We describe one approach to standardless quantification for energy-dispersive (ED) X-ray spectrometry that can achieved unnormalised results with an accuracy better than 5 %. This approach relies on a “factory” standards database, a model of the detector efficiency, calculated peak profiles, and a multi-step process to correct spectral artefacts and extract X-ray intensities from ED spectra. These processes and components, as well as the underlying equations involved in the quantification are detailed to illustrate the similarities between this approach and the classical standard-based k-ratio quantification. The accuracy was assessed by measuring and quantifying standard samples at different accelerating voltages (15 and 20 kV) and input count rates (50 and 200 kcps). In all cases, the measured, unnormalised concentrations yielded a centred distribution with a relative error less than 5 %. Excluding the analysis of light elements (B, C, O, N, F) improved the relative error to around 2 %
New instrumentation which is sensitive to the detection of ultra low energy (<100eV) X-rays [1,2], promises new analysis capability for the SEM; so called 'Soft X-ray Microanalysis'. Only those soft X-rays that are generated close to the surface of the sample escape and therefore they offer potential for surface and higher spatial resolution analysis. The detectability of very low energy K, L and M lines also add useful chemical information when operating SEMs at very low accelerating voltage (2kV or less).To develop EDS hardware that can efficiently detect soft X-rays a number of challenges have been overcome. Although modern SDD detectors are sensitive to low energy X-rays, the absorption of X-rays by the detector window limits the count rate and has a drastic effect for soft X-rays. Therefore, special X-Max N windowless detectors have been fabricated using low noise electronics and high resolution SDD sensors, to maximize ultra low energy sensitivity and deliver more than 10 times improvement at low energy. Performance for SiL (92eV) and AlL (Fig. 1A, 79eV) has been enhanced sufficiently so that these lines may be used for X-ray mapping, and even lower energy lines including LiK (54eV) and MgL (49eV) have been detected. Recent developments in electronic design have further reduced electronic noise and given additional sensitivity enhancements, as seen for LiK (Fig 1B), and MgL (Fig. 1C).Soft X-ray Microanalysis presents new challenges, for X-ray emissions involving transitions from valence shells. In particular, the bonding characteristics of the compounds analysed can affect the intensity of X-ray emission. Sample preparation is a vital consideration, with materials of interest often being highly reactive. Analysis of Li-compounds in Li-Al alloys and Li-ion batteries, have yielded results where it is has proved difficult to determine if deficiency of LiK signal is due to lack of X-ray emission or due to the reactivity of Li and its loss from the sample surface and we need a better understanding of the physics of soft X-ray emission. For sample preparation, techniques used in surface science, for example the use of in-chamber ion milling, may be required.Magnesium and aluminium-based alloys are an interesting application area because their metallic bonding means significant soft X-ray L lines are emitted. Dispersoids and other precipitates can also be very small (<50nm) in size. Preparation of these materials is more straight-forward using established metallographic techniques; although a thin oxide forms on the surface, useful X-ray intensities are achieved. X-ray maps can be obtained to give element distribution information using very low kV with the latest FEG-SEMs. Fig. 2A shows the distribution of precipitates in a Mg alloy from the MgLline signal collected at 1kV. Smaller nano-scale disperoids from Al-alloys can be better studied using the AlL (rather than the AlK) signal at 2-3kV due to its high intensity. Collection times are limited due to carbon contamination, although preparation methods...
The BBC's Assistant Director-General on the coming conflict between the broadcasters and those who wish to manipulate society: ‘Over the next two years we can expect sustained and mounting pressure and criticism of what we do as broadcasters and how we do it’
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