Area on the specimen irradiated by X-rays in
X-ray reflectrometry.
Notes: - In typical commercial equipment, the beam width is \(\pu{200 \upmu\!m}\), so at \(\pu{0.3\!^{\circ}}\) incident angle, the beam footprint is \(\pu{38 mm}\) long; at \(\pu{1\!^{\circ}}\), it is \(\pu{11.5 mm}\) and at zero incidence angle it is infinite. For \(\pu{100 \upmu\!m}\) incident beam width, these values are halved.
- The beam footprint along the beam direction can be reduced by the use of a suitable knife-edge diaphragm mounted in a plane that is normal to the sample surface and whose normal, in turn, aligns with the beam azimuth. The knife-edge is parallel to, and adjusted to be close to, the surface at the point where the X-ray beam centre strikes the sample surface. This closeness limits the footprint size but also reduces the measured signal intensity.
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1847 (https://doi.org/10.1515/pac-2019-0404)