dislocations. This effect is best studied by examining the growth of fine
particles still in intimate contact with dislocations, as these particles
persumably reflect most strongly the influence of dislocations on
precipitate growth kinetics. The advent of weak-beam microscopy has made
such studies possible. Recent work has shown that the technique is able to
reveal the presence of particles as small as 1.5 nm in extent along
dislocation lines.
Contrast From Point Defects in The Infinitesimal Approximation
Authors: Sykes L. J. , Hren J. J.
Published: June 2020

In electron microscope studies of crystalline solids there is a broad
class of very small objects which are imaged primarily by strain contrast.
Typical examples include: dislocation loops, precipitates, stacking fault
tetrahedra and voids. Such objects are very difficult to identify and
measure because of the sensitivity of their image to a host of variables and
a similarity in their images. A number of attempts have been made to publish
contrast rules to help the microscopist sort out certain subclasses of such
defects. For example, Ashby and Brown (1963) described semi-quantitative
rules to understand small precipitates. Eyre et al. (1979) published a
catalog of images for BCC dislocation loops. Katerbau (1976) described an
analytical expression to help understand contrast from small defects. There
are other publications as well.
High Spatial Resolution Compositional Analysis at Interfaces
Authors: Vander Sande John B. , Kelly Thomas F. , Imeson Douglas
Published: June 2020

In the scanning transmission electron microscope (STEM) a fine probe of
electrons is scanned across the thin specimen, or the probe is stationarily
placed on a volume of interest, and various products of the
electron-specimen interaction are then collected and used for image
formation or microanalysis. The microanalysis modes usually employed in STEM
include, but are not restricted to, energy dispersive X-ray analysis,
electron energy loss spectroscopy, and microdiffraction.
Relationships Between Grain Boundary Structure and Material
Properties
Authors: Ralph Brian , Claire Barlow , Ecob Nicola
Published: June 2020

This brief review seeks to summarize some of the main property changes
which may be induced by altering the grain structure of materials. Where
appropriate an interpretation is given of these changes in terms of current
theories of grain boundary structure, and some examples from current studies
are presented at the end of this paper.
Precipitation on Low Angle Boundaries in Al-Zn-Mg
Authors: Vanderwalker Diane M.
Published: June 2020

There is a widespread interest in understanding the properties of
Al-base alloys so that progress can be made toward extending their present
applications in the aircraft industry. Al-Zn-Mg is precipitation hardened to
gain its high strength; however, during aging the formation of heterogeneous
precipitates on the grain boundaries creates a precipitate-free zone in the
adjacent region. Since high angle grain boundaries are not easily
characterized, it is difficult to establish a relationship between the
precipitate and the boundary structure. Therefore, this study involves
precipitation on low angle grain boundaries where the boundary and the
precipitate can be fully analyzed.
Electron Optical Study of Surface Morphologies of Crystals
Authors: Iijima Sumio , Hsu Tung
Published: June 2020

Suppose the thickness of a thin film of a crystal varies periodically
like a regular array of surface steps, kinematical intensities of diffracted
waves from this crystal are modulated by a shape transform,
Accurate Determination of Foil Surface Normal in a Material with Stacking
Faults
Authors: Allen Samuel M.
Published: June 2020

This paper describes a method for determining the foil surface normal in
a transmission electron microscopy (TEM) sample containing stacking faults.
The method makes use of observed dihedral angles at stacking fault
intersections to compute the foil normal, when the beam direction is
known.

Dihedral angles are angles formed at the intersections of surfaces. The
true dihedral angle is observed when viewed parallel to the line of
intersection of the surfaces. For optical metallography, where observations
are made by viewing normal to a plane of polish, the observed dihedral angle
is the angle formed by thetraces of the intersecting surfaces on the plane
of polish. The geometry of this problem was considered by Harker and Parker,
who demonstrated that the observed angle could be either greater or less
than the true angle.