Here, the bandgap energy E g is given in eV. Equation 2 an 3 are also known as the TTP-2M equations and are in general applicable for energies between 50 eV and 200 keV. Neglecting a few materials (diamond, graphite, Cs, cubic-BN and hexagonal BN) that are not following these equations (due to deviations in β β ), the TTP-2M equations show precise agreement with the measurements.