EDX energy-dispersive analysis

A paper on new developments in the characterisation of polymers in the solid state must include a discussion of the possibilities offered by scanning electron transmission and the ancillary detection devices EDX (energy dispersive analysis of X-rays) and EELS (electron energy loss spectroscopy). 

It is often useful to have an EDX (energy dispersive analysis of X-rays) accessory on the SEM to make elemental identification of different features observed in the photomicrographs. Here, the energy of X-rays produced by the primary electron beam is measured and used to identify elements. Elemental information obtained by EDX is more characteristic of the bulk than the surface, however. 

A scanning electron microscope can also be equipped with additional instmmentation for electron-excited x-ray analysis (9). In many systems, this is performed in the mode known as energy dispersive x-ray analysis (edx). Other common acronyms for this method are eds for energy dispersive spectroscopy or edax for energy dispersive analysis of x-rays. 

As indicated in Fig. 7.2, X-rays are among the by-products in an electron microscope. Already at the beginning of this century, people knew that matter emits X-rays when it is bombarded with electrons. The explanation of the phenomenon came with the development of quantum mechanics. Nowadays, it is the basis for determining composition on the submicron scale and, with still increasing spatial resolution, is used in the technique referred to as Electron Microprobe Analysis (EMA), Electron Probe Microanalysis (EPMA) or Energy Dispersive Analysis of X-rays (EDAX, EDX) [21]. 

Within this technique, we include EDX (energy dispersive x-ray analysis), WDX (wavelength dispersive x-ray analysis), and XRF (x-ray fluorescence analysis). In all of these, x-rays emitted from a sample are analyzed. In one case, they are created by bombarding the sample with x-rays (XRF), and in the others, they are created by high energy electron beam as in an SEM (EDX, WDX). 

As illustrated by Fig. 10.4, an electron microscope offers additional possibilities for analyzing the sample. Diffraction patterns (spots from a single-crystal particle and rings from a collection of randomly oriented particles) enable one to identify crystallographic phases as in XRD. Emitted X-rays are characteristic for an element and allow for a determination of the chemical composition of a selected part of the sample (typical dimension 10 nm). This technique is called electron microprobe analysis (EMA, EPMA) or, referring to the usual mode of detection, energy dispersive analysis of X-rays (EDAX or EDX). Also the Auger electrons carry information on sample composition, as do the loss electrons. The latter are potentially informative on the low Z elements, which have a low efficiency for X-ray fluorescence. 

Using a complementary technique, Transmission Electron Microscopy (TEM), the particle sizes were measured in order to choose the best model(s). In this way, the lateral resolution of one technique (TEM) is combined with the surface sensitivity of the other (XPS) to yield some parameters. In this case, however, the results appeared contradictory. Measuring with a resolution of 1 nm, TEM could not find titania or vanadia particles and with EDX (Energy Dispersive X—ray analysis) it was corroborated that, even on a smaller scale, the metals were evenly spread through the catalyst. 

After sulfidation the scales were examined by X-ray diffraction analysis. In some cases the scale was detached from the metallic Substrate, so that the inner scales as well as the metal-scale interface could be examined. Other specimens were mounted and me-tallographically polished in cross sections without using lubricant because AI2S, tends to hydrolysis. These specimens were examined then and inspected using optical and scanning electron (SEM) microscopy as well as X-ray energy dispersive analysis (EDX). 

The high temperature oxidation of (J-NiAl, undoped and doped with Ce, Y and Hf was studied in situ by thermogravimetry in He with p(02) = 5 10 6bar at 1000°C and by high temperature X-ray diffraction at 950 and 1000°C in air. After the in situ experiments the samples were analysed metallographically by optical microscopy and by scanning electron microscopy (SEM) with energy dispersive analysis (EDX). 

Acronyms SEM scanning electron microscopy, SEMPA scanning electron microscopy with polarisation analysis, EDX energy dispersive X-ray analysis, EPMA electron probe microanalysis, STkM scanning Auger microscopy. 

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