Surface States of Anthracene Crystals

The existence of surface states in anthracene crystals can be deduced from the thresh-old energies for photoemission of electrons or holes from various metals into anthracene. These surface states are capable of trapping electrons as well as holes; their density is about 2 × ${10}^{13}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$; their maximum depth is 1.3 ± 0.2 eV. They probably can act as recombination centers for charge carriers.