Making the most of your XRD measurements: The many ways a multilayer monochromator can improve your data quality

Introduction

1. Why is a filter or monochromator needed in XRD measurements?

In lab-based diffractometers, X-rays are generated by accelerating electrons onto a specific target material (anode). In the anode material, the electrons are decelerated and their kinetic energy is mostly converted to heat and a small fraction produces X-rays. The spectrum obtained with a Cu target, a typical X-ray tube anode material, is shown in the report. The profile has a broad, low intensity background, the so-called Bremsstrahlung (from the German word “bremsen” –decelerate), and sharp peaks of high intensity (Kα, Kβ), the so-called characteristic radiation. The Kα peak is even split into two peaks with slightly different wavelengths, Kα1 and Kα2. Although some experimental setups rely on using the whole (white) emission profile (e.g. Laue diffraction), in standard powder XRD it is preferred to have a more defined wavelength. Performing a diffraction experiment with the whole (white) emission profile would lead to poor data quality, e.g. increased background due to the Bremsstrahlung. Additionally, every lattice plane would result in multiple peaks due to the presence of Kα and Kβ radiation. For higher quality data, both the Bremsstrahlung and the Kβ contributions should be removed from the emission profile before interacting with the sample.