High-resolution analytical TEM of nanostructured materials.

The paper reports structural and microchemical investigations of low-dimensional semiconducting materials by combined imaging and spectroscopical techniques of transmission electron microscopy (TEM). The materials systems under investigation comprise graded (Al,Ga)As layers, (In,Ga)As quantum wires in V-grooved (001)InP, and (In,Ga)As quantum dots in GaAs. In order to elucidate structural peculiarities of these objects conventional and high-resolution TEM (CTEM/HRTEM) were performed, whereas information about the chemical composition and element distribution was obtained through electron energy loss spectroscopy (EELS), energy-filtered TEM (EFTEM), and energy-dispersive X-ray spectroscopy (EDXS). Particularly, the application possibilities of EFTEM are here demonstrated for revealing the local element content at high lateral resolution in a semi-quantitative manner.

Among the instruments for solid state characterization working with a free electron probe, the Transmission Electron Microscope (TEM) has the best lateral resolution. The application is restricted, however, by the demand that the samples need to be suitably thinned. TEMs operating in the scanning mode yield several advantages. Equipped additionally with spectrometers, the TEM becomes an Analytical TEM. Energy Dispersive X-ray Spectroscopy (EDXS) and Electron Energy Loss Spectroscopy (EELS) allow the chemical analysis of the observed details of structure; the EELS permits additionally investigations on the electron configuration and on binding relations. Technical developments have increased considerably the information possibilities, such as lateral resolution or detection sensitivity. Recently two new types of instruments are in development, the dedicated Scanning-TEM with a field emission gun, supplying scanning images and analyses up to the nanometer range, and the energy filtering (stationary beam-) microscope which yields images and diffraction diagrams with a sharpness in contrast not previously reached. In the future the construction of an “aberration-free” objective lens promises a further advance into the atomic dimension.

New Approach To Quantitative Subcellular Imaging Of Phosphorus And Calcium Using Energy-filtered Transmission Electron Microscopy And Tomography

Investigation of the atomic structure of a (111) Zr/ZrN interface shows that it is a type-3 incoherent interface (i.e., high-index orientation relationship with a low-index interface plane in only one phase), as determined from conventional transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images, image simulations, and near-coincidence-site atomic modeling of the interface. Long facets and atomic ledges several {111}ZrN planes high form at the interface, indicating that such features cannot be used as criteria to define partial coherency at interfaces. These results also indicate that ledgewise growth is possible during the phase transformation from Zr to ZrN. Composition profiles taken across the interface using energy-filtering TEM and the N K-edge show that the composition changes abruptly at the interface, in accord with the structural transformation. Simulation results on an inclined (111) Zr/ZrN interface indicate that it is possible to judge whether an interface is inclined and faceted at the same time. A rough interface can look faceted in a HRTEM image due to projection effects, but only under a very strict set of conditions. Conversely, an interface cannot be faceted if it looks rough in an HRTEM image.

The paper is concerned with the application of analytical transmission electron microscopy (TEM) to characterize both chemical composition and bond state of the elements detected in interlayers in C- and SiC-fibre reinforced composites. The chemical bond state of nanometre-sized regions is characterized by means of electron energy loss spectroscopy (EELS), where respective information is gained by analysing energy loss near edge structures (ELNES). In this context results of Si-L23 ELNES investigations are presented concerning the chemical bonding of silicon with carbon, nitrogen and oxygen. The specific bond state of silicon is revealed by recording series of EEL spectra at high energy resolution across the fibre/ matrix interlayers of interest. Moreover, the element distribution is imaged by energy-filtered TEM.

High efficiency at low operating temperatures is essential for present and future solid oxide fuel cell (SOFC) applications. This requires the selection of materials with compatible physical and chemical properties for the different SOFC components. La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) has been shown to be a highly performing cathode material [1] while 8 mol% Y2O3-doped ZrO2 (YDZ) is still the state-of-the-art electrolyte material. However, it has been shown that an insulating SrZrO3 (SZO) interlayer forms between LSCF and YDZ during temperature treatment exceeding 900 °C, drastically reducing SOFC performance [2]. One idea of overcoming this problem is the introduction of a chemically compatible electrolyte material, like Gd2O3-doped ceria (GDC), at the interface between LSCF and YDZ. GDC acts as a diffusion barrier and prevents SZO formation. Goal of the present study is a detailed microstructural characterization of the LSCF-GDC-YDZ interfaces by analytical transmission electron microscopy (TEM). We focus particularly on the effect of the GDC sintering temperature on SZO formation. Symmetric-cell samples were fabricated by screen-printing a 5 µm thick Gd0.2Ce0.8O2-δ(GDC) layer on both sides of YDZ substrates. GDC sintering was performed at 1100°C, 1250°C or 1400°C for 3 hours, followed by screen-printing a LSCF layer on top of the GDC. A sintering temperature of 1080°C was used for all LSCF cathode layers. The samples were studied after GDC sintering (i.e. before LSCF deposition), after LSCF sintering and after electrical characterization at application-relevant temperatures (500 – 800 °C) [3]. The element distribution at the LSCF-GDC and GDC-YSZ interfaces, as well as the chemical composition within the layers themselves, were determined by energy dispersive X-ray spectroscopy (EDXS). Imaging was performed by TEM and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), complemented by selected area electron diffraction (SAED) for crystal structure analysis. The study gives new insights into material interactions at the interfaces. Figure 1 shows an overview HAADF-STEM image of the LSCF-GDC-YSZ interface region in the sample with 1100 °C GDC sintering temperature, after LSCF deposition and electrical characteri­zation. It can be clearly seen that the GDC layer has a thickness of approximately 5 µm and partially retains some porosity after fabrication. Moreover, an inter-diffusion region between YDZ and GDZ is revealed by HAADF-STEM (arrows in Figure 1), suggesting chemical composition variation. Hence, detailed elemental distributions of the YDZ-GDC interface were determined using EDXS mapping. Figure 2 shows (a) the HAADF-STEM image of the interface region and (b) the Zr, (c) the Gd and (d) the Sr elemental distributions in the YDZ-GDZ interface region. It is of particular interest that a substantial Sr concentration (Fig. 2(d)) is observed between GDC and YDZ, despite the GDC diffusion barrier layer. This indicates Sr transport from the LSCF cathode through the porous GDC layer. The same region also contains Zr (Fig. 2(b)) which indicates SZO formation. In addition, a second phase containing up to 30 at% Gd (Fig. 2(c)) is observed between SZO and YDZ. Crystal structure determination by SAED is currently in progress. We will also demonstrate that the GDC sintering temperature strongly influences SZO interlayer formation. While the SZO layer is continuous for 1100 °C GDC sintering temperature, sintering at 1400 °C strongly reduces SZO layer formation. In contrast, the Gd-rich layer between GDC and YDZ increases in thickness with increasing GDC sintering temperature. We will discuss the origin of the phase formation between GDC and YDZ and the effects of this microstructural development on electrochemical SOFC performance.

Chapter 4 - Structure of Multi-Walled and Single-Walled Carbon Nanotubes. EELS Study

In this case study we present an application of different analytical electron microscopic methods in biology, to elucidate their usefulness in such investigations. Using analytical electron microscopy, spherites in the digestive gland cells of the helicid snail Chilostoma lefeburiana were examined at three stages: just before the non-feeding period of over-wintering in November, in the middle of over-wintering in February and at its end in March. A detailed characterization of changes in the elemental composition of the spherites was characterized by a combination of transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy filtering TEM (EFTEM). During over-wintering, the spherites passed the following changes. Before over-wintering in November, they consisted of striking concentric layers of electron-dense and electron-lucent zones, while in February and March they showed clear empty zones between materials of different electron density. In November spherites, C, O, Ca, P, Cl, Fe, Si, Na, K, Mg and S were detected, whereas in February ones C, O, N, Cl, Si and S were found and only C, O, N, Si and Cl were detected in March spherites. It is suggested that the elements missing in February and March were used in different physiological processes during over-wintering, like (1) the maintenance of the appropriate elemental composition of the internal environment, (2) accumulation of non-toxic waste materials that cannot be metabolized and (3) avoiding potential intoxication by contamination with toxic metals.

Composition gradients surrounding Ni _4 Ti _3 precipitates in a Ni _{51} Ti _{49} B2 austenite matrix are investigated by a combination of analytical TEM techniques, including electron energy loss spectroscopy (EELS), energy filtered TEM (EFTEM) and energy dispersive X-ray spectroscopy (EDX). A Ni depleted zone in the surrounding matrix was detected. The size and concentration change of the depletion zone compensate very well for the excess Ni in the precipitate. Since different precipitates are often formed in nanoscale proximity, depletion zones from different precipitates can enforce one another in certain regions. A new quantification technique of EELS confirmed the 4:3 atomic ratio between Ni and Ti for the precipitate. No Ni-rich zone in the vicinity of grain boundaries was detected in the solution-treated samples.

Texture, structure and chemistry of a boron nitride fibre studied by high resolution and analytical TEM

Perpendicular magnetic media are expected to replace longitudinal hard-disk media in the near future, and to provide continued increases in areal density beyond the current maximum capacity of longitudinal media. High-resolution analytical electron microscopy is required for the study of these novel thin films because they comprise nanoscale grains and grain boundaries (often {approx}8 nm and {approx} 1 nm, respectively), and because the importance of examining the elemental distribution at near atomic level is paramount to understanding the magnetic performance. While perpendicular media offer many advantages, quantum-mechanical exchange coupling between grains is still problematic and requires the separation of grains similar to that required in longitudinal media. Energy-filtered TEM (EFTEM) imaging, which was used to examine compositional grain separation in longitudinal media, is capable of generating maps of the elemental distribution within the grains and the boundaries thereby depicting the extent of compositional separation. Combining EFTEM with other microanalytical techniques, such as high resolution TEM with energy-dispersive X-ray spectrometry, allows for both corroboration and easy quantification of individual grain and grain boundary areas. For this analytical TEM study, grain separation was attempted by generating non-magnetic oxygen-rich boundaries, either by flowing O{sub 2} gas during deposition or by sputtering a stablemore » oxide into the magnetic film. These CoPt-O and CoPt-oxide films were DC-magnetron sputtered at room temperature with increasing reactive O{sub 2} or oxide content. Magnetic properties were measured using a magneto-optical polar Kerr magnetometer. Both reactive O{sub 2} and oxide deposition methods, individually, increase grain separation and reduce intergranular exchange coupling, as shown by the hysteresis loop trends in Figures 1a and 2a. The difference between coercivity (Hc) and nucleation field (Hn) is a measure of the extent of exchange decoupling. The large increase in this loop shearing parameter as O{sub 2} or oxide content is increased is clear evidence of a corresponding decrease in exchange coupling.« less

Heavy metal pollution has increased in the last decades. Water sources are contaminated and human exposure is often long term exposure to variable amounts of different metals. In this study, male Sprague-Dawley rats were exposed via oral gavage for 28days to cadmium (Cd) and chromium (Cr), alone and in combination at concentrations 1000 times the human World Health Organization's acceptable water limits. Rat equivalent dosages were used. Blood markers of liver and kidney function were measured, changes to cellular morphology was determined with transmission electron microscopy and the intracellular metal localisation was determined with the electron energy-loss spectroscopy and energy filtered transmission electron microscopy analysis. Both Cd and Cr caused changes to the nuclear and mitochondrial membranes and irregular chromatin condensation of hepatocytes. Cr exposure caused dilation of the rough endoplasmic reticulum (rER). The combination caused nuclear and mitochondrial membrane damage as well as irregular chromatin condensation. In the kidney tissue, Cd caused irregular chromatin condensation in the cells of the proximal convoluted tubule (PCT). Cr caused changes to the outer nuclear and mitochondrial membrane and chromatin structure. The combination group caused membrane damage, irregular chromatin condensation and rER changes in the PCT. All the metal groups showed damage to the endothelial cells and pedicles, but not to the mesangial cells. Cd and Cr bio-accumulation was observed in the nucleus, mitochondria and rER of the liver and kidney and therefore are responsible for the cellular observed damage that can cause functional changes to the tissues and organs.

Abstractauthoren Transmission electron microscopy (TEM) analysis, including energy dispersive X-ray (EDX) (elemental mapping, line, and point measurements) and energy filtered TEM (EFTEM) methods, is applied to investigate the high temperature reliability, especially material diffusion, of two types of diffusion barriers: titanium–tungsten-based (TiW-based) and tantalum-based (Ta-based), with nickel (Ni) layer on top. Both barriers were deposited as a form of stacked layers on sili-con (Si) wafers using the physical vapor deposition (PVD) technique. TEM analysis is performed on both barriers before and after annealing (at 600C for 24 h inside a vacuum chamber). No diffusion of material into the Si substrate as observed. Additionally, only diffusion between the Ni and adjoining TiW layers, and between Ni and adjoining Ta layers in the TiW-based and Ta-based barriers, respectively, are observed due to annealing.

The surface properties of materials are believed to control most of the biological reactions toward implanted materials. To study the surface structure, elemental distribution, and morphology, using transmission electron microscopy (TEM) techniques, thin foils of the surface (in cross-section) are needed. These have been cumbersome to produce, in particular, from the normally irregular screw-shaped metal implants. Focused ion beam (FIB) microscopy has been developed partly for TEM sample preparation, mainly within the microelectronics industry. Our study describes a method based on FIB for producing electron transparent foils/sections from a metal implant for TEM analysis. Using a screw-shaped titanium dental implant, it was demonstrated that thin foils can be prepared with submicron specificity and from almost any surface geometry. A comparison of different lift-out techniques showed that the in situ lift-out preparation technique allowed plasma cleaning and produced particularly good samples with excellent yield. The titanium oxide on the implant surface was analyzed using energy-filtered TEM (EFTEM) and high-resolution TEM (HRTEM) and the TiO(2) rutile phase being determined via the lattice parameters. This study provides the first set of data for the optimization of a new route for preparation and analysis of biomaterial surfaces and interfaces.

Investigation of the structure and composition of a {111} incoherent Zr/ZrN interface containing ledges by high-resolution transmission electron microscopy, image simulation, electron energy-loss spectroscopy, energy-filtering transmission electron microscopy, and near-coincidence-site analysis