Photoemission and low-energy electron diffraction studies of 3,4,9,10-perylene tetracarboxylic dianhydride layers on Si(111):H

The electronic and geometric structure of the organic semiconductor 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) deposited on hydrogen-passivated Si(111) has been studied by means of angle-resolved photoelectron spectroscopy (ARPES) and low-energy electron diffraction (LEED). Apparently contradicting results concerning the growth mode are inferred by LEED and PES. The results can be reconciled by assuming that the electron beam in LEED generates holes in the PTCDA film to expose the Si:H substrate. When the beam is removed the structure of the film appears to be restored, indicating that the molecules are mobile, as in a liquid-like state. In ARPES we found that the angular dependence in intensity of the PTCDA peaks due to directional characteristics of the molecular orbitals. Small energy shifts in photoemission are observed in spectra obtained at different emission angles. The angular dependence is ascribed to varying probing depth.