X-ray Microanalysis Of Thin Foils Research Articles

X-Ray Microanalysis in the STEM

Abstract Commercial TEM/STEMs are ill designed for quantitative X-ray microanalysis of thin foils. There have been no fundamental advances in their design since the first instruments appeared in the mid- 1970s. These instruments had thermionic sources with useful probe sizes of ∼10 nm, small (∼ 0.1 sr) detector collection angles, illumination systems giving serious levels of stray radiation, substantial hydrocarbon and water-vapor contamination due to the poor vacuum (∼10-5Pa) and sliding o-ring seals on unstable side-entry goniometer stages. The instruments lacked a direct measure of the probe current at the specimen. Often a 60 s accumulation time resulted in enough drift or contamination that the microanalysis was not trustworthy and spatial resolution was compromised. Today's modern TEM/STEMs, apart from replacement of thermionic source with a FEG, are little better. Dedicated STEMs however, have invariably offered better X-ray performance. The first VG HB 5 DSTEM became available, also in the 1970s, and the X-ray performance improved through to the latest design (the VG HB 603) in the mid-1990s.

AEM of the Solute Redistribution During Discontinuous Dissolution

High spatial resolution X-ray microanalysis of thin foils in a transmission electron microscope has been used for the first time to examine the residual solute content profiles resulting from the discontinuous dissolution reaction in a Ni-4 at. % Sn alloy. The sharp change in the Sn content, detected performing the line scans across the reaction front, indicated that the solute redistribution occurred just at the reaction front. The Sn profiles measured along the reaction front were the reverse of those typical for the discontinuous precipitation reaction, with a relatively higher excess amount of tin stored close to the position where the Ni3Sn lamellae had previously existed. The obtained results also suggest that the chemistry and shape of profiles are not only dependent on the dissolution temperature, but that the initial state of the single cell just before the beginning of the discontinuous dissolution reaction plays an important role.

The Impact of EDS In Materials Science Microanalysis

Abstract Since its invention in 1968, the EDS has played an essential role in X-ray analysis of materials, at the micrometer level, in the electron probe microanalyzer (EPMA). In the EPMA, the characteristic X-ray intensity from bulk specimens is sufficient that, despite its very small collection angle, the wavelength dispersive spectrometer (WDS) can also be used. Given the excellent energy resolution of the WDS it has often been the spectrometer of choice for bulk quantitative X-ray microanalysis. Therefore, the most important role of the EDS has been in X-ray microanalysis of thin specimens in the analytical electron microscope (AEM) because, in an AEM, the limited confines of the stage mean that EDS is the only viable spectrometer. Since the pioneering work of Cliff and Lorimer in the 1970s, EDS has been the method by which all high spatial resolution X-ray microanalysis of thin foils has been performed.

Definition of the spatial resolution of X-ray microanalysis in thin foils

The spatial resolution of X-ray microanalysis in thin foils is defined in terms of the incident electron beam diameter and the average beam broadening. The beam diameter is defined as the full width tenth maximum of a Gaussian intensity distribution. The spatial resolution is calculated by a convolution of the beam diameter and the average beam broadening. This definiyion of the spatial resolution can be related simply to experimental measurements of composition profiles across interphase interfaces. Monte Carlo calculations using a high-speed parallel supercomputer show good agreement with this definition of the spatial resolution and calculations based on this definition. The agreement is good over a range of specimen thicknesses and atomic number, but is poor when excessive beam tailing distorts the assumed Gaussian electron intensity distributions. Beam tailing occurs in low-Z materials because of fast secondary electrons and in high-Z materials because of plural scattering.

The influence of X-ray absorption on the spatial resolution of X-ray microanalysis of thin foils

The spatial resolution of X-ray microanalysis of thin foils is determined by the initial diameter of the electron probe and by subsequent beam broadening in the specimen due to electron scattering. The influence of X-ray absorption on resolution is investigated and found to be negligible up to a critical thickness depending on the composition and tilt conditions of the specimen.

The spatial resolution of x-ray microanalysis in thin foils

The spatial resolution of x-ray microanalysis in a thin foil is determined by the size of the beam-specimen interaction volume. This volume is a combination of the incident electron beam diameter (d) and the beam broadening (b) due to elastic scatter within the specimen. Definitions of spatial resolution have already been proposed on this basis but all present a worst case value for the resolution based on the dimensions of the beam emerging from the exit face of the foil.

A consideration of experimental methods for determining electron beam spreading in stem-eds X-ray microanalysis in thin foils

Etude de la precision qui peut etre obtenue a partir des approches experimentales en tenant compte des limitations dues a la statistique de comptage des rayons X et a la precision de position de la sonde electronique pour l'analyse quantitative des caracteristiques de la microstructure

The Effect of Surface Layers on Thin Foil Standards on the Accuracy of Quantitative E.D.S. Analysis

Quantitative X-ray microanalysis of thin foils may be achieved either by calculation or by making use of standards. This paper, although advocating the use of pure elemental standards for accurate quantification, points out some of the problems involved in the choice of good standards. Specifically, the presence of surface films on as-prepared thin foil standards must be removed or accounted for during data analysis.

The effect of small changes in impurity element content on the creep life of [formula omitted]Cr1Mo steel

Accelerated uniaxial creep tests were carried out on two steels of nominal composition 2 1 4 Cr1Mo containing different concentrations of impurity elements. The specimens were heat treated to produce a flly bainitic microstructure with a prior austenite grain size of about 80 μm. This bainitic microstructure was additionally heat treated to produce an overaged microstructure comprising ferrite laths with a distribution of coarse carbide precipitates. Isothermal tests were carried out under constant load at 873 and 838 K for applied stresses in the range 55 – 217 MPa. Optical microscopy and scanning electron microscopy were used to assess the accumulation of grain boundary cavitation. X-ray microanalysis of thin foils in a scanning transmission electron microscope was used to examine the distribution of impurity elements with atomic numbers greater than 11 within the microstructure including grain boundary carbides. These results are discussed in terms of the effect on the nucleation of creep cavities.

Spatial resolution in x-ray microanalysis of thin foils in stem

The influence of electron scattering in the spatial resolution of X-ray microanalysis of thin foils of silicon has been measured as a function of specimen thickness and accelerating voltage. The experimental observations show that high angle elastic scattering controls the spatial resolution and that this is not influenced by the diffraction conditions. Monte Carlo calculations have also been carried out and the general form of the theoretical and experimental results are in good agreement. For foil thicknesses normally used in defect analysis in silicon, ~5000 A, the spatial resolution as measured in this experiment (taken as the region within which 90% of the X-ray signal is generated) is about 700 A at 100 kV and 1800 A at 40 kV.

Spatial resolution of X-ray microanalysis in thin foils

There is increasing interest in X-ray microanalysis of thin specimens and the present paper attempts to define some of the factors which govern the spatial resolution of this type of microanalysis. One of these factors is the spreading of the electron probe as it is transmitted through the specimen. There will always be some beam-spreading with small electron probes, because of the inevitable beam divergence associated with small, high current probes; a lower limit to the spatial resolution is thus 2αst where 2αs is the beam divergence and t the specimen thickness.In addition there will of course be beam spreading caused by elastic and inelastic interaction between the electron beam and the specimen. The angle through which electrons are scattered by the various scattering processes can vary from zero to 180° and it is clearly a very complex calculation to determine the effective size of the beam as it propagates through the specimen.