Diffusion Measurements by Analytical Electron Microscopy

1985 ◽  
Vol 62 ◽  
Author(s):  
A. D. Romig
Keyword(s):  
Electron Microprobe ◽  
Analytical Electron Microscopy ◽  
Thin Foil ◽  
Diffusion Couples ◽  
Concentration Gradients ◽  
X Ray ◽  
Analytical Electron ◽  
Multiphase Diffusion ◽  
Better Than

ABSTRACTThe analytical electron microscope (AEM) has been used to measure the concentration gradients which form in single and multiphase diffusion couples. The procedures used to collect x-ray microanalytical data and reduce that data to elemental compositions are typical of those used to quantify x-ray data generated in thin films. The primary difficulty in analyzing diffusion couples with the AEM is sample preparation. The principle advantage of the AEM as a tool to measure diffusion induced concentration gradients is its high spatial resolution, approximately 20 to 100 times better than that of the electron microprobe which has been traditionally used to measure these concentration profiles. As a consequence, the AEM data can yield diffusivities as much as 5 orders of magnitude smaller than those obtained from electron microprobe data. This paper will review the fundamental principles of the determination of diffusion coefficients from the concentration gradients measured in single and multiphase diffusion couples and the basic considerations of thin foil x-ray microanalysis. With this understanding of the basic concepts, recent studies of diffusion in Ta-W and U-Nb will be discussed.

On The Limitations of X-Ray Microanalysis of Heterogeneous Specimens Using Analytical Electron Microscopy

1980 ◽  
Vol 38 ◽  
pp. 132-133
Author(s):  
N. J. Zaluzec ◽  
E. A. Kenik ◽  
P. J. Maziasz
Keyword(s):  
Materials Science ◽  
Parent Phase ◽  
Analytical Electron Microscopy ◽  
Second Phase ◽  
Concentration Gradients ◽  
Host Matrix ◽  
X Ray ◽  
Surrounding Matrix ◽  
Analytical Electron

X-ray microanalysis in an analytical electron microscope is becoming a routinely used technique in materials science and it is important to appreciate its limitations in the quantitative analysis of inhomogeneous elemental distributions. Situations in which this can occur are in the measurement of precipitate compositions or the determination of concentration gradients at defects or interfaces. This subject was treated in part by Zaluzec1 where he indicated the errors associated with attempting analysis of precipitates embedded in a host matrix and proposed that the solution to this problem was to isolate the second phase from the surrounding matrix. This usually amounts to extraction of the precipitate from the parent phase which is not always simple. The subject of this note is to outline a procedure in which semiquantitative analysis may be obtained in situations where precipitate extraction is difficult or impossible.

Optimizing conditions for x-ray microchemical analysis in analytical electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 548-549 ◽  
Author(s):  
N. J. Zaluzec
Keyword(s):  
Solid Angle ◽  
Analytical Electron Microscopy ◽  
Incident Beam ◽  
Thin Foil ◽  
Experimental Conditions ◽  
X Ray ◽  
Microchemical Analysis ◽  
Analytical Electron ◽  
Image Position ◽  
Incident Beam Energy

The ultimate sensitivity of microchemical analysis using x-ray emission rests in selecting those experimental conditions which will maximize the measured peak-to-background (P/B) ratio. This paper presents the results of calculations aimed at determining the influence of incident beam energy, detector/specimen geometry and specimen composition on the P/B ratio for ideally thin samples (i.e., the effects of scattering and absorption are considered negligible). As such it is assumed that the complications resulting from system peaks, bremsstrahlung fluorescence, electron tails and specimen contamination have been eliminated and that one needs only to consider the physics of the generation/emission process.The number of characteristic x-ray photons (Ip) emitted from a thin foil of thickness dt into the solid angle dΩ is given by the well-known equation

Quantitative Determination of van Gogh's Painting Grounds Using SEM/EDX

2010 ◽  
Vol 17 (5) ◽  
pp. 686-690 ◽  
Author(s):  
Ralph Haswell ◽  
Leslie Carlyle ◽  
Kees T.J. Mensch
Keyword(s):  
Electron Microscopy ◽  
Cross Sections ◽  
Analytical Electron Microscopy ◽  
Qualitative Approach ◽  
Absolute Amount ◽  
Van Gogh ◽  
X Ray ◽  
Analytical Electron ◽  
Materials Used

AbstractWe have investigated the potential of utilizing analytical electron microscopy to quantitatively examine the grounds used by van Gogh and, in particular, the absolute amount of extender employed. To determine the accuracy that can be achieved, a series of oil paint reconstructions were used as standards. The proportion of extender was measured using scanning electron microscopy and energy dispersive X-ray spectroscopy, and a relative error of 10% or better was achieved. The same method was then used to determine the ground composition of real samples from van Gogh paintings. The results obtained in this work are part of a more quantitative method of comparing and classifying paint cross sections, which will supplement the more traditional qualitative approach. The information obtained from this study is being used to add to our knowledge of the methods and materials used by van Gogh, which is helping in the reconstruction of van Gogh's oeuvre and attribution.

The standard hole-count test: A progress report

1991 ◽  
Vol 49 ◽  
pp. 720-721
Author(s):  
C. E. Lyman ◽  
D. W. Ackland
Keyword(s):  
Standard Specimen ◽  
Analytical Electron Microscopy ◽  
Thin Foil ◽  
X Rays ◽  
Absolute Value ◽  
X Ray ◽  
Disk Specimen ◽  
Illumination System ◽  
Analytical Electron ◽  
Order Of Magnitude

Analytical electron microscopy (AEM) was well served by the original hole count test that prompted microscope manufacturers to reduce, by an order of magnitude, spurious x-ray generation in the specimen. This spurious x-ray signal is caused by hard x-rays or uncollimated electrons from the illumination system and is typically generated over the entire specimen regardless of where the electron probe is placed for analysis. The original test was performed on an ion-milled thin foil disk specimen of Ag or Mo, but the absolute value of hole count was dependent upon both specimen and operator. To make progress in die reduction of spurious xrays at intermediate voltages (if the problem is present), a hole-count test on a standard specimen that does not require operator judgement would be useful. The ultimate goal would be to reduce spurious x-rays to a level that would not affect any experiment on any specimen.

scholarly journals Determination of Mass Attenuation Coefficients of Th, U, Np, and Pu for Oxygen Kα X-Rays Using an Electron Microprobe

2020 ◽  
Vol 26 (2) ◽  
pp. 194-203
Author(s):  
Philipp Pöml ◽  
Xavier Llovet
Keyword(s):  
Electron Microprobe ◽  
Photoionization Cross Section ◽  
X Rays ◽  
Attenuation Coefficients ◽  
X Ray ◽  
Mass Attenuation Coefficients ◽  
Monte Carlo Simulation Program ◽  
Better Than ◽  
Mass Attenuation

AbstractMass attenuation coefficients (MACs) of Th, U, Np, and Pu for oxygen X-rays have been experimentally determined using an electron microprobe. The MACs were obtained by measuring relative X-ray intensities emitted from ThO2, UO2, NpO2, and PuO2 targets, for incident electron energies from 5 to 30 keV, and processing them with the help of the computer program XMAC. The accuracy of the measured MACs is estimated to be better than 5%. Results are compared with MAC tabulations commonly used in electron probe microanalysis as well as with theoretical photoionization calculations. It is concluded that the MACs implemented in the Monte Carlo simulation program PENELOPE which are based on the photoionization cross-section calculations of Sabbatucci & Salvat [(2016). Theory and calculation of the atomic photoeffect. Rad Phys Chem121, 122–140], provide the best agreement with our measurements. The use of different MAC schemes for the analysis of mixed actinide oxide materials is discussed.

Thin-film x-ray quantitation: New insights with the aid of Monte Carlo calculations

1991 ◽  
Vol 49 ◽  
pp. 718-719
Author(s):  
J. R. Michael ◽  
A. D. Romig ◽  
J. I. Goldstein
Keyword(s):  
Monte Carlo ◽  
Depth Distribution ◽  
Analytical Electron Microscopy ◽  
Standard Technique ◽  
Electron Trajectory ◽  
Ionization Cross ◽  
Secondary Electrons ◽  
X Ray ◽  
Analytical Electron

The determination of chemical composition from a ratio of the characteristic x-ray intensities (ratio technique) measured from thin specimens has become a standard technique in analytical electron microscopy. One of the main assumptions used in this technique is that the normalized distribution of characteristic x-ray intensity with mass depth (ρt), termed φ(ρt), is constant with mass depth and approaches one. If this assumption is violated, the x-ray generation must be calculated as a function of mass depth (i.e., a voltage dependence in the ionization cross section is required and the effect of fast secondary electrons must be included) and the standard absorption equation must be modified (since φ(ρt) is not constant with (ρt)). Φ(ρt) curves have been experimentally determined only for a limited number of elements because of the difficulty of performing the experiment in thin specimens. Monte Carlo electron trajectory simulations are therefore the most tractable way to calculate the depth distribution of x-ray generation.

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.

High-resolution x-ray analysis of dislocation networks nn tilt boundaries

1988 ◽  
Vol 46 ◽  
pp. 612-613
Author(s):  
J. R. Michael ◽  
C. H. Lin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Solute Segregation ◽  
X Ray ◽  
Periodic Arrays ◽  
Analytical Electron ◽  
Primary Dislocation ◽  
Tilt Boundaries ◽  
Polycrystalline Solids ◽  
Twist Boundaries

The segregation of solute atoms to grain boundaries in polycrystalline solids can be responsible for embrittlement of the grain boundaries. Although Auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have verified the occurrence of solute segregation to grain boundaries, there has been little experimental evidence concerning the distribution of the solute within the plane of the interface. Sickafus and Sass showed that Au segregation causes a change in the primary dislocation structure of small angle [001] twist boundaries in Fe. The bicrystal specimens used in their work, which contain periodic arrays of dislocations to which Au is segregated, provide an excellent opportunity to study the distribution of Au within the boundary by AEM.The thin film Fe-0.8 at% Au bicrystals (composition determined by Rutherford backscattering spectroscopy), ∼60 nm thick, containing [001] twist boundaries were prepared as described previously. The bicrystals were analyzed in a Vacuum Generators HB-501 AEM with a field emission electron source and a Link Analytical windowless x-ray detector.

Phase identification in SiC whisker reinforced Al2O3-R2O3-based composites

1992 ◽  
Vol 50 (1) ◽  
pp. 152-153
Author(s):  
C.M. Sung ◽  
K.J. Ostreicher ◽  
M.L. Huckabee ◽  
S.T. Buljan
Keyword(s):  
Analytical Electron Microscopy ◽  
Phase Identification ◽  
Reinforced Composites ◽  
Ion Milling ◽  
X Ray ◽  
Binary Oxides ◽  
Analytical Electron ◽  
The Matrix ◽  
Second Phases ◽  
Convergent Beam

A series of binary oxides and SiC whisker reinforced composites both having a matrix composed of an α-(Al, R)2O3 solid solution (R: rare earth) have been studied by analytical electron microscopy (AEM). The mechanical properties of the composites as well as crystal structure, composition, and defects of both second phases and the matrix were investigated. The formation of various second phases, e.g. garnet, β-Alumina, or perovskite structures in the binary Al2O3-R2O3 and the ternary Al2O3-R2O3-SiC(w) systems are discussed.Sections of the materials having thicknesses of 100 μm - 300 μm were first diamond core drilled. The discs were then polished and dimpled. The final step was ion milling with Ar+ until breakthrough occurred. Samples prepared in this manner were then analyzed using the Philips EM400T AEM. The low-Z energy dispersive X-ray spectroscopy (EDXS) data were obtained and correlated with convergent beam electron diffraction (CBED) patterns to identify phase compositions and structures. The following EDXS parameters were maintained in the analyzed areas: accelerating voltage of 120 keV, sample tilt of 12° and 20% dead time.

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