Dedicated X-Ray mapping system with single and multiple SDD detectors for quantitative X-Ray mapping and data processing

Abstract

A JEOL 840 SEM/EDS system has been converted into a dedicated X-Ray Mapping (XRM) instrument, due to the needs of many users from varying disciplines including materials science and engineering, biology, geology and environmental science. The system performs 24 hours-7 days per week XRM electron microscopy (XRMEM). The system has just been upgraded with an Amptek 123 FAST123 silicon drift detector (SDD) with an Ultra Thin C1 window to allow for faster mapping. The XRMEM is setup to maximize its ability to operate with a larger working distance so that the instrument can perform x-ray maps at very low magnifications and high pixel resolution (1024x1024). This is now requested by a large number of users. With the use of the high count rate detectors, such as the Amptek SSD, our research team is collecting XRM's from over 3 hours and up to several days; this is especially true when trace elemental analysis and mapping is required.Quantitative X-ray mapping (QXRM) using multi-detectors and combined detectors, such as WDS/EDS, not only reduces mapping time, but also improves the ability to map minor and trace elements very accurately. One interesting outcome of this is that we now need to improve the collection efficiency of our WDS detectors to enable them to perform at these lower beam currents [1][2][3]. To take advantage of this increased precision and sensitivity of QXRM, careful attention to all those parameters necessary for high quality analysis is required. Important characteristics such as resolution, gain zero calibration, pulse pileup and other artifacts need to be well characterized for each detector used. Images are then created from the fully background corrected, overlap corrected and inter-element corrected calculation at each pixel in the image. As there is a very large dynamic concentration range to be considered (5 orders of magnitude) it is important to understand that the precision at each level will depend on how well this characterization is carried out [1]. To achieve this, time is no longer an issue but a means to accomplish a more precise result. Thus, if we can introduce more efficient detection then we can achieve this result in a shorter time. This may be achieved by counting more x-rays with one detector, as long as the critical quantitative characteristics of the detector is not compromised, or this can easily be achieved by adding more detectors.For QXRM to work correctly for multi-detector systems, the characteristics of each detector must be accurately determined so that the final quantification of the individual detectors can be summed. To accomplish this more effectively, the full spectrum at each pixel for each SDD detector should be saved. As a final check for consistency between detectors, a technique was developed called "Colouring Verification Technique (CVT)" that involves assigning a different RGB colour for each detector for the same element (Fig. 1). When combining the three maps of the same element, a grey scale map should be obtained (Fig. 1), not a colour map. This ind...

A new life for the wavelength-dispersive X-ray spectrometer (WDS): incorporation of a silicon drift detector into the WDS for improved quantification and X-ray mapping

“…The combination of EDS and WDS produces a very powerful analytical technique also allowing for excellent quantitative X-ray mapping (QXRM) [1][2][3][4][5]. Traditionally, the EDS is used for fast elemental analysis to determine what elements are present and the WDS then utilised to acquire precise major and trace elemental quantitative analysis.…”

Incorporation of an Amptek Silicon Drift Detector into a Wavelength Dispersive Spectrometer (WDS) Replacing the Gas Flow Proportional Counter

“…WDS exhibits far better spectral resolution than the conventional EDS. The combination of EDS and WDS produces a very powerful analytical technique allowing for excellent Quantitative X-ray Mapping (QXRM) [2,3]. However, the Electron Microprobe operator using WDS, has to be meticulous in monitoring items such as gas flow, gas purity, gas pressure, noise levels of baseline and window, gas flow proportional counter (GFPC) voltage levels, count rate suppression, anode wire contamination and other parameters [2].Over the last couple years we have been testing the WD spectrometers using Amptek SDD's in place of the sealed proportional counter (PC) and GFPCs [3], see Figure 1a &1b.…”

“…This allows us to operate the detector remotely from its electronics box. This design option allows the SDD detector to be incorporated within the WD spectrometer and the electronics placed outside using a nine pin feedthrough (Figure 1e & g).The incorporation of a SDD, in the light and mid range element range, allows improvement of the detection limit for these elements [3]. It is also possible to obtain much more reliable results at high count rates with a lot less drift in gain and zero.Our current research demonstrates the dramatic superiority of SDD over PC (whether gas flow or sealed).…”

“…The incorporation of a SDD, in the light and mid range element range, allows improvement of the detection limit for these elements [3]. It is also possible to obtain much more reliable results at high count rates with a lot less drift in gain and zero.…”

“…Over the last couple years we have been testing the WD spectrometers using Amptek SDD's in place of the sealed proportional counter (PC) and GFPCs [3], see Figure 1a &1b. Initial work involved using an Amptek pin SDD and more recently the Amptek Fast 123 system.…”