High-voltage Transmission Electron Microscopy Research Articles

Electron energy loss spectroscopy and energy filtered imaging of Xe cavities embedded in Al at 423 and 473 K

Xe ions were implanted into Al in a high-voltage transmission electron microscope at temperatures 423 and 473 K to a dose up to 2.6×10 21 ions m −2. Electron energy loss spectroscopy (EELS) and energy filtered imaging (EFI) were employed to characterise Xe cavities over the temperature range 300–858 K. The precipitates grew up to about 30 nm when Xe ions were introduced at 473 K. The crystalline precipitates start to change to a non-crystalline state at 623 K and converted completely to the non-crystalline state at a temperature up to 773 K. Energy filtered images of Xe were taken with Xe-M 4,5 core loss electrons to get the two-dimensional distribution of Xe for both crystalline and non-crystalline Xe cavities. Low energy loss peaks at about 14.6 and 15.3 eV were identified in the EELS spectra obtained at 300 and 773 K, respectively. These peaks are thought to be related to the Xe precipitates in Al. The analysis of Xe-M 4,5 edge in EELS spectra suggests that Xe-precipitates exist in the gaseous state at 773 K.

TEM investigations of the superdislocations and their interaction with particles in dispersion strengthened intermetallics

The strategy of oxide-dispersion strengthening has recently been applied to intermetallic compounds in order to improve their creep resistance at high temperatures. In this paper, we describe selected results of an extensive transmission electron microscopy (TEM) study of the dislocation structures and the particle/dislocation configurations in Oxide-dispersion strengthed (ODS) NiAl, Ni 3Al and FeAl. High-resolution TEM was employed to characterise the particle/matrix interfaces, and in situ high-temperature deformation in a high-voltage TEM provided insight into the dynamic processes of dislocation detachment from particles. The dissociation of the lattice dislocations into superpartials in FeAl and Ni 3Al has important consequences for the particle/dislocation interactions: the superpartials are observed to surmount, and sometimes detach from, the particles separately, which points to a cooperative effect between the partials. The in situ experiments show, in addition, that the climb step is rapid compared with dislocation detachment from the particle. These observations are discussed in the light of our recent theoretical model of creep strength in ordered ODS materials.

High-resolution electron microscopy study of defect structures in -TiAl irradiated with 15 keV He ions in a high-voltage transmission electron microscope

γ-TiAl intermetallic alloy specimens were irradiated with 15 keV He ions to a dose of 8.6×1020 ions m−2 (4.6 dpa, averaged in the range of the irradiation damage distribution in depth from 0 to 240 nm) in a high-voltage transmission electron microscope (HVTEM) at room temperature. The defect clusters formed during the ion irradiation were characterized with high-resolution transmission electron microscopy (HRTEM). Induced defect clusters are mainly planar defects and rotated domains (RDs). The planar defects have the edges parallel to {111) of the matrix and several nanometers in size. They are formed during ion irradiation and remain stable even after annealing and correspond to the bright streaks along <111] in selected area diffraction (SAD) patterns of the ion-irradiated specimens. The RDs, which are rotated 90° to the matrix, are formed in as-irradiated and post-irradiation annealed specimens. They are identified by the appearance of super-lattice reflection spots in SAD pattern and by image contrast in HRTEM observation as well. Post-irradiation annealing at 673 K for 30 min enhanced the formation of the RD. The mechanism of formation of the RD is discussed.

Analysis of calcitonin gene-related peptide (CGRP)-containing nerve fibres in the rat spinal cord using light and electron microscopy.

Calcitonin gene-related peptide (CGRP) content in areas surrounding the central canals of cervical, thoracic, lumbar and sacral spinal cords of rats were investigated by light microscopy, conventional transmission electron microscopy (CTEM) (100-200 kV) and high-voltage transmission electron microscopy (HVTEM) (1000 kV) using immunocytochemistry. Tissues were examined using either the peroxidase-antiperoxidase technique or an immuno-cryoultramicrotomy technique. Light microscopically, more intense CGRP localization was observed ventral to the central canals in the lumbar and sacral cord compared with the dorsal area in the same regions. HVTEM revealed that high levels of CGRP labelling were found adjacent to the basal side of ependymal cells ventral to the central canal. Analysis using CTEM operated at 200 kV demonstrated that the CGRP immunoreactivity was present within unmyelinated nerve fibres in the vicinity of the basal side of ependymal cells ventral to the central canal. Immuno-cryoultramicrotomy revealed that immuno-gold particles indicating CGRP labelling were localized on vesicle-like electron-dense bodies in unmyelinated and some fine caliber myelinated nerve fibres. Existence of CGRP as a primary afferent marker in the area surrounding the central canal suggest that there may be an intimate relationship between the modulation of nociceptive information and the area surrounding the central canal in rat spinal cord.

Rosette Microstructure in Indented (001) GaAs Single Crystals and the α/β Asymmetry

The characteristic features of the dislocation microstructure that develops around indentations performed at room temperature on (001) GaAs single crystals are analysed by High Voltage Transmission Electron Microscopy. It is shown that perfect rosette dislocations (with Burgers vector parallel to the surface) are nucleated deeply in the crystal and never merge at the sample surface. Perpendicular rosette arms have similar lengths, which raises the question of the α/β asymmetry. Twins are present in one rosette arm only; twinning dislocations are nucleated on — or very close to — the indented surface. These results are discussed in connection with previously reported results.

Recombination-Enhanced Dislocation Motion in SiGe and Ge

In-situstraining experiments on dislocation motion in Ge and Si–5 at% Ge alloy single crystals are performed in a high voltage transmission electron microscope. In comparison with previous results by other methods, the dislocation velocities are found to be enhanced due to a recombination enhancement owing to the excess carrier injection by the electron beam. The reduction in the activation energy of dislocation motion is ascribed to the recombination-assisted kink formation. The kink migration energy is estimated to be 0.7 eV in Ge and 1.5 eV in SiGe.

Immunoultrastructural expression of intercellular adhesion molecule-1 in endothelial cell vesiculotubular structures and vesiculovacuolar organelles in blood-brain barrier development and injury.

Blood vessels from the vasculature of mouse brains during postnatal development and from human brain tumors (hemangiomas) removed at biopsy were examined immunocytochemically by transmission electron microscopy (TEM) or high-voltage transmission electron microscopy (HVEM) to determine the expression of intercellular adhesion molecule-1 (ICAM-1). In the mouse brains, ICAM-1 was shown to be initially expressed on the luminal and abluminal endothelial cell (EC) surfaces on day 3 after birth. ICAM-1 intensity increased on the luminal EC surfaces and labeled vesiculotubular profiles (VTS, defined in the present report) between days 5 and 7. After 2 weeks and at 6 months after birth, ICAM-1 labeling was weak or absent on the luminal EC surfaces. The hemangiomas presented a strong ICAM-1 reaction product on the luminal EC surfaces of small and large blood vessels associated with the VTS, with a weaker labeling of the abluminal or adventitial aspects of larger blood vessels. TEM of vesiculovacuolar structures (VVOs) within ECs from arteries and veins also demonstrated reaction product for ICAM-1 labeling. Three-dimensional stereo-pair images in the HVEM enhanced the visualization of gold particles that were attached to the inner-delimiting membrane surfaces of EC VTS, and VVOs, respectively. These observations raise the possibility that the neonatal leukocytes and tumor cells may utilize these endothelial structures as a route across the developing and injured blood-brain barrier (BBB).

Identification of materials in integrated circuit interconnects using x-ray absorption near-edge spectroscopy

Most integrated circuit interconnects are principally composed of a few metals, including aluminum alloyed with copper, tungsten, titanium, Al3Ti, and Al2Cu, in a silica matrix. Integrated circuit interconnects have recently been proposed as a candidate system for visualization by computerized microtomography using absorption in the soft x-ray region. In this work, we demonstrate the feasibility of materials identification using volume-resolved x-ray absorption near edge spectra (XANES) obtained by tomographic reconstruction. A similar experiment could be performed with an energy-resolved high-voltage transmission electron microscope. We calculate the XANES for interconnect materials near the Al K edge, the Cu LI, LII, and LIII edges, and the Ti LII and LIII, and compare them to experiment when possible. The signal-to-noise ratio required to distinguish among the aluminum compounds from their Al K edge spectra is shown to be about one order of magnitude higher than that needed to detect elemental aluminum.

Growth defects in BSCCO (2212) single crystal whiskers

The defect structure of superconducting single crystal whiskers BSCCO (2212) was studied by high voltage transmission electron microscopy. Dislocations, twins, growth steps, antiphase domains associated with a commensurate modulation and antiphase boundaries of incommensurate modulation were found. The latter are inherent to all whiskers in contrast to any other defects. The defect structures of the whiskers and BSCCO (2212) plate-like single crystals are compared. The influence of some defects on superconducting properties of the material is discussed.

An in situ nanoindentation specimen holder for a high voltage transmission electron microscope.

We describe in detail, the design, construction, and testing of a specimen holder that allows for the nanoindentation of surfaces while viewing in cross-section in a high voltage transmission electron microscope (TEM). This nanoindentation specimen holder, having three-axis position control of a diamond indenter in combination with micromachined specimens, allows for the first time the dynamic observation of subsurface microstructure evolution under an indenter tip. Additionally, the sample design techniques that have been developed for these procedures may eliminate the need for TEM specimen preparation for additional ex situ nanoindentation experiments. Initial experimental results from in situ indentation of Si samples in the high voltage electron microscope are reported here to demonstrate the capability of this new specimen holder.

An in situ nanoindentation specimen holder for a high voltage transmission electron microscope

This report describes the design, construction, and testing of a nanoindentation specimen holder used for dynamic observation of subsurface microstructure evolution under an indenter tip, while viewing in cross-section in a high-voltage transmission electron microscope (TEM). It also discusses the initial experimental results from in-situ indentation of Si samples in the TEM to demonstrate the capability of this new nanoindentation specimen holder, which uses three-axis position control of a diamond indenter in combination with micromachined specimens. Additionally, the sample design techniques developed for these procedures may eliminate the need for TEM specimen preparation in future ex-situ nanoindentation experiments and for sample preparation for characterizing these experiments in the electron microscope.

LBNL and the Materials Microcharacterization Collaboratory

Abstract In 1996 the DOE formed the Materials Microcharacterization Collaboratory (MMC) to bring together the four DOE-sponsored electron microscope user facilities in one collaboratory. The MMC will bring the microanalysis and microcharacterization tools that are available in national centers to geographically dispersed researchers working in industries, universities, and Government laboratories. It will enable these remote users to share on-line the instrumentation, knowledge and expertise available at the individual facilities making up the collaboratory. LBNL first demonstrated on-line remote control of a high-voltage TEM from Kansas City in 1995 in a joint project by LBNL computer scientists and NCEM microscopists. The microscope chosen was a 1.5MeV Kratos EM-1500 that is used for in-situ electron microscopy. In the demonstration, a specimen of an Al/Pb alloy was heated and observed, with remote-operator control of heating rate, microscope focus, and stage movement (translation and tilt).

On the influence of indium addition on the mechanical properties of gallium arsenide at room temperature

Indentations have been performed on (001) faces of indium alloyed GaAs crystals in darkness and under infrared illumination. The Vickers hardness was measured and the dislocation microstructure around the indents observed by high voltage transmission electron microscopy. A softening effect of indium is evidenced by comparison with the Vickers hardness obtained in the same conditions on undoped GaAs. No significant influence of indium on the dislocation microstructure resulting from indentation in darkness is noted. Indentation under infrared illumination does not reveal any macroscopic photoplastic effect; however, a modification of dislocation microstructure is observed. Whatever the experimental conditions, dislocations appear to experience strong lattice friction. The softening effect of indium addition and the enhanced dislocation mobilities under infrared illumination are discussed in the framework of dislocation glide governed by the Peierls mechanism.

Quantitative Analysis of HREM Images of &amp;alpha;-AlB&lt;SUB&gt;12&lt;/SUB&gt; with a High-Voltage Transmission Electron Microscope and the Imaging Plate

High-resolution electron microscope images of α-AlB 12 were quantitatively observed by using a high-voltage transmission electron microscope and the new Imaging Plate having a pixel size of 25 μm. In order to quantitatively evaluate the difference between the observed intensity and the calculated one, a residual index R HREM which indicates the accuracy of a calculated image was evaluated for 1440 sampling points in the unit cell projected along the [111] direction. The residual index R HREM of 0.0576 was obtained with the averaged high-resolution electron microscope image and the calculated image based on the structure model obtained from the X-ray diffraction study. In the observed high-resolution electron microscope image, some regions had extraordinarily higher intensity than other regions which were crystallographically equivalent to the regions. In a quantitative analysis of the observed images including those regions, the minimum R HREM at 0.0738 was obtained by varying the occupancy of Al atoms although the R HREM remarkably increased from the minimum value obtained in the quantitative analysis of the averaged image. The effects of a contamination layer covering the sample on the above quantitative analysis of high-resolution electron microscope images are briefly discussed.

Imaging thin and thick sections of biological tissue with the secondary electron detector in a field‐emission scanning electron microscope

A field-emission scanning electron microscope (FESEM) equipped with the standard secondary electron (SE) detector was used to image thin (70-90 nm) and thick (1-3 microns) sections of biological materials that were chemically fixed, dehydrated, and embedded in resin. The preparation procedures, as well as subsequent staining of the sections, were identical to those commonly used to prepare thin sections of biological material for observation with the transmission electron microscope (TEM). The results suggested that the heavy metals, namely, osmium, uranium, and lead, that were used for postfixation and staining of the tissue provided an adequate SE signal that enabled imaging of the cells and organelles present in the sections. The FESEM was also used to image sections of tissues that were selectively stained using cytochemical and immunocytochemical techniques. Furthermore, thick sections could also be imaged in the SE mode. Stereo pairs of thick sections were easily recorded and provided images that approached those normally associated with high-voltage TEM.

Microstructure and mechanisms of cyclic deformation of aluminum single crystals at 77 K

Aluminum single crystals were cyclically deformed in single slip at small strain amplitudes at 77 K to presaturation. The observed mechanical behavior is consistent with recent work by other investigators. The dislocation substructure can be described as consisting of dense bundles or veins of edge dislocation dipoles, of a single Burgers vector, separated by lower dislocation density regions or channels where substantial debris is evident. This debris was determined as almost exclusively relatively short edge-dipole segments. Screw dislocations with the same Burgers vector span the channels. In situ cyclic reverse (shear) deformation experiments in the high-voltage transmission electron microscope (HVEM) were successfully performed using the X-Y technique where thin foils are stressed in alternating perpendicular directions. Our experiments indicate that loops frequently expand from the dipole bundles into the channel and the edge component is absorbed by nearby bundles, leaving screw segments behind. The screw dislocations that span the channel move easily and reverse direction with shear reversal. Screws may move first with a strain reversal. A comparable fraction of the strain during each cycle appears to be provided by screw and edge dislocations. Dipole “flipping” was not observed. There is no obvious evidence for internal backstresses that assist plastic deformation on reversal of the applied shear.

In situ observation of the tip shape of AuGe liquid alloy ion sources using a high voltage transmission electron microscope

A AuGe liquid alloy ion source was observed in situ under various operating conditions in a 1 MeV transmission electron microscope. The formation of a field-stabilized liquid cone, the change in the cone shape as a function of ion emission current, spatial shifts of the liquid cone, and microdroplet emission were investigated. Below the onset voltage the shape of the tip covered with liquid AuGe alloy is spherical. At the onset voltage a Taylor cone is formed. At ion emission currents Ie larger than 4 μA a jetlike protrusion at the Taylor cone vertex can definitively be seen. At lower emission currents possible jet formation cannot be identified unambiguously. The cone half-angle α decreases linearly with the ion emission current, while the jet length and the jet diameter increase linearly with Ie. Emission of microdroplets was observed from the surroundings of the Taylor cone region. Microdroplets with a radius between 80 and 2300 nm are emitted in time intervals of about 0.1 s and more.

Low-Voltage, High-Resolution, Scanning Electron Microscopy of Platelet-Bound Fibrinogen

An essential element in blood clot formation is fibrinogen-mediated platelet aggregation. Fibrinogen is an adhesive plasma protein which binds to the αIIbp3 integrin on activated platelet surfaces. Platelets do not aggregate in the absence of fibrinogen binding, and fibrinogen bound to surfaces of platelets in aggregates is localized to regions of platelet-platelet contact. The fibrinogen molecule is symmetrical and bifunctional and may directly bridge the gap between platelets to bind to receptors on two adjacent platelets. However, the precise mechanism by which fibrinogen links platelets is unclear.Previously we have utilized colloidal gold labeling with correlative light and electron microscopy to investigate the binding of fibrinogen to receptors on surfaces of spread, substrate adherent platelets. The initial binding of gold-conjugated fibrinogen (FgnAu) and subsequent ligand-triggered receptor movement was followed on living platelets by video-enhanced light microscopy. Fibrinogen receptors initially are dispersed over much of the platelet surface and move centripetally upon fibrinogen binding, ultimately forming a band of bound fibrinogen on the platelet surface overlying a densely woven band of actin filaments surrounding the central granulomere. After preparation for electron microscopy, the same platelets as were followed in the light microscope were located in the high voltage TEM and the low voltage, high resolution, SEM (Hitachi S-900) and the final locations of the gold labeled receptor/ligand complexes were determined relative to internal or surface ultrastructure, respectively. More recently, we have utilized the SEM operated at low (1-2 kV) beam voltage to examine in detail the binding of unlabeled fibrinogen to platelets. With appropriate specimen preparation, individual cell surface macromolecules can be resolved in situ by low voltage SEM. In addition to the centripetal receptor redistribution seen with FgnAu, unlabeled fibrinogen appeared to undergo self-adhesive interactions following binding to platelet fibrinogen receptors, forming small, branched and globular protein aggregates during translocation across the platelet surface.(Fig. 1)

Remote On-Line Control of a High-Voltage in situ Transmission Electron Microscope with A Rational User Interface

Remote on-line electron microscopy is rapidly becoming more available as improvements continue to be developed in the software and hardware of interfaces and networks. Scanning electron microscopes have been driven remotely across both wide and local area networks. Initial implementations with transmission electron microscopes have targeted unique facilities like an advanced analytical electron microscope, a biological 3-D IVEM and a HVEM capable of in situ materials science applications. As implementations of on-line transmission electron microscopy become more widespread, it is essential that suitable standards be developed and followed. Two such standards have been proposed for a high-level protocol language for on-line access, and we have proposed a rational graphical user interface. The user interface we present here is based on experience gained with a full-function materials science application providing users of the National Center for Electron Microscopy with remote on-line access to a 1.5MeV Kratos EM-1500 in situ high-voltage transmission electron microscope via existing wide area networks. We have developed and implemented, and are continuing to refine, a set of tools, protocols, and interfaces to run the Kratos EM-1500 on-line for collaborative research. Computer tools for capturing and manipulating real-time video signals are integrated into a standardized user interface that may be used for remote access to any transmission electron microscope equipped with a suitable control computer.

Practical Performance of Energy-Dispersive X-Ray Spectroscopy with a High-Voltage TEM up to 1,000 kV

Practical Performance of Energy-Dispersive X-Ray Spectroscopy with a High-Voltage TEM up to 1,000 kV