Application of Layered Synthetic Microstructure Crystals to WDX Microanalysis of Ultra-light Elements

Abstract

In the last several years, the use of layered synthetic microstructure (LSM) crystals has resulted in considerable improvement in WDX analysis of light elements. The advantages of LSM crystals compared to conventional lead stearate or lead octodecanoate crystals have been discussed and presented by other investigators, e.g., Bastin and Heijligers.^(2–6) Layered synthetic microstructure crystals are fabricated by vapor deposition of alternate layers of heavy and light elements onto a highly polished substrate. Some of the more commonly used types include: W/Si (LSM-060; 2d ≈ 60 Å), Ni/C (LSM-080; 2d ≈ 80 Å), and Mo/B₄C (LSM-200; 2d ≈ 200 Å). Of these, the LSM-080 is most versatile, since it provides a wide wavelength range (≈22–72 Å) with good performance for O, C, and B, as well as better performance for N than is possible with stearate-type crystals. Another advantage of this crystal is its ability to suppress higher orders of high energy x-ray lines. The LSM-060 has a narrower wavelength range (≈17-55 Å), but provides better spectral resolution for x-ray peaks of O, N, and C as well as better sensitivity for O and N. However, it does not suppress higher order x-ray lines as well as LSM-080. The LSM-200 crystal enables the analysis of Be and provides the highest sensitivity for B.