Performing X-ray microanalysis at beam energies lower than those conventionally used (`10 keV) is known to signi®cantly improve the spatial resolution for compositional analysis. However, the reduction in the beam energy which reduces the Xray interaction diameter also introduces analytical dif®culties and constraints which can diminish the overall analytical performance. This paper critically assesses the capabilities and limitations of performing low beam energy, high spatial resolution X-ray microanalysis. The actual improvement in the spatial resolution and the reduction in the X-ray yield are explored as the beam energy is reduced. The consequences for spectral interpretation, quantitative analysis and imaging due to the lower X-ray yield and the increased occurrence of X-ray line overlaps are discussed in the context of currently available instrumentation.Conventionally, X-ray microanalysis on scanning electron microscopes (SEM) with energy dispersive spectrometers (EDS) has been performed with relatively high primary energies (b 10 keV). For most samples this results in reasonably good separation of the generated X-ray line series from different elements enabling unambiguous identi®cation and therefore accurate qualitative analysis. Under these circumstances it is widely accepted that quantitative analysis of polished bulk samples is possible on a routine basis with relative errors around 1 ± 57 and detection limits of the order of 0.1 wt7. A new generation of high resolution ®eld emission gun (FEG) SEM instruments which can operate with much improved beam sizes at low beam energies (E P ) down to and below 1 keV has opened a wide range of new applications in surface and materials characterisation. The instruments, which are as straightforward to operate as conventional high vacuum SEMs, provide a new, more detailed and realistic view of surfaces. Additionally, the capability of investigating insulating samples without the requirement of a conductive coating becomes possible by utilising low E P operation.The ability of these instruments to maintain high spatial resolution performance at low E P when providing suf®cient beam current to enable practical microanalysis, in conjunction with the ultra-thin window energy dispersive spectrometers (EDS) has also opened new possibilities for materials characterisation. In particular, the analysis of new advanced materials with thin layers and sub-micron features appear to be realistic goals.In general, according to the literature there are several improvements connected with the application of beam energies below those conventionally used for microanalysis, i.e. E P`1 0 keV: ± The electron range and thus the information depth in X-ray microanalysis signi®cantly decreases with decreasing E P and enters the magnitude of a few 10 nm. ± Owing to the small beam diameters in FEG SEMs and the shrinking excitation volume the lateral resolution for X-ray microanalysis can theoretically be improved by reducing E P . ± The analysis sensitivity of near-surface features such as...

The accurate calculation of characteristic peak intensity is essential for interpreting X-ray spectra in electron microprobe analysis. Conventionally, the measured intensity from a standard of known composition is used as a reference to simplify the calculation. However, if no such standard is available, then all factors influencing X-ray generation and X-ray detection efficiency must be included. If the intensity and energy distribution of the background radiation can also be calculated, the investigator can simulate an entire spectrum from an assumed composition, gaining powerful benefits in setting up an experiment and in confirming the results. The study presented here demonstrates a fast method of spectrum simulation, suitable for energydispersive spectroscopy (EDS), and assesses the accuracy using 309 spectra from samples of known composition. These include K, L, and M lines from elements of atomic number 6–92, excited by beam energies in the range of 5–30 keV. The RMS error between 360 measured and calculated peak intensities was found to be 7.1%. Central to the method is the use of the ratio of peak intensity/total background intensity, which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions.

The calculation of surface composition from Auger peak heights requires a knowledge of the matrix effects. These are modifications to the yield of Auger electrons arising from inelastic mean free paths, the Auger backscattering factor and sample density effeets. A method for approximating the Auger backscattering factor for films of any thickness and atomic number is described. The method is based upon the assumption that the contribution of backscattered primary electrons to the Auger yield will change in proportion to the change in the electron backscattering coefficient of the film with thickness. The Auger backscattering factor so calculated varies smoothly from the value corresponding to the bulk material of the film to that of the substrate. Using known generic equations for bulk backscattering coefficients and factors, a simple algebraic expression is obtained. Comparison with experimental data obtained from both high and low atomic number films yields good agreement for various primary beam energies and angles of incidence.

No abstract

Conventionally, x-ray microanalysis on scanning electron microscopes (SEM) with energy dispersive spectrometers (EDS) has been performed with relatively high primary energies (>10 kv). for most samples this results in reasonably good separation of the generated x-ray line series from different elements enabling unambiguous identification and therefore accurate qualitative analysis. Under these circumstances it is widely accepted that quantitative analysis of polished bulk samples is possible on a routine basis with relative errors around 1-5% and detection limits of the order of 0.1%.However, in order to address the analysis requirements of new advanced materials with sub-micron features, there is growing interest in performing x-ray microanalysis at low beam energies(<5kv). this is now a more realistic goal due to the routine availability of field emission sem's which can operate with much improved beam sizes at low beam energies with sufficient beam current to perform practical microanalysis, in conjunction with the improved low energy performance of current, commercially available EDS systems.