Contact Charging and Photoemission of Anthracene Single Crystal

The sign and magnitude of the charge generated on an anthracene single crystal by contact with metals depend on the metal work-function. Equilibrium of change exchange is achieved during a contact period shorter than the order of seconds. The charge generation by contact is described by electron-transfer from/to surface states. The results on contact charging show that the depth of the filled surface-states of anthracene is 4.58 eV from the vacuum level, and that of anthracene pre-uv irradiated in O 2 gas is 4.93 eV. These values almost agree with the threshold energies of photoemission. The pre-uv irradiation in O 2 increases the negative charge-generation. This is due to the increase of electron traps. The density of traps of pre-uv irradiated anthracene is of the order of 10 12 /cm 2 /eV.