bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of a network structure in asphalt cements
Authors: Rozeveld S. J. , Shin E. E. , Bhurke A. , Drzal L.T.
Published: June 2020

Paving asphalts are often judged and selected based on their rheological behavior at prescribed temperatures or aging response. Asphalts are considered as a colloidal mixture, where clusters of polar, aromatic molecules are dispersed in a less polar solvent. Thus, the extent to which the solvent phase disperses the associating molecules will determine many of the fundamental asphalt properties. Asphalts are typically divided into four major groups, namely: asphaltenes, resins, aromatics, and saturates. Asphaltenes are the highest molecular weight group and constitute ∼25% of the total asphalt. Resins are very polar in nature and act as a dispersing agent or peptisers for the asphaltenes. The solvent or oily phase (aromatics and saturates) are the lightest molecular weight group and are the bulk of the total asphalt (40-50%).

The dispersion of the asphaltenes within the oily solvent is an important property and has been studied by separation and titration methods. In this study, asphalt cements were examined using an Environmental Scanning Electron Microscopy (ESEM) (ElectroScan 2020), and confocal Laser Scanning Microscope (LSM) (Zeiss 10).
Direct imaging of charge transfer
Authors: Zhu Yimei , Tafto J.
Published: June 2020

The electron holes confined to the CuO2-plane are the charge carriers in high-temperature superconductors, and thus, the distribution of charge plays a key role in determining their superconducting properties. While it has been known for a long time that in principle, electron diffraction at low angles is very sensitive to charge transfer, we, for the first time, show that under a proper TEM imaging condition, it is possible to directly image charge in crystals with a large unit cell. We apply this new way of studying charge distribution to the technologically important Bi2Sr2Ca1Cu2O8+δ superconductors.

Charged particles interact with the electrostatic potential, and thus, for small scattering angles, the incident particle sees a nuclei that is screened by the electron cloud. Hence, the scattering amplitude mainly is determined by the net charge of the ion. Comparing with the high Z neutral Bi atom, we note that the scattering amplitude of the hole or an electron is larger at small scattering angles. This is in stark contrast to the displacements which contribute negligibly to the electron diffraction pattern at small angles because of the short g-vectors.
Controlling microstructural evolution to in situ toughen and strengthen silicon carbide
Authors: MoberlyChan Warren J. , Cao J. J. , DeJonghe L. C.
Published: June 2020

Nonoxide ceramics are desirable for high temperature structural applications, however, they have typically exhibited inferior room temperature fracture toughness. Similar to processing developments to toughen Si3N4, SiC has recently been processed via control of a phase transformation to produce in situ toughened microstructures. An elongated grain shape, coupled with a tortuous fracture path around grains, can provide bridging behind an advancing crack tip, which increases the crack resistance (rising R curve) and halts crack propagation. Most in situ toughened nonoxide ceramics incorporate upwards of 10-20% secondary phase(s), which simplifies crack propagation through this weaker phase to improve toughness, but typically at the expense of substantially reducing strength at high temperatures. The ABC-SiC in this study can be processed with <3% secondary phases and consequently exhibits record toughness and higher strength than commercial (Hexoloy SA) SiC.
Progress in Electron-Probe Microanalysis of Boron in Geologic Samples
Authors: McGee James J.
Published: June 2020

Despite the availability of modern instrumentation with improved detection and correction systems, the analysis of boron in geologic samples by electron probe microanalysis (EPMA) is often avoided. Many studies resort to using calculated or assumed concentrations of B based upon mineral stoichiometry rather than attempt to quantify the B contents by measurement. Assuming stoichiometric behavior for B is not always valid and disregards the possibility of variations in B content of minerals. Such assumptions can contribute to misleading crystal chemical substitution models for the other mineral constituents.

With modem EPMA instrumentation, analysis of B in minerals where B is present in major concentration levels (such as in tourmaline) is possible and should be incorporated into routine analytical procedures by the mineralogical community. The effort to make B measurement routine will reinforce itself, as techniques, standards, and problems are addressed by the geologic community interested in refining the measurement application. Progress in this effort, and some of the factors in need of further consideration are discussed here.
Energy-filtered electron diffraction from amorphized solids in the dedicated scanning transmission electron microscope (STEM)¶
Authors: Sreeram A. N. , Qin L.-C. , Garratt-Reed A. J. , Hobbs L. W.
Published: June 2020

There is significant current interest in understanding the structure of aperiodic solids, such as originally crystalline material amorphized by ion implantation, impact or application of massive pressures, or deposited amorphous thin films, which occupy small volumes. Radially-averaged real-space distribution functions can be derived from diffraction data, the best of which come from thermal neutron diffraction, which inconveniently requires large volumes. Neutron data are collectable in reciprocal space out to q ≡ 2sin(Θ/2)/λ = 70 nm-1, where Θ is the scattering angle and λ the wavelength, or about twice as far as for X-rays, which also require large diffracting volumes. Electron diffraction is the only recourse for very small volumes because of the much stronger interaction of the electron, but spectra must be energy filtered to remove the large inelastic scattering component. Recently, it has been shown that useful electron diffraction data can be collected conveniently to at least q = 16 nm-1 in the VG HB5 dedicated 100-kV field-emission STEM. This contribution details our experiences with improved collection in the VG HB603 instrument operating at 250 kV.
Charge-density wave modulations in the transition metal chalcogenides
Authors: Bennett J.C. , Boswell F.W.
Published: June 2020

The transition metal chalcogenides, due to the typically large covalency of the metal-chalcogenide bonds, often adopt low-dimensional structures and exhibit charge-density wave (CDW) modulations. Incommensurate (IC) or commensurate (C) modulations structures are observed as well as a rich variety of phase transitions driven by the temperature dependence of the CDW amplitude and phase. Defects of the CDW modulation, including antiphase boundaries (APB) and discommensurations (DC), are of determinate importance for the mediation of these phase transitions. The microstructural phenomena occurring in the quasi-one-dimensional chalcogenides will be surveyed with emphasis on two representative systems: the Nb1-xTaxTe4 solid solution and the MxNb3Te4 (M = In or TI) intercalation compound.

The NbxTa1-xTe4 compounds are based on a tetragonal subcell with axes (a x a x c) and consist of an extended chain of metal atoms centered within an antiprismatic cage of Te atoms.
Superstructures and ordering phenomena in ceramic superconductors
Authors: Gronsky R.
Published: June 2020

It is now well established that the phase transformation behavior of YBa2Cu3O6+δ is significantly influenced by matrix strain effects, as evidenced by the formation of accommodation twins, the occurrence of diffuse scattering in diffraction patterns, the appearance of tweed contrast in electron micrographs, and the generation of displacive modulation superstructures, all of which have been successfully modeled via simple Monte Carlo simulations. The model is based upon a static lattice formulation with two types of excitations, one of which is a change in oxygen occupancy, and the other a small displacement of both the copper and oxygen sublattices. Results of these simulations show that a displacive superstructure forms very rapidly in a morphology of finely textured domains, followed by domain growth and a more sharply defined modulation wavelength, ultimately evolving into a strong <110> tweed with 5 nm to 7 nm period. What is new about these findings is the revelation that both the small-scale deformation superstructures and coarser tweed morphologies can result from displacive modulations in ordered YBa2Cu3O6+δ and need not be restricted to domain coarsening of the disordered phase. Figures 1 and 2 show a representative image and diffraction pattern for fully-ordered (δ = 1) YBa2Cu3O6+δ associated with a long-period <110> modulation.
HREM study of phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal
Authors: Chen L.F. , Wang L.M. , Ewing R.C.
Published: June 2020

Irradiation-induced phase transformation in crystals has been an interesting research field for the past twenty years. Since the discovery of quasicrystals in Al-based alloys, there have been some reports on irradiation-induced phase transformation in quasicrystals by in situ TEM observations. However, detailed study on phase transformation in quasicrystals under ion irradiation at atomic level using HREM is necessary for the fundamental understanding of the process. In this paper, we report the results from a systematic HREM study on phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal (31.4 wt.% Cu, 21.8 wt.% Co and 5.4 wt.% Ge).

The TEM specimens of single decagonal quasicrystal were prepared perpendicular to the tenfold axis. The transformation in single quasicrystal was studied by in situ TEM during 1.5 MeV Xe+ ion irradiation at room temperature using the HVEM-Tandem Facility at Argon National Laboratory and examined in detail by HREM using a JEM2010 microscope at the University of New Mexico after the irradiation.
Microstructures and transport properties: A comparison between grain boundaries artificially produced in YBa2Cu3Ov bicrystal thin films and bulk crystals
Authors: Zhang X.F. , Todt V.R. , Miller D.J. , St. Louis-Weber M. , Talvacchio J.
Published: June 2020

In order to establish the link between grain boundary (GB) structures and transport properties in superconducting materials, electromagnetic measurements and detailed microstructural studies of carefully prepared GBs are required. Frequently, artificially induced GBs prepared by thin film deposition onto bicrystal substrates are used for such studies. Recently, transmission electron microscopy (TEM) studies have revealed a meandering configuration for GBs in YBa2Cu3Oy (YBCO) thin films grown on [001] tilt SrTiO3 bicrystal substrates (Fig. la). The deviation of the meandering GBs away from the underlying substrate GBs varies from a few tens to hundreds of nanometers. We have demonstrated that the magnitude of the meander in terms of amplitude and wavelength can be reduced by lowering the film deposition rate. The meandering GBs were shown to consist of various straight facets which are a few tens to hundreds of nanometers in length. It is possible that the various segments have very different current transport behavior due to a variable misfit dislocation density. Thus, an unambiguous correlation between the microstructure and global transport properties is difficult to attain.
Fate of coronary-artery side branches in balloon angioplasty and wiktor stent placement
Authors: Wolf Michael F. , Coscio Michael R.
Published: June 2020

In healthy coronary arteries an extensive network of sidebranching exists to support the high vascular requirement of the surrounding tissue. The size of such side branches is quite broad, ranging from 10 to over 1000μ in diameter extending away from the major vessel (typically 3-4 mm diameter). In the region of balloon expansion during angioplasty, these vessels may be compromised by damage or stripping away of the natural and normally-healthy nonthrombogenic lining (endothelium). This injury exposes potentially thrombogenic subendothelial tissue about the vessel and side branch entrance points. Side branches become further threatened by potential overlap of stent material upon stent placement. Using scanning electron microscopy, this investigation reports on the chronology of the healing response as observed following stent implantation in a porcine model Particular attention is paid to the fate of local side branches.
Ultrastructural changes in endothelial cells cultured in heparin-enriched media
Authors: Taylor C. A. , Lemley-Gillespie S. , Xu S.M. , George J. , Mandal A.K.
Published: June 2020

The widespread use of heparin is due to its ability to reduce clotting and prevent thrombosis. An additional biological property of heparin is the reduction of blood pressure in rat models. This lowering of blood pressure is endothelin-l dependent and results in cell cytoskeleton reorganization, which suggests a mechanism for vascular relaxation.

Endothelial cells (CRL 1998 ATTC) reach confluency within 3 days when fed media 199/10% FCS (Sigma) and incubated at 37°C with 5% CO2 at 80% humidity. This growth medium is replaced with fresh medium containing 0-100 U/ml heparin, and the incubation continued for 24 hours. The cells are removed with 0.25% trypsin and pelleted for 2 minutes in a microfuge. Routine procedures for TEM include fixation in 2% buffered glutaraldehyde followed by 1% aqueous OsO4, dehydration in a graded series of acetones, and embedding in Medcast (Pella).
Negative-stain electron microscopy (EM) of self-assembled astro virus and calicivirus capsids
Authors: Humphrey Charles D. , Leite Jose P.G. , Jiang Baoming , Monroe Stephan S. , Noel Jacqueline S. , Glass Roger I.
Published: June 2020

Astroviruses (AstV) and caliciviruses (CacV) are members of a group of 20-40nm infectious gastroenteric viruses. These viruses often have few distictive morphologic features and occur only in small numbers, making them difficult to detect by EM or serology. Specific antisera in animals or production of monoclonal antibodies has only recently been achieved for a few serotypes. The genomes of AstV (AstV genotype 2) and CacV (Toronto virus genotype) have recently been characterized. The complete genome of each virus consists of three open reading frames (ORF). ORF-2 of each virus codes for a capsid precursor. We have expressed capsid protein of each virus in Autographica califonica nuclear polyhedrosis virus (AcNPV) infected Spodoptera fruigiperda (Sf9) cells. Capsid protein precursors expressed in AcNPV-infected insect cells self-assembled into virus-like particles (VLPs) that were antigenic by immunofluorescence and enzyme-linked immunosorbent assays as well as immunogenic in laboratory animals. Purification of the VLPs was monitored by negative stain direct EM (2 % phosphotungstic acid pH 6.5 or 0.5% uranyl acetate) or by immune EM. AcNPV expressed preparations were examined by using monoclonal antibodies, anti sera raised in animals, or from humans previously infected with the respective AstV or CacV.
An in-lens cryostage for high-resolution secondary-I and scanning transmission electron microscopy
Authors: Apkarian Robert P.
Published: June 2020

A newly designed cryo-holder was built for the in-lens top stage of a Topcon DS-130 field emission scanning transmission and high resolution secondary electron-I microscope (STEM/HRSEM). The modified Oxford CT-3500 cryo-holder was designed to fit into the narrow bore in-lens of the DS-130F. The cryo-holder was designed to shuttle from the freezing chamber, to the high vacuum chamber of the Denton DV-602 magnetron sputter system for metal coating, and then to the interlock of the DS-130F upper stage. The intention was to provide a single cryo-holder to image frozen specimens by either HRSEM or STEM modes. In this electron optical design, many specimens, prepared by different cryo-preparation procedures, could be imaged by either or both imaging modes. The upper stage of the DS-130F was modified to accept a second liquid nitrogen (LN2) cold trap and a Varian cold cathode ion discharge gauge for monitoring the vacuum at the specimen (Fig. 1).
Monte Carlo simulations of the ion-cascade process in the ESEM
Authors: Thiel B.L. , Bache I.C. , Fletcher A.L. , Meredith P. , Donald A.M.
Published: June 2020

Our Monte Carlo simulations and experimental measurements show the Townsend Gas Capacitor (TGC) model to be highly inappropriate for describing the electron cascade process in the Environmental SEM (ESEM). Previous workers have described the signal collected by the Gaseous Secondary Electron Detector (GSED) as having contributions from secondary as well as backscattered and primary electrons, all being amplified by gas cascade. Although these models are qualitatively correct, they require a more sophisticated description of Townsend’s First Ionisation Coefficient, α. Figure 1 illustrates the short-comings of the TGC models when compared to experimentally obtained amplification curves. (Details of the amplification measurements made with various imaging gases will be given elsewhere, along with specifics of the Monte Carlo Calculations.)

The major flaw in applying the TGC model to the ESEM stems from the assumption that the secondary electrons and their environmental daughters reach a steady-state kinetic energy distribution en-route to the detector.
Modeling the electron-gas interaction in low-vacuum SEMS
Authors: Joy David C
Published: June 2020

The passage of a beam of electrons through the low pressure gas atmosphere in an environmental SEM results in a scattering - and hence a broadening - of the probe, a reduction in the current available for imaging and analysis, and in the production of secondary ions which can also impact the specimen and modify the production of secondary and backscattered electrons. In order to optimize and fully exploit the capabilities of low vacuum SEMs it is desirable to be able to accurately predict these effects. The first step in achieving this aim is to be able to quantitatively predict the behavior of the incident beam.

At a gas pressure of 100Pa. the mean free path for 20keV electrons is of the order of 1cm. For a typical working distance of 1cm., therefore, the average electron is only scattered once.
Quantitative EDS analysis in the environmental ESEM using a bremstrahlung intensity-based correction for primary electron beam variation and scatter
Authors: Griffin B.J. , Nockolds C.E.
Published: June 2020

Quantitative EDS analysis of bulk samples in the scanning electron microscope (SEM) or electron microprobe requires, as a fundamental parameter, a stable and reproducible primary electron beam current Beam current is usually measured with a Faraday cage positioned in the electron column below the objective aperture or in the specimen holder. Reproducibility and stability within 1%/hour is a minimum condition.

Primary beam current measurement in the ESEM or any high pressure SEM is difficult to measure. Electron-gas interaction in the biased chamber generates a positive ion flow highly amplified relative to the primary beam (Danilatos, 1990) and generates an x-ray signal from the gas. The latter signal amplitude is dependent on primary beam current, chamber pressure and backscatter electron signal from the specimen (Griffin et al. 1993). These interactions prevent quantification of EDS data standardised to Faraday cage primary beam current measurements or x-ray counts from a reference standard.
Advanced applications and instrumentation for scanning probe microscopy (SPM)
Authors: Grigg D.A.
Published: June 2020

Scanning probe microscopy (SPM) has continued to advance into new applications and disciplines every year. The development of new techniques and instrumentation for SPM's have enabled researchers to study sample surfaces in a variety of ambient conditions and using a number of contrast mechanisms. A review of new SPM techniques and instrumentation will be presented.

Phase imaging is a new technique that provides nanometer-scale information about variations in surface properties, such as adhesion, friction, viscoelasticity, composition and perhaps others, not revealed by any other single SPM technique. An example using phase imaging to differentiate component phases of composite materials is shown in Fig. 1 of wood pulp fiber. The left image is a normal topographic image acquired using the TappingMode™ technique. The right image is the simultaneous phase image. The phase image highlights cellulose microfibrils and a lignin component atop the cellulose component not seen in the topographic image. The details of phase imaging will be discussed.
Round robin AFM study of dealkahzed float glass
Authors: Gesner K.A. , Votava W. E. , Varner J. F.
Published: June 2020

An extensive study of the surfaces of glass treated in a variety of ways was undertaken at the New York State College Of Ceramics At Alfred University over the past 1.5 years. As the project progressed it became evident that glass surfaces can be very difficult to image because of a variety of factors including, static charge buildup, humidity, and tip reflections, to mention a few. Also, because many of the calibrations and scan parameters are specified by the operator, there is great potential for variability to occur between two or more AFM systems. To study the impact of the variations between operators and instruments, a round robin experiment was initiated, and five identical samples were distributed among five different facilities for AFM analysis; two microscopes were manufactured by Topometrix® and three by Digital Instruments®.

A dealkahzed float glass sample was used for this experiment.
Green fluorescent protein: Use of GFP-chimeras in the analysis of microtubule-associated protein 4 domains and microtubule dynamics
Authors: Olmsted J.B. , Olson K.R. , Gonzalez-Garay M.L. , Cabral F.
Published: June 2020

Green Fluorescent Protein (GFP) is an endogenous 27 kDa fluorophore of the jellyfish, Aequorea victoria. Chalfie et al., first described the exogenous expression of this molecule in bacteria, and its utility as a reporter in higher eukaryotes. Potential applications of GFP have been expanded through the construction of variants with enhanced brightness and/or different spectral properties.

We have explored using GFP for the analysis of the real-time behaviors of microtubules and their associated proteins. Constructs of microtubule-associated protein 4 (MAP 4) or β-tubulin were generated in pRC/CMV vectors and used in either transient or stable transfection assays in a variety of cultured cell lines (3T3, PtKl, BHK, CHO, Cos). The GFP-chimeras were visualized using conventional fluorescence microscopy and confocal laser scanning microscopy. Unusual features of the GFP reporter are that fluorescence intensity increased 2-10 fold upon illumination, and that phototoxicity was low.
Gold liposomes
Authors: Hainfeld James F.
Published: June 2020

Lipids are an important class of molecules, being found in membranes, HDL, LDL, and other natural structures, serving essential roles in structure and with varied functions such as compartmentalization and transport. Synthetic liposomes are also widely used as delivery and release vehicles for drugs, cosmetics, and other chemicals; soap is made from lipids. Lipids may form bilayer or multilammellar vesicles, micelles, sheets, tubes, and other structures. Lipid molecules may be linked to proteins, carbohydrates, or other moieties. EM study of this essential ingredient of life has lagged, due to lack of direct methods to visualize lipids without extensive alteration. OsO4 reacts with double bonds in membrane phospholipids, forming crossbridges. This has been the method of choice to both fix and stain membranes, thus far. An earlier work described the use of tungstate clusters (W11) attached to lipid moieties to form lipid structures and lipid probes.
Localization of Calcium in Porcine Epidermis Using Electron Energy Loss Spectroscopy (EELS)
Authors: Misra Manoj , Siangchaew Krisda , Libera Matthew
Published: June 2020

The properties of biological systems are often governed by variations in the distribution of trace (0.01-0.1%) constituents. The importance of calcium ions for differentiation and proliferation of keratinocytes in vitro is well known. The situation in vivo warrants study. A major contribution to that study involves the determination of calcium ion distribution in the stratified layers of the epidermis. We describe here the first study to localize and verify calcium distribution in chemically fixed porcine skin using EELS.

Freshly dissected porcine skin is processed according to Menon and Elias. Briefly, tissue fixed in a buffer containing 90 mM potassium oxalate and formaldehyde/glutaraldehyde is post fixed in 1% osmium tetroxide containing 2% potassium pyroantimonate. Control specimens are prepared without pyroantimonate treatment. Tissue dried in a graded series of acetone is embedded in Spurr resin and 30-40 nm sections are cut. Stained and unstained sections are examined using a Philips CM 20 FEG TEM equipped with parallel electron energy loss spectrometer (Gatan EELS) and a spectrum imaging system (EMiSpec). The microscope is used in STEM mode for the EELS work and second difference spectra are acquired.
Comparative ultrastructural study of camel, cow, and horse neutrophil
Authors: Hailat N. , Lafi S. , Bataineh Z. , Al-Rawashdeh O. , Al-Bagdadi Fakhri
Published: June 2020

The ultrastructure of Arabian camel, cow, and horse neutrophils in peripheral blood was studied in order to provide detailed description of its constituents and to determine the similarities and the differences between these three species. Peripheral blood was taken from the three animals, centrifuged and the pellets were fixed in glutaraldehyde, dehydrated and embedded in Spurr‘s resin. Silver sections were mounted on copper grids and viewed by Zeiss electron microscope and microphotographs were taken.

Camel's neutrophils were found to have smoother cell surface with small number of short pseudopodia (Fig. 1). The horse's neutrophil had longer pseudopodia while the cow's neutrophil had a large number of small ridges instead. The size of the cell in camel was larger than that in cow and horse. The nucleus of camel's neutrophil appeared less irregular compared with that of cow's and horse's, with marginated non-patchy chromatin, and with abundant heterochromatin.
Fungiform and circumvallate papillae volumes in the pig
Authors: Singh A. , Mack A. , Ireland W. P.
Published: June 2020

Taste buds on the porcine tongue have not been quantitated. The morphometric information would be useful in investigation of nutrition-related issues both in human beings and animals.

The tongue specimens were obtained from three, 6-month-old, castrated, male pigs immediately after they were killed in a local abbatoir. The organs were fixed in 10% buffred formalin, and the fungiform and circumvallate papillae were mapped and counted. Mapping was done by drawing an outline of the dorsal aspect of the specimens and marking the approximate positions of fungiform (dorsal and lateral) and circumvallate papillae. Samples from each tongue were harvested from dorsal, lateral and dorsal root regions. These samples were processed in a tissue processor [Model 166MP; Fischer Scientific]. Paraffin-embedded samples were serially sectioned at 15 μm, and stained with hematoxylin and eosin in a stainer [Varistain; Shandon]. The samples were embedded in such a manner that mucosal surface was cut in a plane transverse to long axis of the tongue.
Observation of passivated Al-1%Cu lines using environmental scanning electron microscopy (ESEM)
Authors: Carpenter D.T. , Smith D.A. , Lloyd J.R.
Published: June 2020

Characterization of failure phenomena in passivated interconnects requires the ability to observe dynamic changes in buried lines (e.g. formation of electromigration voids or microstructural changes during an anneal). Conventional SEM cannot image passivated structures due to surface charging. HVSEM has been used with some success to image voids in metal lines under passivation, but it requires intensive specimen preparation and is not commercially available. The present study is intended to determine whether ESEM is suitable for such dynamic experiments on passivated structures.

The lines were composed of Al-l%Cu and had a uniform thickness of 1.4μm. All lines also had both an underlayer and an anfi-reflective coating of Ti/TiN. The thickness of these layers varied slightly, but was typically around 600 Å. Observations were performed in an Electroscan model 2020 environmental scanning microscope with a LaB6 thermionic source using the gaseous secondary electron detector (GSED) and water vapor as an imaging gas.
SIMS depth profiling and direct ion imaging of a 16-megabit DRAM
Authors: McMahon G. , Phaneuf M. W. , Weaver L.
Published: June 2020

The use of secondary ion mass spectrometry (SIMS) has long been established as a powerful tool forthe analysis of microelectronic devices. However, as newer fabrication technologies emerge, and device dimensions shrink, increasing demands are placed upon the SIMS analyst.

The present work illustrates how the depth profiling and direct ion imaging capabilities of a Cameca ims 4f SIMS can be exploited to determine the structure and dopant chemistry of a state-of-the-art16 megabit DRAM (dynamic random access memory) device. The optical micrograph shown in Fig. 1 is an overview of a portion of the sense amplifiers located between two array blocks. In the centre of this area, p-type devices sitting in an n-well, surrounded on either side by n-type devices, all in a p-type substrate can be observed. The object of the study was to determine if a low concentration p-type implant is present below the n-type devices.
The scanning infra-red microscope (SIRM): Evaluating a new tool for mapping sub-100nm defects in semiconductors
Authors: Mule‘Stagno L. , Holzer J.C. , Falster R. , Fraundorf P.
Published: June 2020

The manufacturing yield and reliability required of modern silicon micro-electronic devices has led to a need for wafer and device manufacturing processes which are immune to metallic contamination. To this end, various ‘gettering’ mechanisms have been developed in which unwanted metallic impurities are ‘gettered’ to regions of the wafer away from the active device layer. ‘Internal (or intrinsic) gettering’ is a method in which silicon-oxide defects are produced in the bulk of the wafer, with a near-surface defect-free zone (denuded zone). In the event ofmetallic contamination during high temperature device manufacturing steps, these bulk microdefects (BMDs) act as heterogeneous sites for metal-silicide precipitation during the cooling, and prevent precipitation of the metals in the device layer. For this reason it is essential to monitor the spatial distribution and density of bulk microdefects during device manufacturing.

The standard method by which the density is measured is termed cleave and etch.
TEM study of precipitation in a Nial-3Ti-0.5Hf single-crystal alloy
Authors: Garg A. , Noebe R. D. , Howe J. M. , Wilson A. W. , Levit V.
Published: June 2020

Three directionally solidified NiAl single-crystal alloys, NiAl-3Ti, NiAl-0.5Hf and NiAl-3Ti-0.5Hf (at.%), were grown by a Bridgeman technique using high purity alumina crucibles. The ingots were homogenized for 32h at 1644 K followed by aging for 6h at 1255 K and finally furnace cooled under an argon atmosphere. This heat treatment was found to be very effective in dissolving Hf-rich interdendritic particles that were present in the as-cast structure, and at the same time it produced fine second-phase precipitates in the alloy.

Samples for transmission electron microscopy (TEM) were prepared from 3 mm diameter cylinders electro-discharge machined from the heat-treated ingots. Slices sectioned from the cylinders were mechanically ground and electrochemically thinned in a twin-jet Tenupol-3 polisher. Microstructural and energy-dispersive X-ray spectroscopy (EDXS) studies were conducted in a Philips 400T TEM equipped with a double tilt goniometer and a KEVEX Si/Li X-ray detector.
Anomalous backscattered electron behavior of MoB and Mo5SiB2(T2) phases in an as-cast Mo-B-Si alloy
Authors: Foumelle J. H. , Nunes C. A. , Perepezko J. H.
Published: June 2020

It is well established that backscattered electron (BSE) image contrast in SEM is primarily associated with differences in mean atomic number (Z) of the phases. The BSE coefficient increases with higher Z with slight dependence on beam energy (Eo), except for some materials at < 5 keV.

We report here the anomalous BSE behavior of MoB and T2(Mo5SiB2) phases observed imaging a 60Mo-30B-10Si (at%) alloy with a CAMECA SX-50. Specifics of the material and EMPA are reported in a companion communication. Mo-ss and Mo3Si are also present. The drastic differences in BSE behavior are shown in Figures 1 (7 keV), 2(15 keV) and 3 (25 keV). The material has not been coated; addition of 100 Å carbon does not change the observed behavior.

At 25 keV (Fig 3), MoB dendrites are the darkest phases present, the expected behavior based on their mean Z (Table 1). The T2matrix is gray, whereas smaller regions containing Mo+Mo3Si have the greatest brightness.
Perfect TEM Membranes by focused ion beams: A stress reduction technique
Authors: Walker John F. , Odum James K. , Carleson Peter D.
Published: June 2020

With the realisation that the critical dimensions in integrated circuits are shrinking to the point where scanning electron microscopy (SEM) techniques are not sufficiently accurate for many applications, advanced semiconductor fabs are looking to the increased resolution and analytical functionality of transmission electron microscopy (TEM) in failure and process analysis. TEM sample preparation is traditionally labour-intensive and needs skilled technical support but, with the acceptance of focused ion beam (FIB) workstations, this preparation and subsequent analysis is now becoming more routine. The reasons are: more reliable preparation with less risk of catastrophic breaking on unique specimens, highly site-specific preparation capable of viewing individual, sub-100 nm features, thin and uniform membranes even with tungsten plugs, and fast and easy preparation techniques.

The initial stages of sample preparation involves preparing a sub-100 um sliver mounted on a TEM grid. When mounting this sliver on the grid, care must be taken to prevent any strain from being transferred to the silicon.
FIB system for TEM specimen preparation and its application
Authors: Yaguchi T. , Kamino T. , Koike H. , Ishitani T. , Kitano Y.
Published: June 2020

The transmission electron microscope(TEM) is one of the most powerful instrument in materials characterization, and various TEM specimen preparation methods have been developed. It is known that Ar-etching method is most widely applied in the studies of high technology materials. However, it is time-consuming when a specific area is desired for examination. Because it is necessary to iterate through Ar-ion etching and TEM examination until the desired information is obtained.There is a great demand on a new specimen preparation technique that has high positional accuracy, reliability, and throughput.

Focused ion beam (FIB) milling has been proposed as a solution to the above requirements. We have developed the FIB system (FB-2000) for SEM/TEM specimen preparation. An external view of the system is shown in Fig.l. The system is designed to use a compatible specimen holder (Fig.2) which allows both FIB milling and TEM observation without re-mounting the specimen. The instrument has maximum accelerating voltage of 30kV and a minimum beam diameter of lOnm. The FIB current density of 15A/cm2 is available.
The role of field-emission SEM in biology in the 21st century
Authors: Erlandsen S. L.
Published: June 2020

To predict how field emission SEM (FESEM) will be applied to biological investigation in the transition to the 21st century requires some recapitulation of how dramatically changes have occurred in the last half of the 20th century. Although, initially developed in the 1930s by Knoll and later, von Ardenne, the commercial production of instruments in the 1960s was brought about chiefly due to contributions in secondary (SE) and backscatter (BS) electron detector design from the Cambridge group led by Oatley. Continued instrumentation development over the next three decades led to numerous improvements, i.e. new lanthanum hexaboride emitters, advances in specimen preparation, and was culminated in the late 1980s, by the commercial development of a high resolution SEM possessing short focal length lenses together with a cold field emission electron gun, resulting in electron probes with diameters of 3nm at 1.5 keV and 0.5nm at 30 keV.

From the perspective of a biologist using FESEM for both structural and immunocytochemical studies, I would like to suggest changes in both instrumentation and methodology that would be of great practical value today, and would hopefully be surpassed by standard features in new instruments available at the turn of the century.
On the nature of linkage between retinal rod outer-segment disk and cellular membrane
Authors: Petrosian A. M. , Haroutounian J. E.
Published: June 2020

In the retina of most vertebrates the cone outer segment disk are in continuity with the cell membrane, thus intradisk space is part of the extracellular space. The rod disk membranes, except for some basal ones, appear to be separated from the cell membrane. On the other hand it has been shown the existence of filament-like structures connecting retinal rod disks to one another and with the cell membrane. However due to the lack of observation of either electron-dense or fluorescent extracellular tracer penetration into rod outer segments, it is believed that rod intradisk space is isolated from the extracellular space. This investigation elucidates upon the nature of filament-like linkage between retinal rod outer segment disk and cell membrane. An incubation solution with 10 times lower than normal osmolarity was used to osmotically explode isolated dark adapted frog retina.

Membranes under this condition were observed by transmission electron microscopy (TEM) using the freeze-fracture replica technique. Regularly spaced filaments were observed that were continuous between outer segment disks and the cell membrane in the retinal rods (Fig. 1). Probably these connections have a supporting function providing mechanical stability of the rod outer segment structure.
Hormonal regulation of adult hippocampal dendritic spine density
Authors: Woolley Catherine S. , McEwen Bruce S.
Published: June 2020

Dendritic spines cover the surface of a wide variety of neuronal types and are the postsynaptic sites of approximately 90% of the excitatory synapses formed in the central nervous system. Interestingly, changes in the morphology and/or density of dendritic spines have been shown to occur naturally, implying that they are a normal part of brain function. Even in the adult, dendritic spines are remarkably plastic. The hormonal state of an animal has been shown to be an important factor in regulation of dendritic spine density, both during development and in the adult.

In the adult female rat, hippocampal CA1 pyramidal cells are particularly sensitive to variation in the circulating levels of the ovarian steroids, estradiol and progesterone. Removal of estradiol and progesterone by ovariectomy results in an approximately 50% decrease in the density of dendritic spines on the lateral branches of the apical dendritic tree. Treatment with estradiol can either protect against or reverse this decrease; subsequent progesterone treatment for as few as 5 hours significantly augments the effect of estradiol. By 18-24 hours following progesterone treatment, spine density returns to low values.
Molecular dosimetry: Using slide-based methods to measure DNA damage and cancer risk from the environment
Authors: Law J. M.
Published: June 2020

A need exists for fish sentinel species for monitoring environmental changes. Ideally, the specieswould be widely distributed, easily cultured in the laboratory, and develop measurable biomarker alterations following contaminant exposure. We have recently begun to examine the suitability of westernmosquitofish (Gambusia affinis) as a sentinel species. Mosquitofish are widely distributed in warm waters and have a limited home range. In the laboratory, mosquitofish are easily cultured using techniques developed for other small fish species such as the guppy (Poecilia reticulata). Theybreed prolifically and appear resistant to infectious diseases.

Molecular methods are increasingly being used to measure extent of exposure to environmental carcinogens and to monitor patients receiving chemotherapy with alkylating agents. DNA adducts are currently detected with such methods as 32P-postlabeling, immunoassays, HPLC with fluorescence detection, and gas chromatography/mass spectrometry. Biomarkers may be assessed with slide-based immunohistochemical methods or in situ hybridization, allowing pathologists to localize pre-neoplastic changes in cells such as mutations in the p53 tumor suppressor gene or inappropriate cell proliferation.
Angular reconstitution of ice embedded macromolecules with arbitrary point group symmetry
Authors: van Heel Marin , Schatz Michael , Dube Prakash , Orlova Elena V.
Published: June 2020

Electron microscopy of individual non-crystallized (large) macromolecules is a very rapid technique for probing the three-dimensional (3D) structure of biological macromolecules. Since there is no need for extensive crystallization experiments, specimen preparation can be simple and fast. In particular the vitreous-ice embedding specimen preparation technique, in which the macromolecules are kept in a waterlike environment, has proved very suited for this purpose. One may extract three-dimensional information from the data - without ever collecting tilt series in the microscope - by exploiting thedifferent ("random") orientations the macromolecules have with respect to the grid. Collecting tilt series can be cumbersome and requires multiple exposure of the sensitive molecules. The only techniquewhich was available for such single-shot 3D microscopy was the common-lines technique for virusses with icosahedral symmetry [Crowther (1971), Fuller (1987)]. The other technique available for asymmetric non-crystalline specimens is the random conical tilt technique [Radermacher (1986)]. However, this technique is a tilt series technique requiring two exposures per specimen area. Moreover, it requiresthe molecules to be preferentially oriented with respect to the plane of the support film which - in turn - requires strong (and thus unfavourable) interactions between molecule and support.
Capsid structure of channel catfish virus, an evolutionarily distant herpesvirus, by cryo-Electron Microscopy
Authors: Trus Benes L. , Davison Andrew J. , Booy Frank P. , Steven Alasdair C.
Published: June 2020

Herpesviruses comprise an extensive family of enveloped DNA-containing animal viruses. Although they infect a wide range of vertebrate hosts and their linear double-stranded genomes vary substantially in size and other properties, the nucleocapsid appears to be a conservative element of viral design. The capsid shell is icosahedrally symmetric (T=16), and in the case of alphaherpesviruses is 125 nm in diameter and 15nm thick. Recently, we have studied the molecular anatomy of herpes simplex virus1 (HSV-1), whose capsid contains four major proteins, by combining cryo-electron microscopy and 3-dimensional reconstruction with biochemical depletion experiments and antibody-labelling. In order to probe structural perturbations attributable to evolutionary differences, we have extended these studies to channel catfish virus. CCV exhibits the gross morphology of a herpesvirus, although no evident relationship to other herpesviruses was found in an analysis of proteins predicted from its complete DNA sequence.
Automatic particle picking from electron micrographs
Authors: Lata K. Ramani , Penczek P. , Frank J.
Published: June 2020

The present-day interactive manual selection of biological molecules from digitized micrographs for single particle averaging and reconstruction requires substantial effort and time. Thus a computer algorithm capable of recognition of structural content and selection of particles would be desirable.A few approaches have been proposed in the past. The method by Frank and Wagenknecht is based on the principle of correlation search. Van Heel's method is based on the computation of the local variance over a small area around each point of the image field. The method by Harauz and Fong-Lochovsky is based on edge-detection. The present work was focussed on the detection and classification of particlesby exploiting the standard statistical methods of discriminant analysis.

The proposed technique is described in the block diagram (Fig.1). As illustrated in the figure, the program consists of three distinct segments devoted to, respectively, preparation of the data, training session and automatic selection based on a discriminant function set up in the training, hi the data preparation segment, the micrograph is (i) reduced four-fold in size, (ii) low-pass filtered and (iii) run through a peak search algorithm.
Fraunhofer in-line electron holography of frozen-hydrated DNA superhelices
Authors: Matsumoto Takao , Tanji Takayoshi , Tonomura Akira
Published: June 2020

We have visualized DNA molecules in solution by Fraunhofer in-line electron holography. So far, applications of the technique at high resolution have been limited to gold particles. This report is the first application of Fraunhofer in-line electron holography to a nanometer-sized biological specimen.

The phase shift of an electron beam due to DNA is so small, estimated as only 2π/33 for 100-keV electrons, that it has been only possible to visualize them with either heavy-atom staining or metal shadowing techniques. However, these methods give only low-resolution images of the molecules, and worst of all, preservation of specimens is poor. The frozen-hydrated specimen preparation improved the preservation of specimen, and images of naturally supercoiled DNA in solution have been visualized using underfocusing of 1-2 μm. Such a defocusing is large enough for such a small object as DNA (diameter ∽ 2 nm) to be in a Fresnel condition;z≈ a2/λ, wherezis the defocusing, a is the diameter of an object, andλis the wavelength.
Induction of chromatoid bodies in trophozoitesof Entamoeba histolyticagrowing in log phase at high CO2tension
Authors: Morales-Vallarta M. , Villareal-Treviño L. , Guerrero-Medrano L. , Ramírez-Bon E. , Said-Fernández S. , Mata Cárdenas B.
Published: June 2020

Chromatoid bodies are typical citoplasmic structures found in ameba of genusEntamoebathey are arrays of helical ribonucleoproteic structures formed by the aggregation of ribosomes. Chromatoid bodies are found only in cystic forms ofEntamoeba, in trophozoites cultured in slow growing conditions, or in the presence of protein synthesis inhibitors. This paper reports the formation of chromatoid bodies in trophozoites ofEntamoeba histolyticaHM-1-IMSS in active growing phase with high CO2tension.

Trophozoites ofE. histolyticaHM-1-IMSS strain were cultured with 103cell/ml in 16 × 150 nm screw - capped tubes, each containing 10 ml of TYI-S-33 medium without vitamine (3), and gassed with CO2- - - (0.2 L/Min/2 Min). The cultures were incubated at 37°C and sampled every 24 h for counting and morpho logic observations. For electron microscopy study, the specimens were fixed in 2.5% glutaraldehide in 0.2 M phosphate buffer, pH 7.2; postfixed in 1% osmium tetroxide in 0.2 M phosphate buffer, pH 7.2; — dehydrated in ethyl alcohol, and embedded in epoxy resin (Medcast).