Abstract
We have investigated the quantum-well-state (QWS) behavior of Ag thin film with tetratetracontane (n-C44H90; TTC) deposited on top by angled-resolved photoemission spectroscopy (AR-PES). We found that QWS shift towards Fermi level and the trend is consistent with vacuum level (VL) shifts. The slight shift of QWS towards Fermi level means that the area of the Fermi surface enclosed by the QWS bands shrinks and consequently the occupied charge density should decrease. It is more reasonable to discuss the charge behaviors at the interface by the investigation of the behaviors of QWS. As the wave functions of QWS are confined within the metal film, they will not be destroyed after the deposition of organic thin films. We had measured the VL shift Δ, which is about - 0.62 eV. We bring up a model to explain the mechanism at the interface. According to the results of QWS change and VL shift, the mirror force seems to dominate the charge distribution and we can speculate that the image charge effect takes place at the interface. We also obtained the energy band dispersion of the occupied molecular orbital state. Both the inter-molecular and the intra-molecular band dispersions were observed, which are consistent with the previous calculated and measured results by Ishii et al. However, extra energy band dispersions were also observed possibly due to the TTC molecules aligning 60 degrees with the others as a result of three-fold symmetry of the Ge(111) symmetry.