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Ultra-Low kV EDS


The surface sensitivity of low- energy EDS, particularly around 1 kV, is also attracting the interest of high-end electronic component manufacturers who are using low-kV SEM to image surface contaminants and defects. The capability to add elemental information to these images reduces or eliminates the need for time-consuming additional analysis techniques such as Auger or SIMS to characterize these defects. Light element analysis . The


Figure 8 : Fine-scale microstructure of Ni 3 Nb γ ” precipitate grains in an Alloy 718 sample. (a) Within-lens BSE image (Zeiss Merlin ESB), (b) spectra collected from a γ ” precipitate and adjacent Fe-Cr-rich matrix using 3 kV accelerating voltage; and (c) spectra collected from a γ ” precipitate and adjacent matrix at 1.5 kV accelerating voltage. The γ ” precipitate is enriched in Ni and also contains Nb and Ti. (d) Composite EDS layered element map of N, O, Fe, Cr, and Nb showing Al 2 O 3 , NbTiCN, and Ni 3 Nb γ ” precipitates collected at 1.5 kV using an FEI Magellan SEM. Ni 3 Nb γ ” precipitates are 30 nm long and less than 10 nm in width. Sample and data courtesy of A. Janssen and M.G. Burke, Materials Performance Centre, The University of Manchester.


In the case of Ti L, its presence as a surface layer is only clearly revealed in the 1 kV data. Only by imaging and carrying out EDS analysis at 1 kV can the morphology and chemistry of the surface structures of this complex device be studied.


2017 March • www.microscopy-today.com


term light element analysis is often used interchangeably with low-energy analysis. In this case light element means Be-F (lithium is treated separately below). The K-line X-rays from these light elements are low in energy and therefore have the same issues as other low-energy L, M, and N lines. Improvements in detector sensitivity described in this article are also relevant to the detection and analysis of these lines. T erefore large sensitivity gains are possible for materials containing boron, carbon, nitrogen, and oxygen. Figure 10 shows X-ray maps collected from a Ni-alloy coating on a valve. This material contains nitrides, carbides, and borides. In the area studied there are numerous Cr boride and some Cr carbide precipi- tates in a Ni matrix. Where the greater sensitivity of this type of technology becomes valuable, however, is in its capability to clearly show the distri- bution of dissolved boron in the Ni matrix, which is present at around 2.5 wt% as measured using WDS. T e boron X-ray map shows the areas with increased dissolved boron as medium-contrast regions, which also have intermediate contrast in the electron image. Samples containing light elements


are oſt en sensitive to damage by the electron beam (for example, organic materials and polymers) and are typically non-conductive, requiring very low kV to eliminate charging (for


example, BN). Figure 11 shows light element distributions in a biological sample (mouse kidney cells). The concentration of nitrogen seen in the nucleus of the cells agrees with earlier data collected by nano-SIMS [ 9 ]. T e low kV EDS technique


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