bluuebunny/crossref_metadata_2025 huggingface dataset:
The Atmosphere and Milling Devices Effect on the Activation Energy for Crystallization of a Partially Amorphized Ni-MO Alloy
Authors: Martínez-Sánchez R , Estrada Guel I , Béjar-Gómez L , Espinosa-Magaña F , Jaramillo Vigueras D , Duarte Moller A , Diaz de la Torre S
Published: July 2020

Although amorphous phases produced by mechanical alloying (MA) in the Ni-Mo system have been reported before. It has not been presented the influence of using different milling devices and atmospheres. This work is focused to the characterization of amorphous structures thus obtained in a Mo-47 at. % Ni alloy. Selected composition corresponds to the equiatomic NiMo intermetallic. The characterization was carried-out by XRD, SEM-EDS, DSC and TEM. High resolution XRD reveals that the MA′ed products undergo partial amorphization, as shows Figure 1. The main difference in the patterns is a region that corresponds to typical Nickel reflections. Nickel preferential amorphization after milling was evident. Apparently, a major grade of amorphization was attained when using the Simoloyer mill. A rough crystallite size was calculated using Scherrer equation, which reveals that this parameter reached its minimum value with the Simoloyer mill. During DTA analysis, it was observed the presence of an exothermic peak in all samples.
Quantification of CeO2 Reduction By In Situ Electron Energy-Loss Spectroscopy
Authors: Sharma Renu , Crozier Peter
Published: July 2020

CeO2 is an important material in many catalyst applications. CeO2, PrO2 and TbO2 are the only lanthanides known to exist as oxides in both 3+ and 4+ oxidation states. The high oxygen mobility at low temperature (≈300°C) results in easy oxidation-reduction cycles; a property utilized in the catalyst industry, especially for CeO2. Studying the oxidation-reduction behavior is thus very important to understanding the reactivity of CeO2 as a catalyst. We have studied CeO2 by in situ electron diffraction, high resolution electron microscopy (HREM) and electron energy-loss spectroscopy (EELS), not only to understand the reduction behavior but also to develop a method to quantify the reducibility of CeO2 or mixed oxides containing CeO2 by EELS. We have applied this method to study the behavior of ZrO2-CeO2 catalyst during reduction.

Experiments were performed on a PHILIPS-430 electron microscope operated at 300KV, fitted with a differentially pumped environmental cell and a Gatan Imaging Filter (GIF).
Deactivation of PT / Zeolite-L Catalysts Studied by Z-Contrast
Authors: Treacy M M J
Published: July 2020

When Pt particles of sub-nanometer dimensions are inserted into the linear channels of the potassium ion form of zeolite L, the resultant Pt/KL catalyst converts linear n-C6 hexane into cyclic C6 benzene with remarkable efficiency [1,2].

However, a drawback to Pt/KL catalysts is that they are exquisitely sensitive to sulfur contamination in the n-hexane feed. The catalyst deactivates rapidly when there are trace amounts (> 50 parts per billion) of sulfur in the feed. Bright field TEM studies show that the Pt particles remain finely dispersed within the channels after sulfur poisoning, with typical particle widths < 1.5 nm, implying that a large percentage of the Pt atoms still reside on the surfaces of the particles. For heterogeneous catalysts such as Pt/γ-alumina, where the Pt particles are always readily accessible on the external surface of the alumina support, such sulfur concentrations are tolerated.
Improved Methanol Oxidation Activity Through Oxidation-Induced Phase Separation of PtRu Electrocatalysts
Authors: Stroud RM , Long JW , Swider KE , Rolison DR
Published: July 2020

Direct methanol fuel cells (DMFCs) offer a simpler, safer technology for point-of-use power sources compared to other hydrogen fuel cells, by avoiding the need to store hydrogen fuel or to carry out the reformation of hydrocarbons. The direct methanol oxidation electrocatalyst of choice is a nanoscale black consisting of a 50:50 atom % mixture of Pt and Ru. It has recently become known that these presumed bimetallic alloys in fact contain an array of metal, oxide and hydrous phases, which are easily misidentified in routine x-ray diffraction measurements due to particle size-broadening and poor crystallinity. By combining transmission electron microscopy, electrochemistry and thermogravimetric studies, we demonstrate here that the route to improved catalytic activity is not by phase purification of the bimetallic alloys, but instead phase engineering of hydrous ruthenium oxide and Pt mixtures.
STEM Observation and EELS Analysis of Dopant and Catalyst Particles in Carbon Nanotubes
Authors: Fan X , Dickey EC , Puretzky AA , Geohegan DB , Pennycook SJ
Published: July 2020

Doping carbon nanotubes with either electron donors or acceptors can improve their electrical conductivity [1-2]. In order to fully understand the doping mechanisms and the corresponding changes in the electronic properties, it is essential to reveal the spatial distribution of the dopants within the carbon nanotubes. In this study we have investigated both iodine- and bromine-doped single wall carbon nanotubes(SWNT) by Z-contrast scanning transmission electron microscopy (STEM). The SWNT bundles were made by arc-discharge method and doped with either molten iodine or bromine vapor. Both iodine and bromine were incorporated linearly within the nanotube bundles as shown in Fig. l and Fig.2 respectively. Higher resolution images of iodine doped nanotubes reveals that two iodine atomic chains are inside each individual SWNT as shown in Fig. lc. This unexpected result is contrary to the common belief that dopants can only enter interstitial site of the SWNT bundles.
Silicon Oxynitride Film Thickness Measurements Using HRTEM and Grazing Incidence X-Ray Photoelectron Spectroscopy (GIXPS)
Authors: Scott John Henry J , Landree Eric W , Jach Terrence , Windsor Eric S
Published: July 2020

The ability to accurately and precisely measure the thickness of ultrathin (∼ 3 nm) dielectric films, used as gate dielectrics in integrated circuits, is critical to the continued success of the semiconductor manufacturing industry. Many metrology tools have been applied to this problem in the past, but recent research has focussed on ellipsometry, x-ray reflectivity, secondary-ion mass spectrometry, capacitance-voltage curves, medium energy ion scattering, high resolution transmission electron microscopy (HRTEM), and grazing incidence x-ray photoelectron spectroscopy (GIXPS). Unfortunately, these techniques disagree about a given film's thickness by amounts larger than their individual precisions. To support the statistical process control methodologies used in production wafer fabrication, these disagreements need to be investigated and the true accuracy and precision of the tools need to be determined. This work compares the ability of two techniques, HRTEM and GIXPS, to measure the thickness of silicon oxynitride films on silicon substrates.
Carbon Filament Growth on Fully Formulated Pd/Rh Automotive Catalysts
Authors: Hangas JW , Graham GW , McCabe RW , Chun W
Published: July 2020

Automotive exhaust catalysts are typically operated under stoichiometric conditions to minimize nitrogen oxide, hydrocarbon, and carbon monoxide pollutants. These catalysts do not form carbon filaments under normal operating conditions. In development of catalysts, however, a stabilization procedure is sometimes utilized on used catalysts (dynamometer or vehicle) to purge the catalyst of sulfur prior to measuring the catalytic activity in sweep and light-off testing. The stabilization procedure consists of running the catalyst under rich (excess fuel) conditions for 0.5hr. This study documents the existence of carbon filaments due to the stabilization procedure and discusses the effect of filaments on subsequent testing.

Two separate catalysts were used in this study. The first was a 50,000 mile vehicle aged catalyst that had also been through the stabilization procedure and then sweep and light-off tested. The other was only dynamometer aged for 120hr at 850°C (1560°F).
Partial Amorphization in a Ni-Mo Alloy by Mechanical Alloying
Authors: Martínez-Sánchez R , Duarte-Möller A , Facundo-Almeraya M , Paraguay-Delgado F
Published: July 2020

In the last decades, amorphous alloys have been the focus of many researchers around the world. Rapid solidification is one of the most employed techniques in obtaining amorphous structures. Important limits of this technique are the high melting point alloys, and in many cases it is restricted to compositions near eutectic deeps. By mechanical alloying it has been possible to obtain amorphous structures in several alloy systems, and in compositions different to eutectic points.

Amorphous phases by mechanical alloying in the Ni-Mo system has been reported before. This work is focused to the characterisation of amorphous structures obtained by mechanical alloying in a Mo-47 at. % Ni alloy. This composition corresponds to the equiatomic NiMo intermetallic. The characterisation was carried-out by XRD, SEM-EDS, DSC and TEM. Full amorphization was obtained after 32.4 ks of milling in a Simoloyer ball mill, as shows conventional XRD, Figure 1.
Assembly Of Myofibrils in Vertebrate Cross-Striated Muscle Cells
Authors: Sanger J W , Sanger J M
Published: July 2020

This presentation will review how myofibrils are formed in both types of vertebrate cross-striated myofibrils, i.e., cardiac and skeletal muscle.

Cardiomyocytes isolated from 7 to 9 day-old chick embryos and myoblasts isolated from 10-day old quail embryos were placed in tissue culture. The cardiac cells were allowed to spread in culture for 3 - 5 days. Similarly, the myoblasts were permitted to fuse to form myotubes which were then fixed at different points of elongation over 3 -5 days. Some cultures were fixed and stained with antibodies (e.g., sarcomeric isoform of alpha-actinin; non-muscle myosin IIB and muscle myosin II) to detect the disposition of the forming and mature myofibrils inside these cells. Sister cultures were transfected with plasmids expressing Green Fluorescent Protein (GFP) ligated sarcomeric proteins like alpha-actinin. The staining and transfection results revealed that three different types of fibrils form during myofibrillogenesis: premyofibrils, nascent myofibrils and mature myofibrils (1-2).
Regulation of Microtubule Assembly: The View From The End
Authors: Cassimeris L , Spittle C , Kratzer M
Published: July 2020

The mitotic spindle is responsible for chromosome movement during mitosis. It is composed of a dynamic array of microtubules and associated proteins whose assembly and constant turnover are required for both spindle formation and chromosome movement. Because microtubule assembly and turnover are necessary for chromosome segregation, we are studying how cells regulate microtubule dynamics. Microtubules are polarized polymers composed of tubulin subunits; they assemble by a process of dynamic instability where individual microtubules exist in persistent phases of elongation or rapid shortening with abrupt transitions between these two states. The switch from elongation to shortening is termed catastrophe, and the switch from shortening to elongation, rescue. Although dynamic instability is an intrinsic property of the tubulin subunits, cells use associated proteins to both speed elongation (∼ 10 fold) and regulate transitions.

The only protein isolated to date capable of promoting fast polymerization consistent with rates in vivo is XMAP215, a 215 kD protein from Xenopus eggs.
3-D Electron Crystallography Reveals the “Off” State of Smooth Muscle Myosin.
Authors: Wendt T , Taylor D , Trybus K , Taylor K
Published: July 2020

The activity of myosin II from vertebrate smooth and non-muscle cells is controlled by phosphorylation of the regulatory light chain (RLC). Smooth muscle heavy meromyosin (HMM) is a truncated double-headed myosin molecule that is soluble at physiological ionic strength. Subfragments of myosin containing two heads retain phosphorylation dependent regulation but single headed subfragments do not and are always “In”(Cremo et al., 1995; Trybus et al., 1997) thereby implicating head-head interactions as a fundamental feature of regulation. We have used a positively charged lipid monolayer to obtain 2-D crystalline arrays of both the unphosphorylated, inactive form (I-form) and thiophosphorylated, activated form (P-form) from chicken gizzard smooth muscle HMM obtained from a Baculovirus expression system.

A comparison of averaged 2-D projections of both forms in negative stain at 2.3 nm resolution reveals distinct structural differences (Wendt et al., 1999). The two crystals have p2 symmetry but vastly different unit cell dimensions.
Role of Calcium Currents in E-C Coupling and Evolution of the T-System and SR in Developing Cultured Embryonic Amphibian Skeletal Muscle Cells
Authors: H Gonzalez-Serratos , R Cordoba-Rodriguez , D.R. Matteson , M. Rozycka
Published: July 2020

Adult frog phasic skeletal muscle cells have slow inward calcium current (ICa) (Stanfield, 1977) carried through L-type voltage dependent calcium channels. It has been suggested that ICa may play a role in E-C coupling (Cota & Stefani, 1981, 1989). However, phasic skeletal muscle cells contract for several minutes after the extracellular Ca2+ concentration ([Ca2+]o) is lowered to <10-8 M (Armstrong et al, 1972). Therefore, extracellular Ca2+ (Ca2+o) is not essential for contraction in these fibers. It has been also shown, by blocking Ica that Ica is not essential for triggering contraction (Gonzalez-Serratos et al., 1982). These results have led to the conclusion that Ica has no obvious role in E-C coupling in adult amphibian phasic skeletal muscle. The question arises then as to what is the biological role Ica in phasic skeletal muscle? We have observed that embryonic skeletal muscle cells are capable of contracting during the first day of development in culture (Cordoba-Rodriguez, et al., 1996), before the T-system and the sarcoplasmic reticulum (SR)may have fully developed (Flucher, et al., 1993).
Quantitative Interpretation and Information Limits in Annular Dark-Field STEM Images
Authors: Nellist P D , Pennycook S J
Published: July 2020

In making quantitative measurements using electron micrographs we must regard the electron microscope as being an information channel. The information about the object is both in some way transformed by the image forming process, and information is lost through the existence of a spatial resolution limit and the addition of noise. To make quantitative measurements, we need to take account of all these effects.

Great progress has been made in making quantitative measurements from high-resolution transmission electron microscope (HRTEM) images (for example see Ref. [1]). However, the simulation of HRTEM images requires a full dynamical electron scattering calculation in addition to computing the effects of the objective lens aberrations. Although such calculations can provide excellent agreement with experimental data, the calculation times involved restrict the number of trial structure models that can be used, with the danger that such trial and error methods might miss the true object solution.
Environmental Optimization for Sub-0.2NM Scanning Transmission Electron Microscopy
Authors: Muller D A , Grazul J , Baumann F H , Hynes R , Hoffman T L
Published: July 2020

Sub-0.2 nm probes can now be readily obtained on Schottky field-emission microscopes[1]. However environmental instabilities are proving to be the limiting factors for atomic resolution spectroscopy and distortion-free annular-dark field imaging, as a result of the long acquisition times (comparable to those required for inline holography[2]), and from the serial nature of the scanning system where instabilities result in image distortions rather than reductions in contrast. Troubleshooting the two most common environmental problems are discussed here.

Electromagnetic interference can cause beam deflections in both the scanning system and the spectrometer [3](< 0.3 mG r.ms for 0.3nm, < 0.2 mG for 0.2 nm). These are most easily dealt with before the machine is installed, as substantial rewiring may be necessary. There is little that can be done about quasi-DC fields, such as from elevators and nearby trains and buses. Major sources of AC electromagnetic interference are unbalanced electrical loads.
Atomic Scale Characterization of Oxygen-Deficient Ceramic Membranes by EELS and Z-Contrast Imaging
Authors: Klie Robert F , Ito Yasuo , Browning Nigel D , Stemmer Susanne , Mazanec Terry J
Published: July 2020

The Perovskite structured ceramic (Lax,Sr1-x)(Fey,Cr1-y)O3-δ being developed for applications in oxygen transporting membranes. The permeability of this material is limited by the number of free ions, point-defects (oxygen vacancies) and electrons in the bulk. As any ordering of these unbound particles will restrict their mobility one key issue for controlling the membrane efficiency is the formation of ordered oxygen vacancies. In particular it is very likely, that at elevated temperatures ordered micro-domains progressively grow and asymptotically reach a stable equilibrium concentration. This is consistent with the observations of Kruidhof that below a specific order-disorder transition temperature equilibrium times of 30-40 h are required to attain steady-state conditions, irrespective of the thermal history of the sample.

We investigate the formation of ordered vacancies in (Lax,Sr1-x)(Fey,Cr1-y)O3-δ by atomic resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) using a 200 keV STEM/TEM JEOL2010L with a post column Gatan Image Filter (GIF).
Solute Atom Segregation to Yttria-Stabilized Cubic Zirconia Grain Boundaries
Authors: Dickey EC , Fan X , Pennycook SJ
Published: July 2020

Grain boundaries in yttria-stabilized cubic zirconia (YSZ) are believed to have positively charged grain boundaries with compensating negative space charge layers at ambient temperatures and pressures [1]. The space charge region is formed by equilibrium segregation of point defects to the vicinity of the grain boundary to establish local charge neutrality. The point defect distributions, calculated from analytical space charge models [1] show that the negative space charge region is formed by a depletion oxygen vacancies and an excess of substitutional Y atoms, indicated as'VO” and YZr’ in standard Kröger-Vink notation (see fig. 1). The grain boundary segregation, in turn, has important ramifications for the mechanical and electrical behavior of the material [1,2]. The present work addresses space-charge segregation in YSZ, specifically addressing variations in segregation with grain boundary misorientation. We have examined a range of symmetric tilt [001] YSZ grain boundaries since they allow us to systematically vary the misorientation while providing the opportunity for atomic scale analysis.
Direct Atomic Scale Characterization of Interfaces and Doping Layers in Field-Effect Transistors.
Authors: Topuria Teya , James Edward M , Browning Nigel D , Ma Zhiyong
Published: July 2020

The demand for the higher performance of semiconductor devices, for instance IC functionality, has stimulated industry to further scale the critical dimensions of the semiconductor devices [6]. Also, as parasitic capacitances are reduced in small device structures, the energy loss in these devices is consequently reduced. [1] Achieving the desired performance from such reduced device structures requires optimization of both the interface properties and dopant redistribution processes, such as diffusion and segregation, under various processing conditions. Only through a careful and accurate characterization of these properties on the atomic scale in the electron microscope we can achieve the understanding of the materials interactions during processing necessary to optimize these properties [2].

Conventional imaging and microanalysis techniques in transmission electron microscopy (TEM), such as phase contrast imaging and energy dispersive X-ray spectroscopy (EDS), lack either the spatial resolution or require extensive simulations and through focal series reconstructions to reveal the structure and composition of such interfaces/doping layers (and in the case of simulations may still not give a unique solution).
Electron Optical Consideration of 1 Å STEM With a Monochromator
Authors: Tsuno Katsu
Published: July 2020

Recent success of spherical aberration (Cs) correctors for TEM and STEM opened a new generation of microscopy. In order to achieve sub Å resolution in experiment, however, it is necessary to use a monochromator to reduce the effect of chromatic aberration due to the energy spread of the electron source. The monochromator is also necessary for the high energy-resolution EELS (HREELS). Three microscopes - sub Å TEM, 1 Å STEM and HREELS - and those combinations are considered to bring the high performance electron microscopes of the next generation. Among those three, 1 Å STEM has the highest technical difficulties from the point of view of electron optics instrumentation. In this investigation, we will describe the main electron optical problems, which we should solve within a few years, to achieve 1 Å STEM.

The main reason, why 1 Å STEM is so difficult, is the spread of the beam due to the second order aberrations of the energy filter used as the monochromator.
Mechanism of Reversible Conductance Transitions in a Crystalline Thin-Film
Authors: Sohlberg Karl , Gao Hongjun , Penny cook Stephen J
Published: July 2020

Recently there has been considerable interest in developing nanometer- and sub-nanometer-scale electronic devices. Of particular interest in this regard is whether individual molecules or molecular complexes can be employed as electronic device elements. Aviram et al. have reported switching and rectification in an organic thin film. More recently, Potember et al. have shown a field-induced conductance transition on a 500 nm scale, but did not demonstrate local reversibility of the transition. The reverse transition was induced only by application of a broad laser pulse or heat. We have observed and replicated reversible conductance transitions in a fully-organic crystalline complex, on a scale close to the dimensions of the unit cell.

A crystalline thin-film organic complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine (NBMN-pDA), exhibits reversible conductance transitions on the sub-nanometer scale when exposed to local electric field pulses from an STM tip.
Nu-Phase in Fe-Al-B Alloys
Authors: Chisholm M F , Duscher G , Pang Lixin , Kumar K S
Published: July 2020

FeAl alloys with 40 to 50 at % Al have an impressive combination of oxidation and sulfidation resistance, low density, and low cost and are thus considered as possible substitutes for stainless steels. However, before these materials can be used in structural applications, the fracture characteristics of the alloy's grain boundaries need to be improved. Small additions of carbon and boron have been considered and the resulting properties have been reported. Boron is found to prevent intergranular fracture in iron-rich alloys and to mitigate environmental embrittlement although the improvement is not as dramatic as is seen with Ni3Al alloyed with boron. Boron segregates to the grain boundaries in Fe-Al alloys and boride precipitates at the boundaries and within the grains have been observed.

In this paper, we report the composition and atomic arrangement in a recently discovered phase (designated v phase) found in Fe-Al alloys containing small boron additions using a combination of Z-contrast imaging and electron energy-loss spectroscopy.
Quantitative Analysis Of Bological Specimens by Spectrum-Imaging in the Energy Filtering Transmission Electron Microscope
Authors: Leapman RD , Brooks CM , Rizzo NW , Talbot TL
Published: July 2020

Electron energy loss spectrum-imaging (EELSI) in the energy filtering transmission electron microscope (EFTEM) can provide more accurate analysis of elemental distributions than that obtainable by the standard two-window or three-window background subtraction techniques. Spectra containing many channels can be extracted from regions of interest and analyzed using established methods for quantitation. For example, the pre-edge background can be fitted by an inverse power law and subtracted from the post-edge spectrum. EELSI in the EFTEM is often superior to spectrum-imaging in the scanning transmission electron microscope for mapping specimen regions of size greater than 1 μm. This is due the much larger total beam current that is available at the specimen in a fixed-beam microscope relative to a scanned-beam microscope. Our aim here is demonstrate the advantages of such EELSI measurements for analysis of biological specimens. However, we also indicate some potential pitfalls in acquiring elemental maps in the EFTEM, which can be attributed to specimen instabilities during the acquisition.
Determining Concentration Limits for Boron Quantification Using EELS and for Energy-Filtered Imaging
Authors: Malac M , Zhu Y , Egerton R F
Published: July 2020

Electron energy-loss spectrometry and energy-filtered imaging allow the possibility of detecting, quantifying and mapping of boron. Boron spatial distribution in biological tissue is of particular interest for boron neutron capture therapy (BNCT) for cancer. We have studied the limits of boron quantification and mapping using electron energy-loss spectroscopy and energy-filtered imaging.

To evaluate the concentration limits for boron mapping and quantification three types of specimens were used. First, a uniform boron layer of well known thickness deposited onto of 50 nm-thick carbon film was used to determine the limits for boron quantification. Second, samples for boron mapping with non-uniform boron distribution were prepared by electron-beam evaporation of boron onto a shadow-masked 50 nm-thick carbon film. Third, tobacco mosaic virus (TMV) in a water solution of boronophenylalanine fructrose (BPA-F) was deposited onto a 2 nm—thick carbon film.
Towards 0.1 EV EELS Using a Beam Monochromator And Maxent Deconvolution
Authors: Tiemeijer PC , Overwijk MHF , de Jong AF
Published: July 2020

The resolution in Electron Energy Loss Spectroscopy (EELS) in (S)TEM is presently limited by the instabilities of the high voltage supply (typically 0.2 eV), by the resolution of the spectrometer (typically 0.7 eV), and by the energy spread of the electron source (typically 0.7 eV for a Schottky field emitter). An increase of this resolution to better than 0.1 eV would enable chemical analysis on a nanometer scale. We are presently following hardware as well as software approaches in order to reach this energy resolution in a 200 kV (S)TEM.

The hardware side of our project focuses on the three limiting factors mentioned in the previous paragraph. The instabilities of the high voltage supply are mostly noise and drift, which can be reduced significantly by isolating the high voltage tank, thermally as well as acoustically. In addition, Gatan is developing an imaging filter for this project, which has sub-0.1 eV resolution.
Development of a Real-Time Elemental Mapping System in a Scanning Transmission Electron Microscope
Authors: Kaji Ueda K , Aoyama T , Taya S , Tanaka H , Isakozawa S
Published: July 2020

The ability to obtain elemental maps in a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) is extremely useful in the analysis of materials, and semiconductor devices such as ULSI's and GMR heads. Hitachi has developed a new type of elemental mapping system, consisting of a STEM (Hitachi, HD-2000) equipped with a two-window electron energy filter. In-situ calculation of the energy-filtered signal makes it possible to observe real time elemental mapping images with nanometer resolution.

Figure 1 shows a schematic of the elemental mapping system. In the STEM, electrons are generated from a cold field emission gun and accelerated to a potential of 200 kV. The electrons arc focused by the objective lens into a small probe (<1 nm), which is then rastered over the specimen using scanning coils. Transmitted electrons are collected by an energy filter, which is located beneath the specimen., and consists of quadrupole lenses, a magnetic prism spectrometer and two kinds of electron beam energy detectors.
Analysis of the Structure of Bulk Metallic Glasses Using EXELFST
Authors: Alamgir FM , Hug G , Williams DB , Jain H , Schwarz RB
Published: July 2020

There has been a rejuvenation of interest in the field of metallic glasses in the last decade, ever since the discovery of alloy compositions which allow bulk glass formation. By definition, bulk metallic glasses (BMGs) are characterized by a critical cooling rate < 10 K/s or a minimum dimension > 1mm. We have chosen to examine the structure of the Pd-Ni-P system in order to explain, from an atomic structural point of view, its precipitously high glass-forming ability in this system with respect to those of the binary alloys. With three constituent elements the study of the Pd-Ni-P system remains tractable in comparison to other BMGs that often contain five or more elements. This system has a critical cooling rate lower than 1 K/s and is one of the simplest prototypes of a BMG. However, binary alloys of transition metals (e.g. Pd, Ni, Cu) with metalloids (P, Si, etc.) will not form BMGs even though they can be forced to retain a glassy structure with rapid quenching from the liquid phase.
Stability Performance of an Energy Filtering TEM
Authors: Benner G , Zellmann E , Harscher A , Härle R , Kabius B , Seybold Volker , Probst W
Published: July 2020

The electron-optical design and the technical realisation of correctors, monochromators and imaging spectrometers as well as methods of resolution improvement (Focus variation, Holography) have made significant progress in the past few years. For all such devices and methods the mechanical and electrical stability of the microscope are the main challenges.

Such requirements are even more critical in case of Energy Filtering Transmission Electron Microscopes (EFTEMs), where the achievement of highly resolved analytical results requires long detection times (in the range of a few 10s of seconds). Resolution in such case could mean both spatial and energy resolution even at the same time. The stability performance of the combined system is more complex than the sum of the stabilities of the single components. Thus, a specified HT short- and long-term stability of 2 ppm is not sufficient to achieve an energy resolution of 0.2 eV at 100 kV acceleration voltage.
Elemental Mapping of Materials Using Omega Filter and Imaging Plate
Authors: Ikematsu Y , Shindo D , Oikawa T , Kersker M
Published: July 2020

Elemental microanalysis has been important in materials characterization, since the elemental distribution strongly affects the property of various materials. A recently developed post-column energy filter coupled with a slow scan CCD camera makes it possible to carry out elemental mapping with a transmission electron microscope. Here, we develop the elemental mapping technique utilizing the omega filter and imaging plates (3760x3000 pixels). Since the data obtained from the imaging plates consist of a large number of pixels, fine and detailed elemental analysis will be expected.

Energy-filtered images were obtained by a JEM-2010 electron microscope installed with an omega-type energy filter, and they were recorded on imaging plates (FDL-UR-V:25 μm/pixel). The width of an energy-selecting slit was set to be 20 eV. Elemental maps were obtained from the energy-filtered images using the three window technique. Special care was taken to reduce the image shifts among the three filtered images used in the three-window method.
Determination of Mean Free Path for Inelastic Scattering in Poly(2-Vinyl Pyridine) by Low-Loss Spectrum Imaging
Authors: Aitouchen A , Chou T , Libera M , Misra M
Published: July 2020

The common experimental method to determine the total inelastic mean free path i by electron energy-loss spectroscopy (EELS) is by the relation : t/λi= ln(It/IO) [1] where t is the specimen thickness, It, is the total integrated intensity, and Io is the intensity of the zero-loss peak. The accuracy of this measurement depends on the thickness determination. Model geometries like cubes, wedges, and spheres enable accurate thickness determination from transmission images.

Spherical polymers with diameters of order 10-200nm can be made from a number of high-Tg polymers by solvent atomization. This research studied atomized spheres of poly(2-vinyl pyridine) [PVP]. A solution of 0.1% PVP in THF was nebulized. After solvent evaporation during free fall within the chamber atmosphere, solid spherical polymer particles with a range of diameters were collected on holey-carbon TEM grids at the bottom of the atomization chamber.
Simulation of in - Line Holograms
Authors: Frost Bernhard , Joy David
Published: July 2020

We simulated in-line holograms as obtained from a point projection microscope (PPM) [1]. The principal of the PPM is shown in Fig.1. A coherent electron wave emitted from a point source illuminates a sample transparent to the wave and travels to an electron detector. Since the wave from a point source is divergent the distance d of two points in the object plane results in a magnified distance D in the detector plane. The magnification of this arrangement is given by M=D/d=(z1+z2)/z1, where z1 and z2 are the tip to sample distance and the sample to detector distance, respectively. As no lenses are used we find a highly defocused shadow image in the detector plane. This arrangement is equivalent to Gabor's in-line holography with a physical source in plane of a lens-focused crossover, and the out-of-focus images are in-line electron holograms.
Mapping Binding Sites of Potential Anti-Cancer Drugs on Tubulin
Authors: Li Huilin , Nogales Eva , Downing Kenneth H
Published: July 2020

Microtubules are involved in many activities within the cell that require highly dynamic activity. For examples, microtubules can grow and shrink as they explore the cell, and the entire microtubule cytoskeleton is restructured as cells prepare for division. Interfering with microtubule dynamics can have serious consequences for the health of the cell, especially in cells that are rapidly dividing. The result of disrupting the normal dynamics is generally an interruption of the cell cycle and consequent induction of apoptosis. This behavior has been exploited with a number of anti-cancer drugs that target tubulin, the main protein in microtubules. Drugs are currently in use that either stabilize or destabilize microtubules. Among the most widely used is Taxol, one of the microtubule stabilizing drugs. Because Taxol produces a range of serious side effects and a substantial fraction of patients treated with Taxol eventually develop resistance to the drug, there is an active search for other drugs that might be more selective and less prone to resistance.
Electron Crystallographic Structure of the Limulus Acrosomal Bundle at 20 Å Resolution
Authors: Sherman Michael B , Waller Guichy , Matsudaira Paul , Chiu Wah , Schmid Michael F
Published: July 2020

Limulus sperm contains a dynamic macromolecular structure that rapidly extends a 50-μum process called the true discharge. The core of this structure is a bundle of ordered filaments composed of a complex of actin, scruin and calmodulin. We have shown that small segments along the bundle can be treated as single crystals with a unit cell spacing of 144 × 144 × 766 Å. A tomographic reconstruction of the bundle was done from multiple tilt series of images to ∼40 Å resolution. To extend the structural determination of the bundle at a higher resolution, we have used electron crystallographic analysis of single images of the bundles preserved in vitreous ice. Furthermore, we did not employ any helical or crystallographic symmetry (other than PI) in the reconstruction procedure.

Acrosomal bundles from Limulus sperm cells were purified as described earlier. Images of frozen hydrated bundles were taken at 40,000x EM magnification in a JEOL 4000EX electron cryomicroscope using an electron dose of 6 - 10 electrons/Å2.
3D Reconstruction of Smooth Muscle A-Actinin by Cryo Electron Microscopy
Authors: Liu Jun , Taylor Dianne , Taylor Kenneth A
Published: July 2020

α-Actinin is an actin crosslinking protein identified in a wide variety of cells. Both muscle and nonmuscle isoforms of α-actinin have been characterized [1]. The molecule consists of two polypeptide chains that form a rod-shaped antiparallel dimer. Each polypeptide is composed of three distinct structural regions: actin-binding domain, four triple helical repeats that form a central rod, and a carboxyl terminal domain that contains two EF hand calcium-binding sites. Here we present the 3D structure of the smooth muscle α-actinin, as determined by cryo electron microscopy at 2.0 nm resolution.

Two dimensional crystals of chicken gizzard α-actinin were formed on positively charged lipid monolayer [2] and preserved frozen hydrated for TEM. The crystal has a unit cell dimension of a = 26.31 nm, b = 20.37 nm, γ= 107.10°, based on internal calibration against TMV.
Electron Microscopy of Myelin Basic Protein (MBP) Organized as Planar Arrays on a Lipid Monolayer Surface: Deimination of MBP Hinders Its Organizational Properties
Authors: Ishiyama N , Matharu P , Bates IR , Wood DD , Moscarello MA , Viner NJ , Harauz G
Published: July 2020

Myelin basic protein (MBP) is one of the principal constituents of the mammalian myelin sheath. It is a basic peripheral membrane protein in the major dense line and is believed to play a structural role in maintaining myelin stability through its close association with lipids and other proteins. Immune responses to MBP have been implicated in the pathogenesis of multiple sclerosis (MS), the most common autoimmune disease of the central nervous system in North America and Northern Europe. The correlation between the severity of MS and the deimination of arginyl to citrullinyl residues in MBP was well illustrated in the acute case of MS (Marburg type) that contained MBP with 18 out of 19 arginines citrullinated.

We have studied a recombinant hexahistidine-tagged murine MBP (rmMBP, 18.5 kDa isoform) by electron microscopy of the protein organized as planar arrays on lipid monolayers that consisted of the nickel chelating lipid, l,2-dioleoyl-.yn-glycero-3-[(N(5-amino-l-carboxypentyl)iminodiacetic acid)succinyl] (Nickel salt) (Ni2+-NTADOGS), and the filler lipid, liver phosphatidylinositol (PI).
Estimates of the Fourier Amplitude Decay of Electron Micrographs of Single Particles
Authors: Saad Ali , Ludtke Steven J , Jakana Joanita , Rixon Frazer J , Tsuruta Hiro , Chiu Wah
Published: July 2020

Several structures of single particles have been resolved to 7-9 Å using electron cryomicroscopy. This field is now poised to make the next step, to near atomic (3-4 Å) resolution. Signal to noise ratio is the critical factor determining the amount of data required for a structural determination at higher resolution. When properly weighted, signal to noise ratio is additive as image data is averaged coherently, however, this relies on perfect alignment of the noisy images. Typical refinement algorithms require as high a signal to noise ratio as possible for accurate alignment. We report a method, which allows accurate, routine determination of signal to noise ratio and other image parameters, both for data quality assessment and microscope quality tracking.

Figure la shows a typical 400 kV electron image of ice-embedded herpesvirus capsids. The incoherent sum of the Fourier transforms of particle images (Fig. lb) shows that the data contains information out to a resolution of 7 Å. When rotationally averaged, this power spectrum can be expressed as:
Advances in High Resolution Cryo-EM Studies: the Quartenary Structure of the 70S E.Coli Ribosome Revealed at 11.5Å Resolution.
Authors: Penczek P , Spahn ChMT , Agrawal RK , Gabashvili IS , Grassucci RA , Frank J
Published: July 2020

Three-dimensional cryo-electron microscopy (EM) of macromolecular assemblies with low or nonexistent symmetry in single-particle form is now recognized as a powerful, legitimate method of structure research. The progress in the resolution achieved has always been related to the introduction of new image processing methods and to improvements in understanding of the overall strategy of single particle analysis. The new techniques either were adopted from methods developed in other fields, or were specifically designed to deal with extremely low Signal-to-Noise Ratio (SNR) data in EM. In the former category we can place multivariate statistical analysis, clustering techniques, correlation techniques, and tomographic methods, in the latter alignment methods, three-dimensional (3D) projection alignment, contrast transfer function (CTF) correction methods, and common-lines based orientational search. In addition, there have been steady improvements of the quality of the data by seeking better electron microscopy conditions (usage of higher microscope voltage and of microscopes equipped with a field emission gun).
Three-Dimensional Structure of Ribosome-Sec61p Translocation Complexes From Mammals
Authors: Ménétret J-F , Morgan D G , Radermacher M , Neuhof A , Rapoport T A , Akey C W
Published: July 2020

Co-translational translocation at the endoplasmic reticulum (ER) plays a critical role in the targeting of both soluble and membrane proteins to their correct intra- and intercellular compartments. We are studying the 3D architecture of the ribosome-Sec61p complex (translocon), with the aim of understanding the physical mechanisms of gating and transport. To this end, we are using single particle electron cryo-microscopy and 3D reconstruction of frozen hydrated channel complexes, to obtain interpretable and biologically relevant maps.

Previously, we have shown that both co- and post-translational translocation utilize a common central channel comprised of a ring-like Sec61p oligomer. Moreover, this channel morphology is shared with the related Sec YE complex from B. subtilus. Mass analysis, volume calculations and ribosome binding experiments suggest a stoichiometry of 3-4 Sec61p heterotrimers per ring. We currently favor 4 copies of the Sec61p complex per channel, as projection maps demonstrate 4 nearly equi-spaced peaks around the central pore.
A Practical Approach to Low Temperature Microscopy and X-Ray Microanalysis
Authors: Echlin Patrick
Published: July 2020

Water is the most abundant and most important molecule in the hydrosphere, outer lithosphere and the biosphere of our planet. It is also the most abundant and energetically the least expensive building block of living material, forms an integral parts of natural inorganic matrices such as soil and is a constituent of many synthetic organic materials such as paints and polymers. Paradoxically, water does not exist naturally, in the pure state. Water, when converted to the solid state, can provide the perfect matrix in which we may observe the structure and study the in situ chemistry of hydrated samples. We will consider the nature of this solid matrix, and its constituent components in a range of sample, and show how it may be formed, manipulated, examined and analysed. In the short amount of time and space available, one can do little more than highlight the main features of the subject.
Cryo Ultramicrotomy of Biological Samples and Polymers
Authors: Gnaegi H
Published: July 2020

Introduction

Cryo Ultramicrotomy gains increasing importance for immunocyto- and immunohisto- chemistry, element analysis, morphological studies and other investigations.

Major advances in immunocyto-chemistry and the sectioning of frozen hydrated specimens have been realized with the appropriate instrumentation and tools (1,2).

In immuno-electron microscopy it has been found that a considerable reduction of structural damage in tissue and cells can be obtained with a modified sectioning and pick-up method using sucrose/methyl cellulose solution (3, 4).

In recent years various scientists have tried to understand cryo sectioning and the problems related to the cry-osectioning process (5, 6, 7, 8).

A promising attempt to eliminate one of the major artefacts in ultramicrotomy, that of compression", was made with the development of the oscillating diamond knife (9).

In polymer research cryo ultramicrotomy is a well established technique.

However, only little information is available about the the cryo sectioning process for the following reasons: Much cryo sectioning is performed in polymer companies.
Cryomicroscopy of Latex and Latex Films
Authors: Shaffer O L , El-Aasser M S
Published: July 2020

Latexes are dispersions of homopolymers and copolymers, usually in water. Uses of these latexes are many such as protective coatings and adhesives. In order to form a continuous film the polymer must have film forming properties such as a low glass transition temperature (Tg). Latexes are being designed such as one polymer in the core of the particle and a shell of another polymer or perhaps a series of shell layers. Microscopy has become a powerful tool in the examination of the morphology of the latex particles. Because of the use of low Tg polymers, sample preparation and examination by electron microscopy at temperatures above the Tg of the polymer causes the particles to become distorted and no longer representative of their true morphology. Low temperature methods therefore have become crucial in the field of latex microscopy.
Identification of Multiple Colloidal Labels of Various Metallic Composition by Means of Electron Energy Loss Spectroscopy
Authors: Meyer DA , Albrecht RM
Published: July 2020

Since it was introduced by Faulk and Taylor in 1971, colloidal gold (cAu) has become the predominant marker used for EM cell labeling. Double labeling, using cAu of two distinct sizes, was pioneered a decade later. However, as interest continues to grow of how the myriad proteins, enzymes, receptors, and other macromolecules function with respect to one another in the cellular environment, this method has proven largely inadequate for high resolution, multiple labeling because each cAu label must be of sufficiently distinct size to prevent size overlap and confusion between different labels. As the particle size increases, so does steric hindrance between different labels competing for binding sites, while the spatial resolution of the labeling and overall labeling efficiency decrease. In order to address these concerns and surmount the limitations of current labeling methodologies, we have developed colloidal particles of uniform size from various metals including Ag, Pt, Pd, Rh, Ru, Ni, and Cu, in addition to Au.
Gold Cluster Compounds are Useful Immunoprobes
Authors: Robinson JM , Takizawa T , Vandré DD
Published: July 2020

Immunocytochemistry generally refers to methods directed toward obtaining information on the in situ distribution of antigens in cells and tissues. Immunocytochemical methods can be applied at either the light or electron microscope levels, or both in concert. The detection of antibody recognition of an antigen (i.e., localization of an antigen) relies upon a reporter system. At the light microscope level, enzymes (e.g., horseradish peroxidase) or fluorochromes are the most widely used reporters in immunocytochemistry. At the electron microscope level, particulate probes (e.g., colloidal gold) are the most widely used reporters. However, enzymes and even fluorochromes can be used at the EM level.

In this abstract, we discuss our use of gold cluster immunoprobes as the reporter system in both light and electron microscope level immuncytochemistry. These gold cluster immunoprobes, are commercially known as NanogoldTM (NG). These probes are very small with a diameter of 1.4-nm.