Materials Research in an Aberration-Free Environment

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In the context of electron microscopists' changing attitudes to charging effects, some basic aspects of these phenomenona are surveyed. Methods of mapping internal charge distributions such as doping levels in semiconductors, trap distributions, or internal electric fields in insulators are discussed.

With the availability of resolution boosting and delocalization minimizing techniques, for example, spherical aberration correction and exit-plane wave function reconstruction, high-resolution transmission electron microscopy is drawing to a breakthrough with respect to the atomic-scale imaging of common semiconductor materials. In the present study, we apply a combination of these two state-of-the-art techniques to investigate lattice defects in GaAs-based heterostructures at atomic resolution. Focusing on the direct imaging of stacking faults as well as the core structure of edge and partial dislocations, the practical capabilities of both techniques are illustrated. For the first time, we apply the technique of bright-atom contrast imaging at negative spherical aberration together with an appropriate overfocus setting for the investigation of lattice defects in a semiconductor material. For these purposes, the elastic displacements associated with lattice defects in GaAs viewed along the [110] zone axis are measured from experimental images using reciprocal space strain map algorithms. Moreover, we demonstrate the benefits of the retrieval of the exit-plane wave function not only for the elimination of residual imaging artefacts but also for the proper on-line alignment of specimens during operation of the electron microscope—a basic prerequisite to obtain a fair agreement between simulated images and experimental micrographs.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Trichomonads are flagellate protists, and among them Trichomonas vaginalis and Tritrichomonas foetus are the most studied because they are parasites of the urogenital tract of humans and cattle, respectively. Microscopy provides new insights into the cell biology and morphology of these parasites, and thus allows better understanding of the main aspects of their physiology. Here, we review the ultrastructure of T. foetus and T. vaginalis, stressing the participation of the axostyle in the process of cell division and showing that the pseudocyst may be a new form in the trichomonad cell cycle and not simply a degenerative form. Other organelles, such as the Golgi and hydrogenosomes, are also reviewed. The virus present in trichomonads is discussed.

Ultrahigh-resolution imaging may be achieved using modifications of the off-axis holography scheme in a scanning transmission electron microscopy (STEM) instrument equipped with one or more electrostatic biprisms in the illuminating system. The resolution is governed by the diameter of a reference beam, reduced by channeling through a line of atoms in an atomic-focuser crystal. Alternatively, the off-axis holography may be combined with the Rodenburg method in which a four-dimensional data set is obtained by recording a nanodiffraction pattern from each point of the specimen as the incident beams are scanned. An ultrahigh-resolution image is derived by computer processing to give a particular two-dimensional section of this data set. The large amount of data recording and data processing involved with this method may be avoided if the two-dimensional section is derived by recording the hologram while the four beams produced by two perpendicular biprisms are scanned in opposing directions across the specimen by varying the voltages on the biprisms. An equivalent scheme for conventional TEM is also possible. In each case, the complex transmission function of the specimen may be derived and resolutions of about 0.05 nm may be expected.

Atom probe tomography is a technique for the nanoscale characterization of microstructural features. Analytical techniques have been developed to estimate the size, composition, and other parameters of features as small as 1 nm from the atom probe tomography data. These methods are outlined and illustrated with examples of yttrium-, titanium-, and oxygen-enriched particles in a mechanically alloyed, oxide-dispersion-strengthened steel.

SC-X11 The Reflected Light Microscope (Metallograph)—Understanding the Basics and Optimizing Results

SC-X12 Modern Practice in Metallurgical and Materials Failure Analysis

SC-X13 Introductory Confocal Microscopy

SC-X14 Fluorescence Imaging of the Living Cell

SC-X15 Digital Imaging 2004

SC-X16 Image Processing and Analysis

SC-X17 Best Practices of Imaging and Microanalysis in Variable Pressure SEM and Environmental SEM

SC-X18 Microspectroscopy—Raman, FT-IR and EDXRF Microscopy

SC-X19 Application Pathways—Native sample to Immunolabeling via Tokayasu and High Pressure Freezing

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Special Event: IMS Henry Clifton Sorby Award and Lecture

Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.

Crystal structure of nano-scale precipitates in age-hardening aluminum alloys is a challenge to crystallography. The utility of selected area electron diffraction intensities from embedded precipitates is limited by double scattering via matrix reflections. This effect can be signally reduced by the precession technique, which we have used to collect extensive intensity data from the semicoherent, metastable η′-precipitate in the Al-Zn-Mg alloy system. A structure model in the space group P-62c is proposed from high-resolution microscopy and electron diffraction intensities. The advantages of using the precession technique for quantitative electron diffraction is discussed.

This article summarizes findings from our previous investigations and recent studies concerning precipitation in a maraging steel of type 13Cr-9Ni-2Mo-2Cu (at.%) with small additions of Ti (1 at.%) and Al (0.7 at.%). The material was investigated after aging at 475°C up to 400 h using both conventional and three-dimensional atom-probe analyses. The process of phase decomposition in the steel proved to be complicated. It consisted of precipitation of several phases with different chemistry. A Cu-rich phase was first to precipitate and Mo was last in the precipitation sequence. The influence of the complex precipitation path on the material properties is discussed. The investigation clearly demonstrated the usefulness of the applied techniques for investigation of nanoscale precipitation. It is also shown that, complementary methods (such as TEM and EFTEM) giving structural and chemical information on a larger scale must be applied to explain the good properties of the steel after prolonged aging.

The three-dimensional structure of the Plasmodium falciparum ring stage has been explored by reconstruction from serial sections and stereoscopic examination of tilted sections. The ring-like light microscopic appearance is related to the shape and contents of the biconcave discoidal parasite at this stage, its thick perimeter containing most of the ribosomes and its thin center containing smooth membrane organelles. The shapes of rings vary between flat and curved cuplike forms. The rough endoplasmic reticulum is a branched network continuous with the nuclear envelope. Evidence for a simple Golgi complex is seen in the presence on the outer nuclear envelope of a locus of coated vesicle budding associated with a single membranous cisterna or cluster of smooth vesicles. In middle and late stage rings this complex migrates along an extension of the nuclear envelope continuous with the rough endoplasmic reticulum. Evidence is also presented for a mechanism of exporting membrane from the parasite into the parasitophorous vacuole membrane and beyond into the red blood cell, by means of double-membraned vesicle-based exocytosis.

When a dielectric is irradiated by electrons with energy E of several kiloelectron volts, a large number of processes take place: backscattering of incident electrons, excitation and ionization of the electrons in the dielectric with binding energies lower than E, creation of excitons, radiative and nonradiative decays of the excited and ionized states, slowing down of the primary and secondary electrons, and thermalization in the conduction band. The thermalized electrons can move freely in the unoccupied conduction states of the material. If electric connection exists between the dielectric and the apparatus, then the charges normally flow out. Thermalized electrons can also be trapped in excited levels localized in the band gap of the dielectric and nonradiative and radiative recombinations from these levels can be observed. The number of the trapped electrons varies with the structural characteristics of the dielectric. In a monocrystal, this number is weak because the number of the defect states in the band gap is small, making the localization of the charges restricted. In contrast, in a polycrystal or amorphous material, the number of the trapped electrons can be large and increases with the disorder. Information on the charge effects suffered by the sample during its irradiation can be deduced by studying the trapping of electrons in localized states and, consequently, by analyzing radiations emitted from these states in the visible and X-ray ranges. In the case of oxides, F+ centers (oxygen–ion vacancy having trapped one electron) and F centers (F+ center having trapped a second electron) are generally present. We will show that the F+ [harr ] F conversion can be used to study the dynamic of the trapping in the oxides. Application to various samples of crystallized and amorphous alumina will be presented.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

This article presents my reminiscences of the work in Chicago on the correction or reduction of lens aberrations. Studies began in the early 1960s and extended over a period of almost 40 years, although it was never the primary focus of the work of the laboratory. The account is almost entirely based on my own memory, which is not a very reliable instrument. It is not intended to be a review and is more accurately describable as a personal recollection.

The pressure of crack-shaped cavities formed in silicon upon implantation with helium and subsequent annealing is quantitatively determined from the measurement of diffraction contrast features visible in transmission electron micrographs taken under well-defined dynamical two-beam conditions. For this purpose, simulated images, based on the elastic displacements associated with a Griffith crack, are matched to experimental micrographs, thus yielding unambiguous quantitative data on the ratio p/μ of the cavity pressure to the silicon matrix shear modulus. Experimental results demonstrate cavity radii of some 10 nm and p/μ values up to 0.22, which may be regarded as sufficiently high for the emission of dislocation loops from the cracks.

Biological Sciences: Advances in Imaging of Cytoskeletal Dynamics, Structure, Regulation, and Functions

Biological Sciences: 3D Electron Microscopy of Macromolecules: Unveiling Structural/Functional Relationships through Imaging Conformational Changes

Biological Sciences: Biomaterials

Biological Sciences: Imaging Technology in the Study of Cardiovascular Development and Disease

Biological Sciences: Microscopy of Plant Pathogenic Microbes and Their Interactions with Host Plants

Biological Sciences: Microscopic Analysis of Nervous System Development and Function

Biological Sciences: Microscopy in Microbiology

Physical Sciences: Characterization of Novel Nanostructures for Applications in Sensing, Nanoelectronics and Biotechnology

Physical Sciences: The Characterization and Performance of Advanced Coatings and Thin Films

Physical Sciences: Interfaces: A Symposium in Honor of Manfred Rühle

Physical Sciences: Metallography of High-Temperature Materials and Life Assessment

Physical Sciences: Microscopy and Microanalysis in Catalysis

Physical Sciences: Microscopy and Microanalysis of Nanotechnology

Physical Sciences: Nanostructure and Dynamics of Molecular Assemblies: Biomembranes, Proteins, Surfactants, Polymers and Liquid-crystals

Physical Sciences: Unraveling Magnetic Structure at the Nanoscale to Understand Magnetic Properties

Advances in Instrumentation and Techniques: Accessorizing the SEM

Advances in Instrumentation and Techniques: Advances in Confocal Optical Microscopy Technology

Advances in Instrumentation and Techniques: Advances in Visualizing Tissue Chemistry at the Cellular Level Using Infrared and Raman Microspectroscopy and Imaging

Advances in Instrumentation and Techniques: Analysis of Protein Dynamics in Living Cells by Quantitative Light Microscopy

Advances in Instrumentation and Techniques: Biological Specimen Preparation and Labeling

Advances in Instrumentation and Techniques: Digital Imaging

Advances in Instrumentation and Techniques: Electron Energy-Loss and X-ray Absorption Spectroscopies: Focus on Anisotropic Properties

Advances in Instrumentation and Techniques: FIB/Dual Platform Applications and Techniques in Biological and Physical Sciences

Advances in Instrumentation and Techniques: In Situ Characterization of Dynamic Processes by Variable Pressure Electron Microscopy

Advances in Instrumentation and Techniques: Metallography: Preparation, Application and Evaluation for the 21st Century

Advances in Instrumentation and Techniques: Metallurgical Failure Analysis: Present and Future

Advances in Instrumentation and Techniques: Microscopy and Microanalysis in the Real World: Textiles, Pharmaceuticals, Photonics, and Biomedical/Forensics

Advances in Instrumentation and Techniques: Micro X-ray Techniques: New Compositional and Structural Characterization Tools

Advances in Instrumentation and Techniques: Order in Disorder: Probing the Structure of Amorphous Materials

Advances in Instrumentation and Techniques: Quantitative Techniques in Biological Imaging

Advances in Instrumentation and Techniques: Quantitative X-ray Microanalysis: Focus on Extraterrestrial and Terrestrial Specimens

Advances in Instrumentation and Techniques: Scanned Probe Microscopy: Probing Surfaces at the Nanoscale

Advances in Instrumentation and Techniques: Stereology and 3D Digital Imaging

Advances in Instrumentation and Techniques: Tomographic Techniques in Biological and Physical Sciences

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The resolution achieved in low-dose electron microscopy of biological macromolecules is significantly worse than what can be obtained on the same microscopes with more robust specimens. When two-dimensional crystals are used, it is also apparent that the high-resolution image contrast is much less than what it could be if the images were perfect. Because specimen charging is one factor that might limit the contrast and resolution achieved with biological specimens, we have investigated the use of holey support films that have been coated with a metallic film before depositing specimens onto a thin carbon film that is suspended over the holes. Monolayer crystals of paraffin (C44H90) are used as a test specimen for this work because of the relative ease in imaging Bragg spacings at ∼0.4 nm resolution, the relative ease of measuring the contrast in these images, and the similar degree of radiation sensitivity of these crystals when compared to biological macromolecules. A metallic coating on the surrounding support film does, indeed, produce a significant improvement in the high-resolution contrast for a small fraction of the images. The majority of images show little obvious improvement, however, and even the coated area of the support film continues to show a significant amount of beam-induced movement under low-dose conditions. The fact that the contrast in the best images can be as much as 25%–35% of what it would be in a perfect image is nevertheless encouraging, demonstrating that it should be possible, in principle, to achieve the same performance for every image. Routine data collection of this quality would make it possible to determine the structure of large, macromolecular complexes without the need to grow crystals of these difficult specimen materials.

The goal of this article is first to review the charging effects occurring when an insulating material is subjected to electron irradiation in a scanning electron microscope (SEM) and next their consequences from both scanning electron microscopy and electron probe microanalysis (EPMA) points of view. When bare insulators are observed, the so-called pseudo mirror effect leads to an anomalous contrast and also to an erroneous surface potential, VS, measurement when a Duane–Hunt limit (DHL) method is used. An alternative possibility is to use an electron toroidal spectrometer (ETS), specially adapted to a SEM, which directly gives the VS value. In the case of a bulk specimen coated with a grounded layer, although the layer prevents external effects of the trapped charge, the electric field beneath the coating is reinforced and leads to loss of ionizations that reduces the number of generated X-ray photons. To take into account both effects mentioned above, whether the studied insulator is coated or not, a method is proposed to deduce the trapped charge inside the insulator and the corresponding internal or external electric field.

Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.