Ultrathin window detector

An example of interface analysis by EDXS line profiling at high lateral resolution is given in Eig. 4.29. It is of particular importance, because the distribution of light elements like carbon, nitrogen, and oxygen is also revealed. This was possible by means of an Si (Li) EDXS detector (Kevex) with an ultrathin window attached to a dedicated STEM HB 501, from Vacuum Generators, with a cold field-emission cathode. 

Other analytical methods can also be applied for the detection of F in archaeological artefacts, especially when it is possible to take a sample or to perform microdestructive analysis. These are namely the electron microprobe with a wavelength-dispersive detector (WDX), secondary ion mass spectrometry (SIMS), X-ray fluorescence analysis under vacuum (XRF), transmission electron or scanning electron microscopy coupled with an energy-dispersive detector equipped with an ultrathin window (TEM/SEM-EDX). Fluorine can also be measured by means of classical potentiometry using an ion-selective electrode or ion chromatography. 

Finally, in order to verify molecular-length scale healing, an energy dispersive spectroscopy (EDS) (15 kV, super-ultrathin window (SUTW) Saphire detector, amplification process time (AMPT) of 25.6 ps) analysis was conducted using a Hitachi 3600 N scanning electron microscope equipped with an EDAX genesis detector. The rationale was that if the CP molecules diffused into the PSMP matrix, the chemical composition near the interface will show a certain gradient. In this study, a specially prepared EDS specimen was used. To prepare the EDS specimen, a SENB specimen made of pure PSMP was fractured and a very thin layer of CP was placed in between the fractured surfaces. Next, the EDS specimen was healed as described in Section 6.1.1. An EDS analysis was conducted at and around the healed interface of the EDS specimen. 

Spectrometer (EDS). Quantification can be quite good if appropriate standards are used. The X-ray detector can be set to only detect and count X-rays that have energies within a narrow range. This output can then be used to generate elemental distribution maps, or line scans. Newer detectors with ultrathin windows can easily detect all elements with an atomic number of 5 (boron) or greater. Some applications of SEM-EDS analysis are given in the metallography chapter of this manual. 

All modern X-ray fluorescence systems are computer controlled and equipped with automatic sample changers. Different matrix correction models are included in the data evaluation software, and further developments on expert systems will reduce manual calibration work. With WDXRF, the detectability of light elements (down to Be) will be optimized, e.g. by using X-ray tubes and detectors with ultrathin windows and widely spaced (focusing) analyser crystals. In EDXRF, trends are for miniaturization, development and optimization of high-resolution room temperature detectors and extension of the application range towards the determination of light elements. 

X-ray photons can enter the cryostat and reach the Si(Li) crystal through a thin beryllium window of typically 5-10 pm thickness. The vacuum enclosure protects the detector from surface contamination and moisture condensation (at LN2 temperatures), light and scattered electrons (in electron microprobes). For measuring very low energy/long-wavelength X-rays, the beryllium window can be replaced by ultrathin diamond or aluminum coated polyimide windows or (in vacuum instruments) removed completely. 

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