The energy of the electron beam, in conventional electron probe microanalysis, is generally in the range of 15-25 keV which provides the necessary overvoltage to excite efficiently the K and L x-ray lines for elements with atomic numbers in the range of about 5-83. One of the primary microanalytical methods for obtaining compositional information on particles is X-ray analysis in the electron probe and these same voltage criteria have been applied to the procedures developed for this purpose. The main difference in analytical procedures for bulk samples and particles is that corrections have to be applied to the particle k-ratios or calculated compositions to compensate for: 1) the penetration or scattering of electrons out of the particle volume and 2) variations in the absorption due to particle geometry of x-rays less than about 3 keV. In general, particle corrections improve the accuracy and reduce the relative uncertainty estimates from several tens of percent for uncorrected data to about 10% for corrected data.

In the recent years the Monte-Carlo simulation has been used successfully to exploit and understand fully the capabilities of electron microscopes. In this paper, we propose a new parametrization of Mott scattering cross-section for the calculation of the total cross-section as well as the polar angle of collision. This parametrization gives better results than Rutherford cross-section for Monte Carlo simulation at low beam energy without the numerous data files needed to use the exact Mott cross-section.

The calculation of elastic scattering cross-section can be performed with the Rutherford equation using the screening parameter, δ, the energy of the incident electron, and the electron wavelength, differential cross-section is given by:

The vast majority of applications of electron probe x-ray microanalysis takes place on specimens which deviate significantly from the ideal configuration. Classic quantitative x-ray microanalysis makes the tacit assumption that the only reason the unknown differs in emitted x-ray intensity from standards is that there is a difference in composition between them. While this seems trivial, it forces the analyst to eliminate a major non-compositional source of possible intensity differences, namely the geometric effects associated with surface roughness. An important early paper by Yakowitz demonstrated that deviations from an ideal flat surface due to surface topography could seriously degrade the accuracy of analysis. Yakowitz interrupted the grinding and polishing procedure on pure elements and alloys at various stages and measured the variance in the x-ray intensity as the probe was scanned across the surface as compared to the predicted distribution based on counting statistics.

In many areas of the world slags pose potential environmental threats to their surroundings. Heavy metals, toxic and radioactive elements contained in some slags may leach into drinking water and contaminate agricultural areas. Leaching experiments can estimate short-term alteration rates, but such tests cannot reproduce long-term weathering processes. Such studies are particularly important in the case of U- and Th-bearing slags which may remain hazardous for 103 104 years. These radioactive slags are of concern to decisions regarding the termination of a nuclear materials license and the subsequent allowances for unrestricted public use of the smelting sites and slag piles. To thoroughly evaluate leaching from slags, one must understand the distribution of elements among the slag phases and the stability of each phase. Questions regarding the distribution of elements among multiple phases are best answered by detailed electron microprobe (EMP) studies.

Slags are often mineralogically and compositionally complex, and may have complicated exposure histories.

Plutonium (Pu), with an atomic number of 94, is the highest atomic number naturally occurring element on Earth. It is formed when naturally occurring Uranium 238 captures a neutron that can be created by spontaneous fission and alphaneutron reactions. The natural abundance of terrestrial Pu is very small; its concentration is about one part in 10 of the uranium present in naturally occurring uranium ores. The first man-made plutonium was produced at the University of California cyclotron and identified on February 23, 1941. Just a few months after the first Pu was produced it became clear how metallurgically complex this material is. Plutonium is known to have six allotropes (crystalline forms) at atmospheric pressure, between room temperature and 640°C, the melting point of the pure metal. This is the largest number of allotropes known for any element.

Lead and bismuth standards for quantitative electron probe microanalysis have always been a problem due to mechanical polishing and surface oxidation upon atmospheric exposure. Some Pb and Bi compounds, such as the selenides and tellurides, can be obtained commercially as solid pieces that are large enough to be mounted as useful standards, but they can also form non-stoichiometric solid solutions. This paper is a description of the initial work done on the testing of some selenides and tellurides to evaluate their usefulness as standards for quantitation. In addition, improved procedures for preparing the Pb and Bi element and compound specimens are being used to reduce surface oxidation. Primarily Pb samples were evaluated here, but the project will be extended in the future to include more Bi materials.

Experimental

Most specimens were mounted in silver epoxy in multi-element mounts that were repolished according to the description below. Additional specimens of PbTe, PbSe, and Pb were mounted in epoxy for this work.

X-ray microanalysis often must estimate limits of detection for specific specimen compositions to optimize analytical strategy and to adequately describe results. Several approaches are available which make use of experimentally measured spectra to obtain peak and local background intensities. One of the oldest and simplest involves the use of pure element spectra. However, such an estimate procedure does not take into account the matrix effects, particularly absorption, which can be quite important in defining limits of detection in a particular multi-element composition. If a microhomogeneous standard is available with the appropriate matrix that also contains the other constituent(s) of interest at a known level, ideally at a minor constituent level (0.01 to 0.1 mass fraction), then the limit of detection, CDL, can be estimated through the use of the expression:

It has been long known that orientation effects in crystalline materials can influence characteristic x-ray emission and microanalysis. Most of the recent studies have concentrated upon using the phenomenon to perform site specific distributions of impurity elements in ordered compounds using the ALCHEMI methodology. For the most part, it has been asserted that increasing the parameters of thickness, orientation and beam convergence effectively averages out these effects. Using High Angular Resolution Electron Channeling X-ray Spectroscopy (HARECXS) we have carefully measured the phenomenon in a number of ordered systems and find that it must be considered in many cases.

All experimental measurements presented here were conducted on a Philips EM 420T analytical electron microscope. The instrument was operated in the TEM mode, at 120 kV using a LaB6 electron source. The characteristic x-ray emission was measured using an ED AX ultra thin window Si(Li) detector having a FWHM of ∼ 145 eV at Mn Ka.

Grain boundary network engineering is an emerging field that encompasses the concept that modifications to conventional thermomechanical processing can result in improved properties through the disruption of the random grain boundary network. Various researchers have reported a correlation between the grain boundary character distribution (defined as the fractions of “special” and “random” grain boundaries) and dramatic improvements in properties such as corrosion and stress corrosion cracking, creep, etc. While much early work in the field emphasized property improvements, the opportunity now exists to elucidate the underlying materials science of grain boundary network engineering. Recent investigations at LLNL have coupled automated electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM)5 and atomic force microscopy (AFM) to elucidate these fundamental mechanisms.

An example of the coupling of TEM and EBSD is given in Figures 1-3. The EBSD image in Figure 1 reveals “segmentation” of boundaries from special to random and random to special and low angle grain boundaries in some grains, but not others, resulting from the 15% compression of an Inconel 600 polycrystal.

Background

Electron backscattered diffraction (EBSD) is a very powerful analysis technique to understand the crystallography of a sample in the SEM. Typically, a high beam current is needed to obtain good results because of inefficient collection of the patterns. In W-filament SEM's, the high beam current necessitates a large spot size and requisite low image resolution. The large beam current can also be a source of problems for insulating samples or sample mounts by causing charging and the resulting image drift.

To reduce the spot size with adequate beam currents for imaging, field-emission (FE) guns are used. For most FESEM's, the beam current is markedly reduced from that produced by W-filament instruments. Even though the image resolution is better, the EBSD performance tends to suffer at low beam currents for standard hardware configurations. To regain the performance of a comparable W-filament system, the EBSD hardware should be changed for the low beam current operation. This paper will address the hardware considerations for low beam current applications.

A group of mixed oxide ceramic capacitors used in several electronic systems recently failed as a result of voltage breakdown in the specified test ranges. These capacitors consist predominantly of mixed oxides of magnesium, titanium, silicon and aluminum (with minor amounts of strontium and calcium) and contain palladium mesh electrodes. Preliminary results suggest that phase transformations have occurred in some lots of capacitors that have been over-fired as a result of a manufacturing change. Several years’ production of capacitors has potentially been affected. The formation of a phase with inferior dielectric properties, and which can exhibit semiconducting properties (P/N junction), probably resulted in the failure of the capacitors. This new phase is typically rich in strontium and is only present at levels of several volume percent. The low concentration of this phase has made its identification difficult. If this new phase could be identified it might be possible to determine/establish if its dielectric properties are consistent with the proposed failure mechanism.

Electron backscatter diffraction (EBSD) is a technique that can provide identification of unknown crystalline phases while exploiting the excellent imaging capabilities of the scanning electron microscope (SEM). Phase identification using EBSD has now progressed to the point that it is commercially available. Phase identification in the SEM requires high quality EBSD patterns that can only be collected using either film or charge coupled device (CCD)-based cameras. High quality EBSD patterns obtained in this manner show many diffraction features that are useful in the determination of the unit cell of the sample.’ This paper will discuss the features in the EBSD patterns and the procedure used to determine the reduced unit cell of the sample.

One of the major advantages of EBSD over electron diffraction in the transmission electron microscope is the remarkable field of view that is routinely attained. The large angular view of the diffraction pattern permits many zone axes and their associated symmetries to be viewed in a single pattern or at most a few patterns.

YAG-A12O3 directionally solidified eutectic composites show great promise in applications requiring high temperature strength and creep resistance.’ The orientation relationships between YAG and Al2O3 have been established within the composite by use of SEM Electron Backscatter Diffraction (EBSD) and x-ray diffraction (XRD). The orientation relationships of were determined. Two related variants of A12O3 were discovered in the sample. EBSD was employed to determine the spatial distribution of the variants within the sample.

The microstructure of the eutectic composite, shown in Figure 1, reflects a “chinese script” pattern, neither lamellar nor fibrous. The directionally solidified eutectic fibers, approximately 2.5 mm in diameter, were cut into disks normal to the fiber axis by a diamond saw and polished by with diamond-imbedded paper to reduce chances of phase-preferential wear. Samples used for EBSD were ion milled for 30 minutes at low power and incident angle to improve the patterns.

A high-resolution serial sectioning specimen preparation technique is described for acquisition of electron backscattered diffraction orientation imaging microscopy (OIM) data. The primary objective is to develop a method to reproducibly remove a controlled thickness of material (a serial section) from a polycrystalline Ta sample while producing quality surfaces for OIM imaging. This is integrated with the ability to accurately measure the amount of material removed with each iteration and experimentally register the ensuing OIM scans.

A Si metrology device is fabricated by lithographic techniques to facilitate the measurement of the amount of material removed with each lapping iteration and the alignment of each serial section image. This metrology device contains a herringbone pattern with two orthogonal etched lines oriented at 45 degrees and one vertical line normal to the OIM surface. The metrology device is epoxied to a polished side surface of the Ta sample. Due to the orthogonality of the lines, the thickness of material removed equals one-half the total linear motion of the etched lines as seen in cross-section. To accurately measure the distance between the grooves after each lapping iteration, a high-resolution (0.1 μm) linear measuring system is attached to the table of a light metallograph.

Boundary properties between two adjacent grains with different crystallographic orientation relation are important factors in deciding the mechanical properties of materials. The concept of the geometric compatibility factor has been introduced in order to explain the relationship between transfer of deformation mode and crystal orientation. In the same manner, when the brittle crack propagates, grain boundary also obstructs crack propagation. Therefore it is also possible to introduce the concept of geometric compatibility considering the crystallographic orientation in analyzing the crack propagation.

In this study, the characteristics of the brittle crack propagation in bainitic low alloy steel with compositions shown in table 1 have been investigated using EBSD analysis. A 3-point bending test was performed at -100°C and the secondary crack below fracture surface was analyzed in relation to the crystallographic orientation. In order to explain the behavior of crack propagation, modified geometric compatibility factor, M was introduced considering loading axis and crystallographic orientation relationship.

Electron Backscattering Diffraction (EBSD) is an important tool for analyzing the crystal grain orientation of a microstructure and can be used to formulate conclusions about microtexture, texture determined from individual grains. This technique has been used to study a 6xxx series aluminum alloy's response to the deformation of the extrusion process. Extrusion is the process by which a billet of material is forced, under high pressure, through a die. The material undergoes a significant decrease in cross sectional area, and is formed into a shape equivalent to the geometry of the die orifice. Different bearing lands are shown in shown in Figure 1. These surfaces form the part, and are designed to control the metal flow making it uniform through the die, thus yielding good mechanical properties. This research was focused on the resultant microstructure. The shaded regions of Figure 2 show the two surface regions where EBSD measurements were taken.

Circumferential mechanical texture (scratches) of hard drive substrates has improved head/media tribology; however, it has also been advantageous to the development of OR (Orientation Ratio) for longitudinal media. The magnetic dipoles prefer to circumferentially align with texture, which matches the direction heads read/write. The corrugated nature of films sputtered on fine texture scratches leads to an anisotropic stress state in the films, especially for those deposited at temperatures above ambient; and OR has been attributed to this anisotropic stress. A review article discusses possible causes of the OR such as: self-shadowing due to the texture lines during deposition, circumferential c-axis alignment, shape anisotropy of media grains, and magnetostrictive effects. Another work listed two requirements for OR: <> Co crystallographic growth texture in addition to circumferential texture scratches. The same study considered frequencies and depths of the texture scratches, and concluded that OR increased as the ratio of depth/frequency increased, rather than just as a function of Ra alone.

Creep process in dental amalgams has been a subject of study. The performance of dental amalgams depends on the creep resistance of different products offered in the market. Creep process occurs at mouth temperatures which are slightly lower than Gamma 1 matrix phase (Ag2Hg3) melting point (310°K). One successful attempt to improve the creep resistance has been the addition of a dispersed phase (particles of eutectic Ag-Cu phase) in conventional amalgams. By this method, a new phase (η- Cu6Sn5) has been produced which inhibits the detrimental gamma 2 (Sn8Hg) formation. It has been proposed that the presence of finely distributed particles of η-Cu6Sn5 in the matrix lowers the creep rate. This behavior has been attributed to the pinning effect of these fine particles on the dislocations produced during the creep process (1). The presence of η-Cu6Sn5 phase finely dispersed in the matrix has been explained by the initial formation of reaction rings around the eutectic Ag-Cu spherical particles.

Apoptosis has been known as a significant element in the process of embryonic morphogenesis (1). Many studies on the role of apoptosis during development have been done using several organ systems, such as limb bud (2), nervous system(3), and inner ear (4). Recently, cell death with many morphological characteristics of apoptosis was reported in the developmental study of chick knee joint (5). This study was designed to observe the appearance of apoptotic cells during the joint cavity formation of mouse knee joint by transmission electron microscopy and TUNEL staining. The fetus were collected from l5thday(15D) to 19th day(l 9D) of pregnancy.

We observed many blood vessels and mesenchymal cells at 15D between the cartilages of femur and tibia. Mesenchymal cells had condensed heterochromatin and dilated rough endoplasmic reticulum (rER). At 16D, the joint clefts were first formed. Apoptotic cells, with characteristic nuclear fragmentation and condensation, appeared between the joint cleft and the capillaries.

In nascent cultured primary chick skeletal myocytes, a l integrin is observed to have a punctate distribution. As early as day 3 in culture, however, it can be found to reorganize into periodic doublet bands. Subsequent to a l integrin reorganization, collagen type III has been found to colocalize with these periodic α l integrin bands. The coordinated appearance of these two proteins is suggestive of a possible regulatory role for one or both proteins in muscle development.

To ascertain whether this same αl integrin/collagen type III reorganization occurs in muscle cell lines, differentiating myocytes from the C2C12 cell line were examined for the temporal appearance and localization of both proteins. Cultured C2C12 cells were immunofluorescently labeled with antibodies to al integrin, collagen type III and other muscle specific proteins on days 1, 3, 6, 9 and 11 after growth medium was replaced with differentiation medium.