Application of analytical electron microscopy to studies of equilibrium and non-equilibrium segregation in materials

1992 ◽  
Vol 50 (2) ◽  
pp. 1214-1215
Author(s):  
Edward A Kenik
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Extended Defects ◽  
Probe Diameter ◽  
Specimen Holder ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Solute Atoms ◽  
Equilibrium Segregation ◽  
Non Equilibrium

Segregation of solute atoms to grain boundaries, dislocations, and other extended defects can occur under thermal equilibrium or non-equilibrium conditions, such as quenching, irradiation, or precipitation. Generally, equilibrium segregation is narrow (near monolayer coverage at planar defects), whereas non-equilibrium segregation exhibits profiles of larger spatial extent, associated with diffusion of point defects or solute atoms. Analytical electron microscopy provides tools both to measure the segregation and to characterize the defect at which the segregation occurs. This is especially true of instruments that can achieve fine (<2 nm width), high current probes and as such, provide high spatial resolution analysis and characterization capability. Analysis was performed in a Philips EM400T/FEG operated in the scanning transmission mode with a probe diameter of <2 nm (FWTM). The instrument is equipped with EDAX 9100/70 energy dispersive X-ray spectrometry (EDXS) and Gatan 666 parallel detection electron energy loss spectrometry (PEELS) systems. A double-tilt, liquid-nitrogen-cooled specimen holder was employed for microanalysis in order to minimize contamination under the focussed spot.

Analytical electron microscopy of planar faults in SrO-doped CaTiO3

1997 ◽  
Vol 12 (9) ◽  
pp. 2438-2446 ◽  
Author(s):  
M. Čeh ◽  
H. Gu ◽  
H. Müllejans ◽  
A. Rečnik
Keyword(s):  
Electron Microscopy ◽  
Perovskite Phase ◽  
Analytical Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Extended Defects ◽  
Spatially Resolved ◽  
Transmission Electron ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Ca Ions

Oxide-rich planar faults within a perovskite matrix are the prevailing type of extended defects in polycrystalline SrO-doped CaTiO3. These defects form, depending on the temperature of sintering, random networks, or ordered structures. The chemistry of the polytypoid, the isolated planar faults, and the perovskite phase have been studied by spatially resolved electron energy-loss and energy-dispersive x-ray spectroscopies using a dedicated scanning transmission electron microscope. We have found that Sr ions from SrO additions preferably substitute Ca in the CaTiO3 lattice, thus forming a solid solution (Ca1–xSrx)TiO3. The surplus of Ca ions forms single and ordered CaO-rich planar faults in the host (Ca1–xSrx)TiO3 phase. Whereas the excess Ca segregates in a form of single planar faults at lower temperatures, it forms a stable polytypoidic phase at higher temperatures. For materials having up to 25 mol% of SrO additions, this phase has (Ca1–xSrx)4Ti3O10 composition, comprising a sequence of CaO faults followed by three (Ca1–xSrx)TiO3 perovskite layers. Analytical electron microscopy revealed that the composition of the single planar faults, formed at lower temperatures, is identical to that of polytypoids, which are stable at higher sintering temperatures.

The effect of small additions of Cu on precipitation in Al-Mg-Si alloys

1990 ◽  
Vol 48 (2) ◽  
pp. 442-443
Author(s):  
M. Tamizifar ◽  
G. Cliff ◽  
R.W. Devenish ◽  
G.W. Lorimer
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Argon Atmosphere ◽  
Age Hardening ◽  
X Ray ◽  
Transmission Electron ◽  
Heat Treated ◽  
Analytical Electron ◽  
Scanning Transmission

Small additions of copper, <1 wt%, have a pronounced effect on the ageing response of Al-Mg-Si alloys. The object of the present investigation was to study the effect of additions of copper up to 0.5 wt% on the ageing response of a series of Al-Mg-Si alloys and to use high resolution analytical electron microscopy to determine the composition of the age hardening precipitates.The composition of the alloys investigated is given in Table 1. The alloys were heat treated in an argon atmosphere for 30m, water quenched and immediately aged either at 180°C for 15 h or given a duplex treatment of 180°C for 15 h followed by 350°C for 2 h2. The double-ageing treatment was similar to that carried out by Dumolt et al. Analyses of the precipitation were carried out with a HB 501 Scanning Transmission Electron Microscope. X-ray peak integrals were converted into weight fractions using the ratio technique of Cliff and Lorimer.

Analytical Formulae for Calculation of X-Ray Detector Solid Angles in the Scanning and Scanning/Transmission Analytical Electron Microscope

2014 ◽  
Vol 20 (4) ◽  
pp. 1318-1326 ◽  
Author(s):  
Nestor J. Zaluzec
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Solid Angle ◽  
Analytical Electron Microscopy ◽  
X Ray ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Scanning Transmission ◽  
Analytical Formulae ◽  
Detector Configurations

AbstractClosed form analytical equations used to calculate the collection solid angle of six common geometries of solid-state X-ray detectors in scanning and scanning/transmission analytical electron microscopy are presented. Using these formulae one can make realistic comparisons of the merits of the different detector geometries in modern electron column instruments. This work updates earlier formulations and adds new detector configurations.

Ion mixing of thin ZrO2 films on α-Al2O3 by Cr+ or Kr+ ions

1993 ◽  
Vol 51 ◽  
pp. 958-959
Author(s):  
N. D. Evans ◽  
D. L. Joslin ◽  
C. J. McHargue
Keyword(s):  
Room Temperature ◽  
Ion Beam ◽  
Analytical Electron Microscopy ◽  
Oxide System ◽  
Excess Oxygen ◽  
Probe Diameter ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Α Al2o3 ◽  
Rf Sputter Deposition

Analytical electron microscopy (AEM) has been used to study ion beam mixing in an oxide-oxide system: ZrO2 thin films on α-Al2O3. This mixing process is useful in applications such as adhesion enhancement.Films of ZrO2 (∼80 nm thick) were deposited on α-Al2O3 by radio frequency (rf) sputter deposition and annealed for 2 h at 500°C in 96%Ar+4%H2 to remove excess oxygen. Samples were bombarded at room temperature with either 340 keV Cr+ or 475 keV Kr+ ions to a fluence of 4×1012 ions/m2. An area of each specimen was masked during implantation to permit analysis of unimplanted interfaces. Specimens for AEM were mounted in cross-section, ground and dimpled to a thickness of ∼20 μm, and Ar+ ion milled to electron transparency. Specimens were sputter-coated with ∼5 nm of carbon to reduce charging effects. The AEM was performed in a Philips EM400T/FEG operated in the scanning transmission mode with a probe diameter of <2 nm (FWTM prior to beam spreading).

Analytical electron microscopy of fresh and vehicle-aged catalysts

1988 ◽  
Vol 46 ◽  
pp. 714-715
Author(s):  
Sooho Kim
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Analytical Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Automotive Catalysts ◽  
Area Reduction ◽  
Transmission Electron ◽  
Analytical Electron ◽  
Scanning Transmission

Automotive catalysts have a general loss of activity during aging, basically due to two principal deactivation mechanisms. One of them is thermally induced “sintering,” which results in catalytic surface area reduction. The other is chemically induced “poisoning,” which in part causes blockage of active metal sites. The conventional bulk techniques have indicated that various catalyst functions were affected differently by poisons and thermal damage; however, they generally did not provide detailed descriptions of the mechanisms of deactivation. Only analytical electron microscopy (AEM) can provide microchemical and microstructural information to gain a more thorough and fundamental understanding of catalytic deactivation.Fresh and vehicle-aged commercial automotive catalysts containing Pt, Pd, and Rh on alumina supports were prepared for AEM by a microtomy technique, which retains the spatial integrity of the catalyst pellet with uniform thickness. Then these AEM specimens were characterized in a transmission electron microscope (TEM) and in a dedicated scanning transmission electron microscope (STEM).

Sources of background X-radiation in analytical electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 504-505 ◽  
Author(s):  
T.J. Headley ◽  
J.J. Hren
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Analytical Electron Microscopy ◽  
Objective Lens ◽  
X Rays ◽  
Relative Importance ◽  
Major Barrier ◽  
Specimen Holder ◽  
Analytical Electron ◽  
Internal Sources

It is well known that a major barrier to quantitative energy dispersive (EDS) measurements of thin films is the background X-radiation generated from stray electrons and X-rays from a variety of internal sources. A number of sources have been reported in a variety of microscopes and there is disagreement over their relative importance. Clearly the sources from each type of microscope must be systematically investigated and suppressed. We report here one such study of a JEM 100C/SEG microscope. Although our data are specific to this instrument, analogous results should be obtained from other analytical transmission microscopes. The major sources of spectral background in the JEM 100C were found to be: 1) the fixed condenser (Cl) aperture, 2) the variable condenser (C2) aperture, and 3) the specimen holder. Other potential background sources such as the objective lens pole pieces and the anticontamination device did not contribute a measurable signal. Still others, such as the objective aperture, could be eliminated simply by prudent operation (e.g. removal during EDS counts).

Electron Beam Damage of Biomolecules Assessed by Energy Loss Spectroscopy

1978 ◽  
Vol 36 (3) ◽  
pp. 61-69
Author(s):  
M. Isaacson ◽  
M.L. Collins ◽  
M. Listvan
Keyword(s):  
Electron Microscopy ◽  
Radiation Damage ◽  
Structural Integrity ◽  
Analytical Electron Microscopy ◽  
High Dose ◽  
Dose Rates ◽  
Special Cases ◽  
Analytical Electron ◽  
Atom Migration ◽  
Beam Damage

Over the past five years it has become evident that radiation damage provides the fundamental limit to the study of blomolecular structure by electron microscopy. In some special cases structural determinations at very low doses can be achieved through superposition techniques to study periodic (Unwin & Henderson, 1975) and nonperiodic (Saxton & Frank, 1977) specimens. In addition, protection methods such as glucose embedding (Unwin & Henderson, 1975) and maintenance of specimen hydration at low temperatures (Taylor & Glaeser, 1976) have also shown promise. Despite these successes, the basic nature of radiation damage in the electron microscope is far from clear. In general we cannot predict exactly how different structures will behave during electron Irradiation at high dose rates. Moreover, with the rapid rise of analytical electron microscopy over the last few years, nvicroscopists are becoming concerned with questions of compositional as well as structural integrity. It is important to measure changes in elemental composition arising from atom migration in or loss from the specimen as a result of electron bombardment.

Analytical Electron Microscopy (AEM) of Meningeal Cells Exposed to Particulate Cobalt During Studies of Experimental Epilepsy

1982 ◽  
Vol 40 ◽  
pp. 186-187
Author(s):  
R.G. Frederickson ◽  
R.G. Ulrich ◽  
J.L. Culberson
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Experimental Epilepsy ◽  
Metallic Cobalt ◽  
Experimental Animals ◽  
X Ray ◽  
Brain Surface ◽  
Meningeal Cells ◽  
Analytical Electron ◽  
The Brain

Metallic cobalt acts as an epileptogenic agent when placed on the brain surface of some experimental animals. The mechanism by which this substance produces abnormal neuronal discharge is unknown. One potentially useful approach to this problem is to study the cellular and extracellular distribution of elemental cobalt in the meninges and adjacent cerebral cortex. Since it is possible to demonstrate the morphological localization and distribution of heavy metals, such as cobalt, by correlative x-ray analysis and electron microscopy (i.e., by AEM), we are using AEM to locate and identify elemental cobalt in phagocytic meningeal cells of young 80-day postnatal opossums following a subdural injection of cobalt particles.

Analytical Electron Microscopy Characterization of Electric Arc Furnace Dust

1981 ◽  
Vol 39 ◽  
pp. 134-135
Author(s):  
J. R. Porter ◽  
J. I. Goldstein ◽  
D. B. Williams
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Electric Arc Furnace ◽  
Electric Arc ◽  
Dust Particles ◽  
Particle Analysis ◽  
Arc Furnace ◽  
Analytical Electron ◽  
Residual Elements ◽  
Industry Practice

Alloy scrap metal is increasingly being used in electric arc furnace (EAF) steelmaking and the alloying elements are also found in the resulting dust. A comprehensive characterization program of EAF dust has been undertaken in collaboration with the steel industry and AISI. Samples have been collected from the furnaces of 28 steel companies representing the broad spectrum of industry practice. The program aims to develop an understanding of the mechanisms of formation so that procedures to recover residual elements or recycle the dust can be established. The multi-phase, multi-component dust particles are amenable to individual particle analysis using modern analytical electron microscopy (AEM) methods.Particles are ultrasonically dispersed and subsequently supported on carbon coated formvar films on berylium grids for microscopy. The specimens require careful treatment to prevent agglomeration during preparation which occurs as a result of the combined effects of the fine particle size and particle magnetism. A number of approaches to inhibit agglomeration are currently being evaluated including dispersal in easily sublimable organic solids and size fractioning by centrifugation.

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