Electron spectroscopy studies of PTCDA on Ag/Si(111)-√3x√3

The growth of 3,4,9,10-perylenetetracarboxylic dianhydride thin films on the Ag/Si (111)-root 3 x root 3 surface has been studied by means of high-resolution photoelectron spectroscopy (PES), near edge x-ray absorption fine structure (NEXAFS) and low-energy electron diffraction (LEED). LEED and NEXAFS data indicate that for the first molecular layer there is a well ordered growth of flat lying molecules in several phases with a preferred ordering relative to the substrate. There is a clear interaction between the perylene core of the molecule and substrate seen from changes of the highest occupied molecular orbital and lowest unoccupied molecular orbital levels in the PES and NEXAFS data. Shifts in the C 1s and O 1s XPS core levels are interpreted as interactions with the carboxylic groups. There are also new components and changes in the low coverage XPS C 1s and O 1s core level spectra compared to spectra from thicker, pure molecular films. The new components can be related to two different parts of the molecule. One is located in the carboxylic groups and the other in the perylene core of the molecule. For thicker films the NEXAFS and core level results suggest a mainly layered growth of flat lying molecules.