Number of electrons emitted from a sample with energies less than
\(\pu{50 eV}\) divided by the number of electrons incident at a given energy and angle of incidence.
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1829 (https://doi.org/10.1515/pac-2019-0404)